Apache Maven

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Apache Maven
Current version
User Guide

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The Apache Software Foundation 2009-07-29

Table of Contents i

Table of Contents
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1 What is Maven? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
2 Features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
3 FAQ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
4 Community Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
4.1 How to Contribute . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
4.2 Getting Help . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
4.3 Issue Tracking . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
4.4 Source Repository . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
4.5 Continuous Integration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
5 Running Maven . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
6 Maven Plugins . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
7 User Centre . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
7.1 Maven in 5 Minutes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
7.2 Getting Started Guide . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
7.3 POM Reference . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56
7.4 Settings Reference . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 90
7.5 Guides . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 99
7.5.1 The Build Lifecycle . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 102
7.5.2 The POM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 110
7.5.3 Profiles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 122
7.5.4 Repositories . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 132
7.5.5 Standard Directory Layout . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 135
7.5.6 The Dependency Mechanism . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 136
7.5.7 Plugin Development . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 152
7.5.8 Configuring Plug-ins . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 155
7.5.9 The Plugin Registry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 165
7.5.10 Plugin Prefix Resolution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 168
7.5.11 Developing Ant Plugins . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 170
7.5.12 Developing Java Plugins . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 184
7.5.13 Creating a Site . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 193
7.5.14 Snippet Macro . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 198
7.5.15 What is an Archetype . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 200
7.5.16 Creating Archetypes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 201
7.5.17 From Maven 1.x to Maven 2.x . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 204
7.5.18 Using Maven 1.x repositories with Maven 2.x . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 207
7.5.19 Relocation of Artifacts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 208
7.5.20 Installing 3rd party JARs to Local Repository . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 210
7.5.21 Deploying 3rd party JARs to Remote Repository . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 211

©2009, The Apache Software Foundation • ALL RIGHTS RESERVED.

Table of Contents ii

7.5.22 Coping with Sun JARs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 212
7.5.23 Remote repository access through authenticated HTTPS . . . . . . . . . . . . . . . . . . . . . . 214
7.5.24 Creating Assemblies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 216
7.5.25 Configuring Archive Plugins . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 220
7.5.26 Configuring Maven . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 221
7.5.26 Mirror Settings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 224
7.5.26 Deployment and Security Settings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 227
7.5.26 Embedding Maven 2.x . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 228
7.5.26 Generating Sources . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 231
7.5.26 Working with Manifests . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 233
7.5.26 Maven Classloading . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 235
7.5.26 Using Multiple Modules in a Build . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 237
7.5.26 Using Multiple Repositories . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 239
7.5.26 Using Proxies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 241
7.5.26 Using the Release Plugin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 242
7.5.26 Using Ant with Maven . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 247
7.5.26 Using Modello . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 249
7.5.26 Webapps . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 252
7.5.26 Using Extensions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 253
7.5.26 Building For Different Environments with Maven 2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . 254
7.5.26 Using Toolchains . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 257
7.5.26 Encrypting passwords in settings.xml . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 260
7.5.26 Reusable Test JARs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 263
7.6 Eclipse Integration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 265
7.7 Netbeans Integration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 266
8 Plugin Developer Centre . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 267
8.1 Testing your Plugin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 268
8.2 Documenting your Plugin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 277
8.3 Common Bugs and Pitfalls . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 278
8.4 Mojo API . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 286
9 Maven Repository Centre . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 298
9.1 Guide to Maven Evangelism . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 299
9.2 Guide to uploading artifacts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 300
10 Maven Developer Centre . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 306
10.1 Developing Maven 2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 308
10.2 Building Maven 2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 311
10.3 Committer Environment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 314
10.4 Committer Settings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 316
10.5 Maven Code Style And Conventions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 317
10.6 Maven JIRA Convention . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 322


Table of Contents iii

10.7 Maven SVN Convention . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 324
10.8 Making GPG Keys . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 326
10.9 Release Process . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 329
10.10 Deploy Maven Current References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 339
11 External Resources . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 340


Table of Contents iv


1 What is Maven? 1

1 What is Maven?
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1.1 Introduction
Maven, a Yiddish word meaning accumulator of knowledge, was originally started as an attempt to
simplify the build processes in the Jakarta Turbine project. There were several projects each with their
own Ant build files that were all slightly different and JARs were checked into CVS. We wanted a
standard way to build the projects, a clear definition of what the project consisted of, an easy way to
publish project information and a way to share JARs across several projects.
The result is a tool that can now be used for building and managing any Java-based project. We hope
that we have created something that will make the day-to-day work of Java developers easier and
generally help with the comprehension of any Java-based project.

1.2 Maven's Objectives
Maven's primary goal is to allow a developer to comprehend the complete state of a development
effort in the shortest period of time. In order to attain this goal there are several areas of concern that
Maven attempts to deal with:
• Making the build process easy
• Providing a uniform build system
• Providing quality project information
• Providing guidelines for best practices development
• Allowing transparent migration to new features

1.2.1 Making the build process easy
While using Maven doesn't eliminate the need to know about the underlying mechanisms, Maven
does provide a lot of shielding from the details.

1.2.2 Providing a uniform build system
Maven allows a project to build using its project object model (POM) and a set of plugins that are
shared by all projects using Maven, providing a uniform build system. Once you familiarize yourself
with how one Maven project builds you automatically know how all Maven projects build saving you
immense amounts of time when trying to navigate many projects.

1.2.3 Providing quality project information
Maven provides plenty of useful project information that is in part taken from your POM and in part
generated from your project's sources. For example, Maven can provide:
• Change log document created directly from source control
• Cross referenced sources
• Mailing lists
• Dependency list
• Unit test reports including coverage
As Maven improves the information set provided will improve, all of which will be transparent to
users of Maven.
Other products can also provide Maven plugins to allow their set of project information alongside
some of the standard information given by Maven, all still based on the POM.


1 What is Maven? 2

1.2.4 Providing guidelines for best practices development
Maven aims to gather current principles for best practices development, and make it easy to guide a
project in that direction.
For example, specification, execution, and reporting of unit tests are part of the normal build cycle
using Maven. Current unit testing best practices were used as guidelines:

• Keeping your test source code in a separate, but parallel source tree
• Using test case naming conventions to locate and execute tests
• Have test cases setup their environment and don't rely on customizing the build for test
preparation.
Maven also aims to assist in project workflow such as release management and issue tracking.
Maven also suggests some guidelines on how to layout your project's directory structure so that once
you learn the layout you can easily navigate any other project that uses Maven and the same defaults.

1.2.5 Allowing transparent migration to new features
Maven provides an easy way for Maven clients to update their installations so that they can take
advantage of any changes that been made to Maven itself.
Installation of new or updated plugins from third parties or Maven itself has been made trivial for this
reason.

1.3 What is Maven Not?
You may have heard some of the following things about Maven:

• Maven is a site and documentation tool
• Maven extends Ant to let you download dependencies
• Maven is a set of reusable Ant scriptlets
While Maven does these things, as you can read above in the "What is Maven?" section, these are not
the only features Maven has, and its objectives are quite different.
Maven does encourage best practices, but we realise that some projects may not fit with these ideals
for historical reasons. While Maven is designed to be flexible, to an extent, in these situations and to
the needs of different projects, it can not cater to every situation without making compromises to the
integrity of its objectives.
If you decide to use Maven, and have an unusual build structure that you cannot reorganise, you may
have to forgo some features or the use of Maven altogether.


2 Features 3

2 Features
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2.1 Feature Summary
The following are the key features of Maven in a nutshell:

• Simple project setup that follows best practices - get a new project or module started in seconds
• Consistent usage across all projects means no ramp up time for new developers coming onto a
project
• Superior dependency management including automatic updating, dependency closures (also
known as transitive dependencies)
• Able to easily work with multiple projects at the same time
• A large and growing repository of libraries and metadata to use out of the box, and arrangements
in place with the largest Open Source projects for real-time availability of their latest releases
• Extensible, with the ability to easily write plugins in Java or scripting languages
• Instant access to new features with little or no extra configuration
• Ant tasks for dependency management and deployment outside of Maven
• Model based builds: Maven is able to build any number of projects into predefined output types
such as a JAR, WAR, or distribution based on metadata about the project, without the need to do
any scripting in most cases.
• Coherent site of project information: Using the same metadata as for the build process, Maven is
able to generate a web site or PDF including any documentation you care to add, and adds to that
standard reports about the state of development of the project. Examples of this information can
be seen at the bottom of the left-hand navigation of this site under the "Project Information" and
"Project Reports" submenus.
• Release management and distribution publication: Without much additional configuration,
Maven will integrate with your source control system such as CVS and manage the release of a
project based on a certain tag. It can also publish this to a distribution location for use by other
projects. Maven is able to publish individual outputs such as a JAR, an archive including other
dependencies and documentation, or as a source distribution.
• Dependency management: Maven encourages the use of a central repository of JARs and
other dependencies. Maven comes with a mechanism that your project's clients can use to
download any JARs required for building your project from a central JAR repository much
like Perl's CPAN. This allows users of Maven to reuse JARs across projects and encourages
communication between projects to ensure that backward compatibility issues are dealt with. We
are collaborating with the folks at Ibiblio who have graciously allowed the central repository to
live on their servers.


3 FAQ 4

3 FAQ
.......................................................................................................................................

3.1 Frequently Asked Technical Questions
1 How do I prevent "[WARNING] Using platform encoding (Cp1252 actually) to copy filtered
resources, i.e. build is platform dependent!"
2 How do I prevent including JARs in WEB-INF/lib? I need a "compile only" scope!
3 How do I list available plugins?
4 How do I determine what version of a plugin I am using?
5 How can I use Ant tasks in Maven 2?
6 How do I set up Maven so it will compile with a target and source JVM of my choice?
7 Is it possible to create my own directory structure?
8 Where is the source code? I couldn't seem to find a link anywhere on the Maven2 site.
9 Maven can't seem to download the dependencies. Is my installation correct?
10I have a jar that I want to put into my local repository. How can I copy it in?
11How do I unsubscribe from Maven mailing lists?
12How do I skip the tests?
13How can I run a single unit test?
14Handle special characters in site
15How do I include tools.jar in my dependencies?
16Maven compiles my test classes but doesn't run them?
17Where are Maven SNAPSHOT artifacts?
18Where are the Maven XSD schemas?
19Maven doesn't work, how do I get help?
20How to produce execution debug output or error messages?
21What is a Mojo?
22How to find dependencies on public Maven repositories?
How do I prevent "[WARNING] Using platform encoding (Cp1252 actually) to copy
filtered resources, i.e. build is platform dependent!"
This or a similar warning is emitted by a plugin that processes plain text files but has not
been configured to use a specific file encoding. So eliminating the warning is simply a
matter of finding out what plugin emits it and how to configure the file encoding for it.
For plugins that follow our guideline for source file encoding, this is as easy as adding the
following property to your POM (or one of its parent POMs):

<project>
...
<properties>
<project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
</properties>
...
</project>

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How do I prevent including JARs in WEB-INF/lib? I need a "compile only" scope!


3 FAQ 5

The scope you should use for this is provided. This indicates to Maven that the
dependency will be provided at run time by its container or the JDK, for example.
Dependencies with this scope will not be passed on transitively, nor will they be bundled in
an package such as a WAR, or included in the runtime classpath.
[top]

How do I list available plugins?
The "Available Plugins" page lists them, and provides additional information to browse the
Maven 2 repository. See http://maven.apache.org/plugins
[top]

How do I determine what version of a plugin I am using?
You can use the Maven Help Plugin's describe goal. For example, to find out the version
of the install plugin:

mvn -Dplugin=install help:describe

Note that you must give the plugin prefix as the argument to plugin, not it's artifact ID.
[top]

How can I use Ant tasks in Maven 2?
There are currently 2 alternatives:

• For use in a plugin written in Java, Beanshell or other Java-like scripting language, you
can construct the Ant tasks using the instructions given in the Ant documentation
• If you have very small amounts of Ant script specific to your project, you can use the
AntRun plugin.
[top]

How do I set up Maven so it will compile with a target and source JVM of my choice?
You must configure the source and target parameters in your pom. For example, to set the
source and target JVM to 1.5, you should have in your pom:


3 FAQ 6

...
<build>
...
<plugins>
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-compiler-plugin</artifactId>
<version>2.0.2</version>
<configuration>
<source>1.5</source>
<target>1.5</target>
</configuration>
</plugin>
</plugins>
...
</build>
...

[top]

Is it possible to create my own directory structure?
Absolutely yes!
By configuring <sourceDirectory>, <resources> and other elements of the <build> section.
In addition, you may need to change the plugin configuration if you are not using plugin
defaults for their files/directories.
[top]

Where is the source code? I couldn't seem to find a link anywhere on the Maven2 site.
The source code can be found in our subversion repository.
For more information, see Building Maven 2.0.
[top]

Maven can't seem to download the dependencies. Is my installation correct?
You most probably need to configure Maven to use a proxy. Please see the information on
Configuring a proxy for information on how to configure your proxy for Maven.
[top]

I have a jar that I want to put into my local repository. How can I copy it in?
If you understand the layout of the maven repository, you can copy the jar directly into
where it is meant to go. Maven will find this file next time it is run.
If you are not confident about the layout of the maven repository, then you can adapt the
following command to load in your jar file, all on one line.


3 FAQ 7

mvn install:install-file
-Dfile=<path-to-file>
-DgroupId=<group-id>
-DartifactId=<artifact-id>
-Dversion=<version>
-Dpackaging=<packaging>
-DgeneratePom=true
Where: <path-to-file> the path to the file to load
<group-id> the group that the file should be registered under
<artifact-id> the artifact name for the file
<version> the version of the file
<packaging> the packaging of the file e.g. jar

This should load in the file into the maven repository, renaming it as needed.
[top]

How do I unsubscribe from Maven mailing lists?
To unsubscribe from a Maven mailing list you simply send a message to

[mailing-list]-unsubscribe@maven.apache.org

So, if you have subscribed to users@maven.apache.org then you would send a message
to users-unsubscribe@maven.apache.org in order to get off the list. People tend
to have problems when they subscribe with one address and attempt to unsubscribe with
another. So make sure that you are using the same address when unsubscribing that you
used to subscribe before asking for help.
If you find you still cannot get off a list then send a message to [mailing-list]-
help@maven.apache.org. These instructions are also appended to every message sent
out on a maven mailing list ...
[top]

How do I skip the tests?
Add the parameter -Dmaven.test.skip=true or -DskipTests=true in the command
line, depending on whether you want to skip test compilation and execution or only
execution. See the example Skipping Tests in the Surefire Plugin's documentation for more
details.
[top]

How can I run a single unit test?
Use the parameter -Dtest=MyTest at the command line. NB: do not specify the entire
package (org.apache.x.y.MyTest)
[top]

Handle special characters in site


3 FAQ 8

Configure your ide to use the correct encoding. With eclipse, add -
Dfile.encoding=ISO-8859-1 in eclipse.ini file
Configure the output encoding in your pom

...
<plugin>
<artifactId>maven-site-plugin</artifactId>
<version>2.0-beta-6</version>
<configuration>
<outputEncoding>UTF-8</outputEncoding>
</configuration>
</plugin>
...

Configure the file encoding use by mvn. add to MAVEN_OPTS the encoding (same as the
ide). This can be made with adding MAVEN_OPTS="-Dfile.encoding=ISO-8859-1" in
$HOME/.profile
[top]

How do I include tools.jar in my dependencies?
The following code includes tools.jar for JDKs on Windows, Linux and Solaris (it is
already included in the runtime for Mac OS X and some free JDKs).

...
<profiles>
<profile>
<id>default-tools.jar</id>
<activation>
<property>
<name>java.vendor</name>
<value>Sun Microsystems Inc.</value>
</property>
</activation>
<dependencies>
<dependency>
<groupId>com.sun</groupId>
<artifactId>tools</artifactId>
<scope>system</scope>
<systemPath>${java.home}/../lib/tools.jar</systemPath>
</dependency>
</dependencies>
</profile>
</profiles>
...

[top]

Maven compiles my test classes but doesn't run them?


3 FAQ 9

Tests are run by the surefire plugin. The surefire plugin can be configured to run certain test
classes and you may have unintentionally done so by specifying a value to ${test}. Check
your settings.xml and pom.xml for a property named "test" which would like this:

...
<properties>
<property>
<name>test</name>
<value>some-value</value>
</property>
</properties>
...

or

...
<properties>
<test>some-value</test>
</properties>
...

[top]

Where are Maven SNAPSHOT artifacts?
If you are trying to build a development version of Maven or plugins, you may need to
access the maven snapshot repositories.
You need to update your settings.xml file using the Guide to Plugin Snapshot Repositories
[top]

Where are the Maven XSD schemas?
The Maven XSD is located here and the Maven Settings XSD is located here.
Your favorite IDE probably supports XSD schema's for pom.xml and settings.xml editing.
You need to specify the following:

<project xmlns="http://maven.apache.org/POM/4.0.0"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://maven.apache.org/POM/4.0.0
http://maven.apache.org/xsd/maven-4.0.0.xsd">
...
</project>

<settings xmlns="http://maven.apache.org/SETTINGS/1.0.0"
xsi:schemaLocation="http://maven.apache.org/SETTINGS/1.0.0
http://maven.apache.org/xsd/settings-1.0.0.xsd">
...
</settings>


3 FAQ 10

[top]

Maven doesn't work, how do I get help?
We have compiled a list of available resources on the getting help page
[top]

How to produce execution debug output or error messages?
You could call Maven with -X parameter or -e parameter. For more information, run:

mvn --help

[top]

What is a Mojo?
A mojo is a Maven plain Old Java Object. Each mojo is an executable goal in Maven, and
a plugin is a distribution of one or more related mojos.
[top]

How to find dependencies on public Maven repositories?
You could use the following search engines:

• http://repository.apache.org
• http://mvnrepository.com
• http://www.mvnbrowser.com
• http://www.jarvana.com
• http://mavensearch.net
[top]


4 Community Overview 11

4 Community Overview
.......................................................................................................................................

4.1 The Maven Community
Maven, like any other opensource project, relies heavily on the efforts of the entire user community
to be ever vigilent for improvements, logging of defects, communicating use-cases, generating
documentation, and being wary of other users in need. This is a quick guide outlining what members
of the Maven community may do to make the system work better for everyone.

4.1.1 Helping With Maven
There is already a comprehensive Guide to Helping With Maven. That guide focuses upon beginning
as a supporter, with information on how to help the coding effort.

4.1.1.1 Commit Questions or Answers to the Maven User FAQ
Documentation is currently a very high priority for the Maven community. Please help out where ever
you can, specifically in the work-in-progress FAQ Wiki.

4.1.1.2 Help Log Defects in JIRA
Just as any other healthy project requires a quick turn-around on defects, and a transparent method of
users to have their wishes heard, so too does Maven need your help. Refer to the Issue Tracking page.

4.1.1.3 Developers
For Maven developers, commiters, PMC: there is a Developers Guide.

4.1.2 Being a Good Maven Citizen
The concept of a public repository built into the core architecture of Maven makes it necessarily
community-centric. There are a few simple things that Maven users may do to help keep that
community thriving.

4.1.2.1 Be a Kind Public Repository User
The best thing that a user can do is to set up their own remote repository mirror containing the
projects needed. There are several tools to make this simpler, such as Nexus or Archiva. This
reduces strain on the Maven central repository, and allows new users to get acquainted with Maven
easier and quicker. This is especially important for power-users and corporations. The incentive
behind this is, controlling your own servers can give you desired level of security and more control
over uptime, resulting in a better experience for your users. With that said, keep the following
sentiment in mind:
DO NOT wget THE ENTIRE REPOSITORY!
Please take only the jars you need. We understand this is may entail more work, but grabbing all 9+
Gigs of binaries really kills our servers.

4.1.2.2 Host a Mirror
As an extention to the previous statement, if you have access to a large data repository with lots of
bandwidth, please consider becomming a mirror for the Maven central repository.
As you can imagine, thousands of users downloading can put quite a strain on one server. If you wish
to be a mirror, please file a request in the Maven Project Administration JIRA project.


4 Community Overview 12

4.1.2.3 Host a Public Repository
If you have any projects that you wish others to use, host them on your own public repository. That
way, your users can simply add your repository to their own project repo list, and viola! Maven can
keep you and your users in synch, growing your user-base due simply to its new-found ease of use.

4.1.3 User Gathering Spots
These are a few of the watering holes around which Maven users tend to gather.

4.1.3.1 Mailing Lists
Maven has a number of Mailing Lists, and the Maven User List is specifically dedicated to answering
questions about all Maven things.

4.1.3.2 IRC (Internet Relay Chat)
Log into the #maven IRC channel on irc.codehaus.org. If you would like to access this over a
web interface, you can do so at http://irc.codehaus.org/ or irc://irc.codehaus.org/maven. IRC logs are
browsable at: http://irc.rectang.com/logs/codehaus/%23maven/.


5 How to Contribute 13

5 How to Contribute
.......................................................................................................................................

5.1 Guide to helping with Maven
As with any open source project, there are several ways you can help:
•Join the mailing list and answer other user's questions
•Report bugs, feature requests and other issues in the issue tracking application.
•Build Maven for yourself, in order to fix bugs.
•Submit patches to reported issues (both those you find, or that others have filed)
•test releases help test releases that are being voted on (see the dev@maven.apache.org mailing
list for release votes
• test snapshot plugins help test the latest development versions of plugins and report issues
• Help with the documentation by pointing out areas that are lacking or unclear, and if you are
so inclined, submitting patches to correct it. You can quickly contribute rough thoughts to the
wiki, or you can volunteer to help collate and organise information that is already there.
Your participation in the community is much appreciated!

5.2 Why Would I Want to Help?
There are several reasons these are good things.
• By answering other people's questions, you can learn more for yourself
• By submitting your own fixes, they get incorporated faster
• By reporting issues, you ensure that bugs don't get missed, or forgotten
• You are giving back to a community that has given you software for free

5.3 How do I Join the Project?
Projects at Apache operate under a meritocracy, meaning those that the developers notice
participating to a high extent will be invited to join the project as a committer.
This is as much based on personality and ability to work with other developers and the community as
it is with proven technical ability. Being unhelpful to other users, or obviously looking to become a
committer for bragging rights and nothing else is frowned upon, as is asking to be made a committer
without having contributed sufficiently to be invited.

5.4 Developers Conventions
There are a number of conventions used in the project, which contributors and developers alike should
follow for consistency's sake.
• Maven Code Style And Convention
• Maven JIRA Convention
• Maven SVN Convention

5.5 Resources for committers
• Developer Resources
• About the Apache Software Foundation
• Committer FAQ


5 How to Contribute 14

• Web Stats
• Mailing List Stats
• Apache Wiki


6 Getting Help 15

6 Getting Help
.......................................................................................................................................

6.1 Getting Help
So something didn't work as you expected it to? You think that Maven is broken. What should you
do?
Here's a list of actions that you can take:

6.1.1 You did check the documentation, didn't you?
Apart from the central Maven site, each of our plugins has a website. Go to the plugins page and
follow the link to the plugin you are having problems with.

6.1.2 Search the user-list archives
Someone else might have experienced the same problem as you before. A list of mail-archives can be
found on mailing list index page. Please search one of them before going any further.

6.1.3 Ask on the user list
Our community is very helpful, just ask it the right way. See the references section, at the end of this
page, for info on how to do that. Subscribe to the users-list and describe your problem there. Don't
expect to get an answer right away. Sometimes it takes a couple of days.

6.1.4 Submit an issue
If it turns out that there is indeed something wrong with Maven or one of the plugins, you should
report it to our issue management system JIRA.
First of all you need to create an account in JIRA. This is so that we can communicate with you while
we work together on the issue. Go to the sign up form to create an account if you don't already have
one.

6.1.4.1 Where?
If the problem is in one of the plugins, check the site of that plugin to get the correct link. Each plugin
has its own section in JIRA, so using the correct link is important. Click on Project Information and
then Issue Tracking. On that page you will find the correct link.
If the problem is in Maven itself you can find the appropriate link on the issue tracking page.

6.1.4.2 How?
Just describing the problem is not enough. It takes a developer a lot of time to make a usable POM to
even attempt to assess the problem. Issues that states problems without something usable to try out
will be closed as incomplete.
Please attach a working POM, or a set of POMs, that we can download and run. We appreciate
reports, but if you don't have something usable for us it's incredibly hard for us to manage the issues.
A POM goes a long way to helping us resolve problems.
Create a POM that can be used to verify that it is a bug. If your pom uses plugins, make sure that you
have specified the version for each and every plugin. If you don't, then we might not be using the
same version as you are when we test it.


6 Getting Help 16

What we like best are patches that fixes the problem. If you want to create a patch for an issue please
read the Maven Developer Guide first.

6.1.5 References

• How To Ask Questions The Smart Way
• How to Get Support from Open Source Mailing Lists


7 Issue Tracking 17

7 Issue Tracking
.......................................................................................................................................

7.1 Overview
Maven projects use JIRA a J2EE-based, issue tracking and project management application.

7.2 Issue Tracking
Issues, bugs, and feature requests should be submitted to the following issue tracking systems
depending projects.

7.2.1 Maven Project
http://jira.codehaus.org/browse/MNG

7.2.2 Maven Website Project
http://jira.codehaus.org/browse/MNGSITE

7.2.3 Maven Project Administration
http://jira.codehaus.org/browse/MPA

7.2.4 Maven Plugins Projects
Please refer you to the Available Plugins page.

7.2.5 Maven Sub Projects

7.2.5.1 Doxia
http://jira.codehaus.org/browse/DOXIA

7.2.5.2 JXR
http://jira.codehaus.org/browse/JXR

7.2.5.3 SCM
http://jira.codehaus.org/browse/SCM

7.2.5.4 Wagon
http://jira.codehaus.org/browse/WAGON


8 Source Repository 18

8 Source Repository
.......................................................................................................................................

8.1 Source Repository
Maven projects use Subversion to manage their source code. Instructions on Subversion use can be
found in the online book Version Control with Subversion.

8.1.1 Web Access
The following list shows the links to the online source repositories for the various development
branches of the Maven core:

http://svn.apache.org/viewvc/maven/maven-2/branches/maven-2.2.x
http://svn.apache.org/viewvc/maven/components/trunk

The source repositories for the various plugins are listed in the documentation of the respective
plugin, reachable via the plugin index.

8.1.2 Anonymous Access
The source can be checked out anonymously from SVN with one of these commands depending on
the development line you are looking for:

$ svn checkout http://svn.apache.org/repos/asf/maven/maven-2/branches/maven-2.2.x ma
$ svn checkout http://svn.apache.org/repos/asf/maven/components/trunk maven-3

8.1.3 Developer Access
Everyone can access the Subversion repository via HTTP, but committers must checkout the
Subversion repository via HTTPS to gain write access:

$ svn checkout https://svn.apache.org/repos/asf/maven/maven-2/branches/maven-2.2.x m
$ svn checkout https://svn.apache.org/repos/asf/maven/components/trunk maven-3

To commit changes to the repository, execute the following command to commit your changes ( svn
will prompt you for your password):

$ svn commit --username your-username -m "A message"

8.1.4 Access from behind a Firewall
For those users who are stuck behind a corporate firewall which is blocking HTTP access to the
Subversion repository, you can try to access it via the developer connection:

$ svn checkout https://svn.apache.org/repos/asf/maven/maven-2/branches/maven-2.2.x m
$ svn checkout https://svn.apache.org/repos/asf/maven/components/trunk maven-3

8.1.5 Access through a Proxy
The Subversion client can go through a proxy, if you configure it to do so. First, edit your servers
configuration file to indicate which proxy to use. The file's location depends on your operating


8 Source Repository 19

system. On Linux or Unix it is located in the directory ~/.subversion. On Windows it is in
%APPDATA%Subversion (try echo %APPDATA%, note this is a hidden directory).
There are comments in the file explaining what to do. If you don't have that file, get the latest
Subversion client and run any command; this will cause the configuration directory and template files
to be created.
Example: Edit the servers file and add something like:

[global]
http-proxy-host = your.proxy.name
http-proxy-port = 3128


9 Continuous Integration 20

9 Continuous Integration
.......................................................................................................................................

9.1 Continuous Integration

9.1.1 CI Servers
Following is an alphabetical list of some CI servers we've heard mentioned around the Maven
community:

• Apache Continuum
• Bamboo (Atlassian)
• Cruise Control
• Hudson
• TeamCity (JetBrains)


10 Running Maven 21

10 Running Maven
.......................................................................................................................................

10.1 Building a Project with Maven
This document centre is for those that have the source code to a project that builds with Maven, and
would like to know how to use Maven to build it (or perform other common tasks).
The documents here are also helpful to new Maven users.
• Download Maven - Download the latest version of Maven
• Quick Start - Get started building the project quickly
• Cookbook - Examples of how to perform other common tasks on a Maven-built project
• Use Maven - Learn how to use Maven on your own project

10.1.1 Quick Start

10.1.1.1 Configuring Maven
Maven will run with sensible defaults, so you can get right into it. However, if you are operating
under a restricted environment or behind a firewall, you might need to prepare to run Maven, as it
requires write access to the home directory ( ~/.m2 on Unix/Mac OS X and C:Documents and
Settingsusername.m2 on Windows) and network access to download binary dependencies.
• Configuring Maven
• Configuring a HTTP Proxy

10.1.1.2 Building a Project
The vast majority of Maven-built projects can be built with the following command:
mvn clean install
This command tells Maven to build all the modules, and to install it in the local repository. The local
repository is created in your home directory (or alternative location that you created it), and is the
location that all downloaded binaries and the projects you built are stored.
That's it! If you look in the target subdirectory, you should find the build output and the final library
or application that was being built.
Note: Some projects have multiple modules, so the library or application you are looking for may be
in a module subdirectory.
While this will build most projects and Maven encourages this standard convention, builds can be
customisable. If this does not suffice, please consult the project's documentation.

10.1.1.3 More than just the Build
Maven can do more than just build software - it can assist with testing, run web applications and
produce reports on projects, as well as any number of other tasks provided by plug-ins.
To try some other tasks, see the Cookbook for Running Maven.

10.1.1.4 When Things go Wrong
The following are some common problems when building with Maven, and how to resolve them.
10.Missing Dependencies
A missing dependency presents with an error like the following:


10 Running Maven 22

[INFO] Failed to resolve artifact.
Missing:
----------
1) jnuit:junit:jar:3.8.1
Try downloading the file manually from the project website.
Then, install it using the command:
mvn install:install-file -DgroupId=jnuit -DartifactId=junit
-Dversion=3.8.1 -Dpackaging=jar -Dfile=/path/to/file
Path to dependency:
1) org.apache.maven:maven:pom:2.1-SNAPSHOT
2) jnuit:junit:jar:3.8.1
----------
1 required artifact is missing.
for artifact:
org.apache.maven:maven:pom:2.1-SNAPSHOT
from the specified remote repositories:
central (http://repo1.maven.org/maven2)

To resolve this issue, it depends on what the dependency is and why it is missing. The most common
cause is because it can not be redistributed from the repository and must be manually installed using
the instructions given in the message. This is most common with some older JARs from Sun (usually
javax.* group IDs), and is further documented in the Guide to Coping with Sun JARs.
You can check the list of repositories at the end of the error to ensure that the expected ones are listed
- it may be that the project requires an alternative repository that has not been declared properly or is
not accessible with your Maven configuration.
In other cases, it may be an incorrectly declared dependency (like the typo in the example above)
which the project would need to fix, like a compilation error.


11 Maven Plugins 23

11 Maven Plugins
.......................................................................................................................................

11.1 Available Plugins
Maven is - at its heart - a plugin execution framework; all work is done by plugins. Looking for a
specific goal to execute? This page lists the core plugins and others.

11.1.1 Supported By The Maven Project
To see the most up-to-date list browse the Maven repository at http://repo1.maven.org/maven2/,
specifically the org/apache/maven/plugins subfolder. (Plugins are organized according to a
directory structure that resembles the standard Java package naming convention)

Source Issue
Plugin Version Release Date Description Repository Tracking
Core plugins Plugins
corresponding
to default
core phases
(ie. clean,
compile). They
may have
muliple goals
as well.
clean 2.3 2009-01-10 Clean up after SVN JIRA
the build.
compiler 2.0.2 2007-02-13 Compiles Java SVN JIRA
sources.
deploy 2.4 2008-08-06 Deploy the SVN JIRA
built artifact
to the remote
repository.
install 2.3 2009-03-25 Install the built SVN JIRA
artifact into the
local repository.
resources 2.3 2008-10-17 Copy the SVN JIRA
resources to
the output
directory for
including in the
JAR.
site 2.0.1 2009-07-14 Generate a site SVN JIRA
for the current
project.
surefire 2.4.3 2008-05-14 Run the SVN JIRA
Junit tests in
an isolated
classloader.


11 Maven Plugins 24

verifier 1.0-beta-1 2006-05-07 Useful for SVN JIRA
integration
tests - verifies
the existence
of certain
conditions.
Packaging These plugins
types / tools relate to
packaging
respective
artifact types.
ear 2.3.2 2009-03-07 Generate an SVN JIRA
EAR from the
current project.
ejb 2.2 2009-07-14 Build an EJB SVN JIRA
(and optional
client) from the
current project.
jar 2.2 2008-01-16 Build a JAR SVN JIRA
from the current
project.
rar 2.2 2007-02-28 Build a RAR SVN JIRA
from the current
project.
war 2.1-beta-1 2009-03-22 Build a WAR SVN JIRA
from the current
project.
shade 1.2.1 2009-04-17 Build an Uber- SVN JIRA
JAR from the
current project,
including
dependencies.
Reporting Plugins which
plugins generate
reports, are
configured
as reports in
the POM and
run under the
site generation
lifecycle.
changelog 2.1 2007-07-25 Generate a SVN JIRA
list of recent
changes from
your SCM.
changes 2.1 2008-11-24 Generate a SVN JIRA
report from
issue tracking
or a change
document.
checkstyle 2.3 2009-07-14 Generate a SVN JIRA
checkstyle
report.


11 Maven Plugins 25

clover 2.4 2007-04-23 Generate SVN JIRA
a Clover
report. NOTE:
Moved to
Atlassian.com
doap 1.0 2008-08-01 Generate a SVN JIRA
Description
of a Project
(DOAP) file
from a POM.
docck 1.0 2008-11-16 Documentation SVN JIRA
checker plugin.
javadoc 2.5 2008-08-26 Generate SVN JIRA
Javadoc for the
project.
jxr 2.1 2007-04-05 Generate a SVN JIRA
source cross
reference.
pmd 2.4 2008-01-08 Generate a SVN JIRA
PMD report.
project- 2.1.2 2009-07-23 Generate SVN JIRA
info- standard
reports project reports.
surefire- 2.4.3 2008-05-14 Generate a SVN JIRA
report report based on
the results of
unit tests.
Tools These are
miscellaneous
tools available
through
Maven by
default.
ant 2.2 2009-07-19 Generate an SVN JIRA
Ant build file for
the project.
antrun 1.3 2008-10-11 Run a set of SVN JIRA
ant tasks from
a phase of the
build.
archetype 2.0-alpha-4 2008-09-26 Generate a SVN JIRA
skeleton project
structure from
an archetype.
assembly 2.2-beta-4 2009-06-05 Build an SVN JIRA
assembly
(distribution) of
sources and/or
binaries.


11 Maven Plugins 26

dependency 2.1 2009-01-10 Dependency SVN JIRA
manipulation
(copy, unpack)
and analysis.
enforcer 1.0-beta-1 2009-02-25 Environmental SVN JIRA
constraint
checking
(Maven
Version, JDK
etc), User
Custom Rule
Execution.
gpg 1.0-alpha-4 2007-09-28 Create SVN JIRA
signatures for
the artifacts and
poms.
help 2.1 2008-09-04 Get information SVN JIRA
about the
working
environment for
the project.
invoker 1.3 2008-08-09 Run a set of SVN JIRA
Maven projects
and verify the
output.
jarsigner 1.0 2009-07-23 Signs or verifies SVN JIRA
project artifacts.
one 1.2 2007-09-12 A plugin for SVN JIRA
interacting with
legacy Maven
1.x repositories
and builds.
patch 1.1 2009-04-13 Use the gnu SVN JIRA
patch tool to
apply patch
files to source
code.
pdf 1.0 2009-06-29 Generate a SVN JIRA
PDF version of
your project's
documentation.
plugin 2.5 2009-02-26 Create a SVN JIRA
Maven plugin
descriptor for
any Mojo's
found in the
source tree, to
include in the
JAR.


11 Maven Plugins 27

release 2.0-beta-9 2009-03-28 Release the SVN JIRA
current project
- updating
the POM and
tagging in the
SCM.
reactor 1.0 2008-09-27 Build a SVN JIRA
subset of
interdependent
projects in a
reactor
remote- 1.0 2008-03-20 Copy remote SVN JIRA
resources resources to
the output
directory for
inclusion in the
artifact.
repository 2.1 2008-06-26 Plugin to help SVN JIRA
with repository-
based tasks.
scm 1.1 2008-08-27 Generate a SVN JIRA
SCM for the
current project.
source 2.1 2009-04-22 Build a JAR SVN JIRA
of sources for
use in IDEs and
distribution to
the repository.
stage 1.0-alpha-2 2009-07-14 Assists with SVN JIRA
release staging
and promotion.
IDEs Plugins that
simplify
integration
with integrated
developer
environments.
eclipse 2.7 2009-06-13 Generate an SVN JIRA
Eclipse project
file for the
current project.
idea 2.2 2008-08-08 Create/update SVN JIRA
an IDEA
workspace for
the current
project
(individual
modules are
created as
IDEA modules)

There are also some sandbox plugins into our source reposity.


11 Maven Plugins 28

11.1.2 Outside The Maven Land

11.1.2.1 At codehaus.org
There are also many plug-ins available at the Mojo project at Codehaus.
To see the most up-to-date list, browse the Codehaus repository at http://repository.codehaus.org/,
specifically the org/codehaus/mojo subfolder. Here are a few common ones:

Plugin (see complete list with version) Description
build-helper Attach extra artifacts and source folders to build.
castor Generate sources from an XSD using Castor.
javacc Generate sources from a JavaCC grammer.
jdepend Generate a report on code metrics using JDepend.
native Compiles C and C++ code with native compilers.
sql Executes SQL scripts from files or inline.
taglist Generate a list of tasks based on tags in your code.

11.1.2.2 At code.google.com
There are also many plug-ins available at the Google Code.

11.1.2.3 Misc
A number of other projects provide their own Maven plugins. This includes:

Plugin Maintainer Description
cargo Cargo Project Start/stop/configure J2EE
containers and deploy to them.
jaxme Apache Web Services Project Use the JaxMe JAXB
implementation to generate Java
sources from XML schema.
jetty Jetty Project Jetty Run a Jetty container for
rapid webapp development.
jalopy Triemax Use Jalopy to format your source
code.
rat Apache Incubator Project Release Audit Tool (RAT) to verify
files.
Genesis Plugins Apache Geronimo Project Verify legal files in artifacts.


12 User Centre 29

12 User Centre
.......................................................................................................................................

12.1 Maven Users Centre
This documentation centre is for those that have decided to use Maven to build their project, and
would like to get started quickly, or are already using Maven and would like to add new functionality
or fix a problem in their build.

• Download Maven - Download the latest version of Maven
• The 5 minute test - Learn how to use Maven in 5 minutes
• Getting Started Tutorial - An in depth tutorial once you've learned the basics
• Build Cookbook - Examples for how to add functionality to your build
• Getting Help - How to get help with Maven

12.1.1 Reference

• POM Reference
• Settings Reference


13 Maven in 5 Minutes 30

13 Maven in 5 Minutes
.......................................................................................................................................

13.1 Maven in 5 Minutes

13.1.1 Installation
Maven is a Java tool, so you must have Java installed in order to proceed.
First, download Maven and follow the installation instructions. After that, type the following in a
terminal or in a command prompt:
mvn --version
It should print out your installed version of Maven, for example:
Maven version: 2.0.8
Java version: 1.5.0_12
OS name: "windows 2003" version: "5.2" arch: "x86" Family: "windows"
Depending upon your network setup, you may require extra configuration. Check out the Guide to
Configuring Maven if necessary.

13.1.2 Creating a Project
On your command line, execute the following Maven goal:
mvn archetype:create -DgroupId=com.mycompany.app -DartifactId=my-app
If you have just installed Maven, it may take a while on the first run. This is because Maven is
downloading the most recent artifacts (plugin jars and other files) into your local repository. You may
also need to execute the command a couple of times before it succeeds. This is because the remote
server may time out before your downloads are complete. Don't worry, there are ways to fix that.
You will notice that the create goal created a directory with the same name given as the artifactId.
Change into that directory.
cd my-app
Under this directory you will notice the following standard project structure.
my-app
|-- pom.xml
`-- src
|-- main
| `-- java
| `-- com
| `-- mycompany
| `-- app
| `-- App.java
`-- test
`-- java
`-- com
`-- mycompany
`-- app
`-- AppTest.java
The src/main/java directory contains the project source code, the src/test/java directory contains the
test source, and the pom.xml is the project's Project Object Model, or POM.



13.1.2.1 The POM
The pom.xml file is the core of a project's configuration in Maven. It is a single configuration file that
contains the majority of information required to build a project in just the way you want. The POM is
huge and can be daunting in its complexity, but it is not necessary to understand all of the intricacies
just yet to use it effectively. This project's POM is:
<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://
www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://
maven.apache.org/xsd/maven-4.0.0.xsd">
<modelVersion>4.0.0</modelVersion>
<groupId>com.mycompany.app</groupId>
<artifactId>my-app</artifactId>
<packaging>jar</packaging>
<version>1.0-SNAPSHOT</version>
<name>Maven Quick Start Archetype</name>
<url>http://maven.apache.org</url>
<dependencies>
<dependency>
<groupId>junit</groupId>
<artifactId>junit</artifactId>
<scope>test</scope>
</dependency>
</dependencies>
</project>

13.1.2.2 What did I just do?
You executed the Maven goal archetype:create, and passed in various parameters to that goal. The
prefix archetype is the plugin that contains the goal. If you are familiar with Ant, you may concieve
of this as similar to a task. This goal created a simple project based upon an archetype. Suffice it to
say for now that a plugin is a collection of goals with a general common purpose. For example the
jboss-maven-plugin, whose purpose is "deal with various jboss items".

13.1.2.3 Build the Project
mvn package
The command line will print out various actions, and end with the following:
...
[INFO] ------------------------------------------------------------------------
[INFO] BUILD SUCCESSFUL
[INFO] ------------------------------------------------------------------------
[INFO] Total time: 2 seconds
[INFO] Finished at: Thu Oct 05 21:16:04 CDT 2006
[INFO] Final Memory: 3M/6M
[INFO] ------------------------------------------------------------------------
Unlike the first command executed ( archetype:create) you may notice the second is simply a single
word - package. Rather than a goal, this is a phase. A phase is a step in the build lifecycle, which
is an ordered sequence of phases. When a phase is given, Maven will execute every phase in the
sequence up to and including the one defined. For example, if we execute the compile phase, the
phases that actually get executed are:

1 validate



2 generate-sources
3 process-sources
4 generate-resources
5 process-resources
6 compile
You may test the newly compiled and packaged JAR with the following command:
java -cp target/my-app-1.0-SNAPSHOT.jar com.mycompany.app.App
Which will print the quintessential:
Hello World!

13.1.3 Running Maven Tools

13.1.3.1 Maven Phases
Although hardly a comprehensive list, these are the most common default lifecycle phases executed.

• validate: validate the project is correct and all necessary information is available
• compile: compile the source code of the project
• test: test the compiled source code using a suitable unit testing framework. These tests should
not require the code be packaged or deployed
• package: take the compiled code and package it in its distributable format, such as a JAR.
• integration-test: process and deploy the package if necessary into an environment where
integration tests can be run
• verify: run any checks to verify the package is valid and meets quality criteria
• install: install the package into the local repository, for use as a dependency in other projects
locally
• deploy: done in an integration or release environment, copies the final package to the remote
repository for sharing with other developers and projects.
There are two other Maven lifecycles of note beyond the default list above. They are

• clean: cleans up artifacts created by prior builds

• site: generates site documentation for this project
Phases are actually mapped to underlying goals. The specific goals executed per phase is dependant
upon the packaging type of the project. For example, package executes jar:jar if the project type is a
JAR, and war:war is the project type is - you guessed it - a WAR.
An interesting thing to note is that phases and goals may be executed in sequence.
mvn clean dependency:copy-dependencies package
This command will clean the project, copy dependencies, and package the project (executing all
phases up to package, of course).

13.1.3.2 Generating the Site
mvn site
This phase generates a site based upon information on the project's pom. You can look at the
documentation generated under target/site.



13.1.4 Conclusion
We hope this quick overview has piqued your interest in the versitility of Maven. Note that this is a
very truncated quick-start guide. Now you are ready for more comprehensive details concerning the
actions you have just performed. Check out the Maven Getting Started Guide.


14 Getting Started Guide 34

14 Getting Started Guide
.......................................................................................................................................

14.1 Maven Getting Started Guide
This guide is intended as a reference for those working with Maven for the first time, but is also
intended to serve as a cookbook with self-contained references and solutions for common use cases.
For first time users, it is recommended that you step through the material in a sequential fashion. For
users more familiar with Maven, this guide endeavours to provide a quick solution for the need at
hand. It is assumed at this point that you have downloaded Maven and installed Maven on your local
machine. If you have not done so please refer to the Download and Installation instructions.
Ok, so you now have Maven installed and we're ready to go. Before we jump into our examples we'll
very briefly go over what Maven is and how it can help you with your daily work and collaborative
efforts with team members. Maven will, of course, work for small projects, but Maven shines in
helping teams operate more effectively by allowing team members to focus on what the stakeholders
of a project require. You can leave the build infrastructure to Maven!

14.2 Sections
• What is Maven?
• How can Maven benefit my development process?
• How do I setup Maven?
• How do I make my first Maven project?
• How do I compile my application sources?
• How do I compile my test sources and run my unit tests?
• How do I create a JAR and install it in my local repository?
• How do I use plug-ins?
• How do I add resources to my JAR?
• How do I filter resource files?
• How do I use external dependencies?
• How do I deploy my jar in my remote repository?
• How do I create documentation?
• How do I build other types of projects?
• How do I build more than one project at once?

14.2.1 What is Maven?
At first glance Maven can appear to be many things, but in a nutshell Maven is an attempt to apply
patterns to a project's build infrastructure in order to promote comprehension and productivity by
providing a clear path in the use of best practices. Maven is essentially a project management and
comprehension tool and as such provides a way to help with managing:
• Builds
• Documentation
• Reporting
• Dependencies
• SCMs
• Releases
• Distribution



If you want more background information on Maven you can check out The Philosophy of Maven
and The History of Maven. Now let's move on to how you, the user, can benefit from using Maven.

14.2.2 How can Maven benefit my development process?
Maven can provide benefits for your build process by employing standard conventions and practices
to accelerate your development cycle while at the same time helping you achieve a higher rate of
success. For a more detailed look at how Maven can help you with your development process please
refer to The Benefits of Using Maven.
Now that we have covered a little bit of the history and purpose of Maven let's get into some real
examples to get you up and running with Maven!

14.2.3 How do I setup Maven?
The defaults for Maven are often sufficient, but if you need to change the cache location or are behind
a HTTP proxy, you will need to create configuration. See the Guide to Configuring Maven for more
information.

14.2.4 How do I make my first Maven project?
We are going to jump headlong into creating your first Maven project! To create our first Maven
project we are going to use Maven's archetype mechanism. An archetype is defined as an original
pattern or model from which all other things of the same kind are made. In Maven, an archetype
is a template of a project which is combined with some user input to produce a working Maven
project that has been tailored to the user's requirements. We are going to show you how the archetype
mechanism works now, but if you would like to know more about archetypes please refer to our
Introduction to Archetypes.
On to creating your first project! In order to create the simplest of Maven projects, execute the
following from the command line:

mvn archetype:create
-DarchetypeGroupId=org.apache.maven.archetypes
-DgroupId=com.mycompany.app
-DartifactId=my-app

Once you have executed this command, you will notice a few things have happened. First, you will
notice that a directory named my-app has been created for the new project, and this directory contains
a file named pom.xml that should look like this:



<dependencies>
<dependency>
<scope>test</scope>
</dependency>
</dependencies>
</project>

pom.xml contains the Project Object Model (POM) for this project. The POM is the basic unit of
work in Maven. This is important to remember because Maven is inherently project-centric in that
everything revolves around the notion of a project. In short, the POM contains every important piece
of information about your project and is essentially one-stop-shopping for finding anything related
to your project. Understanding the POM is important and new users are encouraged to refer to the
Introduction to the POM.
This is a very simple POM but still displays the key elements every POM contains, so let's walk
through each of them to familiarize you with the POM essentials:

• project This is the top-level element in all Maven pom.xml files.
• modelVersion This element indicates what version of the object model this POM is using.
The version of the model itself changes very infrequently but it is mandatory in order to ensure
stability of use if and when the Maven developers deem it necessary to change the model.
• groupId This element indicates the unique identifier of the organization or group that created the
project. The groupId is one of the key identifiers of a project and is typically based on the fully
qualified domain name of your organization. For example org.apache.maven.plugins is the
designated groupId for all Maven plug-ins.
• artifactId This element indicates the unique base name of the primary artifact being generated
by this project. The primary artifact for a project is typically a JAR file. Secondary artifacts
like source bundles also use the artifactId as part of their final name. A typical artifact
produced by Maven would have the form <artifactId>-<version>.<extension> (for example,
myapp-1.0.jar).
• packaging This element indicates the package type to be used by this artifact (e.g. JAR, WAR,
EAR, etc.). This not only means if the artifact produced is JAR, WAR, or EAR but can also
indicate a specific lifecycle to use as part of the build process. (The lifecycle is a topic we will
deal with further on in the guide. For now, just keep in mind that the indicated packaging of a
project can play a part in customizing the build lifecycle.) The default value for the packaging
element is JAR so you do not have to specify this for most projects.
• version This element indicates the version of the artifact generated by the project. Maven goes a
long way to help you with version management and you will often see the SNAPSHOT designator



in a version, which indicates that a project is in a state of development. We will discuss the use
of snapshots and how they work further on in this guide.
• name This element indicates the display name used for the project. This is often used in Maven's
generated documentation.
• url This element indicates where the project's site can be found. This is often used in Maven's
generated documentation.
• description This element provides a basic description of your project. This is often used in
Maven's generated documentation.
For a complete reference of what elements are available for use in the POM please refer to our POM
Reference. Now let's get back to the project at hand.
After the archetype generation of your first project you will also notice that the following directory
structure has been created:

my-app
|-- pom.xml
`-- src
|-- main
| `-- java
| `-- com
| `-- mycompany
| `-- app
| `-- App.java
`-- test
`-- java
`-- com
`-- mycompany
`-- app
`-- AppTest.java

As you can see, the project created from the archetype has a POM, a source tree for your application's
sources and a source tree for your test sources. This is the standard layout for Maven projects
(the application sources reside in ${basedir}/src/main/java and test sources reside in
${basedir}/src/test/java, where ${basedir} represents the directory containing pom.xml).
If you were to create a Maven project by hand this is the directory structure that we recommend using.
This is a Maven convention and to learn more about it you can read our Introduction to the Standard
Directory Layout.
Now that we have a POM, some application sources, and some test sources you are probably asking ...

14.2.5 How do I compile my application sources?
Change to the directory where pom.xml is created by archetype:create and execute the following
command to compile your application sources:

mvn compile

Upon executing this command you should see output like the following:



[INFO] ----------------------------------------------------------------------------
[INFO] Building Maven Quick Start Archetype
[INFO] task-segment: [compile]
[INFO] ----------------------------------------------------------------------------
[INFO] artifact org.apache.maven.plugins:maven-resources-plugin:
checking for updates from central
...
[INFO] artifact org.apache.maven.plugins:maven-compiler-plugin:
...
[INFO] [resources:resources]
...
[INFO] [compiler:compile]
Compiling 1 source file to <dir>/my-app/target/classes
[INFO] ----------------------------------------------------------------------------
[INFO] ----------------------------------------------------------------------------
[INFO] Total time: 3 minutes 54 seconds
[INFO] Finished at: Fri Sep 23 15:48:34 GMT-05:00 2005
[INFO] ----------------------------------------------------------------------------

The first time you execute this (or any other) command, Maven will need to download all the plugins
and related dependencies it needs to fulfill the command. From a clean installation of Maven this can
take quite a while (in the output above, it took almost 4 minutes). If you execute the command again,
Maven will now have what it needs, so it won't need to download anything new and will be able to
execute the command much more quickly.
As you can see from the output, the compiled classes were placed in ${basedir}/target/
classes, which is another standard convention employed by Maven. So, if you're a keen observer,
you'll notice that by using the standard conventions the POM above is very small and you haven't had
to tell Maven explicitly where any of your sources are or where the output should go. By following
the standard Maven conventions you can get a lot done with very little effort! Just as a casual
comparison, let's take a look at what you might have had to do in Ant to accomplish the same thing.
Now, this is simply to compile a single tree of application sources and the Ant script shown is pretty
much the same size as the POM shown above. But we'll see how much more we can do with just that
simple POM!

14.2.6 How do I compile my test sources and run my unit tests?
Now you're successfully compiling your application's sources and now you've got some unit tests that
you want to compile and execute (because every programmer always writes and executes their unit
tests *nudge nudge wink wink*).
Execute the following command:

mvn test

Upon executing this command you should see output like the following:



[INFO] ----------------------------------------------------------------------------
[INFO] task-segment: [test]
[INFO] ----------------------------------------------------------------------------
[INFO] artifact org.apache.maven.plugins:maven-surefire-plugin:
...
[INFO] Nothing to compile - all classes are up to date
[INFO] [resources:testResources]
[INFO] [compiler:testCompile]
Compiling 1 source file to C:TestMaven2testmy-apptargettest-classes
...
[INFO] [surefire:test]
[INFO] Setting reports dir: C:TestMaven2testmy-apptarget/surefire-reports
-------------------------------------------------------
T E S T S
-------------------------------------------------------
[surefire] Running com.mycompany.app.AppTest
[surefire] Tests run: 1, Failures: 0, Errors: 0, Time elapsed: 0 sec
Results :
[surefire] Tests run: 1, Failures: 0, Errors: 0
[INFO] ----------------------------------------------------------------------------
[INFO] ----------------------------------------------------------------------------
[INFO] Finished at: Thu Oct 06 08:12:17 MDT 2005
[INFO] ----------------------------------------------------------------------------

Some things to notice about the output:

• Maven downloads more dependencies this time. These are the dependencies and plugins
necessary for executing the tests (it already has the dependencies it needs for compiling and
won't download them again).
• Before compiling and executing the tests Maven compiles the main code (all these classes are up
to date because we haven't changed anything since we compiled last).
If you simply want to compile your test sources (but not execute the tests), you can execute the
following:

mvn test-compile

Now that you can compile your application sources, compile your tests, and execute the tests, you'll
want to move on to the next logical step so you'll be asking ...

14.2.7 How do I create a JAR and install it in my local repository?
Making a JAR file is straight forward enough and can be accomplished by executing the following
command:

mvn package



If you take a look at the POM for your project you will notice the packaging element is set to jar.
This is how Maven knows to produce a JAR file from the above command (we'll talk more about this
later). You can now take a look in the ${basedir}/target directory and you will see the generated
JAR file.
Now you'll want to install the artifact you've generated (the JAR file) in your local repository (
~/.m2/repository is the default location). For more information on repositories you can refer
to our Introduction to Repositories but let's move on to installing our artifact! To do so execute the
following command:

mvn install

Upon executing this command you should see the following output:

[INFO] ----------------------------------------------------------------------------
[INFO] task-segment: [install]
[INFO] ----------------------------------------------------------------------------
Compiling 1 source file to <dir>/my-app/target/classes
[INFO] [resources:testResources]
[INFO] [compiler:testCompile]
Compiling 1 source file to <dir>/my-app/target/test-classes
[INFO] [surefire:test]
[INFO] Setting reports dir: <dir>/my-app/target/surefire-reports
-------------------------------------------------------
T E S T S
-------------------------------------------------------
[surefire] Running com.mycompany.app.AppTest
[surefire] Tests run: 1, Failures: 0, Errors: 0, Time elapsed: 0.001 sec
Results :
[surefire] Tests run: 1, Failures: 0, Errors: 0
[INFO] [jar:jar]
[INFO] Building jar: <dir>/my-app/target/my-app-1.0-SNAPSHOT.jar
[INFO] [install:install]
[INFO] Installing <dir>/my-app/target/my-app-1.0-SNAPSHOT.jar to
<local-repository>/com/mycompany/app/my-app/1.0-SNAPSHOT/my-app-1.0-SNAPSHOT.jar
[INFO] ----------------------------------------------------------------------------
[INFO] ----------------------------------------------------------------------------
[INFO] Finished at: Tue Oct 04 13:20:32 GMT-05:00 2005
[INFO] ----------------------------------------------------------------------------

Note that the surefire plugin (which executes the test) looks for tests contained in files with a
particular naming convention. By default the tests included are:
• **/*Test.java
• **/Test*.java
• **/*TestCase.java
And the default excludes are:
• **/Abstract*Test.java



• **/Abstract*TestCase.java
You have walked through the process for setting up, building, testing, packaging, and installing a
typical Maven project. This is likely the vast majority of what projects will be doing with Maven and
if you've noticed, everything you've been able to do up to this point has been driven by an 18-line
file, namely the project's model or POM. If you look at a typical Ant build file that provides the same
functionality that we've achieved thus far you'll notice it's already twice the size of the POM and we're
just getting started! There is far more functionality available to you from Maven without requiring
any additions to our POM as it currently stands. To get any more functionality out of our example Ant
build file you must keep making error-prone additions.
So what else can you get for free? There are a great number of Maven plug-ins that work out of the
box with even a simple POM like we have above. We'll mention one here specifically as it is one of
the highly prized features of Maven: without any work on your part this POM has enough information
to generate a web site for your project! You will most likely want to customize your Maven site but if
you're pressed for time all you need to do to provide basic information about your project is execute
the following command:

mvn site

There are plenty of other standalone goals that can be executed as well, for example:

mvn clean

This will remove the target directory with all the build data before starting so that it is fresh.
Perhaps you'd like to generate an IntelliJ IDEA descriptor for the project?

mvn idea:idea

This can be run over the top of a previous IDEA project - it will update the settings rather than
starting fresh.
If you are using Eclipse IDE, just call:

mvn eclipse:eclipse

Note: some familiar goals from Maven 1.0 are still there - such as jar:jar, but they might not
behave like you'd expect. Presently, jar:jar will not recompile sources - it will simply just create
a JAR from the target/classes directory, under the assumption everything else had already been
done.

14.2.8 How do I use plug-ins?
Whenever you want to customise the build for a Maven project, this is done by adding or
reconfiguring plugins.
Note for Maven 1.0 Users: In Maven 1.0, you would have added some preGoal to maven.xml and
some entries to project.properties. Here, it is a little different.
For this example, we will configure the Java compiler to allow JDK 5.0 sources. This is as simple as
adding this to your POM:



...
<build>
<plugins>
<plugin>
<configuration>
<source>1.5</source>
<target>1.5</target>
</configuration>
</plugin>
</plugins>
</build>
...

You'll notice that all plugins in Maven 2.0 look much like a dependency - and in some ways they are.
This plugin will be automatically downloaded and used - including a specific version if you request it
(the default is to use the latest available).
The configuration element applies the given parameters to every goal from the compiler plugin.
In the above case, the compiler plugin is already used as part of the build process and this just changes
the configuration. It is also possible to add new goals to the process, and configure specific goals. For
information on this, see the Introduction to the Build Lifecycle.
To find out what configuration is available for a plugin, you can see the Plugins List and navigate
to the plugin and goal you are using. For general information about how to configure the available
parameters of a plugin, have a look at the Guide to Configuring Plug-ins.

14.2.9 How do I add resources to my JAR?
Another common use case that can be satisfied which requires no changes to the POM that we have
above is packaging resources in the JAR file. For this common task, Maven again relies on the
Standard Directory Layout, which means by using standard Maven conventions you can package
resources within JARs simply by placing those resources in a standard directory structure.
You see below in our example we have added the directory ${basedir}/src/main/resources
into which we place any resources we wish to package in our JAR. The simple rule employed by
Maven is this: any directories or files placed within the ${basedir}/src/main/resources
directory are packaged in your JAR with the exact same structure starting at the base of the JAR.



my-app
|-- pom.xml
`-- src
|-- main
| |-- java
| | `-- com
| | `-- mycompany
| | `-- app
| | `-- App.java
| `-- resources
| `-- META-INF
| `-- application.properties
`-- test
`-- java
`-- com
`-- mycompany
`-- app
`-- AppTest.java

So you can see in our example that we have a META-INF directory with an
application.properties file within that directory. If you unpacked the JAR that Maven created
for you and took a look at it you would see the following:

|-- META-INF
| |-- MANIFEST.MF
| |-- application.properties
| `-- maven
| `-- com.mycompany.app
| `-- my-app
| |-- pom.properties
| `-- pom.xml
`-- com
`-- mycompany
`-- app
`-- App.class

As you can see, the contents of ${basedir}/src/main/resources can be found starting at
the base of the JAR and our application.properties file is there in the META-INF directory.
You will also notice some other files there like META-INF/MANIFEST.MF as well as a pom.xml
and pom.properties file. These come standard with generation of a JAR in Maven. You can
create your own manifest if you choose, but Maven will generate one by default if you don't. (You
can also modify the entries in the default manifest. We will touch on this later.) The pom.xml and
pom.properties files are packaged up in the JAR so that each artifact produced by Maven is self-
describing and also allows you to utilize the metadata in your own application if the need arises. One
simple use might be to retrieve the version of your application. Operating on the POM file would
require you to use some Maven utilities but the properties can be utilized using the standard Java API
and look like the following:

#Generated by Maven
#Tue Oct 04 15:43:21 GMT-05:00 2005
version=1.0-SNAPSHOT
groupId=com.mycompany.app
artifactId=my-app



To add resources to the classpath for your unit tests, you follow the same pattern as you do for adding
resources to the JAR except the directory you place resources in is ${basedir}/src/test/resources. At
this point you would have a project directory structure that would look like the following:

my-app
|-- pom.xml
`-- src
|-- main
| |-- java
| | `-- com
| | `-- mycompany
| | `-- app
| | `-- App.java
| `-- resources
| `-- META-INF
| |-- application.properties
`-- test
|-- java
| `-- com
| `-- mycompany
| `-- app
| `-- AppTest.java
`-- resources
`-- test.properties

In a unit test you could use a simple snippet of code like the following to access the resource required
for testing:

...
// Retrieve resource
InputStream is = getClass().getResourceAsStream( "/test.properties" );
// Do something with the resource
...

14.2.10 How do I filter resource files?
Sometimes a resource file will need to contain a value that can only be supplied at build time.
To accomplish this in Maven, put a reference to the property that will contain the value into your
resource file using the syntax ${<property name>}. The property can be one of the values
defined in your pom.xml, a value defined in the user's settings.xml, a property defined in an external
properties file, or a system property.
To have Maven filter resources when copying, simply set filtering to true for the resource
directory in your pom.xml:



<dependencies>
<dependency>
<scope>test</scope>
</dependency>
</dependencies>
<build>
<resources>
<resource>
<directory>src/main/resources</directory>
<filtering>true</filtering>
</resource>
</resources>
</build>
</project>

You'll notice that we had to add the build, resources, and resource elements which weren't
there before. In addition, we had to explicitly state that the resources are located in the src/main/
resources directory. All of this information was provided as default values previously, but because
the default value for filtering is false, we had to add this to our pom.xml in order to override that
default value and set filtering to true.
To reference a property defined in your pom.xml, the property name uses the names of the XML
elements that define the value, with "pom" being allowed as an alias for the project (root) element. So
${pom.name} refers to the name of the project, ${pom.version} refers to the version of the project,
${pom.build.finalName} refers to the final name of the file created when the built project is packaged,
etc. Note that some elements of the POM have default values, so don't need to be explicitly defined
in your pom.xml for the values to be available here. Similarly, values in the user's settings.xml can be
referenced using property names beginning with "settings" (for example, ${settings.localRepository}
refers to the path of the user's local repository).
To continue our example, let's add a couple of properties to the application.properties file (which we
put in the src/main/resources directory) whose values will be supplied when the resource is filtered:

# application.properties
application.name=${pom.name}
application.version=${pom.version}

With that in place, you can execute the following command (process-resources is the build lifecycle
phase where the resources are copied and filtered):



mvn process-resources

and the application.properties file under target/classes (and will eventually go into the jar) looks like
this:

application.name=Maven Quick Start Archetype
application.version=1.0-SNAPSHOT

To reference a property defined in an external file, all you need to do is add a reference to this
external file in your pom.xml. First, let's create our external properties file and call it src/main/filters/
filter.properties:

# filter.properties
my.filter.value=hello!

Next, we'll add a reference to this new file in the pom.xml:

<dependencies>
<dependency>
<scope>test</scope>
</dependency>
</dependencies>
<build>
<filters>
<filter>src/main/filters/filter.properties</filter>
</filters>
<resources>
<resource>
</resource>
</resources>
</build>
</project>

Then, if we add a reference to this property in the application.properties file:



application.name=${pom.name}
application.version=${pom.version}
message=${my.filter.value}

the next execution of the mvn process-resources command will put our new property value into
application.properties. As an alternative to defining the my.filter.value property in an external file,
you could also have defined it in the properties section of your pom.xml and you'd get the same
effect (notice I don't need the references to src/main/filters/filter.properties either):

<dependencies>
<dependency>
<scope>test</scope>
</dependency>
</dependencies>
<build>
<resources>
<resource>
</resource>
</resources>
</build>
<properties>
<my.filter.value>hello</my.filter.value>
</properties>
</project>

Filtering resources can also get values from system properties; either the system properties built into
Java (like java.version or user.home) or properties defined on the command line using the standard
Java -D parameter. To continue the example, let's change our application.properties file to look like
this:

java.version=${java.version}
command.line.prop=${command.line.prop}



Now, when you execute the following command (note the definition of the command.line.prop
property on the command line), the application.properties file will contain the values from the system
properties.

mvn process-resources "-Dcommand.line.prop=hello again"

14.2.11 How do I use external dependencies?
You've probably already noticed a dependencies element in the POM we've been using as an
example. You have, in fact, been using an external dependency all this time, but here we'll talk about
how this works in a bit more detail. For a more thorough introduction, please refer to our Introduction
to Dependency Mechanism.
The dependencies section of the pom.xml lists all of the external dependencies that our project
needs in order to build (whether it needs that dependency at compile time, test time, run time, or
whatever). Right now, our project is depending on JUnit only (I took out all of the resource filtering
stuff for clarity):

<dependencies>
<dependency>
<scope>test</scope>
</dependency>
</dependencies>
</project>

For each external dependency, you'll need to define at least 4 things: groupId, artifactId, version, and
scope. The groupId, artifactId, and version are the same as those given in the pom.xml for the project
that built that dependency. The scope element indicates how your project uses that dependency,
and can be values like compile, test, and runtime. For more information on everything you can
specify for a dependency, see the Project Descriptor Reference.
For more information about the dependency mechanism as a whole, see Introduction to Dependency
Mechanism.
With this information about a dependency, Maven will be able to reference the dependency when it
builds the project. Where does Maven reference the dependency from? Maven looks in your local
repository ( ~/.m2/repository is the default location) to find all dependencies. In a previous
section, we installed the artifact from our project (my-app-1.0-SNAPSHOT.jar) into the local
repository. Once it's installed there, another project can reference that jar as a dependency simply by
adding the dependency information to its pom.xml:



<artifactId>my-other-app</artifactId>
...
<dependencies>
...
<dependency>
<scope>compile</scope>
</dependency>
</dependencies>
</project>

What about dependencies built somewhere else? How do they get into my local repository?
Whenever a project references a dependency that isn't available in the local repository, Maven will
download the dependency from a remote repository into the local repository. You probably noticed
Maven downloading a lot of things when you built your very first project (these downloads were
dependencies for the various plugins used to build the project). By default, the remote repository
Maven uses can be found (and browsed) at http://repo1.maven.org/maven2/. You can also set up
your own remote repository (maybe a central repository for your company) to use instead of or in
addition to the default remote repository. For more information on repositories you can refer to the
Introduction to Repositories.
Let's add another dependency to our project. Let's say we've added some logging to the code
and need to add log4j as a dependency. First, we need to know what the groupId, artifactId, and
version are for log4j. We can browse ibiblio and look for it, or use Google to help by searching for
"site:www.ibiblio.org maven2 log4j". The search shows a directory called /maven2/log4j/log4j (or /
pub/packages/maven2/log4j/log4j). In that directory is a file called maven-metadata.xml. Here's what
the maven-metadata.xml for log4j looks like:

<metadata>
<groupId>log4j</groupId>
<artifactId>log4j</artifactId>
<versioning>
<versions>
</versions>
</versioning>
</metadata>



From this file, we can see that the groupId we want is "log4j" and the artifactId is "log4j". We see
lots of different version values to choose from; for now, we'll just use the latest version, 1.2.12 (some
maven-metadata.xml files may also specify which version is the current release version). Alongside
the maven-metadata.xml file, we can see a directory corresponding to each version of the log4j
library. Inside each of these, we'll find the actual jar file (e.g. log4j-1.2.12.jar) as well as a pom file
(this is the pom.xml for the dependency, indicating any further dependencies it might have and other
information) and another maven-metadata.xml file. There's also an md5 file corresponding to each of
these, which contains an MD5 hash for these files. You can use this to authenticate the library or to
figure out which version of a particular library you may be using already.
Now that we know the information we need, we can add the dependency to our pom.xml:

<dependencies>
<dependency>
<scope>test</scope>
</dependency>
<dependency>
</dependency>
</dependencies>
</project>

Now, when we compile the project ( mvn compile), we'll see Maven download the log4j
dependency for us.

14.2.12 How do I deploy my jar in my remote repository?
For deploying jars to an external repository, you have to configure the repository url in the pom.xml
and the authentication information for connectiong to the repository in the settings.xml.
Here is an example using scp and username/password authentication:


<dependencies>
<dependency>
<scope>test</scope>
</dependency>
<dependency>
<groupId>org.apache.codehaus.plexus</groupId>
<artifactId>plexus-utils</artifactId>
</dependency>
</dependencies>
<build>
<filters>
<filter>src/main/filters/filters.properties</filter>
</filters>
<resources>
<resource>
</resource>
</resources>
</build>

<distributionManagement>
<repository>
<id>mycompany-repository</id>
<name>MyCompany Repository</name>
<url>scp://repository.mycompany.com/repository/maven2</url>
</repository>
</distributionManagement>
</project>

...
<servers>
<server>
<id>mycompany-repository</id>
<username>jvanzyl</username>

<privateKey>/path/to/identity</privateKey> (default is ~/.ssh/id_dsa)
<passphrase>my_key_passphrase</passphrase>
</server>
</servers>
...
</settings>

Note that if you are connecting to an openssh ssh server which has the parameter
"PasswordAuthentication" set to "no" in the sshd_confing, you will have to type your password each
time for username/password authentication (although you can log in using another ssh client by typing
in the username and password). You might want to switch to public key authentication in this case.

14.2.13 How do I create documentation?
To get you jump started with Maven's documentation system you can use the archetype mechanism to
generate a site for your existing project using the following command:

-DarchetypeArtifactId=maven-archetype-site
-DartifactId=my-app-site

Now head on over to the Guide to creating a site to learn how to create the documentation for your
project.

14.2.14 How do I build other types of projects?
Note that the lifecycle applies to any project type. For example, back in the base directory we can
create a simple web application:
-DarchetypeArtifactId=maven-archetype-webapp
-DartifactId=my-webapp
Note that these must all be on a single line. This will create a directory called my-webapp containing
the following project descriptor:


<artifactId>my-webapp</artifactId>
<packaging>war</packaging>
<dependencies>
<dependency>
<scope>test</scope>
</dependency>
</dependencies>
<build>
<finalName>my-webapp</finalName>
</build>
</project>
Note the <packaging> element - this tells Maven to build as a WAR. Change into the webapp
project's directory and try:
mvn clean package
You'll see target/my-webapp.war is built, and that all the normal steps were executed.

14.2.15 How do I build more than one project at once?
The concept of dealing with multiple modules is built in to Maven 2.0. In this section, we will show
how to build the WAR above, and include the previous JAR as well in one step.
Firstly, we need to add a parent pom.xml file in the directory above the other two, so it should look
like this:
+- pom.xml
+- my-app
| +- pom.xml
| +- src
| +- main
| +- java
+- my-webapp
| +- pom.xml
| +- src
| +- main
| +- webapp
The POM file you'll create should contain the following:
<artifactId>app</artifactId>
<packaging>pom</packaging>
<modules>
<module>my-app</module>
<module>my-webapp</module>



</modules>
</project>
We'll need a dependency on the JAR from the webapp, so add this to my-webapp/pom.xml:
...
<dependencies>
<dependency>
</dependency>
...
</dependencies>
Finally, add the following <parent> element to both of the other pom.xml files in the subdirectories:
<parent>
</parent>
...
Now, try it... from the top level directory, run:
mvn clean install
The WAR has now been created in my-webapp/target/my-webapp.war, and the JAR is included:
$ jar tvf my-webapp/target/my-webapp-1.0-SNAPSHOT.war
0 Fri Jun 24 10:59:56 EST 2005 META-INF/
222 Fri Jun 24 10:59:54 EST 2005 META-INF/MANIFEST.MF
0 Fri Jun 24 10:59:56 EST 2005 META-INF/maven/
0 Fri Jun 24 10:59:56 EST 2005 META-INF/maven/com.mycompany.app/
0 Fri Jun 24 10:59:56 EST 2005 META-INF/maven/com.mycompany.app/my-
webapp/
webapp/pom.xml
0 Fri Jun 24 10:59:56 EST 2005 WEB-INF/
215 Fri Jun 24 10:59:56 EST 2005 WEB-INF/web.xml
webapp/pom.properties
52 Fri Jun 24 10:59:56 EST 2005 index.jsp
0 Fri Jun 24 10:59:56 EST 2005 WEB-INF/lib/
2713 Fri Jun 24 10:59:56 EST 2005 WEB-INF/lib/my-app-1.0-SNAPSHOT.jar
How does this work? Firstly, the parent POM created (called app), has a packaging of pom and a list
of modules defined. This tells Maven to run all operations over the set of projects instead of just the
current one (to override this behaviour, you can use the --non-recursive command line option).
Next, we tell the WAR that it requires the my-app JAR. This does a few things: it makes it available
on the classpath to any code in the WAR (none in this case), it makes sure the JAR is always built
before the WAR, and it indicates to the WAR plugin to include the JAR in its library directory.



You may have noticed that junit-3.8.1.jar was a dependency, but didn't end up in the WAR.
The reason for this is the <scope>test</scope> element - it is only required for testing, and so is
not included in the web application as the compile time dependency my-app is.
The final step was to include a parent definition. This is different to the extend element you may be
familiar with from Maven 1.0: this ensures that the POM can always be located even if the project is
distributed separately from its parent by looking it up in the repository.
Unlike Maven 1.0, it is not required that you run install to successfully perform these steps - you
can run package on its own and the artifacts in the reactor will be used from the target directories
instead of the local repository.
You might like to generate your IDEA workspace again from the top level directory...
mvn idea:idea


15 POM Reference 56

15 POM Reference
.......................................................................................................................................

15.1 POM Reference
1 Introduction

1 What is the POM?
2 Quick Overview
2 The Basics

1 Maven Coordinates
2 POM Relationships

1 Dependencies

1 Exclusions
2 Inheritance

1 The Super POM
2 Dependency Management
3 Aggregation (or Multi-Module)

1 Inheritance v. Aggregation
3 Properties
3 Build Settings

1 Build

1 The BaseBuild Element Set

1 Resources
2 Plugins
3 Plugin Management
2 The Build Element Set

1 Directories
2 Extensions
2 Reporting

1 Report Sets
4 More Project Information

1 Licenses
2 Organization
3 Developers
4 Contributors
5 Environment Settings

1 Issue Management
2 Continuous Integration Management


15 POM Reference 57

3 Mailing Lists
4 SCM
5 Repositories
6 Plugin Repositories
7 Distribution Management

1 Repository
2 Site Distribution
3 Relocation
8 Profiles

1 Activation
2 The BaseBuild Element Set (revisited)
6 Final

15.2 Introduction
• The POM 4.0.0 XSD

15.2.1 What is the POM?
POM stands for "Project Object Model". It is an XML representation of a Maven project held in
a file named pom.xml. When in the presence of Maven folks, speaking of a project is speaking
in the philosophical sense, beyond a mere collection of files containing code. A project contains
configuration files, as well as the developers involved and the roles they play, the defect tracking
system, the organization and licenses, the URL of where the project lives, the project's dependencies,
and all of the other little pieces that come into play to give code life. It is a one-stop-shop for all
things concerning the project. In fact, in the Maven world, a project need not contain any code at all,
merely a pom.xml.

15.2.2 Quick Overview
This is a listing of the elements directly under the POM's project element. Notice that modelVersion
contains 4.0.0. That is currently the only supported POM version for Maven 2, and is always required.


15 POM Reference 58


<groupId>...</groupId>
<artifactId>...</artifactId>
<version>...</version>
<packaging>...</packaging>
<dependencies>...</dependencies>
<parent>...</parent>
<dependencyManagement>...</dependencyManagement>
<modules>...</modules>
<properties>...</properties>

<build>...</build>
<reporting>...</reporting>

<name>...</name>
<description>...</description>
<url>...</url>
<inceptionYear>...</inceptionYear>
<licenses>...</licenses>
<organization>...</organization>
<developers>...</developers>
<contributors>...</contributors>

<issueManagement>...</issueManagement>
<ciManagement>...</ciManagement>
<mailingLists>...</mailingLists>
<scm>...</scm>
<prerequisites>...</prerequisites>
<repositories>...</repositories>
<pluginRepositories>...</pluginRepositories>
<distributionManagement>...</distributionManagement>
<profiles>...</profiles>
</project>

15.3 The Basics
The POM contains all necessary information about a project, as well as configurations of plugins to
be used during the build process. It is, effectively, the declarative manifestation of the "who", "what",
and "where", while the build lifecycle is the "when" and "how". That is not to say that the POM
cannot affect the flow of the lifecycle - it can. For example, by configuring the maven-antrun-
plugin, one can effectively embed ant tasks inside of the POM. It is ultimately a declaration,
however. Where as a build.xml tells ant precisely what to do when it is run (procedural), a POM
states its configuration (declarative). If some external force causes the lifecycle to skip the ant plugin
execution, it will not stop the plugins that are executed from doing their magic. This is unlike a
build.xml file, where tasks are almost always dependant on the lines executed before it.

15 POM Reference 59

<groupId>org.codehaus.mojo</groupId>
<artifactId>my-project</artifactId>
<version>1.0</version>
</project>

15.3.1 Maven Coordinates
The POM defined above is the minimum that Maven 2 will allow. groupId:artifactId:version
are all required fields (although, groupId and version need not be explicitly defined if they are
inherited from a parent - more on inheritance later). The three fields act much like an address and
timestamp in one. This marks a specific place in a repository, acting like a coordinate system for
Maven projects.

• groupId: This is generally unique amongst an organization or a project. For example, all core
Maven artifacts do (well, should) live under the groupId org.apache.maven. Group ID's do not
necessarily use the dot notation, for example, the junit project. Note that the dot-notated groupId
does not have to correspond to the package structure that the project contains. It is, however,
a good practice to follow. When stored within a repository, the group acts much like the Java
packaging structure does in an operating system. The dots are replaced by OS specific directory
separators (such as '/' in Unix) which becomes a relative directory structure from the base
repository. In the example given, the org.codehaus.mojo group lives within the directory
$M2_REPO/org/codehaus/mojo.
• artifactId: The artifactId is generally the name that the project is known by. Although
the groupId is important, people within the group will rarely mention the groupId in
discussion (they are often all be the same ID, such as the Codehaus Mojo project groupId:
org.codehaus.mojo). It, along with the groupId, create a key that separates this project from
every other project in the world (at least, it should :) ). Along with the groupId, the artifactId
fully defines the artifact's living quarters within the repository. In the case of the above project,
my-project lives in $M2_REPO/org/codehaus/mojo/my-project.
• version: This is the last piece of the naming puzzle. groupId:artifactId denote a single
project but they cannot delineate which incarnation of that project we are talking about. Do
we want the junit:junit of today (version 4), or of four years ago (version 2)? In short:
code changes, those changes should be versioned, and this element keeps those versions in
line. It is also used within an artifact's repository to separate versions from each other. my-
project version 1.0 files live in the directory structure $M2_REPO/org/codehaus/mojo/my-
project/1.0.
The three elements given above point to a specific version of a project letting Maven knows who
we are dealing with, and when in its software lifecycle we want them.
• packaging: Now that we have our address structure of groupId:artifactId:version, there
is one more standard label to give us a really complete address. That is the project's artifact type.
In our case, the example POM for org.codehaus.mojo:my-project:1.0 defined above will
be packaged as a jar. We could make it into a war by declaring a different packaging:


15 POM Reference 60

...
...
</project>

When no packaging is declared, Maven assumes the artifact is the default: jar. The valid
types are Plexus role-hints (read more on Plexus for a explanation of roles and role-hints) of
the component role org.apache.maven.lifecycle.mapping.LifecycleMapping. The
current core packaging values are: pom, jar, maven-plugin, ejb, war, ear, rar, par. These
define the default list of goals which execute to each corresponding build lifecycle stage for a
particular package structure.
You will sometimes see Maven print out a project coordinate as
groupId:artifactId:packaging:version.
• classifier: You may occasionally find a fifth element on the coordinate, and that is the
classifier. We will visit the classifier later, but for now it suffices to know that those kinds of
projects are displayed as groupId:artifactId:packaging:classifier:version.

15.3.2 POM Relationships
One powerful aspect of Maven is in its handling of project relationships; that includes dependencies
(and transitive dependencies), inheritance, and aggregation (multi-module projects). Dependency
management has a long tradition of being a complicated mess for anything but the most trivial of
projects. "Jarmageddon" quickly ensues as the dependency tree becomes large and complicated. "Jar
Hell" follows, where versions of dependencies on one system are not equivalent to versions as those
developed with, either by the wrong version given, or conflicting versions between similarly named
jars. Maven solves both problems through a common local repository from which to link projects
correctly, versions and all.

15.3.2.1 Dependencies
The cornerstone of the POM is its dependency list. Most every project depends upon others to build
and run correctly, and if all Maven does for you is manage this list for you, you have gained a lot.
Maven downloads and links the dependencies for you on compilation and other goals that require
them. As an added bonus, Maven brings in the dependencies of those dependencies (transitive
dependencies), allowing your list to focus solely on the dependencies your project requires.


15 POM Reference 61

...
<dependencies>
<dependency>
<type>jar</type>
<scope>test</scope>
<optional>true</optional>
</dependency>
...
</dependencies>
...
</project>

• groupId, artifactId, version:
These elements are self-explanatory, and you will see them often. This trinity represents the
coordinate of a specific project in time, demarcating it as a dependency of this project. You may
be thinking: "This means that my project can only depend upon Maven artifacts!" The answer
is, "Of course, but that's a good thing." This forces you to depend solely on dependencies that
Maven can manage. There are times, unfortunately, when a project cannot be downloaded from
the central Maven repository. For example, a project may depend upon a jar that has a closed-
source license which prevents it from being in a central repository. There are three methods for
dealing with this scenario.

1 Install the dependency locally using the install plugin. The method is the simplest
recommended method. For example:
mvn install:install-file -Dfile=non-maven-proj.jar -
DgroupId=some.group -DartifactId=non-maven-proj -Dversion=1
Notice that an address is still required, only this time you use the command line and the
install plugin will create a POM for you with the given address.
2 Create your own repository and deploy it there. This is a favorite method for companies
with an intranet and need to be able to keep everyone in synch. There is a Maven goal called
deploy:deploy-file which is similar to the install:install-file goal (read the
plugin's goal page for more information).
3 Set the dependency scope to system and define a systemPath. This is not recommended,
however, but leads us to explaining the following elements:
• classifier:
The classifier allows to distinguish artifacts that were built from the same POM but differ in their
content. It is some optional and arbitrary string that - if present - is appended to the artifact name
just after the version number.
As a motivation for this element, consider for example a project that offers an artifact targeting
JRE 1.5 but at the same time also an artifact that still supports JRE 1.4. The first artifact could be
equipped with the classifier jdk15 and the second one with jdk14 such that clients can choose
which one to use.
Another common use case for classifiers is the need to attach secondary artifacts to the project's
main artifact. If you browse the Maven central repository, you will notice that the classifiers


15 POM Reference 62

sources and javadoc are used to deploy the project source code and API docs along with the
packaged class files.
• type:
Corresponds to the dependant artifact's packaging type. This defaults to jar. While it usually
represents the extension on the filename of the dependency, that is not always the case. A
type can be mapped to a different extension and a classifier. The type often correspongs to the
packaging used, though this is also not always the case. Some examples are jar, ejb-client
and test-jar. New types can be defined by plugins that set extensions to true, so this is not
a complete list.
• scope:
This element refers to the classpath of the task at hand (compiling and runtime, testing, etc.) as
well as how to limit the transitivity of a depedency. There are five scopes available:
• compile - this is the default scope, used if none is specified. Compile dependencies are
available in all classpaths. Furthermore, those dependencies are propagated to dependent
projects.
• provided - this is much like compile, but indicates you expect the JDK or a container to
provide it at runtime. It is only available on the compilation and test classpath, and is not
transitive.
• runtime - this scope indicates that the dependency is not required for compilation, but is for
execution. It is in the runtime and test classpaths, but not the compile classpath.
• test - this scope indicates that the dependency is not required for normal use of the
application, and is only available for the test compilation and execution phases.
• system - this scope is similar to provided except that you have to provide the JAR which
contains it explicitly. The artifact is always available and is not looked up in a repository.
• systemPath:
is used only if the the dependency scope is system. Otherwise, the build will fail if this element
is set. The path must be absolute, so it is recommended to use a property to specify the machine-
specific path (more on properties below), such as ${java.home}/lib. Since it is assumed
that system scope dependencies are installed a priori, Maven will not check the repositories for
the project, but instead checks to ensure that the file exists. If not, Maven will fail the build and
suggest that you download and install it manually.
• optional:
Marks optional a dependency when this project itself is a dependency. Confused? For example,
imagine a project A that depends upon project B to compile a portion of code that may not
be used at runtime, then we may have no need for project B for all project. So if project X
adds project A as its own dependency, then Maven will not need to install project B at all.
Symbolically, if => represents a required dependency, and --> represents optional, although
A=>B may be the case when building A X=>A-->B would be the case when building X.
In the shortest terms, optional lets other projects know that, when you use this project, you do
not require this dependency in order to work correctly.
15. Exclusions
Exclusions explicitly tell Maven that you don't want to include the specified project that is a
dependency of this dependency (in other words, its transitive dependency). For example, the maven-
embedder requires maven-core, and we do not wish to use it or its dependencies, then we would
add it as an exclusion.


15 POM Reference 63

...
<dependencies>
<dependency>
<groupId>org.apache.maven</groupId>
<artifactId>maven-embedder</artifactId>
<exclusions>
<exclusion>
<artifactId>maven-core</artifactId>
</exclusion>
</exclusions>
</dependency>
...
</dependencies>
...
</project>

• exclusions: Exclusions contain one or more exclusion elements, each containing a groupId
and artifactId denoting a dependency to exclude. Unlike optional, which may or may not
be installed and used, exclusions actively remove themselves from the dependency tree.

15.3.2.2 Inheritance
One powerful addition that Maven brings to build management is the concept of project inheritance.
Although in build systems such as Ant, inheritance can certainly be simulated, Maven has gone the
extra step in making project inheritance explicit to the project object model.

<artifactId>my-parent</artifactId>
</project>

The packaging type required to be pom for parent and aggregation (multi-module) projects. These
types define the goals bound to a set of lifecycle stages. For example, if packaging is jar, then the
package phase will execute the jar:jar goal. If the packaging is pom, the goal executed will be
site:attach-descriptor. Now we may add values to the parent POM, which will be inherited by
its children. The elements in the parent POM that are inherited by its children are:
• dependencies
• developers and contributors
• plugin lists
• reports lists
• plugin executions with matching ids


15 POM Reference 64

• plugin configuration

<parent>
<relativePath>../my-parent</relativePath>
</parent>
</project>

Notice the relativePath element. It is not required, but may be used as a signifier to Maven to first
search the path given for this project's parent, before searching the local and then remote repositories.
To see inheritance in action, just have a look at the ASF or Maven parent POM's.
15. The Super POM
Similar to the inheritance of objects in object oriented programming, POMs that extend a parent
POM inherit certain values from that parent. Moreover, just as Java objects ultimately inherit from
java.lang.Object, all Project Object Models inherit from a base Super POM. The snippet below
is the Super POM for Maven 2.0.x.


15 POM Reference 65

<project>
<name>Maven Default Project</name>
<repositories>
<repository>
<id>central</id>
<name>Maven Repository Switchboard</name>
<layout>default</layout>
<url>http://repo1.maven.org/maven2</url>
<snapshots>
<enabled>false</enabled>
</snapshots>
</repository>
</repositories>
<pluginRepositories>
<pluginRepository>
<id>central</id>
<name>Maven Plugin Repository</name>
<snapshots>
</snapshots>
<releases>
<updatePolicy>never</updatePolicy>
</releases>
</pluginRepository>
</pluginRepositories>
<build>
<directory>${project.basedir}/target</directory>
<outputDirectory>${project.build.directory}/classes</outputDirectory>
<finalName>${project.artifactId}-${project.version}</finalName>
<testOutputDirectory>${project.build.directory}/test-classes</testOutputDirector
<sourceDirectory>${project.basedir}/src/main/java</sourceDirectory>
<!-- TODO: MNG-3731 maven-plugin-tools-api < 2.4.4 expect this to be relative...
<scriptSourceDirectory>src/main/scripts</scriptSourceDirectory>
<testSourceDirectory>${project.basedir}/src/test/java</testSourceDirectory>
<resources>
<resource>
<directory>${project.basedir}/src/main/resources</directory>
</resource>
</resources>
<testResources>
<testResource>
<directory>${project.basedir}/src/test/resources</directory>
</testResource>
</testResources>
<pluginManagement>
<plugins>
<plugin>
<artifactId>maven-antrun-plugin</artifactId>
</plugin>
<plugin>
<artifactId>maven-assembly-plugin</artifactId>
</plugin>
<plugin>
<artifactId>maven-clean-plugin</artifactId>
</plugin>
<plugin>

15 POM Reference 66

You can take a look at how the Super POM affects your Project Object Model by creating a minimal
pom.xml and executing on the command line: mvn help:effective-pom

15. Dependency Management
Besides inheriting certain top-level elements, parents have elements to configure values for child
POMs and transitive dependencies. One of those elements is dependencyManagement.

• dependencyManagement: is used by POMs to help manage dependency information across all
of its children. If the my-parent project uses dependencyManagement to define a dependency
on junit:junit:4.0, then POMs inheriting from this one can set their dependency giving
the groupId= junit and artifactId= junit only, then Maven will fill in the version
set by the parent. The benefits of this method are obvious. Dependency details can be set in
one central location, which will propagate to all inheriting POMs. In addition, the version and
scope of artifacts which are incorporated from transitive dependencies may also be controlled by
specifying them in a dependency management section.

15.3.2.3 Aggregation (or Multi-Module)
A project with modules is known as a multimodule, or aggregator project. Modules are projects that
this POM lists, and are executed as a group. An pom packaged project may aggregate the build of a set
of projects by listing them as modules, which are relative directories to those projects.

<modules>
<module>my-project<module>
<module>another-project<module>
</modules>
</project>

You do not need to consider the inter-module dependencies yourself when listing the modules, i.e.
the ordering of the modules given by the POM is not important. Maven will topologically sort the
modules such that dependencies are always build before dependent modules.
To see aggregation in action, just have a look at the Maven or Maven Core Plugins base POM's.
15.A final note on Inheritance v. Aggregation
Inheritance and aggregation create a nice dynamic to control builds through a single, high-level POM.
You will often see projects that are both parents and aggregators. For example, the entire maven core
runs through a single base POM org.apache.maven:maven, so building the Maven project can be
executed by a single command: mvn compile. However, although both POM projects, an aggregator
project and a parent project are not one in the same and should not be confused. A POM project may
be inherited from - but does not necessarily have - any modules that it aggregates. Conversely, a POM
project may aggregate projects that do not inherit from it.


15 POM Reference 67

15.3.3 Properties
Properties are the last required piece in understanding POM basics. Maven properties are value
placeholder, like properties in Ant. Their values are accessible anywhere within a POM by using the
notation ${X}, where X is the property. They come in five different styles:

1 env.X: Prefixing a variable with "env." will return the shell's environment variable. For
example, ${env.PATH} contains the PATH environment variable. Note: While environment
variables themselves are case-insensitive on Windows, lookup of properties is case-sensitive. In
other words, while the Windows shell returns the same value for %PATH% and %Path%, Maven
distinguishes between ${env.PATH} and ${env.Path}. As of Maven 2.1.0, the names of
environment variables are normalized to all upper-case for the sake of reliability.
2 project.x: A dot (.) notated path in the POM will contain the corresponding element's
value. For example: <project><version>1.0</version></project> is accessible via
${project.version}.
3 settings.x: A dot (.) notated path in the settings.xml will contain the corresponding
element's value. For example: <settings><offline>false</offline></settings> is
accessible via ${settings.offline}.
4 Java System Properties: All properties accessible via java.lang.System.getProperties()
are available as POM properties, such as ${java.home}.
5 x: Set within a <properties /> element. The value may be used as ${someVar}.

15.4 Build Settings
Beyond the basics of the POM given above, there are two more elements that must be understood
before claiming basic competency of the POM. They are the build element, that handles things like
declaring your project's directory structure and managing plugins; and the reporting element, that
largely mirrors the build element for reporting purposes.

15.4.1 Build
According to the POM 4.0.0 XSD, the build element is conceptually divided into two parts: there
is a BaseBuild type which contains the set of elements common to both build elements (the top-
level build element under project and the build element under profiles, covered below); and
there is the Build type, which contains the BaseBuild set as well as more elements for the top level
definition. Let us begin with an analysis of the common elements between the two.
Note: These different build elements may be denoted "project build" and "profile build".

...

<build>...</build>
<profiles>
<profile>

<build>...</build>
</profile>
</profiles>
</project>

15 POM Reference 68

15.4.1.1 The BaseBuild Element Set
BaseBuild is exactly as it sounds: the base set of elements between the two build elements in the
POM.
<build>
<defaultGoal>install</defaultGoal>
<directory>${basedir}/target</directory>
<finalName>${artifactId}-${version}</finalName>
<filters>
<filter>filters/filter1.properties</filter>
</filters>
...
</build>

• defaultGoal: the default goal or phase to execute if none is given. If a goal is given, it should be
defined as it is in the command line (such as jar:jar). The same goes for if a phase is defined
(such as install).
• directory: This is the directory where the build will dump its files or, in Maven parlance, the
build's target. It aptly defaults to ${basedir}/target.
• finalName: This is the name of the bundled project when it is finally built (sans the file
extension, for example: my-project-1.0.jar). It defaults to ${artifactId}-${version}.
The term "finalName" is kind of a misnomer, however, as plugins that build the bundled project
have every right to ignore/modify this name (but they usually do not). For example, if the
maven-jar-plugin is configured to give a jar a classifier of test, then the actual jar
defined above will be built as my-project-1.0-test.jar.
• filter: Defines *.properties files that contain a list of properties that apply to resources which
accept their settings (covered below). In other words, the " name=value" pairs defined within
the filter files replace ${name} strings within resources on build. The example above defines
the filter1.properties file under the filter/ directory. Maven's default filter directory is
${basedir}/src/main/filters/.
For a more comprehensive look at what filters are and what they can do, take a look at the quick
start guide.
15. Resources
Another feature of build elements is specifying where resources exist within your project. Resources
are not (usually) code. They are not compiled, but are items meant to be bundled within your project
or used for various other reasons, such as code generation.
For example, a Plexus project requires a configuration.xml file (which specifies component
configurations to the container) to live within the META-INF/plexus directory. Although we could
just as easily place this file within src/main/resource/META-INF/plexus, we want instead
to give Plexus its own directory of src/main/plexus. In order for the JAR plugin to bundle the
resource correctly, you would specify resources similar to the following:


15 POM Reference 69

<build>
...
<resources>
<resource>
<targetPath>META-INF/plexus</targetPath>
<filtering>false</filtering>
<directory>${basedir}/src/main/plexus</directory>
<includes>
<include>configuration.xml</include>
</includes>
<excludes>
<exclude>**/*.properties</exclude>
</excludes>
</resource>
</resources>
<testResources>
...
</testResources>
...
</build>
</project>

• resources: is a list of resource elements that each describe what and where to include files
associated with this project.
• targetPath: Specifies the directory structure to place the set of resources from a build. Target
path defaults to the base directory. A commonly specified target path for resources that will be
packaged in a JAR is META-INF.
• filtering: is true or false, denoting if filtering is to be enabled for this resource. Note, that
filter *.properties files do not have to be defined for filtering to occur - resources can also
use properties that are by default defined in the POM (such as ${project.version}), passed into
the command line using the "-D" flag (for example, " -Dname= value") or are explicitly defined
by the properties element. Filter files were covered above.
• directory: This element's value defines where the resources are to be found. The default
directory for a build is ${basedir}/src/main/resources.
• includes: A set of files patterns which specify the files to include as resources under that
specified directory, using * as a wildcard.
• excludes: The same structure as includes, but specifies which files to ignore. In conflicts
between include and exclude, exclude wins.
• testResources: The testResources element block contains testResource elements. Their
definitions are similar to resource elements, but are naturally used during test phases. The
one difference is that the default (Super POM defined) test resource directory for a project is
${basedir}/src/test/resources. Test resources are not deployed.


15 POM Reference 70

15. Plugins

<build>
...
<plugins>
<plugin>
<artifactId>maven-jar-plugin</artifactId>
<extensions>false</extensions>
<inherited>true</inherited>
<configuration>
<classifier>test</classifier>
</configuration>
<executions>...</executions>
</plugin>
</plugins>
</build>
</project>

Beyond the standard coordinate of groupId:artifactId:version, there are elements which
configure the plugin or this builds interaction with it.

• extensions: true or false, whether or not to load extensions of this plugin. It is by default
false. Extensions are covered later in this document.
• inherited: true or false, whether or not this plugin configuration should apply to POMs
which inherit from this one.
• configuration: This is specific to the individual plugin. Without going too in depth into the
mechanics of how plugins work, suffice it to say that whatever properties that the plugin Mojo
may expect (these are getters and setters in the Java Mojo bean) can be specified here. In the
above example, we are setting the classifier property to test in the maven-jar-plugin's Mojo.
It may be good to note that all configuration elements, wherever they are within the POM, are
intended to pass values to another underlying system, such as a plugin. In other words: values
within a configuration element are never explicitly required by the POM schema, but a
plugin goal has every right to require configuration values.
• dependencies: Dependencies are seen a lot within the POM, and are an element under all
plugins element blocks. The dependencies have the same structure and function as under
that base build. The major difference in this case is that instead of applying as dependencies
of the project, they now apply as dependencies of the plugin that they are under. The power
of this is to alter the dependency list of a plugin, perhaps by removing an unused runtime
dependency via exclusions, or by altering the version of a required dpendency. See above
under Dependencies for more information.
• executions: It is important to keep in mind that a plugin may have multiple goals. Each goal
may have a separate configuration, possibly even binding a plugin's goal to a different phase
altogether. executions configure the execution of a plugin's goals.
For example, suppose you wanted to bind the antrun:run goal to the verify phase. We want
the task to echo the build directory, as well as avoid passing on this configuration to its children


15 POM Reference 71

(assuming it is a parent) by setting inherited to false. You would get an execution like
this:

...
<build>
<plugins>
<plugin>
<executions>
<execution>
<id>echodir</id>
<goals>
<goal>run</goal>
</goals>
<phase>verify</phase>
<inherited>false</inherited>
<configuration>
<tasks>
<echo>Build Dir: ${project.build.directory}</echo>
</tasks>
</configuration>
</execution>
</executions>
</plugin>
</plugins>
</build>
</project>
• id: Self explanatory. It specifies this execution block between all of the others. When the phase
is run, it will be shown in the form: [plugin:goal execution: id]. In the case of this
example: [antrun:run execution: echodir]
• goals: Like all pluralized POM elements, this contains a list of singular elements. In this case, a
list of plugin goals which are being specified by this execution block.
• phase: This is the phase that the list of goals will execute in. This is a very powerful option,
allowing one to bind any goal to any phase in the build lifecycle, altering the default behavior of
Maven.
• inherited: Like the inherited element above, setting this false will supress Maven from
passing this execution onto its children. This element is only meaningful to parent POMs.
• configuration: Same as above, but confines the configuration to this specific list of goals, rather
than all goals under the plugin.
15. Plugin Management

• pluginManagement: is an element that is seen along side plugins. Plugin Management contains
plugin elements in much the same way, except that rather than configuring plugin information
for this particular project build, it is intended to configure project builds that inherit from this
one. However, this only configures plugins that are actually referenced within the plugins
element in the children. The children have every right to override pluginManagement
definitions.


15 POM Reference 72

...
<build>
...
<pluginManagement>
<plugins>
<plugin>
<executions>
<execution>
<id>pre-process-classes</id>
<phase>compile</phase>
<goals>
<goal>jar</goal>
</goals>
<configuration>
<classifier>pre-process</classifier>
</configuration>
</execution>
</executions>
</plugin>
</plugins>
</pluginManagement>
...
</build>
</project>

If we added these specifications to the plugins element, they would apply only to a single POM.
However, if we apply them under the pluginManagement element, then this POM and all inheriting
POMs that add the maven-jar-plugin to the build will get the pre-process-classes execution
as well. So rather than the above mess included in every child pom.xml, only the following is
required:


15 POM Reference 73

...
<build>
...
<plugins>
<plugin>
</plugin>
</plugins>
...
</build>
</project>

15.4.1.2 The Build Element Set
The Build type in the XSD denotes those elements that are available only for the "project build".
Despite the number of extra elements (six), there are really only two groups of elements that project
build contains that are missing from the profile build: directories and extensions.
15. Directories
The set of directory elements live in the parent build element, which set various directory structures
for the POM as a whole. Since they do not exist in profile builds, these cannot be altered by profiles.

...
<build>
<sourceDirectory>${basedir}/src/main/java</sourceDirectory>
<scriptSourceDirectory>${basedir}/src/main/scripts</scriptSourceDirectory>
<testSourceDirectory>${basedir}/src/test/java</testSourceDirectory>
<outputDirectory>${basedir}/target/classes</outputDirectory>
<testOutputDirectory>${basedir}/target/test-classes</testOutputDirectory>
...
</build>
</project>

If the values of a *Directory element above is set as an absolute path (when their properties
are expanded) then that directory is used. Otherwise, it is relative to the base build directory:
${basedir}.

15. Extensions
Extensions are a list of artifacts that are to be used in this build. They will be included in the running
build's classpath. They can enable extensions to the build process (such as add an ftp provider for
the Wagon transport mechanism), as well as make plugins active which make changes to the build
lifecycle. In short, extensions are artifacts that activated during build. The extensions do not have to
actually do anything nor contain a Mojo. For this reason, extensions are excellent for specifying one
out of multiple implementations of a common plugin interface.


15 POM Reference 74

...
<build>
...
<extensions>
<extension>
<groupId>org.apache.maven.wagon</groupId>
<artifactId>wagon-ftp</artifactId>
<version>1.0-alpha-3</version>
</extension>
</extensions>
...
</build>
</project>

15.4.2 Reporting
Reporting contains the elements that correspond specifically for the site generation phase. Certain
Maven plugins can generate reports defined and configured under the reporting element, for example:
generating Javadoc reports. Much like the build element's ability to configure plugins, reporting
commands the same ability. The glaring difference is that rather than fine-grained control of plug-in
goals within the executions block, reporting configures goals within reportSet elements. And the
subtler difference is that a plugin configuration under the reporting element works as build
plugin configuration, although the opposite is not true (a build plugin configuration does not
affect a reporting plugin).
Possibly the only item under the reporting element that would not be familiar to someone who
understood the build element is the Boolean excludeDefaults element. This element signifies to
the site generator to exclude reports normally generated by default. When a site is generated via the
site build cycle, a Project Info section is placed in the left-hand menu, chock full of reports, such
as the Project Team report or Dependencies list report. These report goals are generated by maven-
project-info-reports-plugin. Being a plugin like any other, it may also be suppressed in the
following, more verbose, way, which effectively turns off project-info reports.


15 POM Reference 75

...
<reporting>
<outputDirectory>${basedir}/target/site</outputDirectory>
<plugins>
<plugin>
<artifactId>maven-project-info-reports-plugin</artifactId>
<reportSets>
<reportSet></reportSet>
</reportSets>
</plugin>
</plugins>
</reporting>
...
</project>

The other difference is the outputDirectory element under plugin. In the case of reporting, the
output directory is ${basedir}/target/site by default.

15.4.2.1 Report Sets
It is important to keep in mind that an individual plugin may have multiple goals. Each goal may have
a separate configuration. Report sets configure execution of a report plugin's goals. Does this sound
familiar - deja-vu? The same thing was said about build's execution element with one difference:
you cannot bind a report to another phase. Sorry.
For example, suppose you wanted to configure the javadoc:javadoc goal to link to " http://
java.sun.com/j2se/1.5.0/docs/api/", but only the javadoc goal (not the goal maven-javadoc-
plugin:jar). We would also like this configuration passed to its children, and set inherited to
true. The reportSet would resemble the following:


15 POM Reference 76

...
<reporting>
<plugins>
<plugin>
...
<reportSets>
<reportSet>
<id>sunlink</id>
<reports>
<report>javadoc</report>
</reports>
<configuration>
<links>
<link>http://java.sun.com/j2se/1.5.0/docs/api/</link>
</links>
</configuration>
</reportSet>
</reportSets>
</plugin>
</plugins>
</reporting>
...
</project>

Between build executions and reporting reportSets, it should be clear now as to why they
exist. In the simplest sense, they drill down in configuration. The POM must have a way not only to
configure plugins, but they also must configure individual goals of those plugins. That is where these
elements come in, giving the POM ultimate granularity in control of its build destiny.

15.5 More Project Information
Although the above information is enough to get a firm grasp on POM authoring, there are far more
elements to make developer's live easier. Many of these elements are related to site generation, but
like all POM declarations, they may be used for anything, depending upon how certain plugins use it.
The following are the simplest elements:

• name: Projects tend to have conversational names, beyond the artifactId. The Sun engineers
did not refer to their project as "java-1.5", but rather just called it "Tiger". Here is where to set
that value.
• description: Description of a project is always good. Although this should not replace formal
documentation, a quick comment to any readers of the POM is always helpful.
• url: The URL, like the name, is not required. This is a nice gesture for projects users, however,
so that they know where the project lives.
• inceptionYear: This is another good documentation point. It will at least help you remember
where you have spent the last few years of your life.


15 POM Reference 77

15.5.1 Licenses

<licenses>
<license>
<name>Apache 2</name>
<url>http://www.apache.org/licenses/LICENSE-2.0.txt</url>
<distribution>repo</distribution>
<comments>A business-friendly OSS license</comments>
</license>
</licenses>

Licenses are legal documents defining how and when a project (or parts of a project) may be used.
Note that a project should list only licenses that may apply directly to this project, and not list licenses
that apply to this project's dependencies. Maven currently does little with these documents other than
displays them on generated sites. However, there is talk of flexing for different types of licenses,
forcing users to accept license agreements for certain types of (non open source) projects.

• name, url and comments: are self explanatory, and have been encountered before in other
capacities. The fourth license element is:
• distribution: This describes how the project may be legally distributed. The two stated methods
are repo (they may be downloaded from a Maven repository) or manual (they must be manually
installed).

15.5.2 Organization
Most projects are run by some sort of organization (business, private group, etc.). Here is where the
most basic information is set.

...
<organization>
<name>Codehaus Mojo</name>
<url>http://mojo.codehaus.org</url>
</organization>
</project>

15.5.3 Developers
All projects consist of files that were created, at some time, by a person. Like the other systems that
surround a project, so to do the people involved with a project have a stake in the project. Developers
are presumably members of the project's core development. Note that, although an organization may
have many developers (programmers) as members, it is not good form to list them all as developers,
but only those who are immediately responsible for the code. A good rule of thumb is, if the person
should not be contacted about the project, they need not be listed here.


15 POM Reference 78

...
<developers>
<developer>
<id>eric</id>
<name>Eric</name>
<email>eredmond@codehaus.org</email>
<url>http://eric.propellors.net</url>
<organization>Codehaus</organization>
<organizationUrl>http://mojo.codehaus.org</organizationUrl>
<roles>
<role>architect</role>
<role>developer</role>
</roles>
<timezone>-6</timezone>
<properties>
<picUrl>http://tinyurl.com/prv4t</picUrl>
</properties>
</developer>
</developers>
...
</project>

• id, name, email: These corrospond to the developer's ID (presumably some unique ID across an
organization), the developer's name and email address.
• organization, organizationUrl: As you probably guessed, these are the developer's organization
name and it's URL, respectively.
• roles: A role should specify the standard actions that the person is responsible for. Like a single
person can wear many hats, a single person can take on multiple roles.
• timezone: A numerical offset in hours from GMT where the developer lives.
• properties: This element is where any other properties about the person goes. For example,
a link to a personal image or an instant messenger handle. Different plugins may use these
properties, or they may simply be for other developers who read the POM.

15.5.4 Contributors
Contributors are like developers yet play an ancillary role in a project's lifecycle. Perhaps the
contributor sent in a bug fix, or added some important documentation. A healthy open source project
will likely have more contributors than developers.


15 POM Reference 79

...
<contributors>
<contributor>
<name>Noelle</name>
<email>some.name@gmail.com</email>
<url>http://noellemarie.com</url>
<organization>Noelle Marie</organization>
<organizationUrl>http://noellemarie.com</organizationUrl>
<roles>
<role>tester</role>
</roles>
<timezone>-5</timezone>
<properties>
<gtalk>some.name@gmail.com</gtalk>
</properties>
</contributor>
</contributors>
...
</project>

Contributors contain the same set of elements than developers sans the id element.

15.6 Environment Settings

15.6.1 Issue Management
This defines the defect tracking system ( Bugzilla, TestTrack, ClearQuest, etc) used. Although there is
nothing stopping a plugin from using this information for something, its primarily used for generating
project documentation.

...
<issueManagement>
<system>Bugzilla</system>
<url>http://127.0.0.1/bugzilla/</url>
</issueManagement>
...
</project>

15.6.2 Continuous Integration Management
Continuous integration build systems based upon triggers or timings (such as, hourly or daily)
have grown in favor over manual builds in the past few years. As build systems have become more
standardized, so have the systems that run the trigger those builds. Although the majority of the
configuration is up to the specific program used (Continuum, Cruise Control, etc.), there are a few
configurations which may take place within the POM. Maven has captured a few of the recurring


15 POM Reference 80

settings within the set of notifier elements. A notifier is the manner in which people are notified
of certain build statuses. In the following example, this POM is setting a notifier of type mail
(meaning email), and configuring the email address to use on the specified triggers sendOnError,
sendOnFailure, and not sendOnSuccess or sendOnWarning.

...
<ciManagement>
<system>continuum</system>
<url>http://127.0.0.1:8080/continuum</url>
<notifiers>
<notifier>
<type>mail</type>
<sendOnError>true</sendOnError>
<sendOnFailure>true</sendOnFailure>
<sendOnSuccess>false</sendOnSuccess>
<sendOnWarning>false</sendOnWarning>
<configuration><address>continuum@127.0.0.1</address></configuration>
</notifier>
</notifiers>
</ciManagement>
...
</project>

15.6.3 Mailing Lists
Mailing lists are a great tool for keeping in touch with people about a project. Most mailing lists are
for developers and users.

...
<mailingLists>
<mailingList>
<name>User List</name>
<subscribe>user-subscribe@127.0.0.1</subscribe>
<unsubscribe>user-unsubscribe@127.0.0.1</unsubscribe>
<post>user@127.0.0.1</post>
<archive>http://127.0.0.1/user/</archive>
<otherArchives>
<otherArchive>http://base.google.com/base/1/127.0.0.1</otherArchive>
</otherArchives>
</mailingList>
</mailingLists>
...
</project>


15 POM Reference 81

• subscribe, unsubscribe: There elements specify the email addresses which are used for
performing the relative actions To subscribe to the user list above, a user would send an email to
user-subscribe@127.0.0.1.
• archive: This element specifies the url of the archive of old mailing list emails, if one exists. If
there are mirrored archives, they can be specified under otherArchives.
• post: The email address which one would use in order to post to the mailing list. Note that not all
mailing lists have the ability to post to (such as a build failure list).

15.6.4 SCM
SCM (Software Configuration Management, also called Source Code/Control Management or,
succinctly, version control) is an integral part of any healthy project. If your Maven project uses an
SCM system (it does, doesn't it?) then here is where you would place that information into the POM.

...
<scm>
<connection>scm:svn:http://127.0.0.1/svn/my-project</connection>
<developerConnection>scm:svn:https://127.0.0.1/svn/my-project</developerConnecti
<tag>HEAD</tag>
<url>http://127.0.0.1/websvn/my-project</url>
</scm>
...
</project>

• connection, developerConnection: The two connection elements convey to how one is to
connect to the version control system through Maven. Where connection requires read access for
Maven to be able to find the source code (for example, an update), developerConnection requires
a connection that will give write access. The Maven project has spawned another project named
Maven SCM, which creates a common API for any SCMs that wish to implement it. The most
popular are CVS and Subversion, however, there is a growing list of other supported SCMs. All
SCM connections are made through a common URL structure.
scm:[provider]:[provider_specific]
Where provider is the type of SCM system. For example, connecting to a CVS repository may
look like this:
scm:cvs:pserver:127.0.0.1:/cvs/root:my-project
• tag: Specifies the tag that this project lives under. HEAD (meaning, the SCM root) should be the
default.
• url: A publicly browsable repository. For example, via ViewCVS.


15 POM Reference 82

...
<prerequisites>
<maven>2.0.4</maven>
</prerequisites>
...
</project>
• prerequisites: The POM may have certain prerequisites in order to execute correctly. For
example, perhaps there was a fix in Maven 2.0.3 that you need in order to deploy using sftp.
Here is where you give the prerequisites to building. If these are not met, Maven will fail the
build before even starting. The only element that exists as a prerequisite in POM 4.0 is the maven
element, which takes a minimum version number.

15.6.5 Repositories
Repositories are collections of artifacts which adhere to the Maven repository directory layout. In
order to be a Maven 2 repository artifact, a POM file must live within the structure $BASE_REPO/
groupId/artifactId/version/artifactId-version.pom. $BASE_REPO can be local (file
structure) or remote (base URL); the remaining layout will be the same. Repositories exist as a place
to collect and store artifacts. Whenever a project has a dependency upon an artifact, Maven will
first attempt to use a local copy of the specified artifact. If that artifact does not exist in the local
repository, it will then attempt to download from a remote repository. The repository elements within
a POM specify those alternate repositories to search.
The repository is one of the most powerful features of the Maven community. The default central
Maven repository lives on http://repo1.maven.org/maven2/. Another source for artifacts not yet in
iBiblio is the Codehaus snapshots repo.


15 POM Reference 83

...
<repositories>
<repository>
<releases>
<updatePolicy>always</updatePolicy>
<checksumPolicy>warn</checksumPolicy>
</releases>
<snapshots>
<enabled>true</enabled>
<checksumPolicy>fail</checksumPolicy>
</snapshots>
<id>codehausSnapshots</id>
<name>Codehaus Snapshots</name>
<url>http://snapshots.maven.codehaus.org/maven2</url>
</repository>
</repositories>
...
...
</project>

• releases, snapshots: These are the policies for each type of artifact, Release or snapshot. With
these two sets, a POM has the power to alter the policies for each type independent of the other
within a single repository. For example, one may decide to enable only snapshot downloads,
possibly for development purposes.
• enabled: true or false for whether this repository is enabled for the respective type (
releases or snapshots).
• updatePolicy: This element specifies how often updates should attempt to occur. Maven will
compare the local POM's timestamp (stored in a repository's maven-metadata file) to the remote.
The choices are: always, daily (default), interval:X (where X is an integer in minutes) or
never.
• checksumPolicy: When Maven deploys files to the repository, it also deploys corresponding
checksum files. Your options are to ignore, fail, or warn on missing or incorrect checksums.
• layout: In the above description of repositories, it was mentioned that they all follow a common
layout. This is mostly correct. Maven 2 has a default layout for its repositories; however, Maven
1.x had a different layout. Use this element to specify which if it is default or legacy.

15.6.6 Plugin Repositories
Repositories are home to two major types of artifacts. The first are artifacts that are used as
dependencies of other artifacts. These are the majority of plugins that reside within central. The other
type of artifact is plugins. Maven plugins are themselves a special type of artifact. Because of this,
plugin repositories may be separated from other repositories (although, I have yet to hear a convincing
argument for doing so). In any case, the structure of the pluginRepositories element block is


15 POM Reference 84

similar to the repositories element. The pluginRepository elements each specify a remote location
of where Maven can find new plugins.

15.6.7 Distribution Management
Distribution management acts precisely as it sounds: it manages the distribution of the artifact and
supporting files generated throughout the build process. Starting with the last elements first:

...
...
<downloadUrl>http://mojo.codehaus.org/my-project</downloadUrl>
<status>deployed</status>
...
</project>

• downloadUrl: is the url of the repository from whence another POM may point to in order
to grab this POM's artifact. In the simplest terms, we told the POM how to upload it (through
repository/url), but from where can the public download it? This element answers that question.
• status: Warning! Like a baby bird in a nest, the status should never be touched by human hands!
The reason for this is that Maven will set the status of the project when it is transported out to the
repository. Its valid types are as follows.

• none: No special status. This is the default for a POM.
• converted: The manager of the repository converted this POM from an earlier version to
Maven 2.
• partner: This could just as easily have been called synched. This means that this artifact
has been synched with a partner repository.
• deployed: By far the most common status, meaning that this artifact was deployed from a
Maven 2 instance. This is what you get when you manually deploy using the command-line
deploy phase.
• verified: This project has been verified, and should be considered finalized.

15.6.7.1 Repository
Where as the repositories element specifies in the POM the location and manner in which Maven may
download remote artifacts for use by the current project, distributionManagement specifies where
(and how) this project will get to a remote repository when it is deployed. The repository elements
will be used for snapshot distribution if the snapshotRepository is not defined.


15 POM Reference 85

...
<repository>
<uniqueVersion>false</uniqueVersion>
<id>corp1</id>
<name>Corporate Repository</name>
<url>scp://repo1/maven2</url>
</repository>
<snapshotRepository>
<uniqueVersion>true</uniqueVersion>
<id>propSnap</id>
<name>Propellors Snapshots</name>
<url>sftp://propellers.net/maven</url>
<layout>legacy</layout>
</snapshotRepository>
...
...
</project>

• id, name: The id is used to uniquely identify this repository amongst many, and the name is a
human readable form.
• uniqueVersion: The unique version takes a true or false value to denote whether artifacts
deployed to this repository should get a uniquely generated version number, or use the version
number defined as part of the address.
• url: This is the core of the repository element. It specifies both the location and the transport
protocol to be used to transfer a built artifact (and POM file, and checksum data) to the
repository.
• layout: These are the same types and purpose as the layout element defined in the repository
element. They are default and legacy.

15.6.7.2 Site Distribution
More than distribution to the repositories, distributionManagement is responsible for defining
how to deploy the project's site and documentation.


15 POM Reference 86

...
...
<site>
<id>mojo.website</id>
<name>Mojo Website</name>
<url>scp://beaver.codehaus.org/home/projects/mojo/public_html/</url>
</site>
...
...
</project>

• id, name, url: These elements are similar to their counterparts above in the
distributionManagement repository element.

15.6.7.3 Relocation

...
...
<relocation>
<groupId>org.apache</groupId>
<message>We have moved the Project under Apache</message>
</relocation>
...
...
</project>

Projects are not static; they are living things (or dying things, as the case may be). A common thing
that happens as projects grow, is that they are forced to move to more suitable quarters. For example,
when your next wildly successful open source project moves under the Apache umbrella, it would
be good to give your users as heads-up that the project is being renamed to org.apache:my-
project:1.0. Besides specifying the new address, it is also good form to provide a message
explaining why.

15.6.8 Profiles
A new feature of the POM 4.0 is the ability of a project to change settings depending on the
environment where it is being built. A profile element contains both an optional activation (a
profile trigger) and the set of changes to be made to the POM if that profile has been activated. For
example, a project built for a test environment may point to a different database than that of the final


15 POM Reference 87

deployment. Or dependencies may be pulled from different repositories based upon the JDK version
used. The elements of profiles are as follows:

...
<profiles>
<profile>
<id>test</id>
<activation>...</activation>
<build>...</build>
<modules>...</modules>
<repositories>...</repositories>
<pluginRepositories>...</pluginRepositories>
<reporting>...</reporting>
<dependencyManagement>...</dependencyManagement>
<distributionManagement>...</distributionManagement>
</profile>
</profiles>
</project>

15.6.8.1 Activation
Activations are the key of a profile. The power of a profile comes from its ability to modify the basic
POM only under certain circumstances. Those circumstances are specified via an activation
element.


15 POM Reference 88

...
<profiles>
<profile>
<id>test</id>
<activation>
<activeByDefault>false</activeByDefault>
<jdk>1.5</jdk>
<os>
<name>Windows XP</name>
<family>Windows</family>
<arch>x86</arch>
</os>
<property>
<name>mavenVersion</name>
<value>2.0.3</value>
</property>
<file>
<exists>${basedir}/file2.properties</exists>
<missing>${basedir}/file1.properties</missing>
</file>
</activation>
...
</profile>
</profiles>
</project>

Activation occurs when one or more of the specified criteria have been met. When the first positive
result is encountered, processing stops and the profile is marked as active.

• jdk: activation has a built in, Java-centric check in the jdk element. This will activate if
the test is run under a jdk version number that matches the prefix given. In the above example,
1.5.0_06 will match. Ranges are also supported as of Maven 2.1. See the maven-enforcer-
plugin for more details about supported ranges.
• os: The os element can define some operating system specific properties shown above. See the
maven-enforcer-plugin for more details about OS values.
• property: The profile will activate if Maven detects a property (a value which can be
dereferenced within the POM by ${name}) of the corresponding name=value pair.
• file: Finally, a given filename may activate the profile by the existence of a file, or if it is
missing.
The activation element is not the only way that a profile may be activated. The settings.xml
file's activeProfile element may contain the profile's id. They may also be activated explicitly
through the command line via a comma separated list after the -P flag (e.g. -P test).
To see which profile will activate in a certain build, use the maven-help-plugin.
mvn help:active-profiles


15 POM Reference 89

15.6.8.2 The BaseBuild Element Set (revisited)
As mentioned above, the reason for the two types of build elements reside in the fact that it does not
make sense for a profile to configure build directories or extensions as it does in the top level of the
POM. Reguardless of in which environment the project is built, some values will remain constant,
such as the directory structure of the source code. If you find your project needing to keep two sets of
code for different environments, it may be prudent to investigate refactoring the project into two or
more seperate projects.

15.7 Final
The Maven 2 POM is big. However, its size is also a testament to its versatility. The ability to abstract
all of the aspects of a project into a single artifact is powerful, to say the least. Gone are the days of
dozens of disparate build scripts and scattered documentation concerning each individual project.
Along with Maven's other stars that make up the Maven galaxy - a well defined build lifecycle, easy
to write and maintain plugins, centralized repositories, system-wide and user-based configurations, as
well as the increasing number of tools to make developers' jobs easier to maintain complex projects -
the POM is the large, but bright, center.

Aspects of this guide were originally published in the Maven 2 Pom Demystified.


16 Settings Reference 90

16 Settings Reference
.......................................................................................................................................

16.1 Settings Reference
1 Introduction
1 Quick Overview
2 Settings Details
1 Simple Values
2 Servers
1 Password Encryption
3 Mirrors
4 Proxies
5 Profiles
1 Activation
2 Repositories
3 Plugin Repositories
6 Active Profiles

16.2 Introduction

16.2.1 Quick Overview
The settings element in the settings.xml file contains elements used to define values which
configure Maven execution in various ways, like the pom.xml, but should not be bundled to any
specific project, or distributed to an audience. These include values such as the local repository
location, alternate remote repository servers, and authentication information. There are two locations
where a settings.xml file may live:
• The Maven install: $M2_HOME/conf/settings.xml
• A user's install: ${user.home}/.m2/settings.xml
Here is an overview of the top elements under settings:

<localRepository/>
<interactiveMode/>
<usePluginRegistry/>
<offline/>
<pluginGroups/>
<servers/>
<mirrors/>
<proxies/>
<profiles/>
<activeProfiles/>
</settings>



16.3 Settings Details

16.3.1 Simple Values
Half of the top-level settings elements are simple values, representing a range of values which
describe elements of the build system that are active full-time.

<localRepository>${user.home}/.m2/repository</localRepository>
<interactiveMode>true</interactiveMode>
<usePluginRegistry>false</usePluginRegistry>
<offline>false</offline>
<pluginGroups>
<pluginGroup>org.mortbay.jetty</pluginGroup>
</pluginGroups>
...
</settings>

• localRepository: This value is the path of this build system's local repository. The default value
is ${user.home}/.m2/repository. This element is especially useful for a main build server
allowing all logged-in users to build from a common local repository.
• interactiveMode: true if Maven should attempt to interact with the user for input, false if
not. Defaults to true.
• usePluginRegistry: true if Maven should use the ${user.home}/.m2/plugin-
registry.xml file to manage plugin versions, defaults to false. Note that for the current
version of Maven 2.0, the plugin-registry.xml file should not be depended upon. Consider it
dormant for now.
• offline: true if this build system should operate in offline mode, defaults to false. This
element is useful for build servers which cannot connect to a remote repository, either because of
network setup or security reasons.
• pluginGroups: This element contains a list of pluginGroup elements, each contains
a groupId. The list is searched when a plugin is used and the groupId is not provided in
the command line. This list automatically contains org.apache.maven.plugins and
org.codehaus.mojo. For example, given the above settings the Maven command line may
execute org.mortbay.jetty:jetty-maven-plugin:run with the truncated command:
mvn jetty:run

16.3.2 Servers
The repositories for download and deployment are defined by the repositories and
distributionManagement elements of the POM. However, certain settings such as username and
password should not be distributed along with the pom.xml. This type of information should exist
on the build server in the settings.xml.



...
<servers>
<server>
<id>server001</id>
<username>my_login</username>
<password>my_password</password>
<privateKey>${user.home}/.ssh/id_dsa</privateKey>
<passphrase>some_passphrase</passphrase>
<filePermissions>664</filePermissions>
<directoryPermissions>775</directoryPermissions>
<configuration></configuration>
</server>
</servers>
...
</settings>

• id: This is the ID of the server (not of the user to login as) that matches the id element of the
repository/mirror that Maven tries to connect to.
• username, password: These elements appear as a pair denoting the login and password required
to authenticate to this server.
• privateKey, passphrase: Like the previous two elements, this pair specifies a path to a
private key (default is ${user.home}/.ssh/id_dsa) and a passphrase, if required. The
passphrase and password elements may be externalized in the future, but for now they must
be set plain-text in the settings.xml file.
• filePermissions, directoryPermissions: When a repository file or directory is created on
deployment, these are the permissions to use. The legal values of each is a three digit number
corrosponding to *nix file permissions, ie. 664, or 775.
Note: If you use a private key to login to the server, make sure you omit the <password> element.
Otherwise, the key will be ignored.

16.3.2.1 Password Encryption
A new feature - server password and passphrase encryption has been added to 2.1.x and 3.0 trunks.
See details on this page



16.3.3 Mirrors

...
<mirrors>
<mirror>
<id>planetmirror.com</id>
<name>PlanetMirror Australia</name>
<url>http://downloads.planetmirror.com/pub/maven2</url>
<mirrorOf>central</mirrorOf>
</mirror>
</mirrors>
...
</settings>

• id, name: The unique identifier and user-friendly name of this mirror. The id is used to
differentiate between mirror elements and to pick the corresponding credentials from the
<servers> section when connecting to the mirror.
• url: The base URL of this mirror. The build system will use this URL to connect to a repository
rather than the original repository URL.
• mirrorOf: The id of the repository that this is a mirror of. For example, to point to a mirror of
the Maven central repository ( http://repo1.maven.org/maven2/), set this element to
central. More advanced mappings like repo1,repo2 or *,!inhouse are also possible. This
must not match the mirror id.
For a more in-depth introduction of mirrors, please read the Guide to Mirror Settings.

16.3.4 Proxies

...
<proxies>
<proxy>
<id>myproxy</id>
<active>true</active>
<protocol>http</protocol>
<host>proxy.somewhere.com</host>
<port>8080</port>
<username>proxyuser</username>
<password>somepassword</password>
<nonProxyHosts>*.google.com|ibiblio.org</nonProxyHosts>
</proxy>
</proxies>
...
</settings>

• id: The unique identifier for this proxy. This is used to differentiate between proxy elements.



• active: true if this proxy is active. This is useful for declaring a set of proxies, but only one may
be active at a time.
• protocol, host, port: The protocol://host:port of the proxy, seperated into discrete
elements.
• username, password: These elements appear as a pair denoting the login and password required
to authenticate to this proxy server.
• nonProxyHosts: This is a list of hosts which should not be proxied. The delimiter of the list is
the expected type of the proxy server; the example above is pipe delimited - comma delimited is
also common.

16.3.5 Profiles
The profile element in the settings.xml is a truncated version of the pom.xml profile
element. It consists of the activation, repositories, pluginRepositories and properties
elements. The profile elements only include these four elements because they concerns themselves
with the build system as a whole (which is the role of the settings.xml file), not about individual
project object model settings.
If a profile is active from settings, its values will override any equivalently ID'd profiles in a POM
or profiles.xml file.

16.3.5.1 Activation
Activations are the key of a profile. Like the POM's profiles, the power of a profile comes from its
ability to modify some values only under certain circumstances; those circumstances are specified via
an activation element.



...
<profiles>
<profile>
<id>test</id>
<activation>
<activeByDefault>false</activeByDefault>
<jdk>1.5</jdk>
<os>
<arch>x86</arch>
</os>
<property>
<name>mavenVersion</name>
<value>2.0.3</value>
</property>
<file>
<exists>${basedir}/file2.properties</exists>
<missing>${basedir}/file1.properties</missing>
</file>
</activation>
...
</profile>
</profiles>
...
</settings>

Activation occurs when all specified criteria have been met, though not all are required at once.

• jdk: activation has a built in, Java-centric check in the jdk element. This will activate if
the test is run under a jdk version number that matches the prefix given. In the above example,
1.5.0_06 will match. Ranges are also supported as of Maven 2.1. See the maven-enforcer-
plugin for more details about supported ranges.
• os: The os element can define some operating system specific properties shown above. See the
maven-enforcer-plugin for more details about OS values.
• property: The profile will activate if Maven detects a property (a value which can be
dereferenced within the POM by ${name}) of the corresponding name=value pair.
• file: Finally, a given filename may activate the profile by the existence of a file, or if it is
missing.
The activation element is not the only way that a profile may be activated. The settings.xml
file's activeProfile element may contain the profile's id. They may also be activated explicitly
through the command line via a comma separated list after the -P flag (e.g. -P test).
To see which profile will activate in a certain build, use the maven-help-plugin.



16.3.5.2 Properties
Maven properties are value placeholder, like properties in Ant. Their values are accessible anywhere
within a POM by using the notation ${X}, where X is the property. They come in five different styles,
all accessible from the settings.xml file:

1 env.X: Prefixing a variable with "env." will return the shell's environment variable. For
example, ${env.PATH} contains the $path environment variable ( %PATH% in Windows).
2 project.x: A dot (.) notated path in the POM will contain the corresponding element's
value. For example: <project><version>1.0</version></project> is accessible via
${project.version}.
3 settings.x: A dot (.) notated path in the settings.xml will contain the corresponding
element's value. For example: <settings><offline>false</offline></settings> is
accessible via ${settings.offline}.
4 Java System Properties: All properties accessible via java.lang.System.getProperties()
are available as POM properties, such as ${java.home}.
5 x: Set within a <properties /> element or an external files, the value may be used as
${someVar}.

...
<profiles>
<profile>
...
<properties>
<user.install>${user.home}/our-project</user.install>
</properties>
...
</profile>
</profiles>
...
</settings>

The property ${user.install} is accessible from a POM if this profile is active.

16.3.5.3 Repositories
Repositories are remote collections of projects from which Maven uses to populate the local
repository of the build system. It is from this local repository that Maven calls it plugins and
dependencies. Different remote repositories may contain different projects, and under the active
profile they may be searched for a matching release or snapshot artifact.



...
<profiles>
<profile>
...
<repositories>
<repository>
<id>codehausSnapshots</id>
<name>Codehaus Snapshots</name>
<releases>
<updatePolicy>always</updatePolicy>
<checksumPolicy>warn</checksumPolicy>
</releases>
<snapshots>
<checksumPolicy>fail</checksumPolicy>
</snapshots>
<url>http://snapshots.maven.codehaus.org/maven2</url>
</repository>
</repositories>
...
...
</profile>
</profiles>
...
</settings>

• releases, snapshots: These are the policies for each type of artifact, Release or snapshot. With
these two sets, a POM has the power to alter the policies for each type independent of the other
within a single repository. For example, one may decide to enable only snapshot downloads,
possibly for development purposes.
• enabled: true or false for whether this repository is enabled for the respective type (
releases or snapshots).
• updatePolicy: This element specifies how often updates should attempt to occur. Maven will
compare the local POM's timestamp (stored in a repository's maven-metadata file) to the remote.
The choices are: always, daily (default), interval:X (where X is an integer in minutes) or
never.
• checksumPolicy: When Maven deploys files to the repository, it also deploys corresponding
checksum files. Your options are to ignore, fail, or warn on missing or incorrect checksums.
• layout: In the above description of repositories, it was mentioned that they all follow a common
layout. This is mostly correct. Maven 2 has a default layout for its repositories; however, Maven
1.x had a different layout. Use this element to specify which if it is default or legacy.



16.3.5.4 Plugin Repositories
Repositories are home to two major types of artifacts. The first are artifacts that are used as
dependencies of other artifacts. These are the majority of plugins that reside within central. The other
type of artifact is plugins. Maven plugins are themselves a special type of artifact. Because of this,
plugin repositories may be separated from other repositories (although, I have yet to hear a convincing
argument for doing so). In any case, the structure of the pluginRepositories element block is
similar to the repositories element. The pluginRepository elements each specify a remote
location of where Maven can find new plugins.

16.3.6 Active Profiles

...
<activeProfiles>
<activeProfile>env-test</activeProfile>
</activeProfiles>
</settings>

The final piece of the settings.xml puzzle is the activeProfiles element. This contains a set of
activeProfile elements, which each have a value of a profile id. Any profile id defined as
an activeProfile will be active, reguardless of any environment settings. If no matching profile is
found nothing will happen. For example, if env-test is an activeProfile, a profile in a pom.xml
(or profile.xml with a corrosponding id will be active. If no such profile is found then execution
will continue as normal.


17 Guides 99

17 Guides
.......................................................................................................................................

17.1 Documentation

17.1.1 Getting Started with Maven

• Getting Started in 5 Minutes
• Getting Started in 30 Minutes

17.1.2 Introductions

• The Build Lifecycle
• The POM
• Profiles
• Repositories
• Standard Directory Layout
• The Dependency Mechanism

17.1.2.1 Plugins

• Plugin Development
• Configuring Plug-ins
• The Plugin Registry
• Plugin Prefix Resolution
• Developing Ant Plugins
• Developing Java Plugins

17.1.2.2 Site

• Creating a Site
• The APT Format
• Snippet Macro

17.1.2.3 Archetypes

• What is an Archetype
• Creating Archetypes

17.1.2.4 Upgrading

• From Maven 1.x to Maven 2.x
• Using Maven 1.x repositories with Maven 2.x
• Relocation of Artifacts

17.1.2.5 Repositories

• Installing 3rd party JARs to Local Repository
• Deploying 3rd party JARs to Remote Repository


17 Guides 100

• Coping with Sun JARs
• Remote repository access through authenticated HTTPS

17.1.3 Guides

• Creating Assemblies
• Configuring Archive Plugins
• Configuring Maven
• Mirror Settings
• Deployment and Security Settings
• Embedding Maven 2.x
• Generating Sources
• Working with Manifests
• Maven Classloading
• Using Multiple Modules in a Build
• Using Multiple Repositories
• Using Proxies
• Using the Release Plugin
• Using Ant with Maven
• Using Modello
• Webapps
• Using Extensions
• Building For Different Environments with Maven 2
• Using Toolchains
• Encrypting passwords in settings.xml

17.1.3.1 Testing

• Reusable Test JARs

17.1.3.2 Maven Tools and IDE Integration

• Eclipse
• IDEA
• Netbeans 4.0 (4.1 and 5.0)
• Maven 2.x Auto-Completion Using BASH

17.1.4 Development Guides

• Building Maven from Scratch
• Developing Maven
• The Plugin Documentation Standard
• Maven Documentation Style

17.1.5 The Maven Community

• The Maven Community


17 Guides 101

• Helping with Maven
• Guide for New Committers
• Testing Development Versions of Plugins
• 3rd Party Resources

17.1.5.1 Conventions

• Maven Conventions
• Naming Conventions
• When You Can't Use the Conventions

17.1.5.2 The Central Repository

• Uploading Artifacts to the Central Repository
• Improving the Repository

17.1.6 References

• POM Overview ( Technical Project Descriptor)
• Settings Overview ( Technical Settings Descriptor)
• Password Encryption
• Core Plug-ins List
• Mojo API
• Glossary
• Maven Quick Reference Card - PDF

17.1.7 Javadoc API
Here is some useful Javadoc API links to the current version of Maven:

• Maven Artifact
• Maven Reporting
• Maven Plugin API
• Maven Model
• Maven Core
• Maven Settings
You could also browse the full technical documentation references of the current version of Maven.


18 The Build Lifecycle 102

18 The Build Lifecycle
.......................................................................................................................................

18.1 Introduction to the Build Lifecycle

18.1.1 Table Of Contents
• Build Lifecycle Basics
• Setting Up Your Project to Use the Build Lifecycle
• Packaging
• Plugins
• Lifecycle Reference
• Built-in Lifecycle Bindings

18.1.2 Build Lifecycle Basics
Maven 2.0 is based around the central concept of a build lifecycle. What this means is that the process
for building and distributing a particular artifact (project) is clearly defined.
For the person building a project, this means that it is only necessary to learn a small set of commands
to build any Maven project, and the POM will ensure they get the results they desired.
There are three built-in build lifecycles: default, clean and site. The default lifecycle handles your
project deployment, the clean lifecycle handles project cleaning, while the site lifecycle handles the
creation of your project's site documentation.

18.1.2.1 A Build Lifecycle is Made Up of Phases
Each of these build lifecycles is defined by a different list of build phases, wherein a build phase
represents a stage in the lifecycle.
For example, the default lifecycle has the following build phases (for a complete list of the build
phases, refer to the Lifecycle Reference):
• validate - validate the project is correct and all necessary information is available
• compile - compile the source code of the project
• test - test the compiled source code using a suitable unit testing framework. These tests should
not require the code be packaged or deployed
• package - take the compiled code and package it in its distributable format, such as a JAR.
• integration-test - process and deploy the package if necessary into an environment where
integration tests can be run
• verify - run any checks to verify the package is valid and meets quality criteria
• install - install the package into the local repository, for use as a dependency in other projects
locally
• deploy - done in an integration or release environment, copies the final package to the remote
repository for sharing with other developers and projects.
These build phases (plus the other build phases not shown here) are executed sequentially to complete
the default lifecycle. Given the build phases above, this means that when the default lifecycle is used,
Maven will first validate the project, then will try to compile the sources, run those against the tests,
package the binaries (e.g. jar), run integration tests against that package, verify the package, install the
verifed package to the local repository, then deploy the installed package in a specified environment.
To do all those, you only need to call the last build phase to be executed, in this case, deploy:



mvn deploy
That is because if you call a build phase, it will execute not only that build phase, but also every build
phase prior to the called build phase. Thus, doing
mvn integration-test
will do every build phase before it ( validate, compile, package, etc.), before executing
integration-test.
There are more commands that are part of the lifecycle, which will be discussed in the following
sections.
It should also be noted that the same command can be used in a multi-module scenario (i.e. a project
with one or more subprojects). For example:
mvn clean install
This command will traverse into all of the subprojects and run clean, then install (including all of
the prior steps).
[top].

18.1.2.2 A Build Phase is Made Up of Goals
However, even though a build phase is responsible for a specific step in the build lifecycle, the
manner in which it carries out those responsibilities may vary. And this is done by declaring the goals
bound to those build phases.
A goal represents a specific task (finer than a build phase) which contributes to the building and
managing of a project. It may be bound to zero or more build phases. A goal not bound to any
build phase could be executed outside of the build lifecycle by direct invocation. The order of
execution depends on the order in which the goal(s) and the build phase(s) are invoked. For example,
consider the command below. The clean and package arguments are build phases while the
dependency:copy-dependencies is a goal.
mvn clean dependency:copy-dependencies package
If this were to be executed, the clean phase will be executed first (meaning it will run all preceeding
phases of the clean lifecycle, plus the clean phase itself), and then the dependency:copy-
dependencies goal, before finally executing the package phase (and all its preceeding build phases
of the default lifecycle).
Moreover, if a goal is bound to one or more build phases, that goal will be called in all those phases.
Furthermore, a build phase can also have zero or more goals bound to it. If a build phase has no
goals bound to it, that build phase will not execute. But if it has one or more goals bound to it, it
will execute all those goals ( Note: In Maven 2.0.5 and above, multiple goals bound to a phase are
executed in the same order as they are declared in the POM, however multiple instances of the same
plugin are not supported. Multiple instances of the same plugin are grouped to execute together and
ordered in Maven 2.0.11 and above).
[top].

18.1.3 Setting Up Your Project to Use the Build Lifecycle
The build lifecycle is simple enough to use, but when you are constructing a Maven build for a
project, how do you go about assigning tasks to each of those build phases?



18.1.3.1 Packaging
The first, and most common way, is to set the packaging for your project via the equally named
POM element <packaging>. Some of the valid packaging values are jar, war, ear and pom. If no
packaging value has been specified, it will default to jar.
Each packaging contains a list of goals to bind to a particular phase. For example, the jar packaging
will bind the following goals to build phases of the default lifecycle.

process-resources resources:resources
compile compiler:compile
process-test-resources resources:testResources
test-compile compiler:testCompile
test surefire:test
package jar:jar
install install:install
deploy deploy:deploy

This is an almost standard set of bindings; however, some packagings handle them differently. For
example, a project that is purely metadata (packaging value is pom) only binds goals to the install
and deploy phases (for a complete list of goal-to-build-phase bindings of some of the packaging
types, refer to the Lifecycle Reference).
Note that for some packaging types to be available, you may also need to include a particular plugin
in your <build> section of your POM (as described in the next section). One example of a plugin
that requires this is the Plexus plugin, which provides a plexus-application and plexus-
service packaging.
[top].

18.1.3.2 Plugins
The second way to add goals to phases is to configure plugins in your project. Plugins are artifacts
that provide goals to Maven. Furthermore, a plugin may have one or more goals wherein each goal
represents a capability of that plugin. For example, the Compiler plugin has two goals: compile and
testCompile. The former compiles the source code of your main code, while the later compiles the
source code of your test code.
As you will see in the later sections, plugins can contain information that indicates which lifecycle
phase to bind a goal to. Note that adding the plugin on its own is not enough information - you must
also specify the goals you want to run as part of your build.
The goals that are configured will be added to the goals already bound to the lifecycle from the
packaging selected. If more than one goal is bound to a particular phase, the order used is that those
from the packaging are executed first, followed by those configured in the POM. Note that you can
use the <executions> element to gain more control over the order of particular goals.
For example, the Modello plugin binds by default its goal modello:java to the generate-
sources phase (Note: The modello:java goal generates Java source codes). So to use the Modello
plugin and have it generate sources from a model and incorporate that into the build, you would add
the following to your POM in the <plugins> section of <build>:
...
<plugin>



<groupId>org.codehaus.modello</groupId>
<artifactId>modello-maven-plugin</artifactId>
<executions>
<execution>
<configuration>
<model>maven.mdo</model>
</configuration>
<goals>
<goal>java</goal>
</goals>
</execution>
</executions>
</plugin>
...
You might be wondering why that <executions> element is there. That is so that you can run the
same goal multiple times with different configuration if needed. Separate executions can also be
given an ID so that during inheritance or the application of profiles you can control whether goal
configuration is merged or turned into an additional execution.
When multiple executions are given that match a particular phase, they are executed in the order
specified in the POM, with inherited executions running first.
Now, in the case of modello:java, it only makes sense in the generate-sources phase. But
some goals can be used in more than one phase, and there may not be a sensible default. For those,
you can specify the phase yourself. For example, let's say you have a goal display:time that echos
the current time to the commandline, and you want it to run in the process-test-resources
phase to indicate when the tests were started. This would be configured like so:
...
<plugin>
<groupId>com.mycompany.example</groupId>
<artifactId>maven-touch-plugin</artifactId>
<executions>
<execution>
<phase>process-test-resources</phase>
<goals>
<goal>timestamp</goal>
</goals>
</execution>
</executions>
</plugin>
...
[top].

18.1.4 Lifecycle Reference
The following lists all build phases of the default, clean and site lifecycle, which are executed in the
order given up to the point of the one specified.
Clean Lifecycle



pre-clean executes processes needed prior to the actual project
cleaning
clean remove all files generated by the previous build
post-clean executes processes needed to finalize the project
cleaning

Default Lifecycle

validate validate the project is correct and all necessary
information is available.
initialize initialize build state, e.g. set properties or create
directories.
generate-sources generate any source code for inclusion in compilation.
process-sources process the source code, for example to filter any
values.
generate-resources generate resources for inclusion in the package.
process-resources copy and process the resources into the destination
directory, ready for packaging.
compile compile the source code of the project.
process-classes post-process the generated files from compilation,
for example to do bytecode enhancement on Java
classes.
generate-test-sources generate any test source code for inclusion in
compilation.
process-test-sources process the test source code, for example to filter any
values.
generate-test-resources create resources for testing.
process-test-resources copy and process the resources into the test
destination directory.
test-compile compile the test source code into the test destination
directory
process-test-classes post-process the generated files from test compilation,
for example to do bytecode enhancement on Java
classes. For Maven 2.0.5 and above.
test run tests using a suitable unit testing framework.
These tests should not require the code be packaged
or deployed.
prepare-package perform any operations necessary to prepare a
package before the actual packaging. This often
results in an unpacked, processed version of the
package. (Maven 2.1 and above)
package take the compiled code and package it in its
distributable format, such as a JAR.
pre-integration-test perform actions required before integration tests are
executed. This may involve things such as setting up
the required environment.



integration-test process and deploy the package if necessary into an
environment where integration tests can be run.
post-integration-test perform actions required after integration tests have
been executed. This may including cleaning up the
environment.
verify run any checks to verify the package is valid and
meets quality criteria.
install install the package into the local repository, for use as
a dependency in other projects locally.
deploy done in an integration or release environment, copies
the final package to the remote repository for sharing
with other developers and projects.

Site Lifecycle

pre-site executes processes needed prior to the actual project
site generation
site generates the project's site documentation
post-site executes processes needed to finalize the site
generation, and to prepare for site deployment
site-deploy deploys the generated site documentation to the
specified web server

[top].

18.1.5 Built-in Lifecycle Bindings
Some phases have goals binded to them by default. And for the default lifecycle, these bindings
depend on the packaging value. Here are some of the goal-to-build-phase bindings.

18.1.5.1 Clean Lifecycle Bindings

clean clean:clean

18.1.5.2 Default Lifecycle Bindings - Packaging ejb / ejb3 / jar / par / rar / war

test surefire:test
package ejb:ejb or ejb3:ejb3 or jar:jar or
par:par or rar:rar or war:war




18.1.5.3 Default Lifecycle Bindings - Packaging ear

generate-resources ear:generateApplicationXml
package ear:ear

18.1.5.4 Default Lifecycle Bindings - Packaging maven-plugin

generate-resources plugin:descriptor
test surefire:test
package jar:jar and
plugin:addPluginArtifactMetadata
install install:install and
plugin:updateRegistry

18.1.5.5 Default Lifecycle Bindings - Packaging pom

package site:attach-descriptor

18.1.5.6 Site Lifecycle Bindings

site site:site
site-deploy site:deploy

18.1.5.7 References
The full Maven lifecycle is defined by the file components.xml in the module maven-core and
viewable from SVN in the branches for Maven 2.2.0 and Maven 3.0.x.



[top].


19 The POM 110

19 The POM
.......................................................................................................................................

19.1 Introduction to the POM
• What is a POM?
• Super POM
• Minimal POM
• Project Inheritance

• Example 1
• Example 2
• Project Aggregation

• Example 3
• Example 4
• Project Inheritance vs Project Aggregation

• Example 5
• Project Interpolation and Expressions

• Available Variables

19.1.1 What is a POM?
A Project Object Model or POM is the fundamental unit of work in Maven. It is an XML file that
contains information about the project and configuration details used by Maven to build the project. It
contains default values for most projects. Examples for this is the build directory, which is target;
the source directory, which is src/main/java; the test source directory, which is src/main/test;
and so on.
The POM was renamed from project.xml in Maven 1 to pom.xml in Maven 2. Instead of having a
maven.xml file that contains the goals that can be executed, the goals or plugins are now configured
in the pom.xml. When executing a task or goal, Maven looks for the POM in the current directory. It
reads the POM, gets the needed configuration information, then executes the goal.
Some of the configuration that can be specified in the POM are the project dependencies, the plugins
or goals that can be executed, the build profiles, and so on. Other information such as the project
version, description, developers, mailing lists and such can also be specified.
[top]

19.1.2 Super POM
The Super POM is Maven's default POM. All POMs extend the Super POM unless explicitly set,
meaning the configuration specified in the Super POM is inherited by the POMs you created for your
projects. The snippet below is the Super POM for Maven 2.0.x.


19 The POM 111

<project>
<repositories>
<repository>
<id>central</id>
<snapshots>
</snapshots>
</repository>
</repositories>
<pluginRepository>
<id>central</id>
<snapshots>
</snapshots>
<releases>
</releases>
</pluginRepository>
<build>
<directory>target</directory>
<outputDirectory>target/classes</outputDirectory>
<finalName>${artifactId}-${version}</finalName>
<testOutputDirectory>target/test-classes</testOutputDirectory>
<sourceDirectory>src/main/java</sourceDirectory>
<testSourceDirectory>src/test/java</testSourceDirectory>
<resources>
<resource>
</resource>
</resources>
<testResources>
<testResource>
<directory>src/test/resources</directory>
</testResource>
</testResources>
</build>
<reporting>
<outputDirectory>target/site</outputDirectory>
</reporting>
<profiles>
<profile>
<id>release-profile</id>
<activation>
<property>
<name>performRelease</name>
</property>
</activation>
<build>
<plugins>
<plugin>

19 The POM 112

The snippet below is the Super POM for Maven 2.1.x.


19 The POM 113

<project>
<repositories>
<repository>
<id>central</id>
<snapshots>
</snapshots>
</repository>
</repositories>
<pluginRepository>
<id>central</id>
<snapshots>
</snapshots>
<releases>
</releases>
</pluginRepository>
<build>
<directory>${project.basedir}/target</directory>
<outputDirectory>${project.build.directory}/classes</outputDirectory>
<finalName>${project.artifactId}-${project.version}</finalName>
<testOutputDirectory>${project.build.directory}/test-classes</testOutputDirector
<sourceDirectory>${project.basedir}/src/main/java</sourceDirectory>
<!-- TODO: MNG-3731 maven-plugin-tools-api < 2.4.4 expect this to be relative...
<testSourceDirectory>${project.basedir}/src/test/java</testSourceDirectory>
<resources>
<resource>
<directory>${project.basedir}/src/main/resources</directory>
</resource>
</resources>
<testResources>
<testResource>
<directory>${project.basedir}/src/test/resources</directory>
</testResource>
</testResources>
<pluginManagement>
<plugins>
<plugin>
</plugin>
<plugin>
</plugin>
<plugin>
<artifactId>maven-clean-plugin</artifactId>
</plugin>
<plugin>

19 The POM 114

[top]

19.1.3 Minimal POM
The minimum requirement for a POM are the following:

• project root
• modelVersion - should be set to 4.0.0
• groupId - the id of the project's group.
• artifactId - the id of the artifact (project)
• version - the version of the artifact under the specified group
Here's an example:

<project>
<version>1</version>
</project>

A POM requires that its groupId, artifactId, and version be configured. These three values form the
project's fully qualified artifact name. This is in the form of <groupId>:<artifactId>:<version>. As for
the example above, its fully qualified artifact name is "com.mycompany.app:my-app:1".
Also, as mentioned in the first section, if the configuration details are not specified, Maven will use
their defaults. One of these default values is the packaging type. Every Maven project has a packaging
type. If it is not specified in the POM, then the default value "jar" would be used.
Furthermore, as you can see that in the minimal POM, the repositories were not specified. If you
build your project using the minimal POM, it would inherit the repositories configuration in the Super
POM. Therefore when Maven sees the dependencies in the minimal POM, it would know that these
dependencies will be downloaded from http://repo1.maven.org/maven2 which was specified
in the Super POM.
[top]

19.1.4 Project Inheritance
Elements in the POM that are merged are the following:

• dependencies
• developers and contributors
• plugin lists (including reports)
• plugin executions with matching ids
• plugin configuration
• resources
The Super POM is one example of project inheritance, however you can also introduce your own
parent POMs by specifying the parent element in the POM, as demonstrated in the following
examples.


19 The POM 115

19.1.4.1 Example 1

19.The Scenario
As an example, let us reuse our previous artifact, com.mycompany.app:my-app:1. And let us
introduce another artifact, com.mycompany.app:my-module:1.

<project>
<artifactId>my-module</artifactId>
</project>

And let us specify their directory structure as the following:

.
|-- my-module
| `-- pom.xml
`-- pom.xml

Note: my-module/pom.xml is the POM of com.mycompany.app:my-module:1 while pom.xml is
the POM of com.mycompany.app:my-app:1
19.The Solution
Now, if we were to turn com.mycompany.app:my-app:1 into a parent artifact of
com.mycompany.app:my-module:1,we will have to modify com.mycompany.app:my-module:1's
POM to the following configuration:
com.mycompany.app:my-module:1's POM

<project>
<parent>
</parent>
</project>

Notice that we now have an added section, the parent section. This section allows us to specify which
artifact is the parent of our POM. And we do so by specifying the fully qualified artifact name of the
parent POM. With this setup, our module can now inherit some of the properties of our parent POM.
Alternatively, if we want the groupId and / or the version of your modules to be the same as their
parents, you can remove the groupId and / or the version identity of your module in its POM.


19 The POM 116

<project>
<parent>
</parent>
</project>

This allows the module to inherit the groupId and / or the version of its parent POM.
[top]

19.1.4.2 Example 2

19.The Scenario
However, that would work if the parent project was already installed in our local repository or was
in that specific directory structure (parent pom.xml is one directory higher than that of the module's
pom.xml).
But what if the parent is not yet installed and if the directory structure is

.
|-- my-module
| `-- pom.xml
`-- parent
`-- pom.xml

19.The Solution
To address this directory structure (or any other directory structure), we would have to add the
<relativePath> element to our parent section.

<project>
<parent>
<relativePath>.../parent/pom.xml</relativePath>
</parent>
</project>

As the name suggests, it's the relative path from the module's pom.xml to the parent's pom.xml.

19.1.5 Project Aggregation
Project Aggregation is similar to Project Inheritance. But instead of specifying the parent POM from
the module, it specifies the modules from the parent POM. By doing so, the parent project now knows
its modules, and if a Maven command is invoked against the parent project, that Maven command
will then be executed to the parent's modules as well. To do Project Aggregation, you must do the
following:
• Change the parent POMs packaging to the value "pom" .


19 The POM 117

• Specify in the parent POM the directories of its modules (children POMs)
[top]

19.1.5.1 Example 3

19.The Scenario
Given the previous original artifact POMs, and directory structure,
com.mycompany.app:my-app:1's POM

<project>
</project>


<project>
</project>

directory structure

.
|-- my-module
| `-- pom.xml
`-- pom.xml

19.The Solution
If we are to aggregate my-module into my-app, we would only have to modify my-app.

<project>
<modules>
<module>my-module</module>
</modules>
</project>

In the revised com.mycompany.app:my-app:1, the packaging section and the modules sections were
added. For the packaging, it's value was set to "pom", and for the modules section, we have the
element <module>my-module</module>. The value of <module> is the relative path from the
com.mycompany.app:my-app:1 to com.mycompany.app:my-module:1's POM ( by practice, we use
the module's artifactId as the module directory's name).


19 The POM 118

Now, whenever a Maven command processes com.mycompany.app:my-app:1, that same Maven
command would be ran against com.mycompany.app:my-module:1 as well. Furthermore, some
commands (goals specifically) handle project aggregation differently.
[top]

19.1.5.2 Example 4

19.The Scenario
But what if we change the directory structure to the following:

.
|-- my-module
| `-- pom.xml
`-- parent
`-- pom.xml

How would the parent pom specify its modules?
19.The Solution
The answer? - the same way as Example 3, by specifying the path to the module.

<project>
<modules>
<module>../my-module</module>
</modules>
</project>

19.1.6 Project Inheritance vs Project Aggregation
If you have several Maven projects, and they all have similar configurations, you can refactor your
projects by pulling out those similar configurations and making a parent project. Thus, all you have
to do is to let your Maven projects inherit that parent project, and those configurations would then be
applied to all of them.
And if you have a group of projects that are built or processed together, you can create a parent
project and have that parent project declare those projects as its modules. By doing so, you'd only
have to build the parent and the rest will follow.
But of course, you can have both Project Inheritance and Project Aggregation. Meaning, you can have
your modules specify a parent project, and at the same time, have that parent project specify those
Maven projects as its modules. You'd just have to apply all three rules:

• Specify in every child POM who their parent POM is.
• Change the parent POMs packaging to the value "pom" .
• Specify in the parent POM the directories of its modules (children POMs)
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19 The POM 119

19.1.6.1 Example 5

19.The Scenario
Given the previous original artifact POMs again,

<project>
</project>


<project>
</project>

and this directory structure

.
|-- my-module
| `-- pom.xml
`-- parent
`-- pom.xml

19.The Solution
To do both project inheritance and aggregation, you only have to apply all three rules.

<project>
<modules>
<module>../my-module</module>
</modules>
</project>



19 The POM 120

<project>
<parent>
<relativePath>../parent/pom.xml</relativePath>
</parent>
</project>

NOTE: Profile inheritance the same inheritance strategy as used for the POM itself.
[top]

19.1.7 Project Interpolation and Variables
One of the practices that Maven encourages is don't repeat yourself. However, there are circumstances
where you will need to use the same value in several different locations. To assist in ensuring the
value is only specified once, Maven allows you to use both your own and pre-defined variables in the
POM.
For example, to access the project.version variable, you would reference it like so:

<version>${project.version}</version>

One factor to note is that these variables are processed after inheritance as outlined above. This means
that if a parent project uses a variable, then its definition in the child, not the parent, will be the one
eventually used.

19.1.7.1 Available Variables

19.Project Model Variables
Any field of the model that is a single value element can be referenced as a variable. For example,
${project.groupId}, ${project.version}, ${project.build.sourceDirectory} and so
on. Refer to the POM reference to see a full list of properties.
These variables are all referenced by the prefix " project.". You may also see references with pom.
as the prefix, or the prefix omitted entirely - these forms are now deprecated and should not be used.
19.Special Variables

basedir The directory that the current project resides in.
project.baseUri The directory that the current project resides in,
represented as an URI. Since Maven 2.1.0
maven.build.timestamp The timestamp that denotes the start of the build.
Since Maven 2.1.0-M1

The format of the build timestamp can be customized by declaring the property
maven.build.timestamp.format as shown in the example below:


19 The POM 121

<project>
...
<properties>
<maven.build.timestamp.format>yyyyMMdd-HHmm</maven.build.timestamp.format>
</properties>
...
</project>

The format pattern has to comply with the rules given in the API documentation for
SimpleDateFormat. If the property is not present, the format defaults to the value already given in the
example.
19.Properties
You are also able to reference any properties defined in the project as a variable. Consider the
following example:

<project>
...
<properties>
<mavenVersion>2.1</mavenVersion>
</properties>
<dependencies>
<dependency>
<artifactId>maven-artifact</artifactId>
<version>${mavenVersion}</version>
</dependency>
<dependency>
<artifactId>maven-project</artifactId>
<version>${mavenVersion}</version>
</dependency>
</dependencies>
...
</project>

[top]


20 Profiles 122

20 Profiles
.......................................................................................................................................

20.1 Introduction to Build Profiles
Maven 2.0 goes to great lengths to ensure that builds are portable. Among other things, this means
allowing build configuration inside the POM, avoiding all filesystem references (in inhertiance,
dependencies, and other places), and leaning much more heavily on the local repository to store the
metadata needed to make this possible.
However, sometimes portability is not entirely possible. Under certain conditions, plugins may
need to be configured with local filesystem paths. Under other circumstances, a slightly different
dependency set will be required, and the project's artifact name may need to be adjusted slightly. And
at still other times, you may even need to include a whole plugin in the build lifecycle depending on
the detected build environment.
To address these circumstances, Maven 2.0 introduces the concept of a build profile. Profiles are
specified using a subset of the elements available in the POM itself (plus one extra section), and are
triggered in any of a variety of ways. They modify the POM at build time, and are meant to be used
in complementary sets to give equivalent-but-different parameters for a set of target environments
(providing, for example, the path of the appserver root in the development, testing, and production
environments). As such, profiles can easily lead to differing build results from different members of
your team. However, used properly, profiles can be used while still preserving project portability.
This will also minimize the use of -f option of maven which allows user to create another POM with
different parameters or configuration to build which makes it more maintainable since it is runnning
with one POM only.

20.1.1 What are the different types of profile? Where is each defined?

• Per Project
- Defined in the POM itself (pom.xml).
• Per User
- Defined in the Maven-settings (%USER_HOME%/.m2/settings.xml).
• Global
- Defined in the global maven-settings (%M2_HOME%/conf/settings.xml).
• Profile descriptor
- a descriptor located in project basedir (profiles.xml)

20.1.2 How can a profile be triggered? How does this vary according to the type of profile being
used?
A profile can be triggered/activated in several ways:

• Explicitly
• Through Maven settings
• Based on environment variables
• OS settings
• Present or missing files

20.1.2.1 Details on profile activation
Profiles can be explicitly specified using the -P CLI option.


20 Profiles 123

This option takes an argument that is a comma-delimited list of profile-ids to use. When this option is
specified, no profiles other than those specified in the option argument will be activated.

mvn groupId:artifactId:goal -P profile-1,profile-2

Profiles can be activated in the Maven settings, via the <activeProfiles> section. This section
takes a list of <activeProfile> elements, each containing a profile-id inside.

<settings>
...
<activeProfiles>
<activeProfile>profile-1</activeProfile>
</activeProfiles>
...
</settings>

Profiles listed in the <activeProfiles> tag would be activated by default everytime a project use
it.
Profiles can be automatically triggered based on the detected state of the build environment. These
triggers are specified via an <activation> section in the profile itself. Currently, this detection is
limited to prefix-matching of the JDK version, the presence of a system property or the value of a
system property. Here are some examples.
The follwing configuration will trigger the profile when the JDK's version starts with "1.4" (eg.
"1.4.0_08", "1.4.2_07", "1.4"):

<profiles>
<profile>
<activation>
<jdk>1.4</jdk>
</activation>
...
</profile>
</profiles>

Ranges can also be used as of Maven 2.1 (refer to the Enforcer Version Range Syntax for more
information). The following honours versions 1.3, 1.4 and 1.5.

<profiles>
<profile>
<activation>
<jdk>[1.3,1.6)</jdk>
</activation>
...
</profile>
</profiles>

Note: an upper bound such as ,1.5] is likely not to include most releases of 1.5, since they will have
an additional "patch" release such as _05 that is not taken into consideration in the above range.
This next one will activate based on OS settings. See the Maven Enforcer Plugin for more details
about OS values.


20 Profiles 124

<profiles>
<profile>
<activation>
<os>
<arch>x86</arch>
</os>
</activation>
...
</profile>
</profiles>

This will activate the profile when the system property "debug" is specified with any value:

<profiles>
<profile>
<activation>
<property>
<name>debug</name>
</property>
</activation>
...
</profile>
</profiles>

This example will trigger the profile when the system property "environment" is specified with the
value "test":

<profiles>
<profile>
<activation>
<property>
<name>environment</name>
<value>test</value>
</property>
</activation>
...
</profile>
</profiles>

Note: Environment variable FOO would be set like env.FOO.
To activate this you would type this on the command line:

mvn groupId:artifactId:goal -Denvironment=test

This example will trigger the profile when the generated file target/generated-sources/
axistools/wsdl2java/org/apache/maven is missing.


20 Profiles 125

<profiles>
<profile>
<activation>
<file>
<missing>target/generated-sources/axistools/wsdl2java/org/apache/maven</miss
</file>
</activation>
...
</profile>
</profiles>

Note: The tags <exists> and <missing> could be interpolated with some patterns like
${user.home}.
Profiles can also be active by default using a configuration like the following:

<profiles>
<profile>
<id>profile-1</id>
<activation>
<activeByDefault>true</activeByDefault>
</activation>
...
</profile>
</profiles>

This profile will automatically be active for all builds unless another profile in the same pom is
activated using one of the previously described methods. All profiles that are active by default are
automatically deactivated when a profile in the pom is activated on the command line or through its
activation config.

20.1.2.2 Deactivating a profile
Starting with Maven 2.0.10, one or more profiles can be deactivated using the command line by
prefixing their identifier with either the character '!' or '-' as shown below:

mvn groupId:artifactId:goal -P !profile-1,!profile-2

This can be used to deactivate profiles marked as activeByDefault or profiles that would otherwise be
activated through their activation config.

20.1.3 Which areas of a POM can be customized by each type of profile? Why?
Now that we've talked about where to specify profiles, and how to activate them, it will be useful to
talk about what you can specify in a profile. As with the other aspects of profile configuration, this
answer is not straightforward.
Depending on where you choose to configure your profile, you will have access to varying POM
configuration options.

20.1.3.1 Profiles in external files
Profiles specified in external files (i.e in settings.xml or profiles.xml) are not portable in
the strictest sense. Anything that seems to stand a high chance of changing the result of the build is
restricted to the inline profiles in the POM. Things like repository lists could simply be a proprietary


20 Profiles 126

repository of approved artifacts, and won't change the outcome of the build. Therefore, you will only
be able to modify the <repositories> and <pluginRepositories> sections, plus an extra
<properties> section.
The <properties> section allows you to specify free-form key-value pairs which will be included
in the interpolation process for the POM. This allows you to specify a plugin configuration in the
form of ${profile.provided.path}.

20.1.3.2 Profiles in POMs
On the other hand, if your profiles can be reasonably specified inside the POM, you have many more
options. The trade-off, of course, is that you can only modify that project and it's sub-modules. Since
these profiles are specified inline, and therefore have a better chance of preserving portability, it's
reasonable to say you can add more information to them without the risk of that information being
unavailable to other users.
Profiles specified in the POM can modify the following POM elements:

• <repositories>
• <pluginRepositories>
• <dependencies>
• <plugins>
• <properties> (not actually available in the main POM, but used behind the scenes)
• <modules>
• <reporting>
• <dependencyManagement>
• <distributionManagement>
• a subset of the <build> element, which consists of:

• <defaultGoal>
• <resources>
• <testResources>
• <finalName>

20.1.3.3 POM elements outside <profiles>
We don't allow modification of some POM elements outside of POM-profiles because these runtime
modifications will not be distributed when the POM is deployed to the repository system, making that
person's build of that project completely unique from others. While you can do this to some extent
with the options given for external profiles, the danger is limited. Another reason is that this POM
info is sometimes being reused from the parent POM.
External files such as settings.xml and profiles.xml also does not support elements outside
the POM-profiles. Let us take this scenario for elaboration. When the effective POM get deployed to
a remote repository, any person can pickup its info out of the repository and use it to build a Maven
project directly. Now, imagine that if we can set profiles in dependencies, which is very important
to a build, or in any other elements outside POM-profiles in settings.xml then most probably
we cannot expect someone else to use that POM from the repository and be able to build it. And we
have to also think about how to share the settings.xml with others. Note that too many files to
configure is very confusing and very hard to maintain. Bottom line is that since this is build data, it
should be in the POM. One of the goals in Maven 2 is to consolidate all the information needed to run
a build into a single file, or file hierarchy which is the POM.


20 Profiles 127

20.1.4 Profile Pitfalls
We've already mentioned the fact that adding profiles to your build has the potential to break
portability for your project. We've even gone so far as to highlight circumstances where profiles
are likely to break project portability. However, it's worth reiterating those points as part of a more
coherent discussion about some pitfalls to avoid when using profiles.
There are two main problem areas to keep in mind when using profiles. First are external properties,
usually used in plugin configurations. These pose the risk of breaking portability in your project. The
other, more subtle area is the incomplete specification of a natural set of profiles.

20.1.4.1 External Properties
External property definition concerns any property value defined outside the pom.xml but not defined
in a corresponding profile inside it. The most obvious usage of properties in the POM is in plugin
configuration. While it is certainly possible to break project portability without properties, these
critters can have subtle effects that cause builds to fail. For example, specifying appserver paths in
a profile that is specified in the settings.xml may cause your integration test plugin to fail when
another user on the team attempts to build without a similar settings.xml. Consider the following
pom.xml snippet for a web application project:

<project>
...
<build>
<plugins>
<plugin>
<groupId>org.myco.plugins</groupId>
<artifactId>spiffy-integrationTest-plugin</artifactId>
<configuration>
<appserverHome>${appserver.home}</appserverHome>
</configuration>
</plugin>
...
</plugins>
</build>
...
</project>

Now, in your local ~/.m2/settings.xml, you have:


20 Profiles 128

<settings>
...
<profiles>
<profile>
<id>appserverConfig</id>
<properties>
<appserver.home>/path/to/appserver</appserver.home>
</properties>
</profile>
</profiles>
<activeProfiles>
<activeProfile>appserverConfig</activeProfile>
</activeProfiles>
...
</settings>

When you build the integration-test lifecycle phase, your integration tests pass, since the path you've
provided allows the test plugin to install and test this web application.
However, when your colleague attempts to build to integration-test, his build fails spectacularly,
complaining that it cannot resolve the plugin configuration parameter <appserverHome>, or worse,
that the value of that parameter - literally ${appserver.home} - is invalid (if it warns you at all).
Congratulations, your project is now non-portable. Inlining this profile in your pom.xml can help
alleviate this, with the obvious drawback that each project hierarchy (allowing for the effects of
inheritance) now have to specify this information. Since Maven provides good support for project
inheritance, it's possible to stick this sort of configuration in the <pluginManagement> section of a
team-level POM or similar, and simply inherit the paths.
Another, less attractive answer might be standardization of development environments. However, this
will tend to compromise the productivity gain that Maven is capable of providing.

20.1.4.2 Incomplete Specification of a Natural Profile Set
In addition to the above portability-breaker, it's easy to fail to cover all cases with your profiles.
When you do this, you're usually leaving one of your target environments high and dry. Let's take the
example pom.xml snippet from above one more time:

<project>
...
<build>
<plugins>
<plugin>
<groupId>org.myco.plugins</groupId>
<artifactId>spiffy-integrationTest-plugin</artifactId>
<configuration>
<appserverHome>${appserver.home}</appserverHome>
</configuration>
</plugin>
...
</plugins>
</build>
...
</project>


20 Profiles 129

Now, consider the following profile, which would be specified inline in the pom.xml:

<project>
...
<profiles>
<profile>
<id>appserverConfig-dev</id>
<activation>
<property>
<name>env</name>
<value>dev</value>
</property>
</activation>
<properties>
<appserver.home>/path/to/dev/appserver</appserver.home>
</properties>
</profile>
<profile>
<id>appserverConfig-dev-2</id>
<activation>
<property>
<name>env</name>
<value>dev-2</value>
</property>
</activation>
<properties>
<appserver.home>/path/to/another/dev/appserver2</appserver.home>
</properties>
</profile>
</profiles>
..
</project>

This profile looks quite similar to the one from the last example, with a few important exceptions: it's
plainly geared toward a development environment, a new profile named appserverConfig-dev-2
is added and it has an activation section that will trigger its inclusion when the system properties
contain "env=dev" for a profile named appserverConfig-dev and "env=dev-2" for a profile named
appserverConfig-dev-2. So, executing:

mvn -Denv=dev-2 integration-test

will result in a successful build, applying the properties given by profile named appserverConfig-
dev-2. And when we execute

mvn -Denv=dev integration-test

it will result in a successful build applying the properties given by the profile named
appserverConfig-dev. However, executing:

mvn -Denv=production integration-test

will not do a successful build. Why? Because, the resulting non-interpolated literal value of
${appserver.home} will not be a valid path for deploying and testing your web application.
We haven't considered the case for the production environment when writing our profiles. The


20 Profiles 130

"production" environment (env=production), along with "test" and possibly even "local" constitute
a natural set of target environments for which we may want to build the integration-test lifecycle
phase. The incomplete specification of this natural set means we have effectively limited our valid
target environments to the development environment. Your teammates - and probably your manager
- will not see the humor in this. When you construct profiles to handle cases such as these, be sure to
address the entire set of target permutations.
As a quick aside, it's possible for user-specific profiles to act in a similar way. This means that
profiles for handling different environments which are keyed to the user can act up when the team
adds a new developer. While I suppose this could act as useful training for the newbie, it just wouldn't
be nice to throw them to the wolves in this way. Again, be sure to think of the whole set of profiles.

20.1.5 How can I tell which profiles are in effect during a build?
Determining active profiles will help the user to know what particular profiles has been executed
during a build. We can use the Maven Help Plugin to tell what profiles are in effect during a build.


Let us have some small samples that will help us to understand more on the active-profiles goal of
that plugin.
From the last example of profiles in the pom.xml, you'll notice that there are two profiles named
appserverConfig-dev and appserverConfig-dev-2 which has been given different values for
properties. If we go ahead and execute:

mvn help:active-profiles -Denv=dev

The result will be a bulleted list of the id of the profile with an activation property of "env=dev"
together with the source where it was declared. See sample below.

The following profiles are active:
- appserverConfig-dev (source: pom)

Now if we have a profile declared in settings.xml (refer to the sample of profile in
settings.xml) and that have been set to be an active profile and execute:


The result should be something like this

- appserverConfig (source: settings.xml)

Even though we don't have an activation property, a profile has been listed as active. Why? Like
we mentioned before, a profile that has been set as an active profile in the settings.xml is
automatically activated.
Now if we have something like a profile in the settings.xml that has been set as an active profile
and also triggered a profile in the pom. Which profile do you think will have an effect on the build?

mvn help:active-profiles -P appserverConfig-dev

This will list the activated profiles:


20 Profiles 131

- appserverConfig-dev (source: pom)
- appserverConfig (source: settings.xml)

Even though it listed the two active profiles, we are not sure which one of them has been applied. To
see the effect on the build execute:

mvn help:effective-pom -P appserverConfig-dev

This will print the effective POM for this build configuration out to the console. Take note that
profiles in the settings.xml takes higher priority than profiles in the pom. So the profile that has
been applied here is appserverConfig not appserverConfig-dev.
If you want to redirect the output from the plugin to a file called effective-pom.xml, use the
command-line option -Doutput=effective-pom.xml.

20.1.6 Naming Conventions
By now you've noticed that profiles are a natural way of addressing the problem of different build
configuration requirements for different target environments. Above, we discussed the concept of a
"natural set" of profiles to address this situation, and the importance of considering the whole set of
profiles that will be required.
However, the question of how to organize and manage the evolution of that set is non-trivial as well.
Just as a good developer strives to write self-documenting code, it's important that your profile id's
give a hint to their intended use. One good way to do this is to use the common system property
trigger as part of the name for the profile. This might result in names like env-dev, env-test, and
env-prod for profiles that are triggered by the system property env. Such a system leaves a highly
intuitive hint on how to activate a build targeted at a particular environment. Thus, to activate a build
for the test environment, you need to activate env-test by issuing:

mvn -Denv=test <phase>

The right command-line option can be had by simply substituting "=" for "-" in the profile id.


21 Repositories 132

21 Repositories
.......................................................................................................................................

21.1 Introduction to Repositories

21.1.1 Artifact Repositories
A repository in Maven is used to hold build artifacts and dependencies of varying types.
There are strictly only two types of repositories: local and remote. The local repository refers to
a copy on your own installation that is a cache of the remote downloads, and also contains the
temporary build artifacts that you have not yet released.
Remote repositories refer to any other type of repository, accessed by a variety of protocols such as
file:// and http://. These repositories might be a truely remote repository set up by a third party
to provide their artifacts for downloading (for example, repo1.maven.org houses Maven's central
repository). Other "remote" repositories may be internal repositories set up on a file or HTTP server
within your company, used to share private artifacts between development teams and for releases.
The local and remote repositories are structured the same way so that scripts can easily be run on
either side, or they can be synced for offline used. In general use, the layout of the repositories is
completely transparent to the Maven user, however.

21.1.2 Why not Store JARs in CVS?
It is not recommended that you store your JARs in CVS. Maven tries to promote the notion of a user
local repository where JARs, or any project artifacts, can be stored and used for any number of builds.
Many projects have dependencies such as XML parsers and standard utilities that are often replicated
in typical builds. With Maven these standard utilities can be stored in your local repository and shared
by any number of builds.
This has the following advantages:

• It uses less storage - while a repository is typically quite large, because each JAR is only kept in
the one place it is actually saving space, even though it may not seem that way
• It makes checking out a project quicker - initial checkout, and to a small degree updating,
a project will be faster if there are no large binary files in CVS. While they may need to be
downloaded again afterwards anyway, this only happens once and may not be necessary for
some common JARs already in place.
• No need for versioning - CVS and other source control systems are designed for versioning
files, but external dependencies typically don't change, or if they do their filename changes
anyway to indicate the new version. Storing these in CVS doesn't have any added benefit over
keeping them in a local artifact cache.

21.1.3 Using Repositories
In general, you should not need to do anything with the local repository on a regular basis, except
clean it out if you are short on disk space (or erase it completely if you are willing to download
everything again).
For the remote repositories, they are used for both downloading and uploading (if you have the
permission to do so).


21 Repositories 133

21.1.3.1 Downloading from a Remote Repository
Downloading in Maven is triggered by a project declaring a dependency that is not present in the local
repository (or for a SNAPSHOT, when the remote repository contains one that is newer). By default,
Maven will download from the central repository.
To override this, you need to specify a repositories element as follows:

<project>
...
<repositories>
<repository>
<id>my-internal-site</id>
<url>http://myserver/repo</url>
</repository>
</repositories>
...
</project>

You can set this in your settings.xml file to globally use a certain mirror, however note that it is
common for a project to customise the repository in their pom.xml and that your setting will take
precedence. If you find that dependencies are not being found, check you have not overridden the
remote repository.
For more information on dependencies, see Dependency Mechanism.

21.1.3.2 Using Mirrors for the Central Repository
Like any server, the central repository sometimes goes down. If this happens you can make changes to
your settings.xml file to use one or more mirrors. Instructions for this can be found in the guide
Using Mirrors for Repositories.

21.1.4 Building Offline
If you are temporarily disconnected from the internet and you need to build your projects offline you
can use the offline switch on the CLI:

mvn -o package

Note that many plugins will honour the offline setting and not perform any operations that would
connect to the internet. Some examples are resolving Javadoc links and link checking the site.

21.1.5 Uploading to a Remote Repository
While this is possible for any type of remote repository, you must have the permission to do so. To
have someone upload to the central Maven repository, see Repository Center.

21.2 Internal Repositories
When using Maven, particularly in a corporate environment, connecting to the internet to download
dependencies is not acceptable for security, speed or bandwidth reasons. For that reason, it is
desirable to set up an internal repository to house a copy of artifacts, and to publish private artifacts
to.
Such an internal repository can be downloaded from using HTTP or the file system (using a file://
URL), and uploaded to using SCP, FTP, or a file copy.


21 Repositories 134

Note that as far as Maven is concerned, there is nothing special about this repository: it is another
remote repository that contains artifacts to download to a user's local cache, and is a publish
destination for artifact releases.
Additionally, you may want to share the repository server with your generated project sites. For more
information on creating and deploying sites, see Creating a Site.

21.2.1 Setting up the Internal Repository
To set up an internal repository just requires that you have a place to put it, and then start copying
required artifacts there using the same layout as in a remote repository such as repo1.maven.org.
It is not recommended that you scrape or rsync:// a full copy of central as there is a large amount
of data there and doing so will get you banned. You can use a program such as those described on the
Repository Management page to run your internal repository's server, to download from the internet
as required and then hold the artifacts in your internal repository for faster downloading later.
The other options available are to manually download and vet releases, then copy them to the internal
repository, or to have Maven download them for a user, and manually upload the vetted artifacts
to the internal repository which is used for releases. This step is the only one available for artifacts
where the license forbids their distribution automatically, such as several J2EE JARs provided by
Sun. Refer to the Guide to coping with SUN JARs document for more information.
It should be noted that Maven intends to include enhanced support for such features in the future,
including click through licenses on downloading, and verification of signatures.

21.2.2 Using the Internal Repository
Using the internal repository is quite simple. Simply make a change to add a repositories
element:

<project>
...
<repositories>
<repository>
<id>my-internal-site</id>
<url>http://myserver/repo</url>
</repository>
</repositories>
...
</project>

If your internal repository requires authentication, the id element can be used in your settings file to
specify login information.

21.2.3 Deploying to the Internal Repository
One of the most important reasons to have one or more internal repositories is to be able to publish
your own private releases to share.
To publish to the repository, you will need to have access via one of SCP, SFTP, FTP, WebDAV, or
the filesystem. Connectivity is accomplished with the various wagons. Some wagons may need to be
added as extension to your build.


22 Standard Directory Layout 135

22 Standard Directory Layout
.......................................................................................................................................

22.1 Introduction to the Standard Directory Layout
Having a common directory layout would allow for users familiar with one Maven project to
immediately feel at home in another Maven project. The advantages are analogous to adopting a site-
wide look-and-feel.
The next section documents the directory layout expected by Maven and the directory layout created
by Maven. Please try to conform to this structure as much as possible; however, if you can't these
settings can be overridden via the project descriptor.

src/main/java Application/Library sources
src/main/resources Application/Library resources
src/main/filters Resource filter files
src/main/assembly Assembly descriptors
src/main/config Configuration files
src/main/webapp Web application sources
src/test/java Test sources
src/test/resources Test resources
src/test/filters Test resource filter files
src/site Site
LICENSE.txt Project's license
README.txt Project's readme

At the top level files descriptive of the project: a pom.xml file (and any properties, maven.xml or
build.xml if using Ant). In addition, there are textual documents meant for the user to be able to
read immediately on receiving the source: README.txt, LICENSE.txt, etc.
There are just two subdirectories of this structure: src and target. The only other directories that
would be expected here are metadata like CVS or .svn, and any subprojects in a multiproject build
(each of which would be laid out as above).
The target directory is used to house all output of the build.
The src directory contains all of the source material for building the project, its site and so on. It
contains a subdirectory for each type: main for the main build artifact, test for the unit test code and
resources, site and so on.
Within artifact producing source directories (ie. main and test), there is one directory for the
language java (under which the normal package hierarchy exists), and one for resources (the
structure which is copied to the target classpath given the default resource definition).
If there are other contributing sources to the artifact build, they would be under other subdirectories:
for example src/main/antlr would contain Antlr grammar definition files.


23 The Dependency Mechanism 136

23 The Dependency Mechanism
.......................................................................................................................................

23.1 Introduction to the Dependency Mechanism
Dependency management is one of the features of Maven that is best known to users and is one of
the areas where Maven excels. There is not much difficulty in managing dependencies for a single
a project, but when you start getting into dealing with multi-module projects and applications that
consist of tens or hundreds of modules this is where Maven can help you a great deal in maintaining a
high degree of control and stability.
Learn more about:
• Transitive Dependencies
• Excluded/Optional Dependencies
• Dependency Scope
• Dependency Management
• Importing Dependencies
• System Dependencies

23.1.1 Transitive Dependencies
Transitive dependencies are a new feature in Maven 2.0. This allows you to avoid needing to discover
and specify the libraries that your own dependencies require, and including them automatically.
This feature is facilitated by reading the project files of your dependencies from the remote
repositories specified. In general, all dependencies of those projects are used in your project, as are
any that the project inherits from its parents, or from its dependencies, and so on.
There is no limit to the number of levels that dependencies can be gathered from, and will only cause
a problem if a cyclic dependency is discovered.
With transitive dependencies, the graph of included libraries can quickly grow quite large. For this
reason, there are some additional features that will limit which dependencies are included:
• Dependency mediation - this determines what version of a dependency will be used when
multiple versions of an artifact are encountered. Currently, Maven 2.0 only supports using
the "nearest definition" which means that it will use the version of the closest dependency to
your project in the tree of dependencies. You can always guarantee a version by declaring it
explicitly in your project's POM. Note that if two dependency versions are at the same depth in
the dependency tree, until Maven 2.0.8 it was not defined which one would win, but since Maven
2.0.9 it's the order in the declaration that counts: the first declaration wins.
• "nearest definition" means that the version used will be the closest one to your project in the
tree of dependencies, eg. if dependencies for A, B, and C are defined as A -> B -> C -> D
2.0 and A -> E -> D 1.0, then D 1.0 will be used when building A because the path from A
to D through E is shorter. You could explicitly add a dependency to D 2.0 in A to force the
use of D 2.0
• Dependency management - this allows project authors to directly specify the versions of artifacts
to be used when they are encountered in transitive dependencies or in dependencies where no
version has been specified. In the example in the preceding section a dependency was directly
added to A even though it is not directly used by A. Instead, A can include D as a dependency in
its dependencyManagement section and directly control which version of D is used when, or if, it
is ever referenced.



• Dependency scope - this allows you to only include dependencies appropriate for the current
stage of the build. This is described in more detail below.
• Excluded dependencies - If project X depends on project Y, and project Y depends on project Z,
the owner of project X can explicitly exclude project Z as a dependency, using the "exclusion"
element.
• Optional dependencies - If project Y depends on project Z, the owner of project Y can mark
project Z as an optional dependency, using the "optional" element. When project X depends
on project Y, X will depend only on Y and not on Y's optional dependency Z. The owner of
project X may then explicitly add a dependency on Z, at her option. (It may be helpful to think of
optional dependencies as "excluded by default.")

23.1.2 Dependency Scope
Dependency scope is used to limit the transitivity of a depedency, and also to affect the classpath used
for various build tasks.
There are 6 scopes available:
• compile
This is the default scope, used if none is specified. Compile dependencies are available in all
classpaths of a project. Furthermore, those dependencies are propagated to dependent projects.
• provided
This is much like compile, but indicates you expect the JDK or a container to provide the
dependency at runtime. For example, when building a web application for the Java Enterprise
Edition, you would set the dependency on the Servlet API and related Java EE APIs to scope
provided because the web container provides those classes. This scope is only available on the
compilation and test classpath, and is not transitive.
• runtime
This scope indicates that the dependency is not required for compilation, but is for execution. It
is in the runtime and test classpaths, but not the compile classpath.
• test
This scope indicates that the dependency is not required for normal use of the application, and is
only available for the test compilation and execution phases.
• system
This scope is similar to provided except that you have to provide the JAR which contains it
explicitly. The artifact is always available and is not looked up in a repository.
• import (only available in Maven 2.0.9 or later)
This scope is only used on a dependency of type pom in the <dependencyManagement>
section. It indicates that the specified POM should be replaced with the dependencies in that
POM's <dependencyManagement> section. Since they are replaced, dependencies with a scope
of import do not actually participate in limiting the transitivity of a dependency.
Each of the scopes (except for import) affects transitive dependencies in different ways, as is
demonstrated in the table below. If a dependency is set to the scope in the left column, transitive
dependencies of that dependency with the scope across the top row will result in a dependency in the
main project with the scope listed at the intersection. If no scope is listed, it means the dependency
will be omitted.

compile provided runtime test
compile compile(*) - runtime -
provided provided provided provided -
runtime runtime - runtime _



test test - test -

(*) Note: it is intended that this should be runtime scope instead, so that all compile dependencies
must be explicitly listed - however, there is the case where the library you depend on extends a class
from another library, forcing you to have available at compile time. For this reason, compile time
dependencies remain as compile scope even when they are transitive.

23.1.3 Dependency Management
The dependency management section is a mechanism for centralizing dependency information. When
you have a set of projects that inherits a common parent it's possible to put all information about the
dependency in the common POM and have simpler references to the artifacts in the child POMs. The
mechanism is best illustrated through some examples. Given these two POMs which extend the same
parent:
Project A:

<project>
...
<dependencies>
<dependency>
<groupId>group-a</groupId>
<artifactId>artifact-a</artifactId>
<exclusions>
<exclusion>
<groupId>group-c</groupId>
<artifactId>excluded-artifact</artifactId>
</exclusion>
</exclusions>
</dependency>
<dependency>
<artifactId>artifact-b</artifactId>
<type>bar</type>
<scope>runtime</scope>
</dependency>
</dependencies>
</project>

Project B:



<project>
...
<dependencies>
<dependency>
<type>war</type>
</dependency>
<dependency>
<type>bar</type>
</dependency>
</dependencies>
</project>

These two example POMs share a common dependency and each has one non-trivial dependency.
This information can be put in the parent POM like this:


<project>
...
<dependencyManagement>
<dependencies>
<dependency>
<exclusions>
<exclusion>
<artifactId>excluded-artifact</artifactId>
</exclusion>
</exclusions>
</dependency>
<dependency>
<type>war</type>
</dependency>
<dependency>
<type>bar</type>
</dependency>
</dependencies>
</dependencyManagement>
</project>

And then the two child poms would become much simpler:

<project>
...
<dependencies>
<dependency>
</dependency>
<dependency>

<type>bar</type>
</dependency>
</dependencies>
</project>


<project>
...
<dependencies>
<dependency>
<type>war</type>
</dependency>
<dependency>
<type>bar</type>
</dependency>
</dependencies>
</project>

NOTE: In two of these dependency references, we had to specify the <type/> element. This
is because the minimal set of information for matching a dependency reference against a
dependencyManagement section is actually {groupId, artifactId, type, classifier}. In many cases,
these dependencies will refer to jar artifacts with no classifier. This allows us to shorthand the identity
set to {groupId, artifactId}, since the default for the type field is jar, and the default classifier is
null.
A second, and very important use of the dependency management section is to control the versions of
artifacts used in transitive dependencies. As an example consider these projects:
Project A:



<project>
<groupId>maven</groupId>
<artifactId>A</artifactId>
<name>A</name>
<dependencies>
<dependency>
<groupId>test</groupId>
<artifactId>a</artifactId>
</dependency>
<dependency>
<artifactId>b</artifactId>
</dependency>
<dependency>
<artifactId>c</artifactId>
</dependency>
<dependency>
<artifactId>d</artifactId>
</dependency>
</dependencies>
</project>

Project B:



<project>
<parent>
</parent>
<artifactId>B</artifactId>
<name>B</name>
<dependencies>
<dependency>
</dependency>
</dependencies>
<dependencies>
<dependency>
</dependency>
<dependency>
</dependency>
</dependencies>
</project>

When maven is run on project B version 1.0 of artifacts a, b, c, and d will be used regardless of the
version specified in their pom.

• a and c both are declared as dependencies of the project so version 1.0 is used due to dependency
mediation. Both will also have runtime scope since it is directly specified.
• b is defined in B's parent's dependency management section and since dependency management
takes precedence over dependency mediation for transitive dependencies, version 1.0 will be
selected should it be referenced in a or c's pom. b will also have compile scope.
• Finally, since d is specified in B's dependency management section, should d be a dependency
(or transitive dependency) of a or c, version 1.0 will be chosen - again because dependency
management takes precedence over dependency mediation and also because the current pom's
declaration takes precedence over its parent's declaration.
The reference information about the dependency management tags is available from the project
descriptor reference.



23.1.3.1 Importing Dependencies
The features defined in this section are only available in Maven 2.0.9 or later. This means that poms
declaring the import scope will not be parseable by earlier versions of Maven. Weigh this information
carefully before deciding to use it. If you do use it, we suggest you use the enforcer plugin to require
a minimum Maven version of 2.0.9. We currently do not recommend using this for projects that get
deployed to Central.
The examples in the previous section describe how to specify managed dependencies through
inheritence. However, in larger projects it may be impossible to accomplish this since a project can
only inherit from a single parent. To accomodate this, projects can import managed dependencies
from other projects. This is accomplished by declaring a pom artifact as a dependency with a scope of
"import".
Project B:

<project>
<artifactId>B</artifactId>
<name>B</name>
<dependencies>
<dependency>
<type>pom</type>
<scope>import</scope>
</dependency>
<dependency>
</dependency>
</dependencies>
<dependencies>
<dependency>
</dependency>
<dependency>
</dependency>
</dependencies>
</project>



Assuming A is the pom defined in the preceding example, the end result would be the same. All of A's
managed dependencies would be incorporated into B except for d since it is defined in this pom.
Project X:

<project>
<artifactId>X</artifactId>
<name>X</name>
<dependencies>
<dependency>
</dependency>
<dependency>
<artifactId>b</artifactId>
</dependency>
</dependencies>
</project>

Project Y:

<project>
<artifactId>Y</artifactId>
<name>Y</name>
<dependencies>
<dependency>
</dependency>
<dependency>
</dependency>
</dependencies>
</project>



Project Z:

<project>
<artifactId>Z</artifactId>
<name>Z</name>
<dependencies>
<dependency>
<artifactId>X</artifactId>
<type>pom</type>
</dependency>
<dependency>
<artifactId>Y</artifactId>
<type>pom</type>
</dependency>
</dependencies>
</project>

In the example above Z imports the managed dependencies from both X and Y. However, both X
and Y contain depedency a. Here, version 1.1 of a would be used since X is declared first and a is not
declared in Z's dependencyManagement.
This process is recursive. For example, if X imports another pom, Q, when Z is processed it will
simply appear that all of Q's managed dependencies are defined in X.
Imports are most effective when used for defining a "library" of related artifacts that are generally
part of a multiproject build. It is fairly common for one project to use one or more artifacts from
these libraries. However, it has sometimes been difficult to keep the versions in the project using the
artifacts in synch with the versions distributed in the library. The pattern below illustrates how a "bill
of materials" (BOM) can be created for use by other projects.
The root of the project is the BOM pom. It defines the versions of all the artifacts that will be
created in the library. Other projects that wish to use the library should import this pom into the
dependencyManagement section of their pom.



<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001
xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xs
<groupId>com.test</groupId>
<artifactId>bom</artifactId>
<properties>
<project1Version>1.0.0</project1Version>
<project2Version>1.0.0</project2Version>
</properties>
<dependencies>
<dependency>
<artifactId>project1</artifactId>
<version>${project1Version}</version>
</dependency>
<dependency>
</dependency>
</dependencies>
<modules>
<module>parent</module>
</modules>
</project>

The parent subproject has the BOM pom as its parent. It is a normal multiproject pom.



xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/x
<parent>
</parent>
<artifactId>parent</artifactId>
<dependencies>
<dependency>
</dependency>
<dependency>
<groupId>commons-logging</groupId>
<artifactId>commons-logging</artifactId>
</dependency>
</dependencies>
<modules>
<module>project1</module>
<module>project2</module>
</modules>
</project>

Next are the actual project poms.



<parent>
</parent>
<dependencies>
<dependency>
</dependency>
</dependencies>
</project>
<parent>
</parent>
<dependencies>
<dependency>
<groupId>commons-logging</groupId>
<artifactId>commons-logging</artifactId>
</dependency>
</dependencies>
</project>

The project that follows shows how the library can now be used in another project without having to
specify the dependent project's versions.



<artifactId>use</artifactId>
<dependencies>
<dependency>
<type>pom</type>
</dependency>
</dependencies>
<dependencies>
<dependency>
</dependency>
<dependency>
</dependency>
</dependencies>
</project>

Finally, when creating projects that import dependencies beware of the following:

• Do not attempt to import a pom that is defined in a submodule of the current pom. Attempting to
do that will result in the build failing since it won't be able to locate the pom.
• Never declare the pom importing a pom as the parent (or grandparent, etc) of the target pom.
There is no way to resolve the cicularity and an exception will be thrown.
• When referring to artifacts whose poms have transitive dependencies the project will need to
specify versions of those artifacts as managed dependencies. Not doing so will result in a build
failure since the artifact may not have a version specified. (This should be considered a best
practice in any case as it keeps the versions of artifacts from changing from one build to the
next).

23.1.4 System Dependencies
Dependencies with the scope system are always available and are not looked up in repository. They
are usually used to tell Maven about dependencies which are provided by the JDK or the VM. Thus,
system dependencies are especially useful for resolving dependencies on artifacts which are now
provided by the JDK, but where available as separate downloads earlier. Typical example are the
JDBC standard extensions or the Java Authentication and Authorization Service (JAAS).
A simple example would be:



<project>
...
<dependencies>
<dependency>
<groupId>javax.sql</groupId>
<artifactId>jdbc-stdext</artifactId>
<systemPath>${java.home}/lib/rt.jar</systemPath>
</dependency>
</dependencies>
...
</project>

If your artifact is provided by the JDK's tools.jar the system path would be defined as follows:

<project>
...
<dependencies>
<dependency>
<groupId>sun.jdk</groupId>
<artifactId>tools</artifactId>
<systemPath>${java.home}/../lib/tools.jar</systemPath>
</dependency>
</dependencies>
...
</project>


24 Plugin Development 152

24 Plugin Development
.......................................................................................................................................

24.1 Introduction to Maven 2.0 Plugin Development
Maven consists of a core engine which provides basic project-processing capabilities and build-
process management, and a host of plugins which are used to execute the actual build tasks.

24.1.1 What is a Plugin?
"Maven" is really just a core framework for a collection of Maven Plugins. In other words, plugins
are where much of the real action is performed, plugins are used to: create jar files, create war files,
compile code, unit test code, create project documentation, and on and on. Almost any action that you
can think of performing on a project is implemented as a Maven plugin.
Plugins are the central feature of Maven that allow for the reuse of common build logic across
multiple projects. They do this by executing an "action" (i.e. creating a WAR file or compiling unit
tests) in the context of a project's description - the Project Object Model (POM). Plugin behavior can
be customized through a set of unique parameters which are exposed by a description of each plugin
goal (or Mojo).
One of the simplest plugins in Maven 2.0 is the Clean Plugin. The Maven Clean plugin (maven-
clean-plugin) is responsible for removing the target directory of a Maven 2 project. When you run
"mvn clean", Maven 2 executes the "clean" goal as defined in the Clean plug-in, and the target
directory is removed. The Clean plugin defines a parameter which can be used to customize plugin
behavior, this parameter is called outputDirectory and it defaults to ${project.build.directory}.

24.1.2 What is a Mojo ( And Why the H--- is it Named 'Mojo')?
A Mojo is really just a goal in Maven 2, and plug-ins consist of any number of goals (Mojos). Mojos
can be defined as annotated Java classes or Beanshell script. A Mojo specifies metadata about a goal:
a goal name, which phase of the lifecycle it fits into, and the parameters it is expecting.
MOJO is a play on POJO (Plain-old-Java-object), substituting "Maven" for "Plain". Mojo is also an
iteresting word (see definition). From Wikipedia, a "mojo" is defined as: "...a small bag worn by a
person under the clothes (also known as a mojo hand). Such bags were thought to have supernatural
powers, such as protecting from evil, bringing good luck, etc."

24.1.3 What is the Build Lifecycle? (Overview)
The build lifecycle is a series of common stages through which all project builds naturally progress.
Plugin goals are bound to specific stages in the lifecycle.

24.2 Resources
1 Plugin development guide
2 Configuring plugins

24.3 Comparison to Maven 1.x Plugins

24.3.1 Similarities to Maven 1.x
Maven 2.0 is similar to its predecessor in that it has two main functions. First, it organizes project data
into a coherent whole, and exposes this data for use within the build process. Second, Maven marshals
a set of plugins to do the heavy lifting and execute the actual steps of the build.



Many things in Maven 2 will have at least superficial familiarity to users of Maven 1, and the plugin
system is no exception. Maven 2 plugins appear to behave much as their 1.x counterparts do. Like 1.x
plugins, they use both project information and custom-defined configurations to perform their work.
Also, Maven 2 plugins are organized and executed in a coherent way by the build engine itself - that
is to say, the engine is still responsible for organizing and fulfilling a plugin's requirements before
executing the plugin itself.
Operationally, Maven 2.0 should feel very much like a more performant big brother of Maven 1.x.
While the POM has definitely changed, it has the same basic layout and features (with notable
additions). However, this is where the similarity ends. Maven 2.0 is a complete redesign and
reimplementation of the Maven build concept. As such, it has a much different and more evolved
architecture - at least to our minds. ;-)

24.3.2 Differences from Maven 1.x
However similar the architectures may seem, Maven 2 offers a much richer environment for
its plugins than Maven 1 ever did. The new architecture offers a managed lifecycle, multiple
implementation languages, reusability outside of the build system, and many more advantages.
Arguably the biggest advantage is the ability to write Maven plugins entirely in Java, which allows
developers to tap into a rich landscape of development and testing tools to aid in their efforts.
Prior to Maven 2.0, the build system organized relevant plugins into a loosely defined lifecycle,
which was determined based on goal prerequisites and decoration via preGoals and postGoals. That
experience was critical for the Maven community. It taught us that even though there may be a
million different build scenarios out there, most of the activities in those builds fit into just a few
broad categories. Moreover, the category to which a goal fits serves as an accurate predictor for
where in the build process the goal should execute. Drawing on this experience, Maven 2.0 defines a
lifecycle within which plugins are managed according to their relative position within this lifecycle.
Starting with Maven 2.0, plugins implemented in different programming or scripting languages can
coexist within the same build process. This removes the requirement that plugin developers learn a
particular scripting language in order to interact with Maven. It also reduced the risk associated with
the stability or richness of any particular scripting language.
Also starting with Maven 2.0 is an effort to integrate multiproject builds directly into the core
architecture. In Maven 1.x, many large projects were fragmented into smaller builds to sidestep issues
such as conditional compilation of a subset of classes; separation of client-server code; or cyclical
dependencies between distinct application libraries. This in turn created extra complexity with
running builds, since multiple builds had to be run in order to build the application as a whole - one
or more per project. While the first version (1.x) did indeed address this new multiple projects issue,
it did so as an afterthought. The Reactor was created to act as a sort of apply-to-all-these function,
and the multiproject plugin was later added to provide Reactor settings for some common build types.
However, this solution (it is really only one solution, plus some macros) really never integrated the
idea of the multi-project build process into the maven core conceptual framework.

24.3.3 Why Change the Plugin Architecture?
See the previous section for the long version, but the short version can be summed up by the
following list of benefits.
• A managed lifecycle
• Multiple implementation languages
• Reusability outside of the build system
• The ability to write Maven plugins entirely in Java
In Maven 1.0, a plugin was defined using Jelly, and while it was possibly to write a plugin in Java,
you still had to wrap your plugin with some obligatory Jelly script. An XML-based scripting language



which is interpreted at run-time isn't going to be the best choice for performance, and the development
team thought it wise to adopt an approach which would allow plugin developers to choose from an
array of plugin implementation choices. The first choice in Maven 2 should be Java plugins, but you
may also use one of the supported scripting languages like Beanshell.
To summarize, the development team saw some critical gaps in the API and architecture of Maven 1.0
plug-ins, and the team decided that addressing these deficiencies was critical to the future progress of
Maven from a useful tool to something more robust.


25 Configuring Plug-ins 155

25 Configuring Plug-ins
.......................................................................................................................................

25.1 Guide to Configuring Plug-ins
1 Mapping Complex Objects
2 Mapping Collections

1 Mapping Lists
2 Mapping Maps
3 Mapping Properties
3 Using Setters
4 Using the <executions> Tag
In Maven plug-ins are configured by specifying a <configuration> element where the child
elements of the <configuration> element are mapped to fields, or setters, inside your Mojo
(remember that a plug-in consists of one or more Mojos where a Mojo maps to a goal). Say, for
example, we had a Mojo that performed a query against a particular URL, with a specified timeout
and list of options. The Mojo might look like the following:

/**
* @goal query
*/
public class MyQueryMojo
extends AbstractMojo
{
/**
* @parameter expression="${query.url}"
*/
private String url;
/**
* @parameter default-value="60"
*/
private int timeout;
/**
* @parameter
*/
private String[] options;
public void execute()
throws MojoExecutionException
{
...
}
}

To configure the Mojo from your POM with the desired URL, timeout and options you might have
something like the following:



<project>
...
<build>
<plugins>
<plugin>
<artifactId>maven-myquery-plugin</artifactId>
<configuration>
<url>http://www.foobar.com/query</url>
<timeout>10</timeout>
<options>
<option>one</option>
<option>two</option>
<option>three</option>
</options>
</configuration>
</plugin>
</plugins>
</build>
...
</project>

As you can see the elements in the configuration match the names of the fields in the Mojo. The
configuration mechanism Maven employs is very similar to the way XStream works where elements
in XML are mapped to objects. So from the example above you can see that the mapping is pretty
straight forward the url element maps to the url field, the timeout element maps to the timeout
field and the options element maps to the options field. The mapping mechanism can deal with
arrays by inspecting the type of the field and determining if a suitable mapping is possible.
For mojos that are intended to be executed directly from the CLI, their parameters usually provide
a means to be configured via system properties instead of a <configuration> section in the
POM. The plugin documentation for those parameters will list an expression that denotes the
system properties for the configuration. In the mojo above, the parameter url is associated with the
expression ${query.url}, meaning its value can be specified by the system property query.url as
shown below:

mvn myquery:query -Dquery.url=http://maven.apache.org

Note that the name of the system property does not necessarily match the name of the mojo
parameter. While this is a rather common practice, you will often notice plugins that employ some
prefix for the system properties to avoid name clashes with other system properties. Though rarely,
there are also plugin parameters that (e.g. for historical reasons) employ system properties which
are completely unrelated to the parameter name. So be sure to have a close look at the plugin
documentation.

25.1.1 Mapping Complex Objects
Mapping complex types is also fairly straight forward in Maven so let's look at a simple example
where we are trying to map a configuration for Person object. The <configuration> element might
look like the following:



...
<configuration>
<person>
<firstName>Jason</firstName>
<lastName>van Zyl</lastName>
</person>
</configuration>
...

The rules for mapping complex objects are as follows:
• There must be a private field that corresponds to name of the element being mapped. So in our
case the person element must map to a person field in the mojo.
• The object instantiated must be in the same package as the Mojo itself. So if your mojo is in
com.mycompany.mojo.query then the mapping mechanism will look in that package for
an object named Person. As you can see the mechanism will capitalize the first letter of the
element name and use that to search for the object to instantiate.
• If you wish to have the object to be instantiated live in a different package or have a more
complicated name then you must specify this using an implementation attribute like the
following:

...
<configuration>
<person implementation="com.mycompany.mojo.query.SuperPerson">
<firstName>Jason</firstName>
<lastName>van Zyl</lastName>
</person>
</configuration>
...

25.1.2 Mapping Collections
The configuration mapping mechanism can easily deal with most collections so let's go through a few
examples to show you how it's done:

25.1.2.1 Mapping Lists
Mapping lists works in much the same way as mapping to arrays where you a list of elements will be
mapped to the List. So if you have a mojo like the following:

public class MyAnimalMojo
{
/**
* @parameter
*/
private List animals;
{
...
}
}



Where you have a field named animals then your configuration for the plug-in would look like the
following:

<project>
...
<build>
<plugins>
<plugin>
<artifactId>maven-myanimal-plugin</artifactId>
<configuration>
<animals>
<animal>cat</animal>
<animal>dog</animal>
<animal>aardvark</animal>
</animals>
</configuration>
</plugin>
</plugins>
</build>
...
</project>

Where each of the animals listed would be entries in the animals field. Unlike arrays, collections
have no specific component type. In order to derive the type of a list item, the following strategy is
used:
1 If the XML element contains an implementation hint attribute, that is used
2 If the XML tag contains a ., try that as a fully qualified class name
3 Try the XML tag (with capitalized first letter) as a class in the same package as the mojo/object
being configured
4 If the element has no children, assume its type is String. Otherwise, the configuration will fail.

25.1.2.2 Mapping Maps
In the same way, you could define maps like the following:

...
/**
* My Map.
*
* @parameter
*/
private Map myMap;
...

...
<configuration>
<myMap>
<key1>value1</key1>
<key2>value2</key2>
</myMap>
</configuration>
...



25.1.2.3 Mapping Properties
Properties should be defined like the following:

...
/**
* My Properties.
*
* @parameter
*/
private Properties myProperties;
...

...
<configuration>
<myProperties>
<property>
<name>propertyName1</name>
<value>propertyValue1</value>
<property>
<property>
<property>
</myProperties>
</configuration>
...

25.1.3 Using Setters
You are not restricted to using private field mapping which is good if you are trying to make you
Mojos resuable outside the context of Maven. Using the example above we could name our private
fields using the underscore convention and provide setters that the configuration mapping mechanism
can use. So our Mojo would look like the following:



public class MyQueryMojo
{
/**
* @parameter property="url"
*/
private String _url;
/**
* @parameter property="timeout"
*/
private int _timeout;
/**
* @parameter property="options"
*/
private String[] _options;
public void setUrl( String url )
{
_url = url;
}
public void setTimeout( int timeout )
{
_timeout = timeout;
}
public void setOptions( String[] options )
{
_options = options;
}
{
...
}
}

Note the specification of the property name for each parameter which tells Maven what setter and
getter to use when the field's name does not match the intended name of the parameter in the plugin
configuration.

25.1.4 Using the <executions> Tag
You can also configure a mojo using the <executions> tag. This is most commonly used for mojos
that are intended to participate in some phase of the build lifecycle. Using MyQueryMojo as an
example, you may have something that will look like:



<project>
...
<build>
<plugins>
<plugin>
<executions>
<execution>
<id>execution1</id>
<phase>test</phase>
<configuration>
<url>http://www.foo.com/query</url>
<options>
<option>one</option>
<option>two</option>
<option>three</option>
</options>
</configuration>
<goals>
<goal>query</goal>
</goals>
</execution>
<execution>
<id>execution2</id>
<configuration>
<url>http://www.bar.com/query</url>
<options>
<option>four</option>
<option>five</option>
<option>six</option>
</options>
</configuration>
<goals>
<goal>query</goal>
</goals>
</execution>
</executions>
</plugin>
</plugins>
</build>
...
</project>

The first execution with id "execution1" binds this configuration to the test phase. The second
execution does not have a <phase> tag, how do you think will this execution behave? Well, goals can
have a default phase binding as discussed further below. If the goal has a default phase binding then
it will execute in that phase. But if the goal is not bound to any lifecycle phase then it simply won't be
executed during the build lifecycle.



Note that while execution id's have to be unique among all executions of a single plugin within a
POM, they don't have to be unique across an inheritance hierarchy of POMs. Executions of the same
id from different POMs are merged. The same applies to executions that are defined by profiles.
How about if we have a multiple executions with different phases bound to it? How do you think will
it behave? Let us use the example POM above again, but this time we shall bind execution2 to a
phase.

<project>
...
<build>
<plugins>
<plugin>
...
<executions>
<execution>
<id>execution1</id>
<phase>test</phase>
...
</execution>
<execution>
<id>execution2</id>
<phase>install</phase>
<configuration>
<options>
</options>
</configuration>
<goals>
<goal>query</goal>
</goals>
</execution>
</executions>
</plugin>
</plugins>
</build>
...
</project>

If there are multiple executions bound to different phases, then the mojo is executed once for each
phase indicated. Meaning, execution1 will be executed applying the configuration setup when the
phase of the build is test, and execution2 will be executed applying the configuration setup when
the build phase is already in install.
Now, let us have another mojo example which shows a default lifecycle phase binding.



/**
* @goal query
* @phase package
*/
public class MyBindedQueryMojo
{
/**
* @parameter expression="${query.url}"
*/
private String url;
/**
* @parameter default-value="60"
*/
private int timeout;
/**
* @parameter
*/
private String[] options;
{
...
}
}

From the above mojo example, MyBindedQueryMojo is by default bound to the package phase
(see the @phase notation). But if we want to execute this mojo during the install phase and not
with package we can rebind this mojo into a new lifecycle phase using the <phase> tag under
<execution>.



<project>
...
<build>
<plugins>
<plugin>
<executions>
<execution>
<id>execution1</id>
<phase>install</phase>
<configuration>
<options>
</options>
</configuration>
<goals>
<goal>query</goal>
</goals>
</execution>
</executions>
</plugin>
</plugins>
</build>
...
</project>

Now, MyBindedQueryMojo default phase which is package has been overrided by install phase.
Note: Configurations inside the <executions> tag differ from those that are outside
<executions> in that they cannot be used from a direct command line invocation. Instead they are
only applied when the lifecycle phase they are bound to are invoked. Alternatively, if you move a
configuration section outside of the executions section, it will apply globally to all invocations of the
plugin.


26 The Plugin Registry 165

26 The Plugin Registry
.......................................................................................................................................

26.1 Introduction to the Plugin Registry
The Maven 2 plugin registry (~/.m2/plugin-registry.xml) is a mechanism to help the user exert some
control over their build environment. Rather than simply fetching the latest version of every plugin
used in a given build, this registry allows the user to peg a plugin to a particular version, and only
update to newer versions under certain restricted circumstances. There are various ways to configure
or bypass this feature, and the feature itself can be managed on either a per-user or global level.

26.1.1 Warning!
The plugin registry is currently in a semi-dormant state within Maven 2. This is because it has been
shown to have some subtle behavior that is not quite intuitive. While we believe it's important to
allow the user to pin down which version of a particular plugin is used across all builds, it's not clear
that this type of information should be machine-specific (i.e. tied to something outside the project
directory).
Users should be cautious when attempting to use the plugin-registry.xml. Redesign of this
feature in upcoming 2.1 and/or 2.2 is likely.
For now, Maven should keep using the same version of a plugin - assuming a different version is not
specified in the POM - until the user chooses to run with the -U option explicitly enabled.

26.1.2 A Tour of plugin-registry.xml
The plugin registry file (per-user: ~/.m2/plugin-registry.xml, global: $M2_HOME/conf/plugin-
registry.xml) contains a set of plugin-version registrations, along with some configuration parameters
for the registry itself.
Currently, the plugin registry supports configuration options for the following:
• updateInterval - Determines how often (or whether) the registered plugins are checked for
updates.
Combined with the lastChecked plugin attribute, this determines whether a particular plugin will
be checked for updates during a given build. Valid settings are: never, always, and interval:TTT
(TTT is a short specification for a time interval, which follows the pattern /([0-9]+[wdhm])+/).
Intervals are specified down to the minute resolution. An example of an interval specification
might be:
interval:4w2h30m (check every 4 weeks, 2 hours, and 30 minutes)
• autoUpdate - Specifies whether the user should be prompted before registering plugin-version
updates. This is a boolean value, accepting true/false.
• checkLatest - Specifies whether the LATEST artifact metadata should be consulted while
determining versions for unregistered plugins.
LATEST metadata is always published when a plugin is installed or deployed to a repository,
and so will always reference the newest copy of the plugin, regardless of whether this is a
snapshot version or not.
NOTE: Registered plugins will currently only ever be updated with the results of RELEASE
metadata resolution.
Obviously, the plugin registry also contains information about resolved plugin versions. The
following information is tracked for each registered plugin:
• groupId - The plugin's group id.



• artifactId - The plugin's artifact id.
• lastChecked - The timestamp from the last time updates were checked for this plugin.
• useVersion - The currently registered version for this plugin. This is the version Maven will use
when executing this plugin's mojos.
• rejectedVersions - A list of versions discovered for this plugin which have been rejected by the
user. This keeps Maven from continually prompting the user to update a given plugin to the same
new version.

26.1.3 Using (or not) the Plugin Registry
There are many ways you can override the default plugin registry settings. Often, this will be
desirable for a single, one-off build of a project that deviates from your normal environment
configuration. However, before discussing these options, it's important to understand how the plugin
registry resolves versions for unregistered plugins, along with plugins in need of an update check.

26.1.3.1 Resolving Plugin Versions
The plugin registry uses a relatively straightforward algorithm for resolving plugin versions.
However, considerations for when to check, when to prompt the user, and when to persist resolved
plugin versions complicate this implementation considerably. In general, plugin versions are resolved
using a four-step process:
1 Check for a plugin configuration in the MavenProject instance. Any plugin configuration found
in the MavenProject is treated as authoritative, and will stop the plugin-version resolution/
persistence process when found.
2 If the plugin registry is enabled, check it for an existing registered version. If the plugin has been
registered, a combination of the updateInterval configuration and the lastChecked attribute (on
the plugin) determine whether the plugin needs to be checked for updates. If the plugin doesn't
need an update check, the registered version is used.
If the plugin is due for an update check, the plugin-artifact's RELEASE metadata is resolved.
Resolution of this metadata may trigger a prompt to notify the user of the new version, and/
or persistence of the new version in the registry. If the update is performed, the lastChecked
attribute is updated to reflect this.
3 If the checkLatest configuration is set to true, or the '--check-plugin-latest' CLI
option (discussed later) is provided, then the LATEST artifact metadata is resolved for the
plugin.
If this metadata is resolved successfully, that version is used. This may trigger a prompt to ask
the user whether to register the plugin, and a successive persistence step for the new plugin
version.
4 If the version still has not been resolved, RELEASE artifact metadata is checked for the plugin.
If this metadata resolves successfully, it is the version used. This may also trigger a prompt to
ask the user whether to register the plugin, and a persistence step registering the new plugin
version.
I've alluded to prompting the user and persisting the plugin version into the registry. Now, let's
examine the circumstances under which these steps actually take place.
There are two cases where the user may be prompted to change the plugin registry; when the
plugin is not registered, and when the plugin is registered, but an updated version is discovered.
By default, the user is prompted to save the resolved version for each plugin, with the option of
specifying that a decision should be remembered and applied to all (either yes to all, or no to all)
plugins registry updates. However, it is also possible to bypass this behavior in the following
ways:



• Specify autoUpdate == true in the plugin-registry.xml. This configuration parameter
means that the user is not prompted, and all updated/discovered versions are to be persisted.
• Specify '--batch-mode' (or '-B') from the command line. This functions in the same
way as the autoUpdate config parameter above.
• Specify '--no-plugin-updates' | '-npu' from the command line. This prevents any
updates or new registrations from taking place, but existing plugin versions in the registry
will be used when available.
• Specify '--check-plugin-updates' | '--update-plugins' | '-up' | '-cpu'
(synonyms) from the command line.
• Specify '--no-plugin-registry' | '-npr' from the command line. This prevents
resolution of plugin versions using the plugin-registry.xml file. The plugin version will be
resolved either from the project or from the repository in this case.
• Specify usePluginRegistry == false in the settings.xml. This configuration parameter
will disable use of the plugin registry for the entire build environment, as opposed to the
immediate build execution (as in the case of the corresponding command line switch
above).
These force all registered plugins to be updated. The user will still be prompted to approve
plugin versions, unless one of the above switches is also provided.

26.1.3.2 Summary of Command Line Options for the Plugin Registry
The following summary of command line options is provided for quick reference:

• --no-plugin-registry - Bypass the plugin registry.
Synonym: -npr
• --no-plugin-latest - Don't check the LATEST artifact metadata when resolving plugin
versions, regardless of the value of useLatest in the plugin-registry.xml file.
Synonym: -npl
• --check-plugin-latest - Check the LATEST artifact metadata when resolving plugin
versions, regardless of the value of useLatest in the plugin-registry.xml file.
Synonym: -cpl
• --no-plugin-updates - Do not search for updated versions of registered plugins. Only use
the repository to resolve unregistered plugins.
Synonym: -npu
• --check-plugin-updates - Force the plugin version manager to check for updated versions
of any registered plugins, currently using RELEASE metadata only.
Synonyms: --update-plugins -up -cpu


27 Plugin Prefix Resolution 168

27 Plugin Prefix Resolution
.......................................................................................................................................

27.1 Introduction to Plugin Prefix Resolution
When you execute Maven using a standard lifecycle phase, resolving the plugins that participate
in that lifecycle is a relatively simple process. However, when you directly invoke a mojo from the
command line, as in the case of clean, Maven must have some way of reliably resolving the clean
plugin prefix to the maven-clean-plugin. This provides brevity for command-line invocations, while
preserving the descriptiveness of the plugin's real artifactId.
To complicate matters even more, not all plugins should be forced to have the same groupId in the
repository. Since groupIds are presumed to be controlled by one project, and multiple projects may
release plugins for Maven, it follows that plugin-prefix mappings must also accommodate multiple
plugin groupIds.
To address these concerns, Maven provides a new piece of repository-level metadata (not associated
with any single artifact) for plugin groups, along with a plugin mapping manager to organize multiple
plugin groups and provide search functionality.

27.1.1 Specifying a Plugin's Prefix
In order to give users a convenient prefix with which to reference your plugin a prefix must be
associated with your plugin when it is built. By default, Maven will make a guess at the plugin-prefix
to be used, by assuming the plugin's artifactId fits the pattern:

maven-${prefix}-plugin

If your plugin's artifactId fits this pattern, Maven will automatically map your plugin to the correct
prefix in the metadata stored within your plugin's groupId path on the repository. However, if you
want to customize the prefix used to reference your plugin, you can specify the prefix directly through
a configuration parameter on the maven-plugin-plugin in your plugin's POM:

<project>
...
<build>
...
<plugins>
...
<plugin>
<artifactId>maven-plugin-plugin</artifactId>
<configuration>
...
<goalPrefix>somePrefix</goalPrefix>
</configuration>
</plugin>
</plugins>
</build>
</project>

The above configuration will allow users to refer to your plugin by the prefix somePrefix, as in the
following example:


27 Plugin Prefix Resolution 169

mvn somePrefix:goal

27.1.2 Mapping Prefixes to Plugins
For each groupId configured for searching, Maven will:
1 Download maven-metadata.xml from each remote repository into the local repository, and
name it maven-metadata-${repoId}.xml within the path of ${groupId}.
2 Load these metadata files, along with maven-metadata-local.xml (if it exists), within the
path of ${groupId}. Merge them.
3 Lookup the plugin prefix in the merged metadata. If it's mapped, it should refer to a concrete
groupId-artifactId pair. Otherwise, go on to #1 for the next groupId in the user's plugin-groups.
These metadata files consist of the groupId it represents (for clarity when the file is opened outside
the context of the directory), and a group of plugin elements. Each plugin in this list contains a prefix
element denoting the plugin's command-line prefix, and an artifactId element, which provides the
other side of the prefix mapping and provides enough information to lookup and use the plugin. When
a plugin is installed or deployed, the appropriate metadata file is located - and if the prefix mapping is
missing - modified to include the plugin-prefix mapping.

27.1.3 Configuring Maven to Search for Plugins
By default, Maven will search the groupId org.apache.maven.plugins for prefix-to-artifactId
mappings for the plugins it needs to perform a given build. However, as previously mentioned, the
user may have a need for third-party plugins. Since the Maven project is assumed to have control
over the default plugin groupId, this means configuring Maven to search other groupId locations for
plugin-prefix mappings.
As it turns out, this is simple. In the Maven settings file (per-user: ~/.m2/settings.xml; global:
$M2_HOME/conf/settings.xml), you can provide a custom pluginGroups section, listing the
plugin groupIds you want to search (each groupId goes in its own pluginGroup sub-element). For
example, if my project uses a Modello model file, I might have the following in my settings:

<pluginGroups>
<pluginGroup>org.codehaus.modello</pluginGroup>
</pluginGroups>

This allows me to execute the following, which will generate Java classes from the model:

mvn -Dversion=4.0.0 -Dmodel=maven.mdo modello:java

Maven will always search the following groupId's after searching any plugin groups specified in the
user's settings:
• org.apache.maven.plugins
• org.codehaus.mojo
NOTE: When specifying plugin groups to be used in searching for a prefix mapping, order is critical!
By specifying a pluginGroup of com.myco.plugins with a prefix of clean, I can override the
usage of the maven-clean-plugin when clean:clean is invoked.
NOTE2: For more information on settings.xml, see [ 1].

27.1.4 Resources
1 Guide to Configuring Maven


28 Developing Ant Plugins 170

28 Developing Ant Plugins
.......................................................................................................................................

28.1 Developing Ant Plugins for Maven 2.x

28.1.1 WARNING
The documentation below assumes that you have updated your locally cached cached copy of
the maven-plugin-plugin. To update your copy, you will need to include the -U option when you
build your plugin project:

mvn -U clean install

The maven-plugin-plugin is responsible for reading plugin metadata in its various forms and writing
a standard Maven plugin descriptor based on the input. It was designed to accommodate multiple
plugin languages side by side, but its initial design was slightly flawed for plugin languages that don't
include the metadata inline with the source (within the same file). Since the 2.0.1 release of Maven,
the maven-plugin-plugin has contained revisions to handle this scenario. Since the API has changed
(in a backward-compatible way), and since the Ant plugin support requires these changes be in place,
you will see an AbstractMethodError if you try to build an Ant-based plugin using the old maven-
plugin-plugin.

28.1.2 Introduction
The intent of this document is to help users learn to develop Maven plugins using Ant.
As of the 2.0.1 release, Maven supports Ant-driven plugins. These plugins allow the invocation of Ant
targets (specified in scripts embedded in the plugin jar) at specific points in the build lifecycle. They
can also inject parameter values into the Ant project instances when a target is called.

28.1.3 Conventions
In this guide, we'll use the standard Maven directory structure for projects, to keep our POMs as
simple as possible. It's important to note that this is only a standard layout, not a requirement. The
important locations for our discussion are the following:

/<project-root>
|
+- pom.xml
|
+- /src
| |
| +- /main
| | |
| | +- /scripts (source location for script-driven plugins)
| | | |
...

28.1.4 Getting Started
We'll start with the simplest of all possible plugins. This plugin takes no parameters, and will simply
print a message out to the screen when invoked. This should familiarize the reader with the basics of
mapping Ant build scripts to the Maven plugin framework. From there, we will gradually increase the
complexity of our plugin, adding parameters, interacting with standard project locations, and binding


to lifecycle phases. Finally, we'll see how a single Ant build script can be mapped to multiple Maven
mojos within the same plugin.

28.1.4.1 Hello, World
Our first plugin will simply print "Hello, World" to the console.
28.The Build Script
The elemental Ant-driven mojo consists of a simple Ant build script, a mapping metadata file, and of
course the plugin's POM. If our goal is to print "Hello, World", we might use an Ant build script that
looks something like this:

hello.build.xml:
--------------------------------
<project>
<target name="hello">
<echo>Hello, World</echo>
</target>
</project>

28.The Mapping Document
Once we've created this build script, we need to tell Maven how to use it as a plugin. This involves
creating a mapping document. Note that where the build script was named hello.build.xml, the
mapping document is named hello.mojos.xml. The naming of these files is very important, as this is
how the plugin parser matches mapping documents to build scripts. It has the general form:

• basename .build.xml - The Ant build script.
• basename .mojos.xml - The corresponding mapping document.
A simple mapping document used to wire the above build script into Maven's plugin framework might
look as follows:

hello.mojos.xml:
------------------------------
<pluginMetadata>
<mojos>
<mojo>
<goal>hello</goal>


<call>hello</call>
<description>
Say Hello, World.
</description>
</mojo>
</mojos>
</pluginMetadata>

28.The POM
Now that we have the build script and mapping document, we're ready to build this plugin. However,
in order to build, we need to provide a POM for our new plugin. As it turns out, the POM required
for an Ant-driven plugin is fairly complex. This is because we have to configure the maven-plugin-
plugin to use the Ant plugin parsing tools in addition to the defaults (such as the Java parsing tools).
Our POM might look something like this:

pom.xml:
------------------------------
<project>

<groupId>org.myproject.plugins</groupId>
<artifactId>hello-plugin</artifactId>

<packaging>maven-plugin</packaging>

<name>Hello Plugin</name>

<dependencies>
<dependency>
<artifactId>maven-script-ant</artifactId>
</dependency>
</dependencies>

<build>
<plugins>
<plugin>

<artifactId>maven-plugin-plugin</artifactId>


<dependencies>
<dependency>
<artifactId>maven-plugin-tools-ant</artifactId>
</dependency>
</dependencies>


<configuration>
<goalPrefix>hello</goalPrefix>
</configuration>
</plugin>
</plugins>
</build>
</project>


28.Build It and Run It
Once we have a POM for our new plugin, we can install it into the local repository just as we would
any other Maven project:

mvn install

and invoke it like this:

mvn org.myproject.plugins:hello-plugin:hello

This should output the following:

[echo] Hello, World

28.1.5 Using prefix:mojo Invocation Syntax
Our new plugin works, but look at that command line... The next thing is to configure Maven so
we can use the familiar prefix:mojo invocation syntax, and leave that verbose, fully-qualified mess
behind.
As you know, Maven maps plugins to user-friendly prefixes. However, these prefixes might overlap;
that is, multiple plugins may try to use the same prefix inadvertently. To avoid the obvious ambiguity
associated with such a collision, Maven will search a predetermined list of plugin groupIds for a given
prefix, with the first match winning. So, if we want to add our new plugin to this search, we need to
configure the list of plugin groupIds.

28.1.5.1 Configuring Plugin-Prefix Searching
In order to reference our new plugin by prefix, we need to add its groupId to the <pluginGroups/>
list in the settings.xml file. As you probably know, this file is usually found under $HOME/.m2.
The added section to make our plugin's groupId searchable should look like this:

~/.m2/settings.xml:
------------------------------
<settings>
.
.
.
<pluginGroups>
<pluginGroup>org.myproject.plugins</pluginGroup>
</pluginGroups>
.
.
.
</settings>

28.1.5.2 Run It
We can check that this worked by invoking our new mojo once again, this time using the prefix
syntax:

mvn hello:hello



28.1.6 Adding Plugin Parameters
Now, suppose it's not enough that our plugin display static text to the console. Suppose we need it to
display a greeting that is a little more personalized. We can easily add support for this by adding a
name parameter. For good measure, we'll output the current project's name as well.

28.1.6.1 Change the Ant Script
The build script will have to change to output the new information:

hello.build.xml:
--------------------------------
<project>
<target name="hello">
<echo>Hello, ${name}. You're building project: ${projectName}</echo>
</target>
</project>

28.1.6.2 Change the Mapping Document
Now that we have a build script which requires two new parameters, we have to tell the mapping
document about them, so they will be injected into the Ant Project instance.



hello.mojos.xml:
------------------------------
<pluginMetadata>
<mojos>
<mojo>
<goal>hello</goal>

<call>hello</call>

<requiresProject>true</requiresProject>

<description>
Say Hello, including the user's name, and print the project name to the cons
</description>
<parameters>
<parameter>
<name>name</name>
<property>name</property>
<required>true</required>
<expression>${name}</expression>
<type>java.lang.String</type>
<description>The name of the user to greet.</description>
</parameter>

<parameter>
<name>projectName</name>
<property>projectName</property>
<readonly>true</readonly>
<defaultValue>${project.name}</defaultValue>
<description>The name of the project currently being built.</description>
</parameter>
</parameters>
</mojo>
</mojos>
</pluginMetadata>

You'll notice several differences from the old version of the mapping document. First, we've
added requiresProject="true" to the mojo declaration. This tells Maven that our mojo requires a
valid project before it can execute...in our case, we need a project so we can determine the correct
projectName to use. Next, we've added two parameter declarations to our mojo mapping; one for
name and another for projectName.
The name parameter declaration provides an expression attribute...this allows the user to specify -
Dname=somename on the command line. Otherwise, the only way to configure this parameter would
be through a <configuration/> element within the plugin specification in the user's POM. Note
that this parameter is required to have a value before our mojo can execute.
The projectName parameter declaration provides two other interesting items. First, it specifies a
defaultValue attribute, which specifies an expression to be evaluated against Maven's current build
state in order to extract the parameter's value. Second, it specifies a readonly attribute, which means
the user cannot directly configure this parameter - either via command line or configuration within



the POM. It can only be modified by modifying the build state referenced in the defaultValue...in our
case, the name element of the POM. Also note that this parameter is declared to be required before
our mojo can execute.

28.1.6.3 Rebuild It and Run It
Now that we've modified our plugin, we have to rebuild it before running it again.

mvn clean install

Next, we should run the plugin again to verify that it's doing what we expect. However, before we
can run it, we have some requirements to satisfy. First, we have to be sure we're executing in the
context of a valid Maven POM...runnning in the plugin's own project directory should satisfy that
requirement. Then, we have to satisfy the name requirement. We can do this directly through the
command line. So, the resulting invocation of our plugin will look like this:

mvn -Dname=<your-name-here> hello:hello

or, in my case:

mvn -Dname=John hello:hello

This should output the following:

[echo] Hello, John. You're building project: Hello Plugin

28.1.7 Defining Multiple Mojos from One Build Script
If you're familiar with Ant, you're probably familiar with the common usage pattern of defining
multiple build types within a single build script. For instance, you might have a build type for
cleaning the project, another for producing the application jar file, and yet another for producing the
full distribution including javadocs, etc.
The concept is pretty simple. Discrete chunks of the build process are separated into targets within the
script. These targets can reference one another in order to make reuse within the build script possible.
These same concepts map pretty well to Maven, actually. However, instead of targets directly
referencing one another, they would be bound to the appropriate phases of the build lifecycle. In this
way, multiple Ant targets from the same build script can be reused piecemeal at different points in
multiple build lifecycles (clean, site, and the main lifecycle are three examples).
This section will describe how to map multiple logical mojos onto different targets within the same
Ant build script. It's also possible to reference targets from multiple build scripts, but we'll cover this
later.

28.1.7.1 Two Targets, One Script
To test this, we'll split our echo statement into two targets. Then, we'll reference each as separate
mojos in the build. The new script looks like this:



one-two.build.xml:
--------------------------------
<project>
<target name="one">
<echo>Hello, ${name}.</echo>
</target>

<target name="two">
<echo>You're building project: ${projectName}</echo>
</target>
</project>

28.1.7.2 Map the Mojos
Next, we'll modify our original mapping document to map these two new mojos instead of the old
one:



one-two.mojos.xml:
------------------------------
<pluginMetadata>
<mojos>
<mojo>
<goal>one</goal>

<call>one</call>

<description>
Say Hello. Include the user's name.
</description>
<parameters>
<parameter>
<name>name</name>
<property>name</property>
<expression>${name}</expression>
<description>The name of the user to greet.</description>
</parameter>
</parameters>
</mojo>

<mojo>
<goal>two</goal>

<call>two</call>
<requiresProject>true</requiresProject>

<description>
Write the project name to the console.
</description>
<parameters>
<parameter>
<name>projectName</name>
<property>projectName</property>
<readonly>true</readonly>
<defaultValue>${project.name}</defaultValue>
<description>The name of the project currently being built.</description>
</parameter>
</parameters>
</mojo>
</mojos>
</pluginMetadata>

Now that we've split the old functionality into two distinct mojos, there are some interesting
consequences. Aside from the obvious, mojo one no longer requires a valid project instance in order
to execute, since we only require the user's name in order to greet him.



28.1.7.3 Build It, Run It

28.1.7.4 Rebuild It and Run It
Since we've modified our plugin, we have to rebuild it again before re-running it.

mvn clean install

Now that we have two separate mojos, we can execute them singly, or in any order we choose. We
can bind them to phases of the lifecycle using plugin configuration inside the build element of a POM.
We can execute them like this:

mvn -Dname=John hello:one
RETURNS:
[echo] Hello, John.
mvn hello:two (executed in the plugin's project directory)
RETURNS:
[echo] You're building project: Hello Plugin

Alternatively, you could build a POM like this:



test-project/pom.xml:
----------------------------
<project>
<groupId>org.myproject.tests</groupId>
<artifactId>hello-plugin-tests</artifactId>

<name>Test Project</name>

<build>
<plugins>
<plugin>
<groupId>org.myproject.plugins</groupId>
<artifactId>hello-plugin</artifactId>

<configuration>
<name>John</name>
</configuration>

<executions>
<execution>
<phase>validate</phase>
<goals>
<goal>one</goal>
<goal>two</goal>
</goals>
</execution>
</executions>
</plugin>
</plugins>
</build>
</project>

Then, simply call Maven on this new POM:

cd test-project
mvn validate

You should see the following output:

[echo] Hello, John.
...
[echo] You're building project: Test Project

28.1.7.5 A Note on Multiple Build Scripts
It's worth mentioning that Ant-driven plugins can just as easily contain multiple Ant build scripts.
Simply follow the naming rules - naming each A.build.xml, B.build.xml, C.build.xml, etc. for
example - and be sure to provide a mapping document to correspond to each build script that contains
a mojo (other build scripts may be contained in the plugin, and referenced by one of these; they don't
need mapping documents). So, for the above examples (assuming they all contained mojo targets),


you'd need: A.mojos.xml, B.mojos.xml, and C.mojos.xml. If C.build.xml was referenced by A and B,
but didn't contain mojo targets, then you don't need a C.mojos.xml for obvious reasons.

28.1.8 Advanced Usage
Below are some tips on some of the more advanced options related to Ant mojos.

28.1.8.1 Component References
If your plugin needs a reference to a Plexus component, it will have to define something similar to the
following in the mapping document:

<pluginMetadata>
<mojos>
<mojo>
.
.
.
<components>
<component>
<role>org.apache.maven.project.MavenProjectBuilder</role>
<hint>default</hint> 
</component>
</components>
.
.
.
</mojo>
</mojos>
</pluginMetadata>

28.1.8.2 Forking New Lifecycles
In case your plugin needs to fork a new lifecycle, you can include the following in the mapping
document:

<pluginMetadata>
<mojos>
<mojo>
.
.
.
<execute>
<lifecycle>my-custom-lifecycle</lifecycle>
<phase>package</phase>



<goal>some:goal</goal>
</execute>
.
.
.
</mojo>
</mojos>
</pluginMetadata>

28.1.8.3 Deprecation
As time goes on, you will likely have to deprecate part of your plugin. Whether it's a mojo parameter,
or even an entire mojo, Maven can support it, and remind your users that the mojo or configuration
they're using is deprecated, and print a message directing them to adjust their usage.
To deprecate a mojo parameter, simply add this:

<pluginMetadata>
<mojos>
<mojo>
.
.
.
<parameters>
<parameter>
.
.
.
<deprecated>Use this other parameter instead.</deprecated>
.
.
.
</parameter>
</parameters>
.
.
.
</mojo>
</mojos>
</pluginMetadata>

To deprecate an entire mojo, add this:


<pluginMetadata>
<mojos>
<mojo>
.
.
.
<deprecated>Use this other mojo instead.</deprecated>
.
.
.
</mojo>
</mojos>
</pluginMetadata>


29 Developing Java Plugins 184

29 Developing Java Plugins
.......................................................................................................................................

29.1 Introduction
This guide is intended to assist users in developing Java plugins for Maven 2.0.

29.1.1 Your First Plugin
In this section we will build a simple plugin which takes no parameters and simply displays a message
on the screen when run. Along the way, we will cover the basics of setting up a project to create a
plugin, the minimal contents of a Java mojo, and a couple ways to execute the mojo.

29.1.1.1 Your First Mojo
At its simplest, a Java mojo consists simply of a single class. There is no requirement for multiple
classes like EJBs, although a plugin which contains a number of similar mojos is likely to use an
abstract superclass for the mojos to consolidate code common to all mojos.
When processing the source tree to find mojos, the class
org.apache.maven.tools.plugin.extractor.java.JavaMojoDescriptorExtractor
looks for classes with a " goal" annotation on the class. Any class with this annotation are included in
the plugin configuration file.
29.A Simple Mojo
Listed below is a simple mojo class which has no parameters. This is about as simple as a mojo can
be. After the listing is a description of the various parts of the source.

package sample.plugin;
import org.apache.maven.plugin.AbstractMojo;
import org.apache.maven.plugin.MojoExecutionException;
/**
* Says "Hi" to the user.
* @goal sayhi
*/
public class GreetingMojo extends AbstractMojo
{
public void execute() throws MojoExecutionException
{
getLog().info("Hello, world.");
}
}

• The class org.apache.maven.plugin.AbstractMojo provides most of the infrastructure
required to implement a mojo except for the execute method.
• The comment line starting with " @goal" is an example of an annotation. This annotation is
required, but there are a number of annotations which can be used to control how and when the
mojo is executed.
• The execute method can throw two exceptions:

• org.apache.maven.plugin.MojoExecutionException if an unexpected problem
occurs. Throwing this exception causes a "BUILD ERROR" message to be displayed.



• org.apache.maven.plugin.MojoFailureException if an expected problem (such
as a compilation failure) occurs. Throwing this exception causes a "BUILD FAILURE"
message to be displayed.
• The getLog method (defined in AbstractMojo) returns a log4j-like logger object which allows
plugins to create messages at levels of "debug", "info", "warn", and "error". This logger is the
accepted means to display information to the user. Please have a look at the section Retrieving
the Mojo Logger for a hint on its proper usage.
All Mojo annotations are described by the Mojo API Specification.

29.1.1.2 Project Definition
Once the mojos have been written for the plugin, it is time to build the plugin. To do this properly, the
project's descriptor needs to have a number of settings set properly:

groupId This is the group ID for the plugin, and should match
the common prefix to the packages used by the mojos
artifactId This is the name of the plugin
version This is the version of the plugin
packaging This should be set to " maven-plugin"
dependencies A dependency must be declared to the Maven Plugin
Tools API to resolve " AbstractMojo" and related
classes

Listed below is an illustration of the sample mojo project's pom with the parameters set as described
in the above table:

<project>
<groupId>sample.plugin</groupId>
<artifactId>maven-hello-plugin</artifactId>
<name>Sample Parameter-less Maven Plugin</name>
<dependencies>
<dependency>
<artifactId>maven-plugin-api</artifactId>
</dependency>
</dependencies>
</project>

29.1.1.3 Build Goals
There are few goals which are defined with the Maven plugin packaging as part of a standard build
lifecycle:

compile Compiles the Java code for the plugin and builds the
plugin descriptor
test Runs the plugin's unit tests



package Builds the plugin jar
install Installs the plugin jar in the local repository
deploy Deploys the plugin jar to the remote repository

29.1.1.4 Executing Your First Mojo
The most direct means of executing your new plugin is to specify the plugin goal directly on the
command line. To do this, you need to configure the maven-hello-plugin plugin in you project:

...
<build>
<plugins>
<plugin>
</plugin>
</plugins>
</build>
...

And, you need to specify a fully-qualified goal in the form of:

mvn groupID:artifactID:version:goal

For example, to run the simple mojo in the sample plugin, you would enter " mvn
sample.plugin:maven-hello-plugin:1.0-SNAPSHOT:sayhi" on the command line.
Tips: version is not requiered to run a standalone goal.
29.Shortening the Command Line
There are several ways to reduce the amount of required typing:

• If you need to run the latest version of a plugin installed in your local repository, you can omit its
version number. So just use " mvn sample.plugin:maven-hello-plugin:sayhi" to run
your plugin.
• The " maven-$name-plugin" and " $name-maven-plugin" artifactId patterns are treated in
a special way. If no plugin matches the artifactId specified on the command line, Maven will try
expanding the artifactId to these patterns in that order. So in the case of our example, you can
use " mvn sample.plugin:hello:sayhi" to run your plugin. Note: these 2 patterns are used
respectively by the official Maven 2 plugins and the Mojo project plugins.
• Finally, you can also add your plugin's groupId to the list of groupIds searched by default. To do
this, you need to add the following to your ${user.home}/.m2/settings.xml file:

<pluginGroups>
<pluginGroup>sample.plugin</pluginGroup>
</pluginGroups>
At this point, you can run the mojo with " mvn hello:sayhi".
29.Attaching the Mojo to the Build Lifecycle
You can also configure your plugin to attach specific goals to a particular phase of the build lifecycle.
Here is an example:



<build>
<plugins>
<plugin>
<executions>
<execution>
<phase>compile</phase>
<goals>
<goal>sayhi</goal>
</goals>
</execution>
</executions>
</plugin>
</plugins>
</build>

This causes the simple mojo to be executed whenever Java code is compiled. For more information on
binding a mojo to phases in the lifecycle, please refer to the Build Lifecycle document.

29.1.2 Mojo archetype
To create a new plugin project, you could using the Mojo archetype with the following command
line:

-DgroupId=sample.plugin
-DartifactId=maven-hello-plugin
-DarchetypeArtifactId=maven-archetype-mojo

29.1.3 Parameters
It is unlikely that a mojo will be very useful without parameters. Parameters provide a few very
important functions:

• It provides hooks to allow the user to adjust the operation of the plugin to suit their needs.
• It provides a means to easily extract the value of elements from the POM without the need to
navigate the objects.

29.1.3.1 Defining Parameters Within a Mojo
Defining a parameter is as simple as creating an instance variable in the mojo and adding the proper
annotations. Listed below is an example of a parameter for the simple mojo:

/**
* The greeting to display.
*
* @parameter expression="${sayhi.greeting}" default-value="Hello World!"
*/
private String greeting;



The portion before the annotations is the description of the parameter. The parameter annotation
identifies the variable as a mojo parameter. The default-value parameter of the annotation defines
the default value for the variable. This value can include expressions which reference the project, such
as " ${project.version}" (more can be found in the "Parameter Expressions" document). The
expression parameter can be used to allow configuration of the mojo parameter from the command
line by referencing a system property that the user sets via the -D option.

29.1.3.2 Configuring Parameters in a Project
Configuring the parameter values for a plugin is done in a Maven 2 project within the pom.xml file as
part of defining the plugin in the project. An example of configuring a plugin:

<plugin>
<configuration>
<greeting>Welcome</greeting>
</configuration>
</plugin>

In the configuration section, the element name (" greeting") is the parameter name and the contents
of the element (" Welcome") is the value to be assigned to the parameter.
Note: More details can be found in the Guide to Configuring Plugins.

29.1.3.3 Parameter Types With One Value
Listed below are the various types of simple variables which can be used as parameters in your mojos,
along with any rules on how the values in the POM are interpreted.
29.Boolean
This includes variables typed boolean and Boolean. When reading the configuration, the text "
true" causes the parameter to be set to true and all other text causes the parameter to be set to false.
Example:

/**
* My boolean.
*
* @parameter
*/
private boolean myBoolean;

<myBoolean>true</myBoolean>

29.Fixed-Point Numbers
This includes variables typed byte, Byte, int, Integer, long, Long, short, and Short. When
reading the configuration, the text in the XML file is converted to an integer value using either
Integer.parseInt() or the valueOf() method of the appropriate class. This means that the
strings must be valid decimal integer values, consisting only of the digits 0 to 9 with an optional - in
front for a negative value. Example:



/**
* My Integer.
*
* @parameter
*/
private Integer myInteger;

<myInteger>10</myInteger>

29.Floating-Point Numbers
This includes variables typed double, Double, float, and Float. When reading the configuration,
the text in the XML file is converted to binary form using the valueOf() method for the appropriate
class. This means that the strings can take on any format specified in section 3.10.2 of the Java
Language Specification. Some samples of valid values are 1.0 and 6.02E+23.

/**
* My Double.
*
* @parameter
*/
private Double myDouble;

<myDouble>1.0</myDouble>

29.Dates
This includes variables typed Date. When reading the configuration, the text in the XML file is
converted using one of the following date formats: " yyyy-MM-dd HH:mm:ss.S a" (a sample
date is "2005-10-06 2:22:55.1 PM") or " yyyy-MM-dd HH:mm:ssa" (a sample date is "2005-10-06
2:22:55PM"). Note that parsing is done using DateFormat.parse() which allows some leniency
in formatting. If the method can parse a date and time out of what is specified it will do so even if it
doesn't exactly match the patterns above. Example:

/**
* My Date.
*
* @parameter
*/
private Date myDate;

<myDate>2005-10-06 2:22:55.1 PM</myDate>

29.Files and Directories
This includes variables typed File. When reading the configuration, the text in the XML file is used
as the path to the desired file or directory. If the path is relative (does not start with / or a drive letter
like C:), the path is relative to the directory containing the POM. Example:



/**
* My File.
*
* @parameter
*/
private File myFile;

<myFile>c:temp</myFile>

29.URLs
This includes variables typed URL. When reading the configuration, the text in the XML file is used
as the URL. The format must follow the RFC 2396 guidelines, and looks like any web browser URL
( scheme://host:port/path/to/file). No restrictions are placed on the content of any of the
parts of the URL while converting the URL.

/**
* My URL.
*
* @parameter
*/
private URL myURL;

<myURL>http://maven.apache.org</myURL>

29.Plain Text
This includes variables typed char, Character, StringBuffer, and String. When reading the
configuration, the text in the XML file is used as the value to be assigned to the parameter. For char
and Character parameters, only the first character of the text is used.

29.1.3.4 Parameter Types With Multiple Values
Listed below are the various types of composite objects which can be used as parameters in your
mojos, along with any rules on how the values in the POM are interpreted. In general, the class of the
object created to hold the parameter value (as well as the class for each element within the parameter
value) is determined as follows (the first step which yields a valid class is used):

1 If the XML element contains an implementation hint attribute, that is used
2 If the XML tag contains a ., try that as a fully qualified class name
3 Try the XML tag (with capitalized first letter) as a class in the same package as the mojo/object
being configured
4 For arrays, use the component type of the array (for example, use String for a String[]
parameter); for collections and maps, use the class specified in the mojo configuration for the
collection or map; use String for entries in a collection and values in a map
Once the type for the element is defined, the text in the XML file is converted to the appropriate type
of object
29.Arrays
Array type parameters are configured by specifying the parameter multiple times. Example:



/**
* My Array.
*
* @parameter
*/
private String[] myArray;

<myArray>
<param>value1</param>
</myArray>

29.Collections
This category covers any class which implements java.util.Collection such as ArrayList or
HashSet. These parameters are configured by specifying the parameter multiple times just like an
array. Example:

/**
* My List.
*
* @parameter
*/
private List myList;

<myList>
</myList>

For details on the mapping of the individual collection elements, see Mapping Lists.
29.Maps
This category covers any class which implements java.util.Map such as HashMap but does not
implement java.util.Properties. These parameters are configured by including XML tags in
the form <key>value</key> in the parameter configuration. Example:

/**
* My Map.
*
* @parameter
*/
private Map myMap;

<myMap>
<key1>value1</key1>
<key2>value2</key2>
</myMap>

29.Properties
This category covers any map which implements java.util.Properties. These parameters
are configured by including XML tags in the form <property><name>myName</name>
<value>myValue</value> </property> in the parameter configuration. Example:



/**
* My Properties.
*
* @parameter
*/
private Properties myProperties;

<myProperties>
<property>
<property>
<property>
<property>
</myProperties>

29.Other Object Classes
This category covers any class which does not implement java.util.Map,
java.util.Collection, or java.util.Dictionary. Example:

/**
* My Object.
*
* @parameter
*/
private MyObject myObject;

<myObject>
<myField>test</myField>
</myObject>

Please see Mapping Complex Objects for details on the strategy used to configure those kind of
parameters.

29.1.4 Resources

1 Mojo Documentation: Mojo API, Mojo annotations
2 Maven Plugin Testing Harness: Testing framework for your Mojos.
3 Plexus: The IoC container used by Maven.
4 Plexus Common Utilities: Set of utilities classes useful for Mojo development.
5 Commons IO: Set of utilities classes useful for file/path handling.
6 Common Bugs and Pitfalls: Overview of problematic coding patterns.


30 Creating a Site 193

30 Creating a Site
.......................................................................................................................................

30.1 Creating a site

30.1.1 Creating Content
The first step to creating your site is to create some content. In Maven 2.0, the site content is separated
by format, as there are several available.
+- src/
+- site/
+- apt/
| +- index.apt
|
+- xdoc/
| +- other.xml
|
+- fml/
| +- general.fml
| +- faq.fml
|
+- site.xml
You will notice there is now a ${basedir}/src/site directory within which is contained a site
descriptor along with various directories corresponding to the supported document types. Let's take a
look at site descriptor and the examples of the various document types.
The Xdoc format is the same as used in Maven 1.x. However, navigation.xml has been replaced
by the site descriptor (see below).
The APT format, "Almost Plain Text", is a wiki-like format that allows you to write simple, structured
documents (like this one) very quickly. A full reference of the APT Format is available.
The FML format is the FAQ format, also used in Maven 1.x.
Other formats are available, but at this point these 3 are the best tested. There are also several possible
output formats, but as of 2.0, only XHTML is available.
Note that all of the above is optional - just one index file is required in one of the input trees. Each of
the paths will be merged together to form the root directory of the site.

30.1.2 Customizing the Look & Feel
If you want to tune the way your site looks, you can use a custom skin to provide your own CSS
styles. If that is still not enough, you can even tweak the output templates that Maven uses to generate
the site documentation. You can visit the Skins site to have a look at some of the skins that you can
use to change the look of your site.

30.1.3 Generating the Site
Generating the site is very simple, and fast!
mvn site
By default, the resulting site will be in target/site/...
For more information on the Maven Site Plugin, see its plugin reference.



30.1.4 Deploying the Site
To be able to deploy the site, you must first declare a location to distribute to in your pom.xml,
similar to the repository for deployment.
<project>
...
<site>
<id>website</id>
<url>scp://www.mycompany.com/www/docs/project/</url>
</site>
...
</project>
The <id> element identifies the repository, so that you can attach credentials to it in your
settings.xml file using the <servers> element as you would for any other repository.
The <url> gives the location to deploy to. Currently, only SSH is supported, as above which copies
to the host www.mycompany.com in the path /www/docs/project/. If subprojects inherit the site
URL from a parent POM, they will automatically append their <artifactId> to form their effective
deployment location.
Deploying the site is done by using the site-deploy phase of the site lifecycle.
mvn site-deploy

30.1.5 Creating a Site Descriptor
The site.xml file is used to describe the layout of the site, and replaces the navigation.xml file
used in Maven 1.x.
A sample is given below:
<?xml version="1.0" encoding="ISO-8859-1"?>
<project name="Maven">
<bannerLeft>
<name>Maven</name>
<src>http://maven.apache.org/images/apache-maven-project.png</src>
<href>http://maven.apache.org/</href>
</bannerLeft>
<bannerRight>
<src>http://maven.apache.org/images/maven-small.gif</src>
</bannerRight>
<body>
<links>
<item name="Apache" href="http://www.apache.org/" />
<item name="Maven 1.x" href="http://maven.apache.org/maven-1.x/"/>
<item name="Maven 2" href="http://maven.apache.org/"/>
</links>
<menu name="Maven 2.0">
<item name="Introduction" href="index.html"/>
<item name="Download" href="download.html"/>
<item name="Release Notes" href="release-notes.html" />
<item name="General Information" href="about.html"/>
<item name="For Maven 1.x Users" href="maven1.html"/>
<item name="Road Map" href="roadmap.html" />



</menu>
<menu ref="reports"/>
...
</body>
</project>
Note: The <menu ref="reports"/> element above. When building the site, this is replaced by a
menu with links to all the reports that you have configured.
More information about the site descriptor is available at the site for the Maven Site Plugin.

30.1.6 Adding Extra Resources
You can add any arbitrary resource to your site by including them in a resources directory as
shown below. Additional CSS files will be picked up when they are placed in the css directory within
the resources directory.
+- src/
+- site/
+- resources/
+- css/
| +- site.css
|
+- images/
+- pic1.jpg
The file site.css will be added to the default XHTML output, so it can be used to adjust the default
Maven stylesheets if desired.
The file pic1.jpg will be available via a relative reference to the images directory from any page in
your site.

30.1.7 Configuring Reports
Maven has several reports that you can add to your web site to display the current state of the project.
These reports take the form of plugins, just like those used to build the project.
There are many standard reports that are available by gleaning information from the POM. Currently
what is provided by default are:

• Dependencies Report
• Mailing Lists
• Continous Integration
• Source Repository
• Issue Tracking
• Project Team
• License
To find out more please refer to the Project Info Reports Plugin.
To add these reports to your site, you must add the plugins to a special <reporting> section in the
POM. The following example shows how to configure the standard project information reports that
display information from the POM in a friendly format:
<project>
...
<reporting>
<plugins>



<plugin>
<artifactId>maven-project-info-reports-plugin</artifactId>
</plugin>
</plugins>
</reporting>
...
</project>
If you have included the appropriate <menu ref="reports"/> tag in your site.xml descriptor,
then when you regenerate the site those items will appear in the menu.
Note: Many report plugins provide a parameter called outputDirectory or similar to specify
the destination for their report outputs. This parameter is only relevant if the report plugin is run
standalone, i.e. by invocation directly from the command line. In constrast, when reports are
generated as part of the site, the configuration of the Maven Site Plugin will determine the effective
output directory to ensure that all reports end up in a central location.

30.1.8 Internationalization
Internationalization in Maven is very simple, as long as the reports you are using have that particular
locale defined. For an overview of supported languages and instructions on how to add further
languages, please see the related article Internationalization from the Maven Site Plugin.
To enable multiple locales, add a configuration similar to the following to your POM:
<project>
...
<build>
<plugins>
<plugin>
<artifactId>maven-site-plugin</artifactId>
<configuration>
<locales>en,fr</locales>
</configuration>
</plugin>
</plugins>
</build>
...
</project>
This will generate both an English and a French version of the site. If en is your current locale, then
it will be generated at the root of the site, with a copy of the French translation of the site in the fr/
subdirectory.
To add your own content for that translation instead of using the default, place a subdirectory with
that locale name in your site directory and create a new site descriptor with the locale in the file name.
For example:
+- src/
+- site/
+- apt/
| +- index.apt (Default version)
|



+- fr/
| +- apt/
| +- index.apt (French version)
|
+- site.xml (Default site descriptor)
+- site_fr.xml (French site descriptor)
With one site descriptor per language, the translated site(s) can evolve independently.


31 Snippet Macro 198

31 Snippet Macro
.......................................................................................................................................

31.1 Guide to the Snippet Macro
When generating your project website with Maven, you have the option of dynamically including
snippets of source code in your pages.
A snippet is a section of a source code file that is surrounded by specially formatted comments.
This functionality is inspired by the Confluence snippet macro, and is provided by the Maven Doxia
project by way of the Maven Site Plugin.
To include snippets of source code in your documentation, first add comments in the source document
surrounding the lines you want to include, and then refer to the snippet by its id in the documentation
file.
Each snippet must be assigned an id, and the id must be unique within the source document.
Following are examples of snippets in various source documents, as well as the corresponding macros
in the APT documentation format.
See the Doxia Macros Guide for more information and examples.

31.1.1 Snippets in Sources

31.1.1.1 Java
// START SNIPPET: snip-id
public static void main( String[] args )
{
System.out.println( "Hello World!" );
}
// END SNIPPET: snip-id

31.1.1.2 XML

<navigation-rule>
<from-view-id>/logon.jsp</from-view-id>
<navigation-case>
<from-outcome>success</from-outcome>
<to-view-id>/mainMenu.jsp</to-view-id>
</navigation-case>
</navigation-rule>


31.1.1.3 JSP
<%-- START SNIPPET: snip-id --%>
<ul>
<li><a href="newPerson!input.action">Create</a> a new person</li>
<li><a href="listPeople.action">List</a> all people</li>
</ul>
<%-- END SNIPPET: snip-id --%>

31 Snippet Macro 199

31.1.2 Snippets in Documentation

31.1.2.1 APT
%{snippet|id=snip-id|url=http://svn.example.com/path/to/Sample.java}
%{snippet|id=snip-id|url=file:///path/to/Sample.java}
As of doxia-core version 1.0-alpha-9, a 'file' parameter is also available. If a full path is not specified,
the location is assumed to be relative to ${basedir}.
~~ Since doxia-core 1.0-alpha-9
%{snippet|id=abc|file=src/main/webapp/index.jsp}

• Macros in apt must not be indented.
• Exactly one of url or file must be specified.


32 What is an Archetype 200

32 What is an Archetype
.......................................................................................................................................

32.1 Introduction to Archetypes

32.2 What is Archetype?
In short, Archetype is a Maven project templating toolkit. An archetype is defined as an original
pattern or model from which all other things of the same kind are made. The names fits as we are
trying to provide a system that provides a consistent means of generating Maven projects. Archetype
will help authors create Maven project templates for users, and provides users with the means to
generate parameterized versions of those project templates.
Using archetypes provides a great way to enable developers quickly in a way consistent with best
practices employed by your project or organization. Within the Maven project we use archetypes
to try and get our users up and running as quickly as possible by providing a sample project that
demonstrates many of the features of Maven while introducing new users to the best practices
employed by Maven. In a matter of seconds a new user can have a working Maven project to use
as a jumping board for investigating more of the features in Maven. We have also tried to make the
Archetype mechanism additive and by that we mean allowing portions of a project to be captured
in an archetype so that pieces or aspects of a project can be added to existing projects. A good
example of this is the Maven site archetype. If, for example, you have used the quick start archetype
to generate a working project you can then quickly create a site for that project by using the site
archetype within that existing project. You can do anything like this with archetypes.
You may want to standardize J2EE development within your organization so you may want to provide
archetypes for EJBs, or WARs, or for your web services. Once these archetypes are created and
deployed in your organization's repository they are available for use by all developers within your
organization.

32.2.1 What makes up an Archetype?
Archetypes are packaged up in a JAR and they consist of the archetype metadata which describes
the contents of archetype and a set of Velocity templates which make up the prototype project. If
you would like to know how to make your own archetypes please refer to our Guide to creating
archetypes.


33 Creating Archetypes 201

33 Creating Archetypes
.......................................................................................................................................

33.1 Guide to Creating Archetypes
Creating an archetype is a pretty straight forward process. An archetype is a very simple plugin, that
contains the project prototype you wish to create. An archetype is made up of:
• an archetype descriptor ( archetype.xml in directory: src/main/resources/META-INF/).
It lists all the files that will be contained in the archetype and categorizes them so they can be
processed correctly by the archetype generation mechanism.
• the prototype files that are copied by the archetype (directory: src/main/resources/
archetype-resources/)
• the prototype pom ( pom.xml in: src/main/resources/archetype-resources)
• a pom for the archetype ( pom.xml in the archetype's root directory).
To create an archetype follow these steps:

33.1.1 1. Create a new project and pom.xml for the archetype plugin
An example pom.xml for an archetype plugin looks as follows:

<project>
<groupId>my.groupId</groupId>
<artifactId>my-archetype-id</artifactId>
</project>

All you need to specify is a groupId, artifactId and version. These three parameters will be
needed later for invoking the archetype via archetype:create from the commandline.

33.1.2 2. Create the archetype descriptor
The archetype descriptor is a file called archetype.xml which must be located in the src/main/
resources/META-INF/ directory. An example of an archetype descriptor can be found in the
quickstart archetype:

<archetype>
<id>quickstart</id>
<sources>
<source>src/main/java/App.java</source>
</sources>
<testSources>
<source>src/test/java/AppTest.java</source>
</testSources>
</archetype>

The <id> tag should be the same as the artifactId in the archetype pom.xml.
An optional <allowPartial>true</allowPartial> tag makes it possible to run the
archetype:create even on existing projects.
The <sources>, <resources>, <testSources>, <testResources> and <siteResources>
tags represent the different sections of the project:



• <sources> = src/main/java
• <resources> = src/main/resources
• <testSources> = src/test/java
• <testResources> = src/test/resources
• <siteResources> = src/site
<sources> and <testSources> can contain <source> elements that specify a source file.
<testResources> and <siteResources> can contain <resource> elements that specify a
resource file.
Place other resources such as the ones in the src/main/webapp directory inside the <resources>
tag.
At this point one can only specify individual files to be created but not empty directories.
Thus the quickstart archetype shown above defines the following directory structure:

archetype
|-- pom.xml
`-- src
`-- main
`-- resources
|-- META-INF
| `-- maven
| `--archetype.xml
`-- archetype-resources
|-- pom.xml
`-- src
|-- main
| `-- java
| `-- App.java
`-- test
`-- java
`-- AppTest.java

33.1.3 3. Create the prototype files and the prototype pom.xml
The next component of the archetype to be created is the prototype pom.xml. Any pom.xml will do,
just don't forget to the set artifactId and groupId as variables ( ${artifactId} / ${groupId}
). Both variables will be initialized from the commandline when calling archetype:create.
An example for a prototype pom.xml is:



<project>
<groupId>${groupId}</groupId>
<artifactId>${artifactId}</artifactId>
<version>${version}</version>
<name>A custom project</name>
<url>http://www.myorganization.org</url>
<dependencies>
<dependency>
<scope>test</scope>
</dependency>
</dependencies>
</project>

33.1.4 4. Install and run the archetype
Now you are ready to install the archetype:

mvn install

Now that you have created an archetype you can try it on your local system by using the following
command. In this command, you need to specify the full information about the archetype you want to
use (its groupId, its artifactId, its version) and the information about the new project you want
to create ( artifactId and groupId). Don't forget to include the version of your archetype (if you
don't include the version, you archetype creation may fail with a message that version:RELEASE was
not found)

-DarchetypeGroupId=<archetype-groupId>
-DarchetypeArtifactId=<archetype-artifactId>
-DarchetypeVersion=<archetype-version>
-DgroupId=<my.groupid>
-DartifactId=<my-artifactId>

Once you are happy with the state of your archetype you can deploy (or submit it to ibiblio) it as any
other artifact and the archetype will then be available to any user of Maven.

33.1.5 Alternative way to start creating your Archetype
Instead of manually creating the directory structure needed for an archetype, simply use

-DgroupId=[your project's group id]
-DartifactId=[your project's artifact id]
-DarchetypeArtifactId=maven-archetype-archetype

Afterwhich, you can now customize the contents of the archetype-resources directory, and
archetype.xml, then, proceed to Step#4 (Install and run the archetype plugin).


34 From Maven 1.x to Maven 2.x 204

34 From Maven 1.x to Maven 2.x
.......................................................................................................................................

34.1 Guide to Moving from Maven 1.x to Maven 2.x
This document is intended to be continously updated from the mail list archives. For an only
slightly out-of-date reference with concrete examples, check out Vincent Massol's JavaZone2005
presentation.

34.1.1 Parallel Builds
It is possible to establish parallel Maven builds, one using the old M1 settings, and a second using
M2. The Maven 2 configuration file names and uses have been modified, so the two builds should not
conflict.
A Maven 1.x build is configured with the following files:

• [project.xml] Project Object Model (POM) definition
• [maven.xml] Custom build scripts
• [project.properties] general build settings
• [build.properties] local build settings
A Maven 2 build is configured with a different file set:
• [pom.xml] POM definition
• [settings.xml] local configuration

34.1.2 Migrating the POM
The Project Object Model (POM) has moved from the project.xml file to pom.xml. The XML
schema has also changed, from Version 3 to Version 4.
The new POM is nominally a superset of the old, so the first step in creating a pom.xml is to copy
over project.xml. Then start tweaking. There are several new elements that can be added to a
POM, but all are optional so should not cause a problem with an initial build.
If you want some help converting your project.xml into a pom.xml you can use the maven-one-
plugin. If you run the following command, it will convert your project.xml into a pom.xml:

mvn one:convert

project.xml:



<project>
<pomVersion>3</pomVersion>
<id>util</id>
<name>Generic utility code</name>
<groupId>project</groupId>
<currentVersion>1.1</currentVersion>
<package>org.apache.project.util</package>
<dependencies>
...
</dependencies>
<build>
...
</build>
...
</project>

pom.xml:

<project>
<artifactId>util</artifactId>
<name>Generic Utility Code</name>
<groupId>org.apache.project.util</groupId>
<dependencies>
...
</dependencies>
<build>
...
</build>
...
</project>

For more details, check out the POM Guide.

34.1.3 build.properties and project.properties
These files have been replaced with settings.xml. Like with the POM, you can establish a parallel
build environment, so the m1 build never breaks while the m2 build is being debugged.
Additional local build customization options can also be created using profiles.

34.1.4 What to do with maven.xml?
See How do I write custom scripts without a maven.xml file? for an explanation of why maven.xml
was discarded, and Introduction to Maven 2.0 Plugin Development for a guide to writing your own
plug-ins.

34.1.5 Directory Structure
The POM allows customization of the directory structure in both Maven 1 and Maven 2 using the
<build> tag. For simplicity, it would be ideal to move source to the Maven 2 default structure, but



it is not required. You can begin by customizing the directories in Maven 2, then when satisfied that
both build paths are working, move to the Maven 2 structure and customize the settings in Maven 1.

34.1.6 Migrating Plug-ins
The main conceptual change in plugins and their use has to do with the concept of a build cycle in
Maven 2. Instead of using preGoal and postGoal tags in maven.xml to tie plugin goals into the
build process, the goals of a plugin are associated with the pre-defined stages of the build cycle. See
the Introduction to the Build Lifecycle for more on how plugins relate.

34.1.6.1 Re-use Ant Tasks
See the Ant Script FAQ.

34.1.6.2 Replace scripts with Mojos
The new plugin architecture does not specify a specific language implementation, so Jelly scripts and
other such artifacts should be re-usable with wrappers. It is recommended that you look into moving
to Mojos.

34.1.6.3 Utilize built-in Maven 2 capabilities

34.Resource filtering to inject POM variables into application
You can turn on resource filtering in your POM. Tokens of the form ${pom.variable} in resource
files will be replaced with the corresponding POM property.

<project>
...
<build>
<resources>
<resource>
</resource>
</resources>
</build>
</project>

34.Multiproject Builds
The old reactor+multiproject plugin combination was established more as an afterthought of the core
development. In Maven 2, multiproject support is included in the core, so any scripts required in the
past to work around problems with the multiproject plugin should be unnecessary.

34.1.7 Migrating repositories
Every four hours the Maven 1.x repository is converted over to a Maven 2.x repository and we plan to
release a plug-in based on our conversion tool but currently.

34.1.8 Related links

• Maven 2 One Plugin
• XSLT from MNG-2337
• using preGoal and postGoal in m2? Thread.


35 Using Maven 1.x repositories with Maven 2.x 207

35 Using Maven 1.x repositories with Maven 2.x
.......................................................................................................................................

35.1 Guide to using Maven 1.x repositories with Maven 2.x
When you are migrating from Maven 1.x to Maven 2.x you will first be trying to convert your build
and to make this easier we have provided a way for you to use your existing Maven 1.x repository so
that you don't have to convert your repository before trying to migrate your projects. To use a Maven
1.x repository with your Maven 2.x project you need to specify this in your POM as follows:

<project>
...
<repositories>
<repository>
<snapshots>
</snapshots>
<id>my-m1-repository</id>
<name>Maven 1.x Repository</name>
<url>http://repostory.mycompany.com/maven1</url>
<layout>legacy</layout>
</repository>
</repositories>
...
</project>

Enabling the snapshots is important as Maven 2.x makes a distinction between repositories that
contain snapshots and those that don't. In Maven 1.x there is no distinction, so setting snapshots to
true will give you the Maven 1.x style repository behaviour while using Maven 2.x.


36 Relocation of Artifacts 208

36 Relocation of Artifacts
.......................................................................................................................................

36.1 Guide to relocation
Sometimes it is necessary to relocate artifacts in the repository. One example of that is when a project
moves from Maven 1 to Maven 2. Maven 1 projects have traditionally used a flat repository structure,
while Maven 2 uses a deep repository structure. As an example the Maven 1 project has a groupId of
maven while the Maven 2 project has a groupId of org.apache.maven.
Making changes to the repository can have far reaching consequences. So it is best to get it right the
first time, hence this guide. It will go through a couple of different kinds of relocations:

• Maven 1 to Maven 1
The goal of the examples below is to relocate the groupId from bar to org.bar for the foo project.

36.1.1 How to relocate a Maven 1 artifact to a different groupId

1 Copy all foo-related files from /bar/ in your Maven 1 repository to a temporary location.
2 Change the groupId to org.bar in all the foo-related pom files in the temporary location.
3 If your project uses MD5 or SHA1 checksums you must now create new checksums for the
changed pom files in the temporary location. If the pom file needs to be signed, do that as well.
4 Copy all files from the temporary location to /org.bar/ in your Maven 1 repository.
5 If your project syncs with ibiblio, you should now initiate that sync. This might happen
automatically depending on your projects sync policy.
Your foo-artifacts are now available to Maven 1 users with both the old and the new groupId.

36.1.1.1 Releasing the next version
When the next release of foo is made, you publish the Maven 1 pom as you have always done.
Unfortunately Maven 1 does not have a concept of automatic relocation and notification, so you will
have to inform your users of the changed groupId through your regular information channels.

36.1.2 How to relocate a Maven 2 artifact to a different groupId

1 Copy all foo-related files from /bar/foo/ in your Maven 2 repository to a temporary location.
2 Change the groupId to org.bar in all foo-related pom files in the temporary location.
3 Copy all files from the temporary location to /org/bar/foo/ in your Maven 2 repository.
4 Create a minimal Maven 2 pom file for every old release of foo in your Maven 2 repository. The
pom files only need to include groupId, artifactId, version and the relocation section.
Note: Before you replace your old pom files in /bar/foo/ with these minimal pom files, make
sure you have made backups!
The minimal pom file might look like this for version 1.0 of foo:


36 Relocation of Artifacts 209

<project>
<groupId>bar</groupId>
<artifactId>foo</artifactId>
<relocation>
<groupId>org.bar</groupId>
</relocation>
</project>

In this case we are relocating because the groupId has changed. We only need to add the element
that has changed to the relocation element. For information on which elements are allowed in
the relocation element, see the pom reference.
5 If your project uses MD5 or SHA1 checksums you must now create new checksums for the pom
files in /bar/foo/ in your Maven 2 repository. If the pom file needs to be signed, do that as
well.
6 If your project syncs with ibiblio, you should now initiate that sync. This might happen
automatically depending on your projects sync policy.
Your foo-artifacts are now available to Maven 2 users with both the old and the new groupId.
Projects using the old groupId will automatically be redirected to the new groupId and a warning
telling the user to update their dependencies will be issued.

When the next release of foo is made, you should publish two Maven 2 pom files. First you should
publish a pom with the new groupId org.bar.
Because data in the repository is not supposed to change, Maven 2 doesn't download pom files that it
has already downloaded. Therefor you will also need to publish a pom file with the old groupId bar
for the new version. This should be a minimal relocation pom (as described in step 4 above), but for
the new version of foo.
For the release after that, you only need to publish a Maven 2 pom with a groupId of org.bar, since
users of the previous version have been informed of the changed groupId.

36.1.3 How to relocate a Maven 1 artifact to a Maven 2 artifact with a different groupId
This is only of interest to organizations (like the Apache Software Foundation) that automatically
converts the contents of their Maven 1 repository to their Maven 2 repository.
Follow steps 4 to 6 in the section How to relocate a Maven 2 artifact to a different groupId above.

When the next release of foo is made, you should publish the Maven 1 pom as you have always done.
In addition to that, you should publish a Maven 2 pom with a groupId of bar, a version of <next-
version> and include a relocation section. This step can be done once for the first release of a project,
after the groupId has been changed, but your users will be happier if you do it more times.


37 Installing 3rd party JARs to Local Repository 210

37 Installing 3rd party JARs to Local Repository
.......................................................................................................................................

37.1 Guide to installing 3rd party JARs
Often times you will have 3rd party JARs that you need to put in your local repository for use in
your builds. The JARs must be placed in the local repository in the correct place in order for it to be
correctly picked up by Maven. To make this easier, and less error prone, we have provide a goal in the
install plug-in which should make this relatively painless. To install a JAR in the local repository use
the following command:

mvn install:install-file -Dfile=<path-to-file> -DgroupId=<group-id>
-DartifactId=<artifact-id> -Dversion=<version> -Dpackaging=<packaging>


38 Deploying 3rd party JARs to Remote Repository 211

38 Deploying 3rd party JARs to Remote Repository
.......................................................................................................................................

38.1 Guide to deploying 3rd party JARs to remote repository
Same concept of the install:install-file goal of the maven-install-plugin where the 3rd party JAR is
installed in the local repository. But this time instead to local repository the JAR will be install both in
the local and remote repository.
To deploy a 3rd party JAR use the deploy:deploy-file goal under maven-deploy-plugin.
First, the wagon-provider(wagon-ftp, wagon-file, etc..) must be placed to your %M2_HOME%/lib.
Then execute the command:

mvn deploy:deploy-file -DgroupId=<group-id>
-DartifactId=<artifact-id>
-Dversion=<version>
-Dpackaging=<type-of-packaging>
-DrepositoryId=<id-to-map-on-server-section-of-settings.xml>
-Durl=<url-of-the-repositor-to-deploy>

38.1.1 Deploying a 3rd party JAR with a generic POM
By default, deploy:deploy-file generates a generic POM(.pom) to be deploy together with the 3rd
party JAR. To disable this feature we should set the generatePOM argument to false.

-DgeneratePom=false

38.1.2 Deploying a 3rd party JAR with a customed POM
If a POM is already existing for the 3rd Party JAR and you want to deploy it together with the JAR
we should use the pomFile argument of the deploy-file goal. See sample below.

mvn deploy:deploy-file -DpomFile=<path-to-pom>
-DrepositoryId=<id-to-map-on-server-section-of-settings.xml>
-Durl=<url-of-the-repositor-to-deploy>

Note that groupId, artifactId, version and packaging arguments are not included here
because deploy-file goal will get these information from the given POM.

38.1.3 Deploying Source Jars
To deploy a 3rd party source jar, packaging should be set to java-source, and generatePom should
be set to false.


39 Coping with Sun JARs 212

39 Coping with Sun JARs
.......................................................................................................................................

39.1 Coping with Sun JARs
Often users are confronted with the need to build against JARs provide by Sun like the JavaMail
JAR, or the Activation JAR and users have found these JARs not present in central repository
resulting in a broken build. Unfortunately most of these artifacts fall under Sun's Binary License
which disallows us from distributing them from Ibiblio.
Another problem is that Sun's appears not to have any sort of convention for naming their own JARs
so we have taken steps in suggesting some common names for Sun's artifacts. You can find a list of
our suggestions here:

Product artifact Group ID Artifact ID
Java Activation Framework javax.activation activation
J2EE javax.j2ee j2ee
Java Data Object (JDO) javax.jdo jdo
Java Message Service (JMS) javax.jms jms
JavaMail javax.mail mail
Java Persistence API (JPA) / EJB javax.persistence persistence-api
3
J2EE Connector Architecture javax.resource connector
J2EE Connector Architecture API javax.resource connector-api
Java Authentication and javax.security jaas
Authorization Service (JAAS)
Java Authorization Contract for javax.security jacc
Containers
Servlet API javax.servlet servlet-api
Servlet JavaServer Pages (JSP) javax.servlet jsp-api
Servlet JavaServer Pages javax.servlet jstl
Standard Tag Library (JSTL)
JDBC 2.0 Optional Package javax.sql jdbc-stdext
Java Transaction API (JTA) javax.transaction jta
Java XML RPC javax.xml jaxrpc
Portlet javax.portlet portlet-api
Java Naming and Directory javax.naming jndi
Interface (JNDI)

If you use our suggestions as noted above when adding a Sun dependency to your POM, Maven 2.x
can help you locate the JARs by providing the site where they can be retrieved. It is important that
you follow the suggested naming conventions as we cannot store the JARs at the central repository.
We can only store metadata about those JARs and it is the metadata that contains location and
retrieval information.


39 Coping with Sun JARs 213

Once you have downloaded a particular Sun JAR to your system you can install the JAR in your
local repository. Please refer to our Guide to installing 3rd party JARs for instructions on how to
accomplish this.
Note: Java.net provides a Maven 2 repository. You could specify it directly in your POM or in your
settings.xml between the tags <repositories>:
...
<repositories>
<repository>
<id>maven2-repository.dev.java.net</id>
<name>Java.net Repository for Maven</name>
<url>http://download.java.net/maven/2/</url>
</repository>
</repositories>
...


40 Remote repository access through authenticated HTTPS 214

40 Remote repository access through authenticated
HTTPS
.......................................................................................................................................

40.1 Guide to Remote repository access through authenticated HTTPS
This document describes how to configure Maven for accessing a remote repository that sits behind
an HTTPS server which requires client authentication with certificates. It is expected that this
documentation be valid both for Maven 1.x and Maven 2.0.

40.1.1 The problem
You have a server storing a maven repository at addresse https://my.server.com/maven. This
server only serves clients authenticated through SSL protocol by a valid certificate signed by an
approved certificate authority's certificate which we call the CACert. In the simplest case where the
server is used internally by an identified community of users (eg. corporate intranet), the server's
certificate is the certificate authority as the server is used only internally.
So we assume that we have access to the trusted certificate in X.509 format stored in a file named:
/somewhere/in/filesystem/CACert.cert
The client's certificate has been issued by some other mean not described in this document in
PKCS#12 format, which is the format that is accepted by browsers (at least Firefox and Internet
Explorer) for importation in their keystore. This file is named:
/home/directory/mycertificate.p12
and we assume it is accessible when launching maven. Note that this file contains the client's private
key which may be very sensitive information and so is secured by a password:
CeRtPwD
The remote repository is referenced either through the pom.xml file (maven2.0) or one of
build.properties or project.properties (Maven1.X). In Maven 1.X:
maven.repo.remote=https://my.server.com/maven,http://www.ibiblio.org/maven

40.1.2 The solution
For maven to use this repository, we should take the following steps:
1 Create a store to hold the server's certificate usings Sun's keytool,
2 Defines properties to be used by HttpClient for finding keys and certificate

40.1.2.1 Storing certificate
The following command line imports the certififcate authority's certificate into a JKS formatted key
store named trust.jks, the trust store.
$> keytool -v -alias mavensrv -import
-file /somewhere/in/filesystem/CACert.cert
-keystore trust.jks
Enter keystore password:
Owner: ....
Issuer: ....
Serial number: ....
Valid from: Mon Feb 21 22:34:25 CET 2005 until: Thu Feb 19 22:34:25 CET 2015
Certificate fingerprints:
MD5: .......


40 Remote repository access through authenticated HTTPS 215

SHA1: .....
Trust this certificate? [no]: yes
Certificate was added to keystore
[Storing trust.jks]
$>
Note that it should be possible to import a full chain of certificates with only one root certificate being
trusted but the author did not test it.

40.1.2.2 Setting properties
The following properties must be set at start of maven to be accessible when HttpClient starts up.
javax.net.ssl.trustStore
the path to the keystore where trusted certificates are stored
javax.net.ssl.trustStoreType
the type of storage for this store, maybe either jks (default) or pkcs12
javax.net.ssl.trustStorePassword
the password protecting the store
javax.net.ssl.keyStore
the path to the keystore where user's private key is stored
javax.net.ssl.keyStoreType
the type of storage for this store, maybe either jks (default) or pkcs12
javax.net.ssl.keyStorePassword
the password protecting the store
Not all the properties must be set depending of your precise settings: type of store may left to default,
password may be empty.
40.Maven 2.0
They may be set either on maven's command-line, in .mavenrc file or in MAVEN_OPTS environment
variable. For the setting defined in this document, here is an example .mavenrc file:
MAVEN_OPTS="-Xmx512m -Djavax.net.ssl.trustStore=trust.jks
-Djavax.net.ssl.trustStorePassword=
-Djavax.net.ssl.keyStore=/home/directory/
mycertificate.p12
-Djavax.net.ssl.keyStoreType=pkcs12
-Djavax.net.ssl.keyStorePassword=XXXXXX"

40.For maven 1.X users
Setting these properties in build.properties or project.properties does not work: the
properties are needed before any of theses files are opened.

40.1.3 Links
The following links may be useful in understanding SSL infrastructure management in Java:

• Javasecurity infrastructure (1.4.2)
• HttpClient's SSL guide


41 Creating Assemblies 216

41 Creating Assemblies
.......................................................................................................................................

41.1 Guide to creating assemblies
The assembly mechanism in Maven 2.x provides an easy way to create distributions using a assembly
descriptor and dependency information found in you POM. In order to use the assembly plug-in you
need to configure the assembly plug-in in your POM and it might look like the following:

<project>
<parent>
<artifactId>maven</artifactId>
<version>2.0-beta-3-SNAPSHOT</version>
</parent>
<name>Maven Embedder</name>
<version>2.0-beta-3-SNAPSHOT</version>
<build>
<plugins>
<plugin>
<configuration>
<descriptor>src/main/assembly/dep.xml</descriptor>
</configuration>
</plugin>
</plugins>
</build>
...
</project>

You'll notice that the assembly descriptor is located in ${basedir}/src/main/assembly which is
the standard location for assembly descriptors.

41.1.1 Creating a binary assembly
This is the most typical usage of the assembly plugin where you are creating a distribution for
standard use.



<assembly>
<id>bin</id>
<formats>
<format>tar.gz</format>
<format>tar.bz2</format>
<format>zip</format>
</formats>
<fileSets>
<fileSet>
<includes>
<include>README*</include>
<include>LICENSE*</include>
<include>NOTICE*</include>
</includes>
</fileSet>
<fileSet>
<directory>target</directory>
<outputDirectory></outputDirectory>
<includes>
<include>*.jar</include>
</includes>
</fileSet>
</fileSets>
</assembly>


<assembly>

<id>dep</id>
<formats>
<format>jar</format>
</formats>
<includeBaseDirectory>false</includeBaseDirectory>
<fileSets>
<fileSet>
<outputDirectory>/</outputDirectory>
</fileSet>
</fileSets>
<dependencySets>
<dependencySet>
<outputDirectory>/</outputDirectory>
<unpack>true</unpack>
<excludes>
<exclude>junit:junit</exclude>
<exclude>commons-lang:commons-lang</exclude>
<exclude>commons-logging:commons-logging</exclude>
<exclude>commons-cli:commons-cli</exclude>
<exclude>jsch:jsch</exclude>
<exclude>org.apache.maven.wagon:wagon-ssh</exclude>

<exclude>plexus:plexus-container-default</exclude>
</excludes>
</dependencySet>
</dependencySets>
</assembly>

<assembly>
<id>src</id>
<formats>
<format>tar.gz</format>
<format>tar.bz2</format>
<format>zip</format>
</formats>
<fileSets>
<fileSet>
<includes>
<include>README*</include>
<include>LICENSE*</include>
<include>NOTICE*</include>
<include>pom.xml</include>
</includes>
</fileSet>
<fileSet>
<directory>src</directory>
</fileSet>
</fileSets>
</assembly>


mvn assembly:assembly


42 Configuring Archive Plugins 220

42 Configuring Archive Plugins
.......................................................................................................................................

42.1 Guide to Configuring Archive Plugins
Many Java archive generating plugins accept the archive configuration element to customise the
generation of the archive. In the standard Maven Plugins, this includes the jar, war, ejb, ear and
assembly plugins.

42.1.1 Disabling Maven Meta Information
By default, Maven generated archives include the META-INF/maven directory, which contains
the pom.xml file used to build the archive, and a pom.properties file that includes some basic
properties in a small, easier to read format.
To disable the generation of these files, include the following configuration for your plugin (in this
example, the WAR plugin is used):

<project>
...
<build>
<plugins>
<plugin>
<artifactId>maven-war-plugin</artifactId>
<configuration>
<archive>
<addMavenDescriptor>false</addMavenDescriptor>
</archive>
</configuration>
</plugin>
</plugins>
</build>
...
</project>

42.1.2 Configuring the Manifest
The archive configuration also accepts manifest configuration. See Guide to Working with Manifests
for more information.


43 Configuring Maven 221

43 Configuring Maven
.......................................................................................................................................

43.1 Configuring Maven
Maven configuration occurs at 3 levels:

• Project - most static configuration occurs in pom.xml
• Installation - this is configuration added once for a Maven installation
• User - this is configuration specific to a particular user
The separation is quite clear - the project defines information that applies to the project, no matter
who is building it, while the others both define settings for the current environment.
Note: the installation and user configuration cannot be used to add shared project information - for
example, setting <organization> or <distributionManagement> company-wide.
For this, you should have your projects inherit from a company-wide parent pom.xml.
You can specify your user configuration in ${user.home}/.m2/settings.xml. A full
reference to the configuration file is available. This section will show how to make some common
configurations. Note that the file is not required - defaults will be used if it is not found.

43.1.1 Configuring your Local Repository
The location of your local repository can be changed in your user configuration. The default value is
${user.home}/.m2/repository/.
<settings>
...
<localRepository>/path/to/local/repo/</localRepository>
...
</settings>
Note: The local repository must be an absolute path.

43.1.2 Configuring a Proxy
Proxy configuration can also be specified in the settings file.
For more information, see the Guide to using a Proxy.

43.1.3 Configuring Parallel Artifact Resolution
By default, Maven 2.1.0+ will download up to 5 artifacts (from different groups) at once. To change
the size of the thread pool, start Maven using -Dmaven.artifact.threads. For example, to only
download single artifacts at a time:
mvn -Dmaven.artifact.threads=1 clean install
You may wish to set this option permanently, in which case you can use the MAVEN_OPTS
environment variable. For example:
export MAVEN_OPTS=-Dmaven.artifact.threads=3

43.1.4 Security and Deployment Settings
Repositories to deploy to are defined in a project in the <distributionManagement> section.
However, you cannot put your username, password, or other security settings in that project. For that


reason, you should add a server definition to your own settings with an id that matches that of the
deployment repository in the project.
In addition, some repositories may require authorization to download from, so the corresponding
settings can be specified in a server element in the same way.
Which settings are required will depend on the type of repository you are deploying to. As of the first
release, only SCP deployments and file deployments are supported by default, so only the following
SCP configuration is needed:
<settings>
...
<servers>
<server>
<id>repo1</id>
<username>repouser</username>

</server>
...
</servers>
...
</settings>
To encrypt passwords in these sections, refer to Encryption Settings.

43.1.5 Using Mirrors for Repositories
Repositories can be declared inside a project, which means that if you have your own custom
repositories, those sharing your project easily get the right settings out of the box. However, you may
want to use an alternative mirror for a particular repository without changing the project files.
Some reasons to use a mirror are:
• There is a synchronized mirror on the internet that is geographically closer and faster
• You want to replace a particular repository with your own internal repository which you have
greater control over
• You want to run maven-proxy to provide a local cache to a mirror and need to use its URL
instead
To configure a mirror of a given repository, you provide it in your settings file, giving the new
repository its own id and url, and specify the mirrorOf setting that is the ID of the repository
you are using a mirror of. For example, the id of the main Maven repository included by default is
central, so to use an Australian mirror, you would configure the following:
<settings>
...
<mirrors>
<mirror>
<id>planetmirror</id>
<name>Australian Mirror of http://repo1.maven.org/maven2/</name>
<url>http://public.planetmirror.com/maven2/</url>
</mirror>


...
</mirrors>
...
</settings>
More info about mirrors is available in the Guide to Mirror Settings.

43.1.6 Profiles
Repository configuration can also be put into a profile. You can have multiple profiles, with one set to
active so that you can easily switch environments. Read more about profiles in Introduction to Build
Profiles.


44 Mirror Settings 224

44 Mirror Settings
.......................................................................................................................................

44.1 Using Mirrors for Repositories
Repositories are declared inside a project, which means that if you have your own custom
repositories, those sharing your project easily get the right settings out of the box. However, you may
want to use an alternative mirror for a particular repository without changing the project files.
Some reasons to use a mirror are:
• There is a synchronized mirror on the internet that is geographically closer and faster
• You want to replace a particular repository with your own internal repository which you have
greater control over
• You want to run maven-proxy to provide a local cache to a mirror and need to use its URL
instead
To configure a mirror of a given repository, you provide it in your settings file (
${user.home}/.m2/settings.xml), giving the new repository its own id and url, and specify
the mirrorOf setting that is the ID of the repository you are using a mirror of. For example, the ID of
the main Maven repository included by default is central, so to use the mirror at ibiblio, you would
configure the following:

<settings>
...
<mirrors>
<mirror>
<id>ibiblio.org</id>
<name>ibiblio Mirror of http://repo1.maven.org/maven2/</name>
<url>http://mirrors.ibiblio.org/pub/mirrors/maven2</url>
</mirror>
</mirrors>
...
</settings>

Note that there can be at most one mirror for a given repository. In other words, you cannot map a
single repository to a group of mirrors that all define the same <mirrorOf> value. Maven will not
aggregate the mirrors but simply picks the first match. If you want to provide a combined view of
several repositories, use a repository manager instead.
The settings descriptor documentation can be found on the Maven Local Settings Model Website.
Note: The official Maven 2 repository is at http://repo1.maven.org/maven2. A list of known
mirrors is available in our wiki article Mirrors Repository. These mirrors may not have the same
contents and we don't support them in any way, although we try to keep info in this page accurate.

44.2 Using A Single Repository
You can force Maven to use a single repository by having it mirror all repository requests. The
repository must contain all of the desired artifacts, or be able to proxy the requests to other
repositories. This setting is most useful when using an internal company repository with the Maven
Repository Manager to proxy external requests.
To achieve this, set mirrorOf to *.
Note: This feature is only available in Maven 2.0.5+.



<settings>
...
<mirrors>
<mirror>
<id>internal-repository</id>
<name>Maven Repository Manager running on repo.mycompany.com</name>
<url>http://repo.mycompany.com/proxy</url>
<mirrorOf>*</mirrorOf>
</mirror>
</mirrors>
...
</settings>

44.3 Advanced Mirror Specification
A single mirror can handle multiple repositories when used in conjunction with a repository manager.
The syntax as of Maven 2.0.9:

• * matches all repo ids.
• external:* matches all repositories except those using localhost or file based repositories.
This is used in conjunction with a repository manager when you want to exclude redirecting
repositories that are defined for Integration Testing.
• multiple repositories may be specified using a comma as the delimiter
• an exclamation mark may be used in conjunction with one of the above wildcards to exclude a
repository id
The position of wildcards within a comma separated list of repository identifiers is not important
as the wildcards defer to further processing and explicit includes or excludes stop the processing,
overruling any wildcard match.
When you use the advanced syntax and configure multiple mirrors, keep in mind that their declaration
order matters. When Maven looks for a mirror of some repository, it first checks for a mirror whose
<mirrorOf> exactly matches the repository identifier. If no direct match is found, Maven picks the
first mirror declaration that matches according to the rules above (if any). Hence, you may influence
match order by changing the order of the definitions in the settings.xml
Examples:

• * = everything
• external:* = everything not on the localhost and not file based.
• repo,repo1 = repo or repo1
• *,!repo1 = everything except repo1
Note: This feature is only available in Maven 2.0.9+.



<settings>
...
<mirrors>
<mirror>
<id>internal-repository</id>
<name>Maven Repository Manager running on repo.mycompany.com</name>
<url>http://repo.mycompany.com/proxy</url>
<mirrorOf>external:*,!foo</mirrorOf>
</mirror>
<mirror>
<id>foo-repository</id>
<name>Foo</name>
<url>http://repo.mycompany.com/foo</url>
<mirrorOf>foo</mirrorOf>
</mirror>
</mirrors>
...
</settings>

44.4 FTP Access
The repository is available through FTP at ftp://mirrors.ibiblio.org/pub/mirrors/
maven2

44.5 Creating Your Own Mirror
The central repository requires several dozens GB and growing. Apparently, to save us bandwidth and
you time, mirroring the entire central repository is not recommended. Instead, we suggest to setup a
repository manager as a proxy.
If you really want to become an official mirror, email us to dev@maven.apache.org with your
location and we'll add you to the list of mirrors.


45 Deployment and Security Settings 227

45 Deployment and Security Settings
.......................................................................................................................................

45.1 Security and Deployment Settings
Repositories to deploy to are defined in a project in the distributionManagement section.
However, you cannot put your username, password, or other security settings in that project. For that
reason, you should add a server definition to your own settings with an id that matches that of the
deployment repository in the project.
In addition, some repositories may require authorisation to download from, so the corresponding
settings can be specified in a server element in the same way.
Which settings are required will depend on the type of repository you are deploying to. As of the first
release, only SCP deployments and file deployments are supported by default, so only the following
SCP configuration is needed:

<settings>
.
.
<servers>
<server>
<id>repo1</id>
<username>repouser</username>

</server>
</servers>
.
.
</settings>

To encrypt passwords in these sections, refer to Encryption Settings.
Note: The settings descriptor documentation can be found on the Maven Local Settings Model
Website.

46 Embedding Maven 2.x 228

46 Embedding Maven 2.x
.......................................................................................................................................

46.1 The Maven Embedder
The Maven Embedder is used by the Maven CLI, by IDE integration projects like Mevenide
and potentially any tool that needs to embed Maven's capabilities. You could embed Maven in a
Continuous Integration application to run Maven build, an application lifecycle management (ALF)
tool, or Ant tasks that utilize Maven's functionality. These are just a few examples of what the Maven
Embedder can be used for.



46.2 A Simple Example
File projectDirectory = new File( getBasedir(), "src/examples/simple-project
File user = new File( projectDirectory, "settings.xml" );
Configuration configuration = new DefaultConfiguration()
.setUserSettingsFile( user )
.setClassLoader( Thread.currentThread().getContextClassLoader() );
ConfigurationValidationResult validationResult = MavenEmbedder.validateConfi
if ( validationResult.isValid() )
{
MavenEmbedder embedder = new MavenEmbedder( configuration );
MavenExecutionRequest request = new DefaultMavenExecutionRequest()
.setBaseDirectory( projectDirectory )
.setGoals( Arrays.asList( new String[]{"clean", "install"} ) );
MavenExecutionResult result = embedder.execute( request );
if ( result.hasExceptions() )
{
fail( ((Exception)result.getExceptions().get( 0 )).getMessage() );
}
// ---------------------------------------------------------------------
// You may want to inspect the project after the execution.
// ---------------------------------------------------------------------
MavenProject project = result.getProject();
// Do something with the project
String groupId = project.getGroupId();
String artifactId = project.getArtifactId();
String version = project.getVersion();
String name = project.getName();
String environment = project.getProperties().getProperty( "environment"
assertEquals( "development", environment );
System.out.println( "You are working in the '" + environment + "' enviro
}
else
{
if ( ! validationResult.isUserSettingsFilePresent() )
{
System.out.println( "The specific user settings file '" + user + "'
}
else if ( ! validationResult.isUserSettingsFileParses() )
{
System.out.println( "Please check your settings file, it is not well
}
}

46.3 A Note on Configuring Settings
Currently there is a notion of a user settings, and a global settings where either can specify
information about the following:

• Local Repository
• Proxies
• Mirrors
• Server Configurations



• Plugin Groups
If you are using the embedder it is entirely your responsibility to take user and global settings
information and specify it in the embedder configuration. The embedder carries with it no defaults
about where these are located and how they are used. If you want your embedded use of Maven to
mimic the behavior of the Maven CLI insofar as settings use then use the following code:

.setUserSettingsFile( MavenEmbedder.DEFAULT_USER_SETTINGS_FILE )
.setGlobalSettingsFile( MavenEmbedder.DEFAULT_GLOBAL_SETTINGS_FILE )
{
// If the configuration is valid then do your thang ...
}

Also note that the user and global settings are merged, and the user settings are dominant.

46.4 Accessing the Underlying Plexus Container
Though it is not recommended for general use, it is possible to get at the underlying Plexus Container
instance if you wish to lookup custom components. The Maven Embedder was specifically designed
to be used for Maven and not a general purpose use of Plexus. So if you use this method then you use
it at your peril. You can access the Plexus Container using the following:

.setUserSettingsFile( MavenEmbedder.DEFAULT_USER_SETTINGS_FILE )
.setGlobalSettingsFile( MavenEmbedder.DEFAULT_GLOBAL_SETTINGS_FILE )
{
// If the configuration is valid then do your thang ...
}
MavenEmbedder embedder = new MavenEmbedder( configuration );
PlexusContainer container = embedder.getPlexusContainer();
// Do what you like with the container ...


47 Generating Sources 231

47 Generating Sources
.......................................................................................................................................

47.1 Guide to generating sources
Let's run though a short example to try and help. To generate sources you must first have a plugin that
participates in the generate-sources phase like the Antlr plugin:

/**
* Generates files based on grammar files with Antlr tool.
*
* @goal generate
* @phase generate-sources
* @requiresDependencyResolution compile
* @author <a href="mailto:vincent.siveton@gmail.com">Vincent Siveton</a>
* @version $Id$
*/
public class AntlrPlugin
extends AbstractAntlrMojo
{
/**
* @see org.apache.maven.plugin.Mojo#execute()
*/
{
executeAntlr();
}

The first two lines say "I want to be fit into the generate-sources phase and my 'handle' is generate".
So this is all fine and dandy, we have a plugin that wants to generate some sources from a Antlr
grammar but how do we use it. You need to specify that you want to use it in your POM:


47 Generating Sources 232

<project>
...
<build>
<plugins>
<plugin>
<artifactId>maven-antlr-plugin</artifactId>
<configuration>
<grammars>java.g</grammars>
</configuration>
<executions>
<execution>
<goals>
<goal>generate</goal>
</goals>
</execution>
</executions>
</plugin>
</plugins>
</build>
...
</project>

If you then type "mvn compile" Maven will walk through the lifecycle and will eventually hit the
generate-sources phase and see you have a plugin configured that wants to participate in that
phase and the Antlr plugin is executed with your given configuration.


48 Working with Manifests 233

48 Working with Manifests
.......................................................................................................................................

48.1 Guide to Working with Manifests
In order to modify the manifest of the resultant JAR produced by the jar plug-in you need to create
a configuration for the jar plug-in. In this first example we'll add some entries to the manifest by
specifying what we'd like in the configuration element of the jar plug-in:

<project>
...
<build>
<plugins>
<plugin>
<configuration>
<archive>
<manifestEntries>
<mode>development</mode>
<url>${pom.url}</url>
</manifestEntries>
</archive>
</configuration>
</plugin>
</plugins>
</build>
...
</project>

As you see above you can use literal values or you can have values from the POM interpolated into
literals or simply use straight POM expressions. So this is what your resultant MANIFEST.MF will
look like inside the generated JAR:

Manifest-Version: 1.0
Archiver-Version: Plexus Archiver
Created-By: Apache Maven
Built-By: jvanzyl
Build-Jdk: 1.4.2_09
Extension-Name: my-app
Specification-Vendor: MyCompany Inc
Implementation-Vendor: MyCompany Inc
Implementation-Title: my-app
Implementation-Version: 1.0-SNAPSHOT
mode: development
url: http://maven.apache.org

If you need to do more then simply add some manifest entries there are more options like activating
indexing of the JAR, setting the main-class, packageName ... Here's an example of what the
configuration element of the JAR plug-in might look like:


48 Working with Manifests 234

<project>
...
<build>
<plugins>
<plugin>
<configuration>
<archive>

<manifest>
<mainClass>com.mycompany.app.App</mainClass>
<packageName>com.mycompany.app</packageName>

</manifest>
<manifestEntries>
<mode>development</mode>
<url>${pom.url}</url>
</manifestEntries>
<manifestFile>src/main/resources/META-INF/MANIFEST.MF</manifestFile>
</archive>
</configuration>
</plugin>
</plugins>
</build>
...
</project>

So this is what your resultant MANIFEST.MF will look like inside the generated JAR:

Manifest-Version: 1.0
Archiver-Version: Plexus Archiver
Created-By: Apache Maven
Built-By: jvanzyl
Package: org.com.foo.app
Build-Jdk: 1.4.2_09
Extension-Name: my-app
Specification-Vendor: MyCompany Inc
Implementation-Vendor: MyCompany Inc
Implementation-Title: my-app
Implementation-Version: 1.0-SNAPSHOT
Main-Class: org.com.foo.App
mode: development
url: http://maven.apache.org

49 Maven Classloading 235

49 Maven Classloading
.......................................................................................................................................

49.1 Guide to Maven Classloading
This is a description of the classloader hierarchy in Maven 2.0.6+.

49.1.1 Overview
• System Classloader
• Core Classloader
• Plugin Classloaders
• Custom Classloaders

49.1.2 1. System Classloader
Maven uses the Classworlds classloading framework with which we create our classloader graph.
If you look in your ${maven.home}/boot directory you will see a single JAR which is the
Classworlds JAR we use to boot the classloader graph. The Classworlds JAR is the only element of
the Java CLASSPATH and Classworlds then builds the other classloaders or realms in Classworlds
terminology.
An Ant script like this will show the contents of the system classloader:
<target name="info">
<echo>java.class.path=${java.class.path}</echo>
</target>

49.1.3 2. Core Classloader
The second classloader down the graph contains the core requirements of Maven. More precisely, the
core classloader has the libraries in ${maven.home}/lib. In general these are just Maven libraries,
e.g. instances of MavenProject belong to this classloader. We hope to further separate these in
the future to just be Maven APIs and have the implementations selected at runtime as required by the
system.
You can add elements to this classloader by extensions. These are loaded into the same place as
${maven.home}/lib and hence are available to the Maven core and all plugins for the current
project and subsequent projects (in future, we plan to remove it from subsequent projects).

49.1.4 3. Plugin Classloaders
After that, each plugin has its own classloader that is a child of Maven's core classloader. The classes
in this classloader are taken from the dependencies in the plugin's dependency list.
Users can add dependencies to this classloader by adding dependencies to a plugin in the
plugins/plugin section of their project pom.xml. Here is a sample of adding ant-nodeps to the
plugin classloader of the Antrun Plugin and hereby enabling the use of additional/optional Ant tasks:
<plugin>
<dependencies>
<dependency>
<groupId>org.apache.ant</groupId>


49 Maven Classloading 236

<artifactId>ant-nodeps</artifactId>
</dependency>
</dependencies>
...
</plugin>
Plugins can inspect their effective runtime class path via the expressions ${plugin.artifacts} or
${plugin.artifactMap} to have a list or map, respectively, of resolved artifacts injected from the
PluginDescriptor.
Please note that the plugin classloader does neither contain the dependencies of the current
project nor its build output. Instead, plugins can query the project's compile, runtime
and test class path from the MavenProject in combination with the mojo annotation
requiresDependencyResolution from the Mojo API Specification. For instance, flagging a
mojo with @requiresDependencyResolution runtime enables it to query the runtime class
path of the current project from which it could create further classloaders.
When a build plugin is executed, the thread's context classloader is set to the plugin classloader.

49.1.5 4. Custom Classloaders
Plugins are free to create further classloaders on their discretion. For example, a plugin might want to
create a classloader that combines the plugin class path and the project class path.
It is important to understand that the plugin classloader cannot load classes from any of those
custom classloaders. Some factory patterns require that. Here you must add the classes to the plugin
classloader as shown before.


50 Using Multiple Modules in a Build 237

50 Using Multiple Modules in a Build
.......................................................................................................................................

50.1 Guide to Working with Multiple Modules
As seen in the introduction to the POM, Maven supports project aggregation in addition to project
inheritance. This section outlines how Maven processes projects with multiple modules, and how you
can work with them more effectively.

50.1.1 The Reactor
The mechanism in Maven that handles multi-module projects is referred to as the reactor. This part of
the Maven core does the following:

• Collects all the available modules to build
• Sorts the projects into the correct build order
• Builds the selected projects in order

50.1.1.1 Reactor Sorting
Because modules within a multi-module build can depend on each other, it is important that The
reactor sorts all the projects in a way that guarantees any project is built before it is required.
The following relationships are honoured when sorting projects:

• a project dependency on another module in the build
• a plugin declaration where the plugin is another modules in the build
• a plugin dependency on another module in the build
• a build extension declaration on another module in the build
• the order declared in the <modules> element (if no other rule applies)
Note that only "instantiated" references are used - dependencyManagement and
pluginManagement elements will not cause a change to the reactor sort order

50.1.1.2 Command Line Options
No special configuration is required to take advantage of the reactor, however it is possible to
customize its behavior.
The following command line switches are available:

• -r - ignore the modules declared in the current project, and instead build the list of projects listed
after the -r switch (which may include wildcards)
• --resume-from - resumes a reactor the specified project (e.g. when it fails in the middle)
• --also-make - build the specified projects, and any of their dependencies in the reactor
• --also-make-dependents - build the specified projects, and any that depend on them
• --fail-fast - the default behavior - whenever a module build fails, stop the overall build
immediately
• --fail-at-end - if a particular module build fails, continue the rest of the reactor and report
all failed modules at the end instead
• --non-recursive - do not use a reactor build, even if the current project declares modules and
just build the project in the current directory
Refer to the Maven command line interface reference for more information on these switches.


50 Using Multiple Modules in a Build 238

50.1.1.3 The Reactor Plugin
For versions of Maven prior to Maven 2.1, or for additional capabilities with the reactor such as
building only the modules with SCM changes, the Reactor plugin can be used to further customize
the execution of the projects. For information on how to use this, refer to the Reactor Plugin
documentation.

50.1.2 More information

• Chapter 6. A Multi-module Project (Maven: The Definitive Guide)


51 Using Multiple Repositories 239

51 Using Multiple Repositories
.......................................................................................................................................

51.1 Setting up Multiple Repositories
There are two different ways that you can specify the use of multiple repositories. The first way is to
specify in a POM which repositories you want to use:

<project>
...
<repositories>
<repository>
<id>my-repo1</id>
<name>your custom repo</name>
<url>http://jarsm2.dyndns.dk</url>
</repository>
<repository>
<id>my-repo2</id>
</repository>
</repositories>
...
</project>

The repositories element is inherited so you would usually specify the repositories to use for a
group of projects by defining a repositories element at the top of your inheritance chain.
NOTE: You will also get the standard set of repositories as defined in the Super POM.
The other way you can specify the use of multiple repositories by creating a profile in your ~/.m2/
settings.xml file like the following:

<settings>
...
<profiles>
...
<profile>
<id>myprofile</id>
<repositories>
<repository>
<id>my-repo2</id>
</repository>
</repositories>
</profile>
...
</profiles>
<activeProfiles>
<activeProfile>myprofile</activeProfile>
</activeProfiles>
...
</settings>


51 Using Multiple Repositories 240

If you specify repositories in profiles you must remember to activate that particular profile! As you
can see above we do this by registering a profile to be active in the activeProfiles element.
You could also activate this profile on the command like by executing the following command:

mvn -Pmyprofile ...

In fact the -P option will take a CSV list of profiles to activate if you wish to activate multiple
profiles simultaneously.
Note: The settings descriptor documentation can be found on the Maven Local Settings Model
Website.


52 Using Proxies 241

52 Using Proxies
.......................................................................................................................................

52.1 Configuring a proxy
You can configure a proxy to use for some or all of your HTTP requests in Maven 2.0. The username
and password are only required if your proxy requires basic authentication (note that later releases
may support storing your passwords in a secured keystore - in the mean time, please ensure your
settings.xml file (usually ${user.home}/.m2/settings.xml) is secured with permissions appropriate for
your operating system).
The nonProxyHosts setting accepts wild cards, and each host not to proxy is separated by the |
character. This matches the JDK configuration equivalent.

<settings>
.
.
<proxies>
<proxy>
<active>true</active>
<protocol>http</protocol>
<host>proxy.somewhere.com</host>
<port>8080</port>
<username>proxyuser</username>
<password>somepassword</password>
<nonProxyHosts>www.google.com|*.somewhere.com</nonProxyHosts>
</proxy>
</proxies>
.
.
</settings>

Please note that urrently NTLM proxies are not supported as they have not been tested. You may be
able to use the relevant system properties on JDK 1.4+ to make this work.

52.1.1 Resources

1 Settings descriptor documentation
2 Configuring Maven


53 Using the Release Plugin 242

53 Using the Release Plugin
.......................................................................................................................................

53.1 Releasing

53.1.1 Introduction
The main aim of the maven-release plugin is to provide a standard mechanism to release project
artifacts outside the immediate development team. The plugin provides basic functionality to create a
release and to update the project's SCM accordingly.
To create a release the maven-release plugin is executed through maven in 2 stages:
1 Preparing the release.
2 Performing the release.

53.1.2 Preparing the release
The plugin will record release information into a new revision of the project's pom.xml file as well as
applying SCM versioning to the project's resources.
The release:prepare goal will:
1 Verify that there are no uncommitted changes in the workspace.
2 Prompt the user for the desired tag, release and development version names.
3 Modify and commit release information into the pom.xml file.
4 Tag the entire project source tree with the new tag name.
The following example shows how to run the release:prepare goal with a Subversion SCM. The
commandline example directs the plugin to locate a Subversion SCM on a local file system.
mvn release:prepare
-Dproject.scm.developerConnection=scm:svn:file:///D:/
subversion_data/repos/my_repo/my-app-example/trunk
-DtagBase=file:///D:/subversion_data/repos/my_repo/my-app-example/
tags
When using the release:prepare goal, the user must supply maven with information regarding the
current location of the project's SCM. In the previous example maven was supplied with the current
location of the development trunk and the new location to record tagged instances of the project.
• project.scm.developerConnection
The current location of the development trunk. A valid SCM URL format appropriate to the
SCM provider. The "SCM:Provider:" prefix is used to determine the provider being used.
• tagbase
The new location to record a tagged release. A valid SCM URL format appropriate to the SCM
provider without the "SCM:Provider:" prefix.
The previous goal parameters can be supplied while executing maven on the commandline, (as shown
in the previous example) or they can be defined and maintained within the project's pom.xml file. The
location of the current development trunk is defined within the pom.xml file in the following form:
<project>
<name>Application</name>



<url>http://app.mycompany.com</url>
...
<scm>
<developerConnection>scm:svn:file:///D:/subversion_data/repos/my_repo/
my-app-example/trunk</developerConnection>
</scm>
...
<build>
<plugins>
...
<plugin>
<artifactId>maven-release-plugin</artifactId>
<configuration>
...
<tagBase>
file:///D:/subversion_data/repos/my_repo/my-app-example/tags
</tagBase>
...
</configuration>
</plugin>
...
</plugins>
</build>
...
</project>
To define the tagBase parameter within the pom.xml file a tagBase element must be defined within a
plugins/plugin/configuration element. The following example shows how this would look within the
pom.xml file.
<project>
...
<scm>
<developerConnection>scm:svn:file:///D:/subversion_data/repos/my_repo/
my-app-example/trunk</developerConnection>
</scm>
...
<build>
<plugins>
...
<plugin>
<configuration>
...
<tagBase>
file:///D:/subversion_data/repos/my_repo/my-app-example/tags



</tagBase>
...
</configuration>
</plugin>
...
</plugins>
</build>
...
</project>
During the execution of the release:prepare goal maven will interact with the user to gather
information about the current release. Maven will prompt the user for the following information:
• A Desired SCM provider tag name.
This is a SCM provider specific value, in the case of the Subversion SCM provider this value is
equal to the folder name that will appear under the URL provided by the the tagBase parameter.
• A Desired project release version.
This value is placed in the pom.xml that will define the current release. If a development pom.xml
holds a version value of 1.0-SNAPSHOT then the release version would be 1.0. This is not
enforced and can be a value appropriate to yourself or a company environment.
• A New development version.
This value is the placed in the next revision of the pom.xml file used for continuing development.
If the current release represented version 1.0 then an appropriate value could be 2.0-
SNAPSHOT. The SNAPSHOT designator is required to prepare and perform future releases.
This value is then committed in the next development revision of the pom.xml file.
After maven has been supplied with the required information the maven-release plugin will interact
with the project's SCM and define a relese to be extracted and deployed. At the same time the
project's development trunk is updated allowing developers to continue with further modifications that
will be included within future releases.

53.1.3 Performing the release
The plugin will extract file revisions associated with the current release. Maven will compile, test and
package the versioned project source code into an artifact. The final deliverable will then be released
into an appropriate maven repository.
The release:perform goal will:
1 Extract file revisions versioned under the new tag name.
2 Execute the maven build lifecycle on the extracted instance of the project.
3 Deploy the versioned artifacts to appropriate local and remote repositories.
The following example shows how to run the release:perform goal from the commandline.
mvn release:perform
The release:perform goal requires a file called release.properties to be present within the
project root directory. The release.properties file is constructed during the execution of the
release:prepare goal and contains all the information needed to locate and extract the correctly
tagged version of the project. Shown below is an example of the contents that can appear within an
instance of the release.properties file.
Note: The location of the release.properties file is under review and could be moved to the target
directory.
#Generated by Release Plugin on: Sat Nov 12 11:22:33 GMT 2005
#Sat Nov 12 11:22:33 GMT 2005
maven.username=myusername



checkpoint.transformed-pom-for-release=OK
scm.tag=1.0
scm.url=scm:svn:file:///D:/subversion_data/repos/my_repo/my-app-
example/trunk
scm.tag-base=file:///D:/subversion_data/repos/my_repo/my-app-example/tags
checkpoint.transform-pom-for-development=OK
checkpoint.local-modifications-checked=OK
checkpoint.initialized=OK
checkpoint.checked-in-release-version=OK
checkpoint.tagged-release=OK
checkpoint.prepared-release=OK
checkpoint.check-in-development-version=OK
The release.properties file is created while preparing the release. After performing the release the file
remains within the project root directory until the maven user deletes it. The release.properties file
can be given to any developer within the team and by simply excuting the release:perform goal
can create and deploy a new instance of the project artifact time and again.
During the execution of the release:perform goal the entire maven build lifecycle is executed on
the project. The tagged project source code is extracted, compiled, tested, documented and deployed.
An instance of the release artifact is deployed to the machine's local repository. An another instance
of the release can be deployed to a remote repository by configuring the distributionManagement
element within the pom.xml file.
The following is an example of how a distributionManagement element can be configured within a
project pom.xml file.
<project>
...
<repository>
<id>myRepoId</id>
<name>myCompanyReporsitory</name>
<url>ftp://repository.mycompany.com/repository</url>
</repository>
...
</project>
If the distributionManagement element is not configured within the pom.xml file then the deployment
of the artifact will fail. Maven will report a failure back to the user for the execution of the maven-
deploy plugin. Please refer maven documentationa and additional mini guides for the use of the
maven-deploy plugin.
The following delvierables are created and deployed to local and remoted repositories after the
execution of the release:perform goal has finished.

• artifact id- version.jar
The binaries for the current release of the project.
• artifact id- version-javadoc.jar



The javadoc explaining the current functionality of the classes within the current release.
• artifact id- version-source.jar
The source code revisions used to build the current release of the project.
• artifact id- version.pom
The contents of the pom.xml file used to create the current release of the project.

53.1.4 Troubleshooting

53.1.4.1 I get a "The authenticity of host ' host' can't be established." error and the build hangs
This is because your ~user/.ssh/known_hosts file doesn't have the host listed. You'd normally
get a prompt to add the host to the known host list but Maven doesn't propagate that prompt. The
solution is to add the host the known_hosts file before executing Maven. On Windows, this can
be done by installing an OpenSSH client (for example SSHWindows), running ssh <host> and
accepting to add the host.

53.1.4.2 The site deploy goal hangs
First, this means that you have successfully deployed the artifacts to the remote repo and that it's only
the site deployment that is now an issue. Stop your build, cd to target/checkout> and run the build
again by executing mvn site:deploy. You should see a prompt asking you to enter a password.
This happens if your key is not in the authorized keys on the server.


54 Using Ant with Maven 247

54 Using Ant with Maven
.......................................................................................................................................

54.1 Guide to using Ant with Maven
The example above illustrates how to bind an ant script to a lifecycle phase. You can add a script to
each lifecycle phase, by duplicating the execution/ section and specifying a new phase.

<project>
<artifactId>my-test-app</artifactId>
<groupId>my-test-group</groupId>
<build>
<plugins>
<plugin>
<executions>
<execution>
<phase>generate-sources</phase>
<configuration>
<tasks>

</tasks>
</configuration>
<goals>
<goal>run</goal>
</goals>
</execution>
</executions>
</plugin>
</plugins>
</build>
</project>

So a concrete example would be something like the following:

54 Using Ant with Maven 248

<project>
<artifactId>my-test-app</artifactId>
<groupId>my-test-group</groupId>
<build>
<plugins>
<plugin>
<executions>
<execution>
<phase>generate-sources</phase>
<configuration>
<tasks>
<exec
dir="${basedir}"
executable="${basedir}/src/main/sh/do-something.sh"
failonerror="true">
<arg line="arg1 arg2 arg3 arg4" />
</exec>
</tasks>
</configuration>
<goals>
<goal>run</goal>
</goals>
</execution>
</executions>
</plugin>
</plugins>
</build>
</project>


55 Using Modello 249

55 Using Modello
.......................................................................................................................................

55.1 Guide to using Modello
Modello is a tool for generating resources from a simple model. From a simple model you can
generate things like:

• Java sources
• XML serialization code for the model
• XML deserialization code for model
• Model documentation
• XSD
A typical modello model looks like the following:



<model xmlns="http://modello.codehaus.org/MODELLO/1.0.0" xmlns:xsi="http://www.w3.or
xsi:schemaLocation="http://modello.codehaus.org/MODELLO/1.0.0 http://modello.codeh
<id>archetype</id>
<name>Archetype</name>
<description><![CDATA[Maven's model for the archetype descriptor.]]></description>
<defaults>
<default>
<key>package</key>
<value>org.apache.maven.archetype.model</value>
</default>
</defaults>
<classes>
<class rootElement="true" xml.tagName="archetype">
<name>ArchetypeModel</name>
<description>Describes the assembly layout and packaging.</description>
<fields>
<field>
<name>id</name>
<type>String</type>
</field>
<field>
<name>allowPartial</name>
<type>boolean</type>
</field>
<field>
<name>sources</name>
<association>
<type>String</type>
<multiplicity>*</multiplicity>
</association>
</field>
<field>
<name>resources</name>
<association>
<type>String</type>
</association>
</field>
<field>
<name>testSources</name>
<association>
<type>String</type>
</association>
</field>
<field>
<name>testResources</name>
<association>
<type>String</type>
</association>
</field>
<field>

To utilize Modello you would configure the maven-modello-plugin something like the following
where you want to generate the Java sources for the model, the xpp3 serialization code and the xpp3
deserialization code:

<project>
...
<build>
<plugins>
<plugin>
<groupId>org.codehaus.modello</groupId>
<artifactId>modello-maven-plugin</artifactId>
<executions>
<execution>
<goals>

<goal>xpp3-reader</goal>

<goal>xpp3-writer</goal>

<goal>java</goal>
</goals>
</execution>
</executions>
<configuration>
<models>
<model>src/main/mdo/descriptor.mdo</model>
</models>
</configuration>
</plugin>
</plugins>
</build>
...
</project>

56 Webapps 252

56 Webapps
.......................................................................................................................................
mvn archetype:create -DgroupId=com.mycompany.app -DartifactId=my-webapp -DarchetypeA

<project>
<artifactId>my-webapp</artifactId>
<dependencies>
<dependency>
<scope>test</scope>
</dependency>
</dependencies>
<build>
<finalName>my-webapp</finalName>
</build>
</project>

Note the packaging element - this tells Maven to build as a WAR. Change into the webapp project's
directory and try:

mvn clean package

You'll see target/my-webapp.war is built, and that all the normal steps were executed.
Now you can modify this webapp project and turn it into anything you need!


57 Using Extensions 253

57 Using Extensions
.......................................................................................................................................

57.1 Using Extensions
Extensions are used to enable Wagon providers, used for the transport of artifact between repositories,
and plug-ins which provide lifecycle enhancements.

57.1.1 Wagon providers

<project>
...
<build>
<extensions>
<extension>
<groupId>org.apache.maven.wagon</groupId>
<artifactId>wagon-ftp</artifactId>
</extension>
</extensions>
</build>
...
</project>

Note: Wagon 1.0-beta-3+ requires Maven 2.1.0 or above. For Maven 2.0.10 and earlier, use Wagon
1.0-beta-2.
Note: Some Wagons require JDK 5.0 to operate correctly.

57.1.2 Plug-ins which provide lifecycle enhancements

<project>
...
<build>
<plugins>
<plugin>
<groupId>org.codehaus.plexus</groupId>
<artifactId>plexus-maven-plugin</artifactId>
<version>1.1-alpha-8-SNAPSHOT</version>
<extensions>true</extensions>
<configuration>
...
</configuration>
</plugin>
</plugins>
</build>
...
</project>


58 Building For Different Environments with Maven 2 254

58 Building For Different Environments with Maven
2
.......................................................................................................................................

58.1 Building For Different Environments with Maven 2
Building the same artifact for different environments has always been an annoyance. You have
multiple environments, for instance test and production servers or, maybe a set of servers that run the
same application with different configurations. In this guide I'll explain how you can use profiles to
build and package artifacts configured for specific environments. See Introduction to Build Profiles
for a more in-depth explanation of the profile concept.
Note:
• This guide assume that you have basic Maven 2 knowledge.
• It will show a way to configure Maven to solve simple configuration set-ups only. By simple
configuration set-up I mean cases where you only have a single file or a small set of files that
vary for each environment. There are other and better ways to handle two and many-dimensional
configuration issues.
This example assume the use of the Standard Directory Layout. Also available for download is a
fully-working example project.
pom.xml
src/
main/
java/
resources/
test/
java/
Under src/main/resources there are three files:
• environment.properties - This is the default configuration and will be packaged in the
artifact by default.
• environment.test.properties - This is the variant for the test environment.
• environment.prod.properties - This is basically the same as the test variant and will be
used in the production environment.
In the project descriptor, you need to configure the different profiles. Only the test profile is
showed here, see the accompanying source code for the full pom.xml.
<profiles>
<profile>
<id>test</id>
<build>
<plugins>
<plugin>
<executions>
<execution>
<phase>test</phase>
<goals>
<goal>run</goal>
</goals>
<configuration>
<tasks>
<delete file="${project.build.outputDirectory}/
environment.properties"/>



<copy file="src/main/resources/
environment.test.properties"
tofile="${project.build.outputDirectory}/
environment.properties"/>
</tasks>
</configuration>
</execution>
</executions>
</plugin>
<plugin>
<artifactId>maven-surefire-plugin</artifactId>
<configuration>
<skip>true</skip>
</configuration>
</plugin>
<plugin>
<executions>
<execution>
<phase>package</phase>
<goals>
<goal>jar</goal>
</goals>
<configuration>
<classifier>test</classifier>
</configuration>
</execution>
</executions>
</plugin>
</plugins>
</build>
</profile>
.. Other profiles go here ..
</profiles>
Three things are configured in this snippet:
1 It configures the antrun plugin to execute the run goal in the test phase where it will copy
the environment.test.properties file to environment.properties.
2 It will configure the test plugin to skip all tests when building the test and production
artifacts. This is useful as you probably don't want to run tests against the production system
3 It configures the JAR plugin to create an "attached" JAR with the "test" classifier.
To activate this profile execute mvn -Ptest install and maven will execute the steps
in the profile in addition to the normal steps. From this build you will get two artifacts,
"foo-1.0.jar" and "foo-1.0-test.jar". These two jars will identical.

58.2 Caveats
• Currently Maven 2 doesn't allow a project build to only produce attached artifacts. (i.e. it has to
produce a "main" artifact as well) This results in two equal JARs beeing packaged and installed.
The JAR plugin probably should also get improved support for this use case to that two different
output directories will be used as the basis for building the JAR.
• The usage of the delete task might seem a bit odd but is required to make sure that the copy
task actually will copy the file. The copy task will look at the timestamps of the source and



destination files, only when copying the files it won't know that the actualy source file might be
different than the last time it was executed.
• After the build the test configuration will be in target/classes and won't be overridden because
the resources plugin uses the same timestamp checking, so you should always do a clean after
executing Maven with a profile.
• For the reasons given above it's imperative that you only build an artifact for a single
environment in a single execution at a time and that you execute "mvn clean" whenever you
change the profile switches. If not, you might get artifacts with a mixed set of configuration files.

58.3 Resources
1 Introduction to Build Profiles
2 Standard Directory Layout
3 The accompanying source code


59 Using Toolchains 257

59 Using Toolchains
.......................................................................................................................................

59.1 Guide to Using Toolchains

59.1.1 What is Toolchains?
The Maven Toolchains provide a way for plugins to discover what JDK (or other tools) are to be
used during the build, without the need to configure them. With toolchains, a project can now be built
using a specific version of JDK independent from the one Maven is running with. (Think how JDK
versions can be set in IDEs like Idea, Netbeans and Eclipse)
Toolchains would only work in Maven 2.0.9 and higher versions. For more details about it's design
and implementation, please see Toolchains.
Below are the plugins which are toolchain-aware, meaning they can be used with toolchains. Please
note that these are still SNAPSHOT versions and are not yet released.
1 maven-compiler-plugin-2.1-SNAPSHOT
2 maven-javadoc-plugin-2.5-SNAPSHOT
3 maven-surefire-plugin-2.5-SNAPSHOT
4 exec-maven-plugin-1.1.1-SNAPSHOT (Codehaus MOJO)

59.1.2 Using Toolchains in Your Project
There are two essential components that you need to configure in order to use toolchains. These are
the maven-toolchains-plugin and the toolchains.xml file.
The maven-toolchains-plugin is the one that sets the toolchain to be used by the toolchain-
aware plugins in your project. For example, you want to use a different JDK version to build your
project. You can configure the version you want to use via this plugin as shown in the pom.xml
below.
<plugins>
...
<plugin>
</plugin>
<plugin>
<artifactId>maven-toolchains-plugin</artifactId>
<executions>
<execution>
<phase>validate</phase>
<goals>
<goal>toolchain</goal>
</goals>
</execution>
</executions>
<configuration>
<toolchains>
<jdk>



<vendor>sun</vendor>
</jdk>
</toolchains>
</configuration>
<plugin>
...
</plugins>
As you can see in the example above, a JDK toolchain with <version> "1.5" and <vendor>
"sun" is to be used. Now how does the plugin know where this JDK is installed? This is where the
toolchains.xml file comes in.
The toolchains.xml file (see below) is the configuration file where you set the installation paths
of your toolchains. This file should be put in your $ user.home/.m2 directory. When the maven-
toolchains-plugin executes, the maven-toolchain component used by the plugin would look
for the toolchains.xml file, read it and look for the matching toolchain configured in the plugin.
In our example, that would be a JDK toolchain with <version> "1.5" and <vendor> "sun". Once a
match is found, the plugin then sets the toolchain to be used in the MavenSession. As you can see in
our toolchains.xml below, there is indeed a JDK toolchain with <version> "1.5" and <vendor>
"sun" configured. So when the maven-compiler-plugin we've configured in our pom.xml above
executes, it would see that a JDK toolchain is set in the MavenSession and would thereby use that
toolchain (that would be the JDK installed at /path/to/jdk/1.5 for our example) to compile the
sources.
<?xml version="1.0" encoding="UTF8"?>
<toolchains>
<toolchain>
<type>jdk</type>
<provides>
<id>default</id>
</provides>
<configuration>
<jdkHome>/path/to/jdk/1.5</jdkHome>
</configuration>
</toolchain>
<toolchain>
<type>jdk</type>
<provides>
<id>ide</id>
</provides>
<configuration>
<jdkHome>/path/to/jdk/1.6</jdkHome>
</configuration>
</toolchain>
<toolchain>
<type>netbeans</type>
<provides>
</provides>
<configuration>



<installDir>/path/to/netbeans/5.5</installDir>
</configuration>
</toolchain>
</toolchains>
Note that you can configure as many toolchains as you want in your toolchains.xml file.


60 Encrypting passwords in settings.xml 260

60 Encrypting passwords in settings.xml
.......................................................................................................................................

60.1 Password Encryption
1 Introduction
2 How to create a master password
3 How to encrypt server passwords
4 How to keep the master password on removable drive
5 Tips

60.1.1 Introduction
Maven 2.1.0+ now supports server password encryption. The main use case, addressed by this
solution is:
• multiple users share the same build machine (server, CI box)
• some users have the privilege to deploy Maven artifacts to repositories, some don't.
• this applies to any server operations, requiring authorization, not only deployment
• settings.xml is shared between users
The implemented solution adds the following capabilities:
• authorized users have an additional settings-security.xml file in their ~/.m2 folder
• this file either contains encrypted master password, used to encrypt other passwords
• or it can contain a relocation - reference to another file, possibly on removable storage
• this password is created first via CLI for now
• server entries in the settings.xml have passwords and/or keystore passphrases encrypted
• for now - this is done via CLI after master password has been created and stored in
appropriate location

60.1.2 How to create a master password
Use the following command line:

mvn --encrypt-master-password <password>

This command will produce an encrypted version of the password, something like

{jSMOWnoPFgsHVpMvz5VrIt5kRbzGpI8u+9EF1iFQyJQ=}

Store this password in the ~/.m2/settings-security.xml; it should look like

<settingsSecurity>
<master>{jSMOWnoPFgsHVpMvz5VrIt5kRbzGpI8u+9EF1iFQyJQ=}</master>
</settingsSecurity>

When this is done, you can start encrypting existing server passwords.

60.1.3 How to encrypt server passwords
You will have to use the following command line:



mvn --encrypt-password <password>

This command will produce an encrypted version of it, something like

{COQLCE6DU6GtcS5P=}

Cut-n-paste it into your settings.xml file in the server section. This will look like:

<settings>
...
<servers>
...
<server>
<id>my.server</id>
<username>foo</username>
<password>{COQLCE6DU6GtcS5P=}</password>
</server>
...
</servers>
...
</settings>

Please note that password can contain any information outside of the curly brackets, so that the
following will still work:

<settings>
...
<servers>
...
<server>
<id>my.server</id>
<username>foo</username>
<password>Oleg reset this password on 2009-03-11, expires on 2009-04-11 {COQLC
</server>
...
</servers>
...
</settings>

Then you can use, say, deploy plugin, to write to this server:

mvn deploy:deploy-file -Durl=https://maven.corp.com/repo
-DrepositoryId=my.server
-Dfile=your-artifact-1.0.jar

60.1.4 How to keep the master password on removable drive
Create the master password exactly as described above, and store it on a removable drive, for instance
on OSX, my USB drive mounts as /Volumes/mySecureUsb, so I store

<settingsSecurity>
<master>{jSMOWnoPFgsHVpMvz5VrIt5kRbzGpI8u+9EF1iFQyJQ=}</master>
</settingsSecurity>



in the file /Volumes/mySecureUsb/secure/settings-security.xml
And then I create ~/.m2/settings-security.xml with the following content:

<settingsSecurity>
<relocation>/Volumes/mySecureUsb/secure/settings-security.xml</relocation>
</settingsSecurity>

This assures that encryption will only work when the usb drive is mounted by OS. This addresses a
use case where only certain people are authorized to deploy and are issued these devices.

60.1.5 Tips

60.1.5.1 Escaping curly-brace literals in your password (Since: Maven 2.2.0)
At times, you might find that your password (or the encrypted form of it) may actually contain ' ' or
'' as a literal value. If you added such a password as-is to your settings.xml file, you would find that
Maven does strange things with it. Specifically, Maven will treat all the characters preceding the ' '
literal, and all the characters after the '' literal, as comments. Obviously, this is not the behavior you
want in such a situation. What you really need is a way of escaping the curly-brace literals in your
password.
Starting in Maven 2.2.0, you can do just this, with the widely used '' escape character. If your
password looks like this:

jSMOWnoPFgsHVpMvz5VrIt5kRbzGpI8u+{EF1iFQyJQ=

Then, the value you would add to your settings.xml would look like this:

{jSMOWnoPFgsHVpMvz5VrIt5kRbzGpI8u+{EF1iFQyJQ=}


61 Reusable Test JARs 263

61 Reusable Test JARs
.......................................................................................................................................

61.1 Guide to using attached tests
Many times you may want to reuse the tests that you have created for a project in another. For
example if you have written foo-core and it contains test code in the ${basedir}/src/test/
java it would be useful to package up those compiled tests in a JAR and deploy them for general
reuse. To do this you would configure the maven-jar-plugin as follows:

<project>
<build>
<plugins>
<plugin>
<executions>
<execution>
<goals>
<goal>test-jar</goal>
</goals>
</execution>
</executions>
</plugin>
</plugins>
</build>
</project>

61.1.1 Installing the attached test JAR
In order to install the attached test JAR you simply use the standard install phase by executing the
following command:

mvn install

61.1.2 Deploying the attached test JAR
In order to deploy the attached test JAR you simply use the standard deploy phase by executing the
following command:

mvn deploy

61.1.3 Using the attached test JAR
In order to use the attached test JAR that was created above you simply specify a dependency on the
main artifact with a specified type of test-jar:


61 Reusable Test JARs 264

<project>
...
<dependencies>
<dependency>
<groupId>com.myco.app</groupId>
<artifactId>foo</artifactId>
<type>test-jar</type>
<scope>test</scope>
</dependency>
</dependencies>
...
</project>

Note that previous editions of this guide suggested to use <classifier>tests</classifier>
instead of <type>test-jar</type>. While this currently works for some cases, it does not
properly work during a reactor build of the test JAR module and any consumer if a lifecycle phase
prior to install is invoked. In such a scenario, Maven will not resolve the test JAR from the output
of the reactor build but from the local/remote repository. Apparently, the JAR from the repositories
could be outdated or completely missing, causing a build failure (cf. MNG-2045).


62 Eclipse Integration 265

62 Eclipse Integration
.......................................................................................................................................

62.1 Eclipse plugins for Maven
The following plugins allow using Maven from the Eclipse IDE, avoiding the use of the Maven
command line interface. They integrate Maven in the IDE in different ways, please check their sites
for more information. Both plugins allow running Maven goals from Eclipse, see the output in a view
inside the IDE and synchronize Maven POM information with Eclipse project information to some
extent.

62.2 The Maven Integration for Eclipse (m2eclipse, Eclipse m2e)
The Maven Integration for Eclipse is the first and most mature of the projects aimed at integrating
Maven within the Eclipse IDE. It is released under the EPL 1.0 license.
Features include:

• Launching Maven builds from within Eclipse
• Dependency management for Eclipse build path based on Maven's pom.xml
• Resolving Maven dependencies from the Eclipse workspace without installing to local Maven
repository
• Automatic downloading of the required dependencies and sources from the remote Maven
repositories
• Wizards for creating new Maven projects, pom.xml and to enable Maven support on existing
projects
• Quick search for dependencies in remote Maven repositories
• Quick fixes in the Java editor for looking up required dependencies/jars by the class or package
name
• Integration with other Eclipse tools, such as WTP, AJDT, Mylyn, Subclipse and others.
For installation instructions, see the m2eclipse website. For the most recent list of features, see the
New and Noteworthy page on the m2eclipse wiki.
Currently, this project is being incubated at Eclipse. Subscribe to the Eclipse eclipse.technology.m2e
newsgroup or use the web interface to stay up-to-date with the latest progress.

62.3 Eclipse Integration for Apache Maven (Eclipse IAM), formerly Q for
Eclipse
Eclipse IAM is a newer Apache Maven plugin for Eclipse with a fresh approach for Maven
integration with the Eclipse IDE and other Eclipse plugins (JDT, WTP, Candy for Appfuse,...), also
opening the doors for other Eclipse plugin developers to access Maven features as easy as possible.
With five releases already, and continuing to make one every other month it's quickly maturing.
Check the FAQ and Installation instructions
You can join the newsgroup at

• server: news.eclipse.org
• group: eclipse.technology.iam
• or at the web interface


63 Netbeans Integration 266

63 Netbeans Integration
.......................................................................................................................................

63.1 Maven 2.x Module for Netbeans
The Netbeans integration was for a long time developed at http://mevenide.codehaus.org, it was
moved to netbeans.org and will be part of standard NetBeans distribution since 7.0. It allows to load
any Maven 2 project into Netbeans and start coding immediately. To get a current feature list along
with screenshots, description and hints please refer to the NetBeans.org wiki page.

63.1.1 Binaries and Installation
The Maven integration is easily accessible in NetBeans 6.0, 6.1 and 6.5 via the Tools/Plugins dialog.
In 7.0 and later it's part of the standard installation. More detailed instructions on installation available
(for older versions of NetBeans) at the Mevenide site.

63.1.2 Bugs reports and enhancement requests
Bug, enhancements and feature requests are to be filed in the NetBeans.org issue tracking system.


64 Plugin Developer Centre 267

64 Plugin Developer Centre
.......................................................................................................................................

64.1 Plugin Developers Centre
This documentation centre is for those that are developing Maven plugins. This might be for your own
build, or as an accompaniment to your third party tool.
What is a Mojo? A mojo is a Maven plain Old Java Object. Each mojo is an executable goal in
Maven, and a plugin is a distribution of one or more related mojos.

• Your First Mojo - Learn how to write your first plugin
• Testing your Plugin - How to write tests for your plugins
• Documenting your Plugin - How to write documentation for your plugins
• Plugins Cookbook - Examples for how to perform common tasks in plugins
• Common Bugs and Pitfalls - Overview of problematic coding patterns

64.1.1 Reference

• Mojo API and Annotation Reference
• Maven API Reference
• Maven Class Loading

64.1.2 Examples

• Injecting POM Properties via settings.xml


65 Testing your Plugin 268

65 Testing your Plugin
.......................................................................................................................................

65.1 Introduction
Currently, Maven only supports unit testing out of the box. This document is intended to help Maven
Developers to test Plugins with Unit Tests, Integration Tests or Functional tests.
Note: There are a lot of different ways to test a Maven plugin. For a review of different strategies
and tools, please refer to Review of Plugin Testing Strategies

65.2 Testing Styles: Unit Testing vs. Functional/Integration Testing
A unit test attempts to verify a mojo as an isolated unit, by mocking out the rest of the Maven
environment. A mojo unit test does not attempt to run your plugin in the context of a real Maven
build. Unit tests are designed to be fast.
A functional/integration test attempts to use a mojo in a real Maven build, by launching a real instance
of Maven in a real project. Normally this requires you to construct special dummy Maven projects
with real POM files. Often this requires you to have already installed your plugin into your local
repository so it can be used in a real Maven build. Functional tests run much more slowly than unit
tests, but they can catch bugs that you may not catch with unit tests.
The general wisdom is that your code should be mostly tested with unit tests, but should also have
some functional tests.

65.3 Unit Tests

65.3.1 Using JUnit alone
In principle, you can write a unit test of a plugin Mojo the same way you'd write any other JUnit test
case, by writing a class that extends TestCase.
However, most mojos need more information to work properly. For example, you'll probably need to
inject a reference to a MavenProject, so your mojo can query project variables.

65.3.2 Using PlexusTestCase
Mojo variables are injected using Plexus, and many Mojos are written to take specific advantage of
the Plexus container (by executing a lifecycle or having various injected dependencies).
If you all you need is Plexus container services, you can write your class with extends
PlexusTestCase instead of TestCase.
With that said, if you need to inject Maven objects into your mojo, you'll probably prefer to use the
maven-plugin-testing-harness.

65.3.3 maven-plugin-testing-harness
The maven-plugin-testing-harness is explicitly intended to test the
org.apache.maven.reporting.AbstractMavenReport#execute() implementation.
In general, you need to include maven-plugin-testing-harness as dependency, and create a
*MojoTest (by convention) class which extends AbstractMojoTestCase.



...
<dependencies>
...
<dependency>
<groupId>org.apache.maven.shared</groupId>
<artifactId>maven-plugin-testing-harness</artifactId>
<scope>test</scope>
</dependency>
...
</dependencies>
...

public class YourMojoTest
extends AbstractMojoTestCase
{
/**
* @see junit.framework.TestCase#setUp()
*/
protected void setUp() throws Exception {
// required for mojo lookups to work
super.setUp();
}
/**
* @throws Exception
*/
public void testMojoGoal() throws Exception
{
File testPom = new File( getBasedir(),
"src/test/resources/unit/basic-test/basic-test-plugin-config.xml" );
YourMojo mojo = (YourMojo) lookupMojo ( "yourGoal", testPom );
assertNotNull( mojo );
}
}

For more information, please refer to Maven Plugin Harness Wiki

65.4 Integration/Functional testing

65.4.1 maven-verifier
maven-verifier tests are run using JUnit or TestNG, and provide a simple class allowing you to
launch Maven and assert on its log file and built artifacts. It also provides a ResourceExtractor, which
extracts a Maven project from your src/test/resources directory into a temporary working directory
where you can do tricky stuff with it.
Maven itself uses maven-verifier to run its core integration tests. For more information, please refer to
Creating a Maven Integration Test.



public class TrivialMavenVerifierTest extends TestCase
{
public void testMyPlugin ()
throws Exception
{
// Check in your dummy Maven project in /src/test/resources/...
// The testdir is computed from the location of this
// file.
File testDir = ResourceExtractor.simpleExtractResources( getClass(), "/my-du
Verifier verifier;
/*
* We must first make sure that any artifact created
* by this test has been removed from the local
* repository. Failing to do this could cause
* unstable test results. Fortunately, the verifier
* makes it easy to do this.
*/
verifier = new Verifier( testDir.getAbsolutePath() );
verifier.deleteArtifact( "org.apache.maven.its.itsample", "parent", "1.0", "
verifier.deleteArtifact( "org.apache.maven.its.itsample", "checkstyle-test",
verifier.deleteArtifact( "org.apache.maven.its.itsample", "checkstyle-assemb
/*
* The Command Line Options (CLI) are passed to the
* verifier as a list. This is handy for things like
* redefining the local repository if needed. In
* this case, we use the -N flag so that Maven won't
* recurse. We are only installing the parent pom to
* the local repo here.
*/
List cliOptions = new ArrayList();
cliOptions.add( "-N" );
verifier.executeGoal( "install" );
/*
* This is the simplest way to check a build
* succeeded. It is also the simplest way to create
* an IT test: make the build pass when the test
* should pass, and make the build fail when the
* test should fail. There are other methods
* supported by the verifier. They can be seen here:
* http://maven.apache.org/shared/maven-verifier/apidocs/index.html
*/
verifier.verifyErrorFreeLog();
/*
* Reset the streams before executing the verifier
* again.
*/
verifier.resetStreams();
/*
* The verifier also supports beanshell scripts for
* verification of more complex scenarios. There are
* plenty of examples in the core-it tests here:
* http://svn.apache.org/repos/asf/maven/core-integration-testing/trunk
*/
}



Note: maven-verifier and maven-verifier-plugin sound similar, but are totally different unrelated
pieces of code. maven-verifier-plugin simply verifies the existence/absence of files on the filesystem.
You could use it for functional testing, but you may need more features than maven-verifier-plugin
provides.

65.4.2 maven-invoker-plugin
You can use maven-invoker-plugin to invoke Maven and to provide some BeanShell tests. Tests
written in this way don't run under JUnit/TestNG; instead, they're run by Maven itself.

<project
xmlns="http://maven.apache.org/POM/4.0.0"
...
<build>
<plugins>
<plugin>
<artifactId>maven-invoker-plugin</artifactId>
<configuration>
<debug>true</debug>
<projectsDirectory>src/it</projectsDirectory>
<pomIncludes>
<pomInclude>**/pom.xml</pomInclude>
</pomIncludes>
<postBuildHookScript>verify.bsh</postBuildHookScript>
</configuration>
<executions>
<execution>
<phase>integration-test</phase>
<goals>
<goal>run</goal>
</goals>
</execution>
</executions>
</plugin>
...
</plugins>
</build>
...
</project>

65.4.3 shitty-maven-plugin
The shitty-maven-plugin (Super Helpful Integration Testing ThingY) provides a simple way to run
integration tests for a project (single module or multi-module).
shitty-maven-plugin does many of the same things as the maven-invoker-plugin (it supports Groovy
tests instead of BeanShell tests), though it has some features that aren't available in maven-invoker-
plugin. Notably, it provides some advanced setup steps to automatically install your plugin using a
special version name ("TESTING"), so your dummy projects can depend on that version explicitly.



65.4.4 maven-it-plugin
Note: maven-it-plugin is not at 1.0 yet. Use it at your own risk.
The maven-it-plugin is used directly in the integration-test phase.
Note: this it plugin can not be used to test a plugin that is being built for the first time (i.e. with
no release). In this case, you could, for instance, defined an it-snapshot of the plugin with maven-
install-plugin. during the pre-integration-test phase.


<project
...
<artifactId>maven-XXX-plugin</artifactId>
<description>Test Report plugin in the site phase</description>
...
<build>
<plugins>
...
<plugin>
<artifactId>maven-it-plugin</artifactId>
<version>1.0-alpha-1-SNAPSHOT</version>
<configuration>
<integrationTestsDirectory>${basedir}/src/it</integrationTestsDirectory>
<includes>
<include>**/pom.xml</include>
</includes>
<goals>site</goals>
</configuration>
<executions>
<execution>
<phase>integration-test</phase>
<goals>
<goal>test</goal>
</goals>
</execution>
</executions>
</plugin>

<plugin>
<artifactId>maven-install-plugin</artifactId>
<executions>
<execution>
<id>it-test</id>
<phase>pre-integration-test</phase>
<goals>
<goal>install-file</goal>
</goals>
<configuration>
<file>${basedir}/target/maven-XXX-plugin-1.0-SNAPSHOT.jar</file>
<version>1.0-it-SNAPSHOT</version> 
<pomFile>${basedir}/pom.xml</pomFile>
</configuration>
</execution>
</executions>
</plugin>

<plugin>


The it pom should use the it snapshot:

...
<reporting>
<outputDirectory>
${basedir}/../../../../../target/it/it1/target/site
</outputDirectory>
<plugins>
<plugin>
<version>1.0-it-SNAPSHOT</version>
</plugin>
</plugins>
</reporting>
...
</project>

65.4.5 maven-plugin-management-plugin
The maven-plugin-management-plugin is to stage/unstage a plugin into the local repository for pre/
post-integration-test.
You need to configure the maven-plugin-test-plugin and the maven-surefire-plugin:


<project
...
<description>Test Report plugin in the site phase</description>
<prerequisites>
<maven>2.0.4</maven>
</prerequisites>
...
<dependencies>
...

<dependency>
<scope>test</scope>
</dependency>
<dependency>
<artifactId>maven-core</artifactId>
<scope>test</scope>
</dependency>
</dependencies>
<build>
<plugins>
...
<plugin>
<artifactId>maven-plugin-management-plugin</artifactId>
<executions>
<execution>
<id>pre-it-test</id>
<phase>pre-integration-test</phase>
<goals>
<goal>stage</goal>
</goals>
</execution>
<execution>
<id>post-it-test</id>
<phase>post-integration-test</phase>
<goals>
<goal>unstage</goal>
</goals>
</execution>
</executions>
</plugin>

<plugin>
<executions>
<execution>


The *TestIt classes could use the Maven Embedder to provide tests:

public class MyMojoTestIt
extends PlexusTestCase
{
/**
* @throws Exception
*/
public void testDefaultProject()
throws Exception
{
MavenEmbedder maven = new MavenEmbedder();
ClassLoader classLoader = Thread.currentThread().getContextClassLoader();
maven.setClassLoader( classLoader );
maven.setLogger( new MavenEmbedderConsoleLogger() );
maven.setOffline( true );
maven.setLocalRepositoryDirectory( getTestFile( "target/local-repo" ) );
maven.start();
File itbasedir = new File( getBasedir(), "src/it/it1" );
MavenProject pom =
maven.readProjectWithDependencies( new File( itbasedir, "pom.xml" ) );
EventMonitor eventMonitor =
new DefaultEventMonitor(
new PlexusLoggerAdapter(
new MavenEmbedderConsoleLogger() ) );
maven.execute( pom,
Collections.singletonList(
"org.apache.maven.plugins:maven-XXX-plugin:1.0-SNAPSHOT:yourGoal" ),
eventMonitor,
new ConsoleDownloadMonitor(),
null,
itbasedir );
maven.stop();
}
}

Note: The maven-plugin-management-plugin is similar to maven-plugin-test-plugin.


66 Documenting your Plugin 277

66 Documenting your Plugin
.......................................................................................................................................

66.1 Introduction
A Guide to the Plugin Documentation Standard was created. This document is intended to verify it
during the Plugins development.

66.2 Verify Plugin Documentation
The maven-docck-plugin checks that a project complies with the Plugin Documentation Standard.
You should verify that all Plugin documentation respects this standard. The maven-docck-plugin can
be run:

mvn docck:check

66.3 References
• Maven Plugin Documentation


67 Common Bugs and Pitfalls 278

67 Common Bugs and Pitfalls
.......................................................................................................................................

67.1 Common Bugs and Pitfalls
Maven is not the smallest project in terms of source code and has as such already suffered from many
bugs. Having a closer look at all the issues revealed some coding problems that had widespread
among the various subcomponents. This document lists these commonly occurring anti patterns in
order to help the Maven community to prevent rather than fix bugs. Note that the primary focus is on
pointing out problems that are subtle in their nature rather than giving a comprehensive guide for Java
or Maven development.

• Reading and Writing Text Files
• Converting between URLs and Filesystem Paths
• Handling Strings Case-insensitively
• Creating Resource Bundle Families
• Using System Properties
• Using Shutdown Hooks
• Resolving Relative Paths
• Determining the Output Directory for a Site Report
• Retrieving the Mojo Logger
• Depending on Plexus Utilities 1.1+

67.1.1 Reading and Writing Text Files
Textual content is composed of characters while file systems merely store byte streams. A file
encoding (aka charset) is used to convert between bytes and characters. The challenge is using the
right file encoding.
The JVM has this notion of a default encoding (given by the file.encoding property) which
it derives from a system's locale. While this might be a convenient feature sometimes, using this
default encoding for a project build is in general a bad idea: The build output will depend on the
machine/developer who runs the build. As such, usage of the default encoding threatens the dream of
a reproducible build.
For example, if developer A has UTF-8 as default encoding while developer B uses ISO-8859-1, text
files are very likely to get messed up during resource filtering or similar tasks.
Therefore, developers should avoid any direct or indirect usage of the classes/methods that simply
employ the platform's default encoding. For instance, FileWriter and FileReader should usually
be avoided:

/*
* FIXME: This assumes the source file is using the platform's default encoding.
*/
Reader reader = new FileReader( javaFile );

Instead, the classes OutputStreamWriter and OutputStreamReader can be used in combination
with an explicit encoding value. This encoding value can be retrieved from a mojo parameter such
that the user can configure the plugin to fit his/her needs.
To save the user from configuring each plugin individually, conventions have been established that
allow a user to centrally configure the file encoding per POM. Plugin developers should respect these
conventions whereever possible:



• Source File Encoding
• Report Output Encoding
Finally note that XML files require special handling because they are equipped with an encoding
declaration in the XML prolog. Reading or writing XML files with an encoding that does not match
their XML prolog's encoding attribute is a bad idea:

/*
* FIXME: This assumes the XML encoding declaration matches the platform's default e
*/
Writer writer = new FileWriter( xmlFile );
writer.write( xmlContent );

To ease the correct processing of XML files, developers are encouraged to use
ReaderFactory.newXmlReader() and WriterFactory.newXmlWriter() from the Plexus
Utilities.

67.1.2 Converting between URLs and Filesystem Paths
URLs and filesystem paths are really two different things and converting between them is not trivial.
The main source of problems is that different encoding rules apply for the strings that make up a
URL or filesystem path. For example, consider the following code snippet and its associated console
output:

File file = new File( "foo bar+foo" );
URL url = file.toURI().toURL();
System.out.println( file.toURL() );
> file:/C:/temp/foo bar+foo
System.out.println( url );
> file:/C:/temp/foo%20bar+foo
System.out.println( url.getPath() );
> /C:/temp/foo%20bar+foo
System.out.println( URLDecoder.decode( url.getPath(), "UTF-8" ) );
> /C:/temp/foo bar foo

First of all, please note that File.toURL() does not escape the space character (and others). This
yields an invalid URL, as per RFC 2396, section 2.4.3 "Excluded US-ASCII Characters". The class
java.net.URL will silently accept such invalid URLs, in contrast java.net.URI will not (see also
URL.toURI()). For this reason, File.toURL() has been deprecated and should be replaced with
File.toURI().toURL().
Next, URL.getPath() does in general not return a string that can be used as a filesystem path. It
returns a substring of the URL and as such can contain escape sequences. The prominent example is
the space character which will show up as "%20". People sometimes hack around this by means of
replace("%20", " ") but that does simply not cover all cases. It's worth to mention that on the
other hand the related method URI.getPath() does decode escapes but still the result is not a
filesystem path (compare the source for the constructor File(URI)). To summarize, the following
idiom is to be avoided:

URL url = new URL( "file:/C:/Program%20Files/Java/bin/java.exe" );
/*
* FIXME: This does not decode percent encoded characters.
*/
File path = new File( url.getPath() );



To decode a URL, people sometimes also choose java.net.URLDecoder. The pitfall with this
class is that is actually performs HTML form decoding which is yet another encoding and not the
same as the URL encoding (compare the last paragraph in class javadoc about java.net.URL).
For instance, a URLDecoder will erroneously convert the character "+" into a space as illustrated by
the last sysout in the example above.
In an ideal world, code targetting JRE 1.4+ could easily avoid these problems by using the constructor
File(URI) as suggested by the following snippet:

URL url = new URL( "file:/C:/Documents and Settings/user/.m2/settings.xml" );
/*
* FIXME: This assumes the URL is fully compliant with RFC 3986.
*/
File path = new File( new URI( url.toExternalForm() ) );

The remaining source of frustration is the conversion from URL to URI. As already said, the URL class
accepts malformed URLs which will make the constructor of URI throw an exception. And indeed,
class loaders from Sun JREs up to Java 1.4 will deliver malformed URLs when queried for a resource.
Likewise, the class loaders employed by Maven 2.x deliver malformed resource URLs regardless of
the JRE version (see MNG-3607).
For all these reasons, it is recommended to use FileUtils.toFile() from Commons IO or
FileUtils.toFile() from a recent Plexus Utilities.

67.1.3 Handling Strings Case-insensitively
When developers need to compare strings without regard to case or want to realize a map
with case-insensitive string keys, they often employ String.toLowerCase() or
String.toUpperCase() to create a "normalized" string before doing a simple String.equals().
Now, the to*Case() methods are overloaded: One takes no arguments and one takes a Locale
object.
The gotcha with the arg-less methods is that their output depends on the default locale of the JVM but
the default locale is out of control of the developer. That means the string expected by the developer
(who runs/tests his code in a JVM using locale xy) does not necessarily match the string seen by
another user (that runs a JVM with locale ab). For example, the comparison shown in the next code
snippet is likely to fail for systems with default locale Turkish because Turkish has unusual casing
rules for the characters "i" and "I":

/*
* FIXME: This assumes the casing rules of the current platform
* match the rules for the English locale.
*/
if ( "info".equals( debugLevel.toLowerCase() ) )
logger.info( message );

For case-insensitive string comparisions which should be locale-insensitive, the method
String.equalsIgnoreCase() should be used instead. If only a substring like a prefix/suffix
should be compared, the method String.regionMatches() can be used instead.
If the usage of String.to*Case() cannot be avoided, the overloaded version taking a Locale
object should be used, passing in Locale.ENGLISH. The resulting code will still run on Non-
English systems, the parameter only locks down the casing rules used for the string comparison such
that the code delivers the same results on all platforms.



67.1.4 Creating Resource Bundle Families
Especially reporting plugins employ resource bundles to support internationalization. One language
(usually English) is provided as the fallback/default language in the base resource bundle. Due to
the lookup strategy performed by ResourceBundle.getBundle(), one must always provide
a dedicated resource bundle for this default language, too. This bundle should be empty because it
inherits the strings via the parent chain from the base bundle, but it must exist.
The following example illustrates this requirement. Imagine the broken resource bundle family shown
below which is intended to provide localization for English, German and French:

src/
+- main/
+- resources/
+- mymojo-report.properties
+- mymojo-report_de.properties
+- mymojo-report_fr.properties

Now, if a resource bundle is to be looked up for English on a JVM whose default locale happens to be
French, the bundle mymojo-report_fr.properties will be loaded instead of the intended bundle
mymojo-report.properties.
Reporting plugins that suffer from this bug can easily be detected by executing mvn site -D
locales=xy,en where xy denotes any other language code supported by the particular plugin.
Specifying xy as the first locale will have the Maven Site Plugin change the JVM's default locale to
xy which in turn causes the lookup for en to fail as outlined above unless the plugin has a dedicated
resource bundle for English.

67.1.5 Using System Properties
Maven's command line supports the definition of system properties via arguments of the form -
D key=value. While these properties are called system properties, plugins should never use
System.getProperty() and related methods to query these properties. For example, the following
code snippet will not work reliably when Maven is embedded, say into an IDE or a CI server:

public MyMojo extends AbstractMojo
{
{
/*
* FIXME: This prevents proper embedding into IDEs or CI systems.
*/
String value = System.getProperty( "maven.test.skip" );
}
}

The problem is that the properties managed by the System class are global, i.e. shared among
all threads in the current JVM. To prevent conflicts with other code running in the same JVM,
Maven plugins should instead query the execution properties. These can be obtained from
MavenSession.getExecutionProperties().

67.1.6 Using Shutdown Hooks
People occasionally employ shutdown hooks to perform cleanup tasks, e.g. to delete temporary files
as shown in the example below:



{
{
File tempFile = File.createTempFile( "temp", null );
/*
* FIXME: This assumes the JVM terminates soon after
* the Maven build has finished.
*/
tempFile.deleteOnExit();
}
}

The problem is that the JVM executing Maven can be running much longer than the actual Maven
build. Of course, this does not apply to the standalone invocation of Maven from the command line.
However, it affects the embedded usage of Maven in IDEs or CI servers. In those cases, the cleanup
tasks will be deferred, too. If the JVM is then executing a bunch of other Maven builds, many such
cleanup tasks can sum up, eating up resources of the JVM.
For this reason, plugin developers should avoid usage of shutdown hooks and rather use try/
finally blocks to perform cleanup as soon as the resources are no longer needed.

67.1.7 Resolving Relative Paths
It is common practice for users of Maven to specify relative paths in the POM, not to mention that
the Super POM does so, too. The intention is to resolve such relative paths against the base directory
of the current project. In other words, the paths target/classes and ${basedir}/target/
classes should resolve to the same directory for a given POM.
Unfortunately, the class java.io.File does not resolve relative paths against the project's base
directory. As mentioned in its class javadoc, it resolves relative paths against the current working
directory. In plain English: Unless a Maven component has complete control over the current working
directory, any usage of java.io.File in combination with a relative path is a bug.
At first glance, one might be tempted to argue that the project base directory is equal to the current
working directory. However, this assumption is generally not true. Consider the following scenarios:

a Reactor Builds
When a child module is build during a reactor build, the current working directory is usually the
base directory of the parent project, not the base directory of the current module. That is the most
common scenario where users are faced with the bug.
b Embedded Maven Invocations
Other tools, most notably IDEs, that run Maven under the hood may have set the current working
directory to their installation folder or whatever they like.
c Maven Invocations using the -f Switch
While it is surely an uncommon use-case, the user is free to invoke Maven from an arbitrary
working directory by specifying an absolute path like mvn -f /home/me/projects/demo/
pom.xml.
Hence this example code is prone to misbehave:



{
/**
* @parameter
*/
private String outputDirectory;
{
/*
* FIXME: This will resolve relative paths like "target/classes" against
* the user's working directory instead of the project's base directory.
*/
File outputDir = new File( outputDirectory ).getAbsoluteFile();
}
}

In order to guarantee reliable builds, Maven and its plugins must manually resolve relative paths
against the project's base directory. A simple idiom like the following will do just fine:

File file = new File( path );
if ( !file.isAbsolute() )
{
file = new File( project.getBasedir(), file );
}

Many Maven plugins can get this resolution automatically if they declare their affected mojo
parameters of type java.io.File instead of java.lang.String. This subtle difference
in parameter types will trigger a feature known as path translation, i.e. the Maven core will
automatically resolve relative paths when it pumps the XML configuration into a mojo.

67.1.8 Determining the Output Directory for a Site Report
Most reporting plugins inherit from AbstractMavenReport. In doing so, they need to implement
the inherited but abstract method getOutputDirectory(). To implement this method, plugins
usually declare a field named outputDirectory which they return in the method. Nothing wrong so
far.
Now, some plugins need to create additional files in the report output directory that accompany
the report generated via the sink interface. While it is tempting to use either the method
getOutputDirectory() or the field outputDirectory directly in order to setup a path for the
output files, this leads most likely to a bug. More precisely, those plugins will not properly output
files when run by the Maven Site Plugin as part of the site lifecycle. This is best noticed when the
output directory for the site is configured directly in the Maven Site Plugin such that it deviates from
the expression ${project.reporting.outputDirectory} that the plugins use by default. Multi-
language site generation is another scenario to exploit this bug which is illustrated below:



public MyReportMojo extends AbstractMavenReport
{
/**
* @parameter default-value="${project.reporting.outputDirectory}"
*/
private File outputDirectory;
protected String getOutputDirectory()
{
return outputDirectory.getAbsolutePath();
}
public void executeReport( Locale locale )
{
/*
* FIXME: This assumes the mojo parameter reflects the effective
* output directory as used by the Maven Site Plugin.
*/
outputDirectory.mkdirs();
}
}

There are in principal two situations in which a report mojo could be invoked. The mojo might
be run directly from the command line or the default build lifecycle or it might be run indirectly
as part of the site generation along with other report mojos. The glaring difference between these
two invocations is the way the output directory is controlled. In the first case, the parameter
outputDirectory from the mojo itself is used. In the second case however, the Maven Site Plugin
takes over control and will set the output directory according to its own configuration by calling
MavenReport.setReportOutputDirectory() on the reports being generated.
Therefore, developers should always use MavenReport.getReportOutputDirectory()
if they need to query the effective output directory for the report. The implementation of
AbstractMavenReport.getOutputDirectory() is only intended as a fallback in case the mojo
is not run as part of the site generation.

67.1.9 Retrieving the Mojo Logger
Maven employs an IoC container named Plexus to setup a plugin's mojos before their execution. In
other words, components required by a mojo will be provided by means of dependency injection,
more precisely field injection. The important point to keep in mind is that this field injection happens
after the mojo's constructor has finished. This means that references to injected components are
invalid during the construction time of the mojo.
For example, the next snippet tries to retrieve the mojo logger during construction time but the mojo
logger is an injected component and as such has not been properly initialized yet:


{
/*
* FIXME: This will retrieve a wrong logger instead of the intended mojo logger.
*/
private Log log = getLog();
{
log.debug( "..." );
}
}

In case of the logger, the above mojo will simply use a default console logger, i.e. the code defect is
not immediately noticeable by a NullPointerException. This default logger will however use a
different message format for its output and also outputs debug messages even if Maven's debug mode
was not enabled. For this reason, developers must not try to cache the logger during construction time.
The method getLog() is fast enough and can simply be called whenever one needs it.

67.1.10 Depending on Plexus Utilities 1.1+
Up to Maven 2.0.5, version 1.1 of the artifact plexus-utils was included in the Maven core class
loader which is shared with the plugin class realm. This effectively prevented plugins from using
another/newer version of plexus-utils. This has been solved starting with Maven 2.0.6 by shading
(most of) the classes from plexus-utils (see MNG-2892).
In short, plugins that strictly require a newer version of plexus-utils also require Maven 2.0.6 as a
minimum. Hence, a POM snippet for a Maven plugin like shown below is misleading:

<project>
...
<prerequisites>

<maven>2.0</maven>
</prerequisites>
...
<dependencies>
<dependency>
<groupId>org.codehaus.plexus</groupId>
<artifactId>plexus-utils</artifactId>
</dependency>
</dependencies>
...
</project>

68 Mojo API 286

68 Mojo API
.......................................................................................................................................

68.1 Introduction
Starting with Maven, plugins can be written in Java or any of a number of scripting languages.
Plugins consists of one or more Mojos, each one being the implementation for one of the plugin's
goals. Maven tries to stay out of the way of the programmer with its new Mojo API. This opens up
the opportunity for many Mojos to be reused outside of Maven, or bridged into Maven from external
systems like Ant.
NOTE: For now, we will limit the discussion to Java-based Mojos, since each scripting language will
present these same basic requirements with various forms of implementation.
Although the requirements on Mojos are minimal by design, there are still a very few requirements
that Mojo developers must keep in mind. Basically, these Mojo requirements are embodied by the
org.apache.maven.plugin.Mojo interface, which the Mojo must implement (or else extend
its abstract base class counterpart org.apache.maven.plugin.AbstractMojo ). This interface
guarantees the correct execution contract for the Mojo: no parameters, void return type, and a
throws clause that allows only org.apache.maven.plugin.MojoExecutionException and its
derivatives. It also guarantees that the Mojo will have access to the standard Maven user-feedback
mechanism, org.apache.maven.monitor.logging.Log , so the Mojo can communicate
important events to the console or other log sink.
As mentioned before, each Plugin - or packaged set of Mojos - must provide a descriptor called
plugin.xml under the path META-INF/maven inside the Plugin jar file. Fortunately, Maven also
provides a set of Javadoc annotations and tools to generate this descriptor, so developers don't have to
worry about directly authoring or maintaining a separate XML metadata file.
To serve as a quick reference for the developer, the rest of this page will document these features (the
API, along with the annotations) which are considered the best practice for developing Mojos.

68.2 API Documentation

68.2.1 org.apache.maven.plugin.Mojo
This interface forms the contract required for Mojos to interact with the Maven infrastructure. It
features an execute() method, which triggers the Mojo's build-process behavior, and can throw a
MojoExecutionException if an error condition occurs. See below for a discussion on proper use
of this Exception class. Also included is the setLog(..) method, which simply allows Maven to
inject a logging mechanism which will allow the Mojo to communicate to the outside world through
standard Maven channels.
68.Method Summary:

• void setLog( org.apache.maven.monitor.logging.Log )
Inject a standard Maven logging mechanism to allow this Mojo to communicate events and
feedback to the user.
• void execute() throws org.apache.maven.plugin.MojoExecutionException
Perform whatever build-process behavior this Mojo implements. This is the main trigger for the
Mojo inside the Maven system, and allows the Mojo to communicate fatal errors by throwing an
instance of MojoExecutionException.
The MojoExecutionException (and all error conditions inside the Mojo) should be handled
very carefully. The simple wrapping of lower-level exceptions without providing any indication
of a user-friendly probable cause is strictly discouraged. In fact, a much better course of action


68 Mojo API 287

is to provide error handling code (try/catch stanzas) for each coherent step within the Mojo's
execution. Developers are then in a much better position to diagnose the cause of any error, and
provide user-friendly feedback in the message of the MojoExecutionException.

68.2.2 org.apache.maven.plugin.AbstractMojo
Currently, this abstract base class simply takes care of managing the Maven log for concrete
derivations. In keeping with this, it provides a protected method, getLog():Log , to furnish Log
access to these concrete implementations.
68.Method Summary:
• public void setLog( org.apache.maven.monitor.logging.Log )
[IMPLEMENTED]
Inject a standard Maven logging mechanism to allow this Mojo to communicate events and
feedback to the user.
• protected Log getLog()
[IMPLEMENTED]
Furnish access to the standard Maven logging mechanism which is managed in this base class.
• void execute() throws org.apache.maven.plugin.MojoExecutionException
[ABSTRACT]
Perform whatever build-process behavior this Mojo implements. See the documentation for
Mojo above for more information.

68.2.3 org.apache.maven.monitor.logging.Log
This interface supplies the API for providing feedback to the user from the Mojo, using standard
Maven channels. There should be no big surprises here, although you may notice that the methods
accept java.lang.CharSequence rather than java.lang.String . This is provided mainly as a
convenience, to enable developers to pass things like StringBuffer directly into the logger, rather
than formatting first by calling toString() .
68.Method Summary:
• void debug( java.lang.CharSequence )
Send a message to the user in the debug error level.
• void debug( java.lang.CharSequence, java.lang.Throwable )
Send a message (and accompanying exception) to the user in the debug error level. The error's
stacktrace will be output when this error level is enabled.
• void debug( java.lang.Throwable )
Send an exception to the user in the debug error level. The stack trace for this exception will be
output when this error level is enabled.
• void info( java.lang.CharSequence )
Send a message to the user in the info error level.
• void info( java.lang.CharSequence, java.lang.Throwable )
Send a message (and accompanying exception) to the user in the info error level. The error's
• void info( java.lang.CharSequence )
Send an exception to the user in the info error level. The stack trace for this exception will be
• void warn( java.lang.CharSequence )


68 Mojo API 288

Send a message to the user in the warn error level.
• void warn( java.lang.CharSequence, java.lang.Throwable )
Send a message (and accompanying exception) to the user in the warn error level. The error's
• void warn( java.lang.CharSequence )
Send an exception to the user in the warn error level. The stack trace for this exception will be
• void error( java.lang.CharSequence )
Send a message to the user in the error error level.
• void error( java.lang.CharSequence, java.lang.Throwable )
Send a message (and accompanying exception) to the user in the error error level. The error's
• void error( java.lang.CharSequence )
Send an exception to the user in the error error level. The stack trace for this exception will be

68.3 The Descriptor and Annotations
In addition to the normal Java requirements in terms of interfaces and/or abstract base classes which
need to be implemented, a plugin descriptor must accompany these classes inside the plugin jar. This
descriptor file is used to provide metadata about the parameters and other component requirements for
a set of Mojos so that Maven can initialize the Mojo and validate its configuration before executing
it. As such, the plugin descriptor has a certain set of information that is required for each Mojo
specification to be valid, as well as requirements for the overall plugin descriptor itself.
NOTE: In the following discussion, bolded items are the descriptor's element name along with
a Javadoc annotation (if applicable) supporting that piece of the plugin descriptor. A couple
of examples are: someElement (@annotation parameterName="parameterValue") or
someOtherElement (@annotation <rawAnnotationValue>) .
The plugin descriptor must be provided in a jar resource with the path: META-INF/maven/
plugin.xml , and it must contain the following:

Descriptor Element Required? Notes
mojos Yes Descriptors for each Mojo provided
by the plugin, each inside a mojo
sub-element. Mojo descriptors are
covered in detail below. Obviously,
a plugin without any declared
Mojos doesn't make sense, so
the mojos element is required,
along with at least one mojo sub-
element.


68 Mojo API 289

dependencies Yes A set of dependencies which the
plugin requires in order to function.
Each dependency is provided
inside a dependency sub-element.
Dependency specifications are
covered below. Since all plugins
must have a dependency on
maven-plugin-api , this
element is effectively required.
Using the plugin toolset, these
dependencies can be extracted
from the POM's dependencies.

Each Mojo specified inside a plugin descriptor must provide the following (annotations specified here
are at the class level):

Descriptor Element Annotation Required? Notes
aggregator @aggregator No Flags this Mojo to run it in
a multi module way, i.e.
aggregate the build with
the set of projects listed
as modules.
configurator @configurator <roleHint> No The configurator type
to use when injecting
parameter values
into this Mojo. The
value is normally
deduced from the Mojo's
implementation language,
but can be specified
to allow a custom
ComponentConfigurator
implementation to be
used. NOTE: This will
only be used in very
special cases, using
a highly controlled
vocabulary of possible
values. (Elements like this
are why it's a good idea to
use the descriptor tools.)


68 Mojo API 290

execute • @execute No When this goal is invoked,
phase="<phaseName>" it will first invoke a parallel
lifecycle="<lifecycleId>" lifecycle, ending at the
• @execute given phase. If a goal
phase="<phaseName>" is provided instead of a
phase, that goal will be
• @execute
executed in isolation.
goal="<goalName>"
The execution of either
will not affect the current
project, but instead
make available the
${executedProject}
expression if required.
An alternate lifecycle
can also be provided: for
more information see the
documentation on the
build lifecycle.
executionStrategy @executionStrategy No Specify the execution
<strategy> strategy. NOTE: Currently
supports once-per-
session, always.
goal @goal <goalName> Yes The name for the Mojo
that users will reference
from the command line to
execute the Mojo directly,
or inside a POM in order
to provide Mojo-specific
configuration.
inheritByDefault @inheritByDefault <true| No. Default: true Specify that the Mojo is
false> inherited.
instantiationStrategy @instantiationStrategy No. Default: per- Specify the instantiation
<per-lookup> lookup strategy.
phase @phase <phaseName> No Binds this Mojo to a
particular phase of the
standard build lifecycle, if
specified. NOTE: This is
only required if this Mojo
is to participate in the
standard build process.
requiresDependencyResolution
@requiresDependencyResolution
No Flags this Mojo
<requiredScope> as requiring the
dependencies in the
specified scope (or
an implied scope) to
be resolved before it
can execute. Currently
supports compile,
runtime, and test
scopes. If this annotation
is present but no scope
is specified, the scope
defaults to runtime.
requiresDirectInvocation @requiresDirectInvocation No. Default: false Flags this Mojo to be
<true|false> invoke directly.


68 Mojo API 291

requiresOnline @requiresOnline <true| No. Default: true Flags this Mojo to be run
false> in online mode.
requiresProject @requiresProject <true| No. Default: true Flags this Mojo to run
false> inside of a project.
requiresReports @requiresReports <true| No. Default: false Flags this Mojo to require
false> reports.
description none (detected) No The description of this
Mojo's functionality. Using
the toolset, this will be
the class-level Javadoc
description provided.
NOTE: While this is not a
required part of the Mojo
specification, it SHOULD
be provided to enable
future tool support for
browsing, etc. and for
clarity.
implementation none (detected) Yes The Mojo's fully-qualified
class name (or script path
in the case of non-Java
Mojos).
language none (detected) No. Default: java The implementation
language for this Mojo
(Java, beanshell, etc.).
deprecated @deprecated No Specify the version when
<deprecated-text> the Mojo was deprecated
to the API. Similar to
Javadoc deprecated.
This will trigger a warning
when a user tries to
configure a parameter
marked as deprecated.
since @since <since-text> No Specify the version when
the Mojo was added
Javadoc since.

Each Mojo specifies the parameters that it expects in order to work. These parameters are the Mojo's
link to the outside world, and will be satisfied through a combination of POM/project values, plugin
configurations (from the POM and configuration defaults), and System properties.
NOTE[1]: For this discussion on Mojo parameters, a single annotation may span multiple elements in
the descriptor's specification for that parameter. Duplicate annotation declarations in this section will
be used to detail each parameter of an annotation separately.
NOTE[2]: In many cases, simply annotating a Mojo field with @parameter will be enough to allow
injection of a value for that parameter using POM configuration elements. The discussion below
shows advanced usage for this annotation, along with others.
Each parameter for a Mojo must be specified in the plugin descriptor as follows:

Descriptor Element Annotation Required? Notes


68 Mojo API 292

alias @parameter No Specifies an alias which
alias="myAlias" can be used to configure
this parameter from the
POM. This is primarily
useful to improve user-
friendliness, where Mojo
field names are not
intuitive to the user or are
otherwise not conducive
to configuration via the
POM.
configuration @component role="..." No Populates the field with
roleHint="..." an instance of a Plexus
component. This is like
declaring a requirement
in a Plexus component.
The default requirement
will have a role equal to
the declared type of the
field, and will use the role
hint "default". You can
customise either of these
by providing a role and/
or roleHint parameter.
e.g. @component
role="org.apache.maven.artifact
roleHint="ear".
Note: This is identical
to the deprecated
form of parameter:
@parameter
expression="${component.yourpac


68 Mojo API 293

configuration @parameter No Specifies the expressions
expression="${aSystemProperty}" used to calculate the
default- value to be injected into
value="${anExpression}" this parameter of the
Mojo at buildtime. The
expression given by
default-value is
commonly used to refer
to specific elements
in the POM, such as
${project.resources},
which refers to the list
of resources meant to
accompany the classes
in the resulting JAR file.
Of course, the default
value need not be an
expression but can also
be a simple constant
like true or 1.5.
And for parameters
of type String one
can mix expressions
with literal values, e.g.
${project.artifactId}-
${project.version}-
special. The system
property given by
expression enables
users to override the
default value from the
command line via -
DaSystemProperty=value.
NOTE: If neither
default-value
nor expression are
specified, the parameter
can only be configured
from the POM. The use
of '${' and '}' is required to
delimit actual expressions
which may be evaluated.


68 Mojo API 294

editable @readonly No Specifies that this
parameter cannot be
configured directly
by the user (as in the
case of POM-specified
configuration). This is
useful when you want
to force the user to use
common POM elements
rather than plugin
configurations, as in the
case where you want
to use the artifact's final
name as a parameter.
In this case, you want
the user to modify
<build><finalName/
></build> rather than
specifying a value for
finalName directly in
the plugin configuration
section. It is also useful to
ensure that - for example
- a List-typed parameter
which expects items
of type Artifact doesn't
get a List full of Strings.
NOTE: Specification
of this annotation flags
the parameter as non-
editable; there is no true/
false value.
required @required No Whether this parameter
is required for the Mojo to
function. This is used to
validate the configuration
for a Mojo before it is
injected, and before
the Mojo is executed
from some half-state.
NOTE: Specification of
this annotation flags the
parameter as required;
there is no true/false
value.
description none (detected) No The description of this
parameter's use inside
the Mojo. Using the
toolset, this is detected as
the Javadoc description
for the field. NOTE: While
this is not a required
part of the parameter
specification, it SHOULD
be provided to enable
future tool support for
browsing, etc. and for
clarity.


68 Mojo API 295

name none (detected) Yes The name of the
parameter, to be used in
configuring this parameter
from the Mojo's declared
defaults (discussed
below) or from the POM.
Using the toolset, this is
detected as the Java field
name.
type none (detected) Yes The Java type for this
parameter. This is used
to validate the result of
any expressions used
to calculate the value
which should be injected
into the Mojo for this
parameter. Using the
toolset, this is detected
as the class of the Java
field corresponding to this
parameter.
deprecated @deprecated No Specify the version when
<deprecated-text> the Mojo was deprecated
Javadoc deprecated.
This will trigger a warning
when a user tries to
configure a parameter
marked as deprecated.
since @since <since-text> No Specify the version when
the Mojo was added
Javadoc since.

The final component of a plugin descriptor is the dependencies. This enables the plugin to function
independently of its POM (or at least to declare the libraries it needs to run). Dependencies are taken
from the runtime scope of the plugin's calculated dependencies (from the POM). Dependencies
are specified in exactly the same manner as in the POM, except for the <scope> element (all
dependencies in the plugin descriptor are assumed to be runtime, because this is a runtime profile for
the plugin).

68.4 Plugin Tools
By now, we've mentioned the plugin tools several times without telling you what they are or how to
use them. Instead of manually writing (and maintaining) the metadata detailed above, Maven ships
with some tools to aid in this task. In fact, the only thing a plugin developer needs to do is declare
his project to be a plugin from within the POM. Once this is done, Maven will call the appropriate
descriptor generators, etc. to produce an artifact that is ready for use within Maven builds. Optional
metadata can be injected via Javadoc annotation (and possibly JDK5 annotations in the future) as
described above, enabling richer interactions between the Mojo and the user. The section below
describes the changes to the POM which are necessary to create plugin artifacts.


68 Mojo API 296

68.5 Project Descriptor (POM) Requirements
From the POM, Maven plugin projects look quite similar to any other project. For pure Java plugins,
the differences are even smaller than for script-based plugins. The following details the POM
elements which are necessary to build a Maven plugin artifact.

Required for Java
POM Element Mojos? Sample Declaration Notes
packaging Yes <packaging> The POM must declare a
maven-plugin </ packaging element which
packaging> describes this project as a
Maven plugin project.
scriptSourceDirectory No <scriptSourceDirectory>case of script-
In the
src/main/ based Mojos (which are
scripts </ not covered in detail
scriptSourceDirectory> this document),
within
the POM must include
an additional element
to distinguish script
sources from (optional)
Java supporting
classes. This element is
scriptSourceDirectory,
inside the build section.
This directory is included
in the list of resources
which accompany any
compiled code in the
resulting artifact. It is
specified separately
from the resources in the
build section to denote
its special status as an
alternate source directory
for scripts.

After making the changes above, the developer can simply call

mvn install

to install the plugin to the local repository. (Any of the other standard lifecycle targets like package,
deploy, etc. are also available in like fashion.)

68.6 IDE integration
If you're using JetBrains IntelliJ IDEA to develop your plugin, you can use the following to configure
the javadoc annotations as live templates.
1 Download this file, and place it in $USER_HOME/.IntelliJIdea/config/templates
2 (re)startup IntelliJ IDEA (templates are loaded on startup)
3 add the following list to Settings -> IDE -> Errors -> General -> Unknown javadoc tags ->
Additional javadoc tags
4 aggregator, execute, goal, phase, requiresDirectInvocation, requiresProject, requiresReports,
requiresOnline, parameter, component, required, readonly


68 Mojo API 297

68.7 Resources
This section simply gives a listing of pointers for more information.

• QDox Project (Javadoc annotations) [ link ]
• Plexus Project (Plexus container) [ link ]
• Maven Plugin Descriptor API [ link ]
• MojoDescriptor API [ link ]


69 Maven Repository Centre 298

69 Maven Repository Centre
.......................................................................................................................................

69.1 Maven Repository Centre
This documentation centre is for those that need to use or contribute to the Maven repository. This
includes those that need dependencies for their own build, notice errors in the repository metadata, or
projects that wish to have their releases added to the Maven repository.

• Maintaining your Metadata - Information for third-party projects
• Guide to Maven Evangelism - Helping to improve the metadata of the dependencies you use
• Guide to uploading artifacts - How to get things uploaded to the repository


70 Guide to Maven Evangelism 299

70 Guide to Maven Evangelism
.......................................................................................................................................

70.1 Guide to add, improve or fix metadata in the Central Maven 2 repository
There are artifacts in the repository that don't have POMs. They come from the Maven 1 repositories
of our partners (Apache Software Foundation, Codehaus,...). We know it but can't do anything unless
you provide a POM for it or you ask the project in question to add the POM when they add the
artifacts.
We don't change dependencies in POMs already in the repository anymore as builds need to be
reproducible. Same applies to POMs that don't exist. We can add a POM with no dependencies,
because doing any other way would break previous builds that were using that project.
An alternative is to create a new version with the fixes. If the broken project is org.foo/bar/1.0 you can
provide a fixed POM,JAR,... under org.foo/bar/1.0-1 (add a comment to the POM explaining what is
being fixed and why). See Maven Respository Upload for the instructions to get this new version in
the repository.
You need to contact the original publisher of the metadata to make sure in next versions it will be
fixed or improved before getting it into the repository.
For any other types of issues related to metadata in the repository, open an issue at JIRA MEV with
the relevant information and explain the reasons why it is an issue.

• Important:* by default assume that we won't trust your info, so you must provide all links to the
project documentation you can to convince us that your solution is right.


71 Guide to uploading artifacts 300

71 Guide to uploading artifacts
.......................................................................................................................................

71.1 Guide to uploading artifacts to the Central Repository
In order for users of Maven to utilize artifacts produced by your project you must deploy them to a
remote repository. Many open source projects want to allow users of their projects who build with
Maven to have transparent access to their project's artifacts. In order to allow for this a project must
have their artifacts deployed to the Central Repository.

71.2 Requirements
Only releases can be uploaded to the central repository, that means files that won't change and that
only depend on other files already released and available in the repository.
There are some requirements for the minimal information in the POMs that are in the central
repository. At least these must be present:
• modelVersion
• groupId
• artifactId
• packaging
• name
• version
• description
• url
• licenses
• scm url
• dependencies

71.2.1 groupId
The groupId will identify your project uniquely across all projects, so we need to enforce a naming
schema. For projects with artifacts already uploaded to the Central Repository it can be equal to the
one used previously, but for new projects it has to follow the package name rules, what means that
has to be at least as a domain name you control, and you can create as many subgroups as you want.
There are a lot of poorly defined package names so you must provide proof that you control the
domain that matches the groupId. Provide proof means that the project is hosted at that domain or it's
owned by a member, in that case you must give the link to the registrar database (whois) where the
owner is listed and the page in the project web where the owner is associated with the project. eg. If
you use a com.sun.xyz package name we expect that the project is hosted at http://xyz.sun.com.
Look at More information about package names. Check also the guide about Maven naming
conventions.
Examples:
• www.springframework.org -> org.springframework
• oness.sf.net -> net.sf.oness

71.2.2 Explanation
Some folks have asked why do we require all this information in the POM for deployed artifacts so
here's a small explanation. The POM being deployed with the artifact is part of the process to make


transitive dependencies a reality in Maven. The logic for getting transitive dependencies working is
really not that hard, the problem is getting the data. The other applications that are made possible by
having all the POMs available for artifacts are vast, so by placing them into the repository as part of
the process we open up the doors to new ideas that involve unified access to project POMs.
We also ask for license now because it is possible that your project's license may change in the course
of its life time and we are trying create tools to help normal people sort out licensing issues. For
example, knowing all the licenses for a particular graph of artifacts we could have some strategies that
would identify potential licensing problems.

71.2.3 A basic sample:

<project>
<artifactId>maven</artifactId>
<name>Maven core</name>
<description>The maven main core project description</description>
<licenses>
<license>
<name>The Apache Software License, Version 2.0</name>
<url>http://www.apache.org/licenses/LICENSE-2.0.txt</url>
<distribution>repo</distribution>
</license>
</licenses>
<scm>
<url>http://svn.apache.org/viewcvs.cgi/maven</url>
</scm>
<dependencies>
<dependency>
<groupId>...</groupId>
<artifactId>...</artifactId>
<version>...</version>
</dependency>
...
</dependencies>

</project>

71.2.4 FAQ and common mistakes

• I have other repositories or pluginRepositories listed in my POM, is that a problem?
Yes, the central repository must be self contained, which means that all your dependencies
must already be in the central repository. You need to remove the repositories and
pluginRepositories entries and make sure your project still builds when your local
repository cache is empty.


The only exception allowed is when a dependency can not be distributed from the central
repository due to the license. In that case only the POM for that dependency is required, listing
where the dependency can be downloaded from. See an example.
• I have a patched version of the foo project developed at foo.com, what groupId should I use?
When you patch / modify a third party project, that patched version becomes your project and
therefore should be distributed under a groupId you control as any project you would have
developed, never under com.foo. See above considerations about groupId.
• My project is hosted at a project hosting service like SourceForge or dev.java.net, what should I
use as groupId?
If your project name is foo at SourceForge, then net.sf.foo. If it's foo at dev.java.net, then
net.java.dev.foo

71.3 Sync'ing your own repository to the central repository automatically
This is the preferred process. You first have to setup your project to deploy to a remote repository.
You must make sure the remote repository server has rsync or rsync over ssh, there are free services
like Sourceforge that provide you ssh server access. Or you can setup your own server.
After you are able to deploy to your remote repository make sure you only deploy releases. Then
you need to provide us the following information in a comma delimited format
• groupId, eg. org.apache.maven
• location, eg. mavensync@web.sourceforge.net:/home/groups/m/ma/maven-js-
plugin/htdocs/m2repo for rsync over ssh or rsync://maven2.hortis.ch/releases
for non secure rsync
• protocol, rsync or rsync_ssh
• contactName, your name
• contactMail, your email (not a mailing list)
The comma delimited version would be something like this. Note that the two last columns are for
internal purposes, so you can omit them.

"org.apache.maven","mavensync@web.sourceforge.net:/home/groups/m/ma/maven-js-plugin/
"org.apache.maven","rsync://maven2.hortis.ch/releases","rsync","John Doe","doe@doe.c

You can see the list of automatically synchronized repositories.
Open an issue in JIRA with the information (in the comma delimited format), and we'll add it to the
list of automatically synced repositories.
Make sure you provide proof of owning the domain that matches the groupId (see groupId
considerations above). Proof means either the server to sync from has a name under that domain, your
name shows up in a prominent place in the domain or you provide a link to a whois database where
your name shows up as the domain owner.
If you are using ssh in your own server you need to add the maven public key to the authorized ones
to allow us to log in to the machine.
Remember to subscribe to the repo-maintainers mailing list. (Or watch the Atom feed.)
Important: nothing is deleted or changed in the Central Repository after it is synced (except maven-
metadata.xml files).

71.3.1 Sync FAQ
• Can I provide a sync for a groupId of a third party project?



If the third party project is not willing to provide a repository to sync from, and you are a regular
user of Maven and the third party project, the answer is yes. You can set up a repository as if the
project were yours (see instructions above). Please create a JIRA issue first describing what you
are trying to do and why, and you may be designated the "unofficial" mantainer of the repository
section associated with that project, and you will be responsible of publishing the new releases
for that project in your repository if other users request it. You can opt out at any time.

71.4 Manual upload of artifacts
Note that this manual process is time consuming and will only be accepted for a limited number of
requests. If you want to upload frequently read the section above about automatic sync.
Estimated process time is FOUR WEEKS. If you want to use the manual process, that is the
estimated time to process if no problems are detected. It means that for each version you release and
want to upload to the central repository you will have to wait that time. If a problem is detected, it will
be noted in the JIRA issue and you will wait again until the next time the issues are processed.

71.4.1 Step 1: Create an upload bundle
Use the repository plugin provided with the standard Maven distribution to create an upload bundle:

mvn repository:bundle-create

The bundle will be created in your target directory with the name: ${pom.artifactId}-
${pom.currentVersion}-bundle.jar
If you want to include a jar with java sources in your upload (recommended, unless your license
doesn't allow sources to be redistributed) the command to run is:
Note: due to a bug in repository:bundle-create you will need to manually add the javadoc
jar to the bundle jar, using zip or any other compression program.

mvn source:jar javadoc:jar repository:bundle-create

If you are not using Maven as your build system, and want something uploaded to the Central
Repository then you just need to make a bundle jar manually. Please use the jar executable, not zip,
pkzip or equivalent. The bundle should have the following content:

pom.xml
foo-1.0.jar (or whatever artifact is referred to in the pom.xml)
foo-1.0-sources.jar (optional, jar containing java sources)
foo-1.0-javadoc.jar (optional, jar containing javadocs)

The names of the jar files inside the bundle must be built from the <artifactId> and <version> in the
pom.xml file, like this:

${artifactId}-${version}.jar
${artifactId}-${version}-sources.jar (optional)
${artifactId}-${version}-javadoc.jar (optional)

Note: the bundle will be read by a script, so it must follow the above format.
Be sure to always check previous versions of the POMs in the repository to use the information
already there as a base.



71.4.2 Step 2: Posting the request
Post your request to JIRA. Make sure that the project is "Maven Upload Requests" and the issue type
is "Wish". In the Description field, you must write the URL to the upload bundle. If you're uploading
more than one bundle please add all the URLs under the same issue. Then leave a blank line and
provide the following information:
• A URL where the project can be found.
• If you are one of its developers, a URL where your name or email can be found inside the project
site.
This will speed up the uploading process.
You can place any additional comments in the following paragraph. So the Description field might
look like:

http://wiggle.sourceforge.net/downloads/wiggle-1.0-bundle.jar
http://wiggle.sourceforge.net
http://wiggle.sourceforge.net/team-list.html
I'm a developer in wiggle, please upload!

or

http://wiggle.sourceforge.net/downloads/wiggle-1.0-bundle.jar
http://wiggle.sourceforge.net
http://wiggle.sourceforge.net/team-list.html
I'm a developer in wiggle, and want to use the org.wiggle groupId
I own wiggle.org domain, you can see my name in
http://reports.internic.net/cgi/whois?whois_nic=wiggle.org&type=domain
or you can see the project web page in www.wiggle.org

71.4.3 Manual process FAQ and common mistakes
• I use parent POMs. How do I include them in the bundle?
You can't. You need to use the automated synchronization process noted above.
• I want to upload several bundles. Do I need to create a JIRA issue for each one?
No, please ignore the Bundle URL field in this case. Just put the URLs of all the bundles in the
Description or Comments fields of one single JIRA issue.

71.5 Maven partners
There is a list of sites that automatically sync their project repository with the central one. If you want
a project from any of these sites to be uploaded to the Central Repository you'll have to contact their
project maintainers. Check the updated list
Some of the most known groups automatically synced are:
• The Apache Software Foundation
• Codehaus
• MortBay Jetty
• OpenSymphony

71.6 For Maven developers
The scripts to make the upload to the repository are at https://svn.apache.org/repos/asf/
maven/repository-tools/trunk in the src/bin directory.



Those scripts are checked out to repo1.maven.org in the directory /home/maven/bin, so after
logging in as the user maven you can go to the directory bin/bundle-upload and run

./deploy-bundle bundle_URL [groupId] [version] [classifier]

That script will download the bundle, decompress it and show the POM. You have to make sure
that the POM is correct. The script uses the command less to show the POM. Use the space key
to step through it to the end. The press the q key to proceed. After that a summary with groupId,
artifactId and version will be shown, and whether or not the group already exists. This is useful
as we have to be careful creating new groups, making sure they follow the conventions and that they
don't already exist with another name. If the POM is not correct or there's any doubt the upload must
be aborted with Ctrl-C, and a comment posted in the upload request in JIRA. If there's no response
from the reporter within one month the request will be closed as "Incomplete".
If groupId and version are not specified in the command line, the script will try to get the values
from the POM. It won't work if the POM extends another POM and those elements are not present in
the POM included in the bundle.
Things to remember:

• All the dependencies have to already be present in the central repository.
• If there are no dependencies it's suspicious, and the reporter must be asked if that's correct. Do
that in an issue comment in JIRA.
• Parent POMs have to already be present in the central repository.
• All the minimal information previously mentioned has to be in the POM.
• POMs must include at least as much information as previous versions, and the dependencies
shouldn't change too much.
• While checking a previous version, also check if it was relocated. If so ask the reporter to update
the bundle with the new information.
• GroupIds have to follow the previously stated naming conventions.
• Upload requests for popular projects require you to be extremely careful (javax.* groups, spring,
hibernate, ...).


72 Maven Developer Centre 306

72 Maven Developer Centre
.......................................................................................................................................

72.1 Maven Developer Centre
This documentation centre is for people who are Maven developers, or would like to contribute.
If you cannot find your answers here, feel free to ask the Maven Developer List.

72.1.1 Contributors Resources

• Guide to helping with Maven
• Developing Maven 2
• Common Bugs and Pitfalls
• Building Maven 2
• Continuous Integration
• Source Repository

72.1.2 Committers Resources

72.1.2.1 General Resources

• Guide for new Maven committers
• Committer Environment
• Committer Settings

72.1.3 Developers Conventions
There are a number of conventions used in the Maven projects, which contributors and developers
alike should follow for consistency's sake.
• Maven Code Style And Conventions
Note: If you cannot find your answers here, feel free to ask the Maven Developer List.

72.1.4 Making Releases

• Making GPG Keys
• Release Process

72.1.5 Deploy Maven references

• Deploy Maven Current References

72.1.6 Others Resources

• Maven Web Stats
• Maven Mailing List Stats
• ASF Development Infrastructure Information


72 Maven Developer Centre 307

• About the Apache Software Foundation


73 Developing Maven 2 308

73 Developing Maven 2
.......................................................................................................................................

73.1 Developing Maven 2
This document describes how to get started into developing Maven 2 itself. There is a separate page
describing how to building Maven 2.

73.1.1 Finding some work to do
First of all you need something to work on! Unless you have found a particular issue you would like
to work on the Maven team has categorized a few issues that we could use your help to solve them.
JIRA has RSS feeds available if you'd like to include those in your favorite feed aggregator.
We categorize the issues in three different categories:

• Novice: No previous exposure to the code needed. ( rss feed)
• Intermediate: Exposure to Maven pluins and/or internals required. ( rss feed)
• Expert: Good knowledge of Maven internals and it's dependencies required. ( rss feed)
When you find a issue you would like to work on add a comment in the issue log so the core
developers and other people looking for work know that someone is already working on it.

73.1.2 Creating and submitting a patch
When you have either completed an issue or just want some feedback on the work you have done,
create a patch and attach the patch to the issue in question. We have a couple of guidelines when
creating patches:

• Patch the trunk, not a tag. Otherwise, your patch is outdated the moment you create it and might
not be applicable to the development head.
• Always create the patch from the root of the Maven project, i.e. where the pom.xml file is.
• If this was a new piece of work without a JIRA issue, create a JIRA issue for it now.
• Name the file MNG-<issue number>-<artifact id>.patch.
• Attach the patch to the JIRA issue you were working on (do not paste its content in as a comment
though). When adding the patch add a comment to the issue explaining what it does. Shortly
after, someone will apply the patch and close the issue.
An example on how to create a patch from the command line:
$ svn diff > MNG-123-maven-core.patch
If you are picking up an issue with a existing patch attached to the issue you can apply the patch to
your working directory directly from JIRA like this. The wget and patch commands will only be
available if you are on a UNIX platform or using Cygwin on windows.
$ wget -O - -q <URL to the patch from JIRA> | patch -p0
If the patch is in a local file MNG-123.patch and you want to apply that use this command:
$ patch -p0 < MNG-123.patch
A couple of notes:

• If you are using another tool for creating patches, make sure that the patch doesn't include
absolute paths. Including absolute paths in the patch will make the useless for us as we most
likely don't have the same directory structure as you.
• Make sure that you follow our code style, see Further Links.



73.1.3 Patch acceptance criteria

73.2 There are a number of criteria that a patch will be judged on:
• Whether it works and does what is intended. This one is probably obvious!
• Whether it fits the spirit of the project. Some patches may be rejected as they take the project
in a different direction to that which the current development community has chosen. This is
usually discussed on an issue well before a patch is contributed, so if you are unsure, discuss it
there or on the mailing lists first. Feel free to continue discussing it (with new justification) if
you disagree, or appeal to a wider audience on the mailing lists.
• Whether it contains tests. It is expected that any patches relating to functionality will be
accompanied by unit tests and/or integration tests. It is strongly desired (and will be requested)
for bug fixes too, but will not be the basis for not applying it. At a bare minimum, the change
should not decrease the amount of automated test coverage. As a community, we are focusing on
increasing the current coverage, as there are several areas that do not receive automated testing.
• Whether it contains documentation. All new functionality needs to be documented for users,
even if it is very rough for someone to expand on later. While rough is acceptable, incomplete is
not. As with automated testing, as a community we are striving to increase the current coverage
of documentation.

73.3 Above all, don't be discouraged. These are the same requirements the
current committers should hold each other to as well. And remember, your
contributions are always welcome!

73.3.1 Related Projects
Maven 2 has a few dependencies on other projects.
• Plexus
Plexus is a full-fledged container supporting different kinds of component lifecycles. It's native
lifecycle is like any other modern IoC container, using field injection of both requirements and
configuration. All core Maven 2 functionality are Plexus components.
You can read more about Plexus.
• Modello
Modello is a simple tool for representing an object model and generate code and resources from
the model. Maven is using Modello to generate all Java objects, XML readers and writers, XML
Schema and HTML documentation.
You can read more about Modello.
• Surefire
Surefire is a testing framework. It can run regular JUnit tests so you won't have to change
anything in your code to use it. It support scripting tests in BeanShell and Jython and has special
"batteries" for writing acceptance and functional tests for the web and for testing XML-RPC
code.
You can read more about Surefire.
• Doxia
Doxia is Maven's documentation engine. It has a sink and parser API that can be used to plug in
support for input and output documents.
You can read more about Doxia and the currently supported document formats.
• Mojo



"Mojo" is really two things when it comes to Maven. It is both Maven's plug-in API but also a
separate Codehaus project hosting these plugins.
The Mojo Project is a plugin forge for all non-core Maven plugins. As we try to keep the Mojos
as independent of Maven as possible to increase their reuse we try to keep them a bit away from
Maven itself. There is also a lower bar for becoming a part of the project.

73.3.2 Sub Projects

73.3.2.1 Maven SCM
Maven SCM (Source Control Management) is an reusable API which is independent of Maven itself
and it is used by the SCM related Maven Plugins. The core part of Maven itself doesn't depend on
Maven SCM.

73.3.2.2 Maven Wagon
Maven Wagon is also a standalone API that deals with transporting files and directories. Maven Core
uses the Wagon API to download and upload artifacts and artifact metadata and the site plug-in uses it
to publish the site.

73.3.3 Further Links

• Maven Code Style And Code Convention


74 Building Maven 2 311

74 Building Maven 2
.......................................................................................................................................

74.1 Building Maven

74.1.1 Why would I want to build Maven?
Building Maven yourself is for one of two reasons:
• to try out a bleeding edge feature or bugfix (issues can be found in JIRA),
• to fix a problem you are having and submit a patch to the developers team.
Note, that you don't need to bootstrap Maven for day to day use, or to develop plugins. While we
encourage getting involved and fixing bugs that you find, for day to day use we recommend using the
latest release.

74.1.2 Checking out the sources
All of the source code for Maven and its related libraries is in Subversion. You can browse the
repository, or checkout specific modules directly.
To build Maven 2.2 (the current stable branch), you need the maven-2.2.x branch of the maven-2
module. To check that out, run the command:
svn co https://svn.apache.org/repos/asf/maven/maven-2/branches/
maven-2.2.x maven-2.2.x
To build Maven 3.0 (unstable development branch), you need the trunk of the components module.
To check that out, run the command:
svn co https://svn.apache.org/repos/asf/maven/components/trunk maven-3
Alternatively, you can check out all Maven projects in one directory using:
svn co https://svn.apache.org/repos/asf/maven/trunks maven
If you have checked out trunks, the maven-2.2.x directory will contain the Maven 2.2 source
code, and the components directory will contain the 3.0 source code. Note that neither directory
contains any of the plugins.
Note: For Windows users, the checkout could be not complete with the following message:
svn: Can't open file 'XXX': The system cannot find the path specified.
The problem is that while Windows allows filenames up to 256 characters the maximum path length it
allows is 260 characters. You will be able to check it out to the root directory without problem.

74.1.2.1 Other Modules
Other modules you might be interested in related to Maven development are:
• plugins/trunk - The sources of the Maven plugins. These can be individually installed, or
built together.
• plugin-tools/trunk - Set of tools for Maven plugins like test harness.
• release/trunk - Release manager and plugin.
• site/trunk - The Maven website.
• skins/trunk - Skins for generated site used by site plugin.
• Some Maven sub projects
• wagon/trunk - Maven Wagon, used by the artifact code and others for providing the
transport layer to get and put artifacts in a repository.



• scm/trunk - Maven SCM, a generic API to communicate with various different SCM
providers, used by Continuum and the release and SCM plugins.
• doxia/trunk - The Doxia site generation library used by several report plugins and site
plugin.
• surefire/trunk - The Surefire test runner.
• shared/trunk - Collection of shared libraries like file/path handling.
• sandbox/trunk - Sandbox codes.
• Plexus - the IoC container used by Maven.
If you're looking at the trunks directory with ViewVC, there is seemingly nothing there. We use
externals definitions to link together all the trunks into one logical location for convenience. If you
want to see what is being linked into one logical location you can use the following command:
svn propget svn:externals

74.1.3 Building Maven

74.1.3.1 Building Maven With Maven Installed
If you already have Maven installed, it can be faster to build a new version with Maven, rather than a
clean bootstrap.
To do this, run from the components or maven-2.2.x directory:
mvn install
Optionally, you can use the following to run the full (long) suite of integration tests:
mvn install -Prun-its
The assemblies will be created in apache-maven/target for Maven 2.0.x or maven-
distribution for Maven 2.1, and can be unzipped to the location where you'd like Maven installed.

74.1.3.2 Building Maven Without Maven Installed
If you do not have Maven installed, you can use Apache Ant to build Maven.
Once you have checked out the code, change into the components or maven-2.2.x directory that
was created.
Set the M2_HOME environment variable to the location that should contain Maven. This directory
must be named after the Maven version you want to build and install, for example /usr/local/
maven-2.2-SNAPSHOT.
export M2_HOME=/usr/local/maven-2.2-SNAPSHOT
PATH=$M2_HOME/bin:$PATH
or
set M2_HOME=c:maven-2.2-SNAPSHOT
set PATH=%M2_HOME%bin;%PATH%
From this, run the ant command:
ant
This will download dependencies, build Maven, and install it into the directory you specified as
M2_HOME above.
If you have any problems or get any failures during the run, please report them to the Maven
Developers List.



For more information, consult the project help in the Ant build file.
ant -projecthelp
The result is included here for convenience:

Buildfile: build.xml
The first time you build Maven from source, you have to build Maven without
Maven. This Ant script builds a minimal Maven, just enough to re-launch
Maven again in this directory and generate an installation assembly. Then we
extract the assembly and re-run the Maven build one more time, this time
with the full generated Maven.
To run this script, you must set the M2_HOME environment variable or the
maven.home property to the location that should contain Maven. This
directory *must* be named after the maven version you want to install, e.g.
/usr/local/maven-2.1-SNAPSHOT.
You can set the maven.repo.local property to specify a custom location for
your local repository for the bootstrap process.
Main targets:
classpath-pre constructs a classpath reference containing our dependencies,
and verifies that all files are present
clean-bootstrap cleans up generated bootstrap classes
compile-boot compiles the bootstrap sources
extract-assembly extracts the maven assembly into maven.home
generate-sources generates Java sources from Modello mdo model files
maven-assembly generates the Maven installation assembly using the bootstrap
Maven
maven-compile compiles Maven using the bootstrap Maven, skipping automated
tests
pull copies all required dependencies from the Maven remote
repository into your local repository. Set the 'skip.pull'
property to skip this step, but only if you're sure you
already have all of the dependencies downloaded to
your local repository
run-full-maven runs the full extracted Maven, now with tests
Default target: all


75 Committer Environment 314

75 Committer Environment
.......................................................................................................................................

75.1 Introduction
This document is intended to set up the Maven committer environment.

75.2 Source File Encoding
When editing source files, make sure you use the right file encoding. For the Maven project, UTF-8
has been chosen as the default file encoding. UTF-8 is an encoding scheme for the Unicode character
set and as such allows to encode all characters that Java can handle. The source files should not
contain the byte order mark (BOM). There can be exceptions to this general rule, e.g. properties files
are usually encoded using ISO-8859-1 as per the JRE API, so please keep this in mind, too.

75.3 Subversion Configuration
Before committing files in subversion repository, you need to read the Committer Subversion Access
document and you must set your svn client with this properties file: svn-eol-style.txt

75.4 Maven Code Style
The following sections show how to set up the code style for Maven in IDEA and Eclipse. It is
strongly preferred that patches use this style before they are supplied.

75.4.1 IntelliJ IDEA 4.5+
Download maven-idea-codestyle.xml and copy it to ~/.IntelliJIDEA/config/
codestyles then restart IDEA. On Windows, try C:Documents and Settings<username>
.IntelliJIDEAconfigcodestyles
After this, restart IDEA and open the settings to select the new code style.

75.4.2 Eclipse 3.2+
Download maven-eclipse-codestyle.xml.
After this, select Window > Preferences, and open up the configuration for Java > Code Style > Code
Formatter. Click on the button labeled Import... and select the file you downloaded. Give the style a
name, and click OK.

75.5 Setting up SSH public/private keys
By default, SSH (Secure Shell) asks you to enter your password each time, i.e.:

>ssh vsiveton@apache.org
Password:

SSH can be set up with public/private key pairs so that you don't have to type the password each time.
You need to execute the following on your development machine:


75 Committer Environment 315

> ssh-keygen -t dsa
Generating public/private dsa key pair.
Enter file in which to save the key (~/.ssh/id_dsa): (just type return)
Enter passphrase (empty for no passphrase): (just type return)
Enter same passphrase again: (just type return)
Your identification has been saved in ~/.ssh/id_dsa
Your public key has been saved in ~/.ssh/id_dsa.pub
The key fingerprint is:
ec:06:c7:44:9e:a6:2c:c0:8a:87:04:07:a0:5b:94:d2 YOUR_MACHINE_USERNAME @ YOUR_MACHINE

Then, paste the content of the local ~/.ssh/id_dsa.pub file into the file /home/
YOUR_APACHE_USERNAME/.ssh/authorized_keys on the Apache remote host.
Note: under Cygwin, it is located at {cygwin.install.path}homeYOUR_MACHINE_USERNAME
.ssh. You need to copy the content of {cygwin.install.path}home
YOUR_MACHINE_USERNAME.ssh into C:Documents and Settings
YOUR_MACHINE_USERNAME.ssh for Maven.
To test the installation, try to log in again on Apache. You should not be asked for your password any
more.

>ssh vsiveton@apache.org
Last login: Tue Oct 10 03:50:10 2006 from ipXXX-XXX-XXX-XXX
Copyright (c) 1980, 1983, 1986, 1988, 1990, 1991, 1993, 1994
The Regents of the University of California. All rights reserved.
FreeBSD 6.1-RELEASE (SMP-turbo) #0: Thu May 11 11:50:25 PDT 2006
This is an Apache Software Foundation server.
For more information, see http://www.apache.org/dev/
Time to change your password? Type "passwd" and follow the prompts.
-- Dru <genesis@istar.ca>
-bash-2.05b$

75.6 Useful software
The Maven Team uses several software. Here is a partial list:

• Cygwin: collection of free software tools to allow various versions of Microsoft Windows to act
somewhat like a Unix system
• WinSCP: SFTP client for Windows.
• TortoiseSVN: Subversion client, implemented as a Windows shell extension.
• GnuPG: GNU Privacy Guard.


76 Committer Settings 316

76 Committer Settings
.......................................................................................................................................

76.1 Introduction
This document is intended to set up the Maven committer settings, i.e. the ${user.home}/.m2/
settings.xml.

76.2 Enable Apache Servers
Maven uses several servers configuration to deploy snapshots, releases and documentation on the
Apache servers. You need to tell to Maven what your Apache username is. Please note that some
servers use your SVN credentials while others use your SSH credentials.

<settings>
...
<servers>

<server>
<id>apache.snapshots.https</id>
<username>  </username>
<password>  </password>
</server>

<server>
<id>apache.website</id>
<username>  </username>
</server>

<server>
<id>apache.releases.https</id>
<username>  </username>
<password>  </password>
</server>

<server>
<id>stagingSite</id>  </username>
</server>
...
</servers>
</settings>

You also need to be a member of the group apcvs and maven on people.apache.org.

77 Maven Code Style And Conventions 317

77 Maven Code Style And Conventions
.......................................................................................................................................

77.1 Maven Code Style And Code Conventions
This document describes how developers and contributors should write code. The reasoning of these
styles and conventions is mainly for consistency, readability and maintainability reasons.

77.1.1 Generic Code Style And Convention
All working files (java, xml, others) should respect the following conventions:

• License Header: Always add the current ASF license header in all versionned files.
• Trailing Whitespaces: Remove all trailing whitespaces. If your are an Eclipse user, you could
use the Anyedit Eclipse Plugin.
and the following style:

• Indentation: Never use tabs!
• Line wrapping: Always use a 120-column line width.
Note: The specific styles and conventions, listed in the next sections, could override these generic
rules.

77.1.2 Java

77.1.2.1 Java Code Style
The Maven style for Java is mainly:

• White space: One space after control statements and between arguments (i.e. if ( foo )
instead of if(foo)), myFunc( foo, bar, baz ) instead of myFunc(foo,bar,baz)). No
spaces after methods names (i.e. void myMethod(), myMethod( "foo" ))
• Indentation: Always use 4 space indents and never use tabs!
• Blocks: Always enclose with a new line brace.
• Line wrapping: Always use a 120-column line width for Java code and Javadoc.
• Readingness: Specify code grouping members, if needed. For instance in a Mojo class, you
could have:



public class MyMojo
{
// ----------------------------------------------------------------------
// Mojo components
// ----------------------------------------------------------------------
/**
* Artifact factory.
*
* @component
*/
private ArtifactFactory artifactFactory;
...
// ----------------------------------------------------------------------
// Mojo parameters
// ----------------------------------------------------------------------
/**
* The POM.
*
* @parameter expression="${project}"
* @required
*/
private MavenProject project;
...
// ----------------------------------------------------------------------
// Mojo options
// ----------------------------------------------------------------------
...
// ----------------------------------------------------------------------
// Public methods
// ----------------------------------------------------------------------
/**
* {@inheritDoc}
*/
{
...
}
// ----------------------------------------------------------------------
// Protected methods
// ----------------------------------------------------------------------
...
// ----------------------------------------------------------------------
// Private methods
// ----------------------------------------------------------------------
...
// ----------------------------------------------------------------------
// Static methods
// ----------------------------------------------------------------------
...
}



The following sections show how to set up the code style for Maven in IDEA and Eclipse. It is
strongly preferred that patches use this style before they are applied.
77.IntelliJ IDEA 4.5+
Download maven-idea-codestyle.xml and copy it to ~/.IntelliJIDEA/config/
codestyles then restart IDEA. On Windows, try C:Documents and Settings<username>
.IntelliJIDEAconfigcodestyles
After this, restart IDEA and open the settings to select the new code style.
77.Eclipse 3.2+
Download maven-eclipse-codestyle.xml.
After this, select Window > Preferences, and open up the configuration for Java > Code Style > Code
Formatter. Click on the button labeled Import... and select the file you downloaded. Give the style a
name, and click OK.

77.1.2.2 Java Code Convention
For consistency reasons, our Java code convention is mainly:
• Naming: Constants (i.e. static final members) values should always be in upper case. Using
short, descriptive names for classes and methods.
• Organization: Avoid using a lot of public inner classes. Prefer interfaces instead of default
implementation.
• Modifier: Avoid using final modifier on all member variables and arguments. Prefer using
private or protected member instead of public member.
• Exceptions: Throw meaningful exceptions to makes debugging and testing more easy.
• Documentation: Document public interfaces well, i.e. all non-trivial public and protected
functions should include Javadoc that indicates what it does. Note: it is an ongoing convention
for the Maven Team.
• Testing: All non-trivial public classes should include corresponding unit or IT tests.

77.1.2.3 JavaDoc Convention
TO BE DISCUSSED

77.1.3 XML

77.1.3.1 XML Code Style
The Maven style for XML files is mainly:
• Indentation: Always use 2 space indents, unless you're wrapping a new XML tags line in which
case you should indent 4 spaces.
• Line Breaks: Always use a new line with indentation for complex XML types and no line break
for simple XML types. Always use a new line to separate XML sections or blocks, for instance:

<aTag>
<simpleType>This is a simple type</simpleType>
<complexType>
<simpleType>This is a complex type</simpleType>
</complexType>
</aTag>

In some cases, adding comments could improve the readability of blocks, for instance:


<!-- Simple XML documentation

or

<!-- ======================================================================
<!-- Block documentation
<!-- ======================================================================

77.1.3.2 Generic XML Code Convention
No generic code convention exists yet for XML files.

77.1.3.3 POM Code Convention
The team has voted during the end of June 2008 to follow a specific POM convention to ordering
POM elements. The consequence of this vote is that the Maven project descriptor is no more
considered as the reference for the ordering.
The following is the recommended ordering for all Maven POM files:

<modelVersion/>
<parent/>
<groupId/>
<artifactId/>
<version/>
<packaging/>
<name/>
<description/>
<url/>
<inceptionYear/>
<organization/>
<licenses/>
<developers/>
<contributors/>
<mailingLists/>
<prerequisites/>
<modules/>
<scm/>
<issueManagement/>
<ciManagement/>
<distributionManagement/>
<properties/>
<dependencyManagement/>
<dependencies/>
<repositories/>
<pluginRepositories/>
<build/>
<reporting/>
<profiles/>
</project>

Comments:
1 The <project/> element is always on one line.


2 The blocks are voluntary separated by a new line to improve the readingness.
3 The dependencies in <dependencies/> and <dependencyManagement/> tags have no specific
ordering. Developers are free to choose the ordering, but grouping dependencies by topics (like
groupId i.e. org.apache.maven) is a good practice.
Note: The team plans to create a Maven plugin with reorder and reformat goals (See MOJO-928).

77.1.3.4 XDOC Code Convention
For consistency and readability reasons, XDOC files should respect:

• Metadata: Always specify metadata in the <properties/> tag.
• Sections: Always use a new line with indentation for <section/> tags.

77.1.3.5 FML Code Convention
For readability reasons, FML files should respect:

• FAQ: Always use a new line with indentation for <faq/> tags.


78 Maven JIRA Convention 322

78 Maven JIRA Convention
.......................................................................................................................................

78.1 Maven JIRA Convention
This document describes how Maven developers should use JIRA, our issue tracking.

78.1.1 When To Create a JIRA Issue?
This section discusses when to create a JIRA issue versus just committing a change in SVN.
• Minor changes, like code reformatting, documentation fixes, etc. that aren't going to impact
other users can be committed without much issue.
• Larger changes, like bug fixes, API changes, significant refactoring, new classes, and pretty
much any change of more than 100 lines, should have a JIRA ticket associated with it, or at least
an email discussion.

78.1.2 How To Use Issue Details?
This section presents some conventions about the issue fields.

78.1.2.1 Priority
Committers has the responsibility to realign priority by editing the issue.
Reasoning: having a correct release note.

78.1.2.2 Assignee
Committers could assign an issue to a specific committer if he thinks it is the right committer.

78.1.2.3 Component/s
Committers has the responsibility to specify the correct the component by editing the issue.

78.1.2.4 Affects Version/s
By default, the Maven team considers that an issue, which affects a given version, affects also
precedent versions, i.e. issue which affects Maven 2.0.9 will affect also 2.0, 2.0.1 ... 2.0.9. If it is a
regression, the committers should specify the affected versions.

78.1.2.5 Fix Version/s
TO BE DISCUSSED

78.1.2.6 Time Tracking
The Maven team never uses it. Committers could do it, but like said, it will never be used.

78.1.3 Further Links

• JIRA Documentation
• What is an Issue?
• What is a project?


78 Maven JIRA Convention 323

• how we handle JIRA versions Thread


79 Maven SVN Convention 324

79 Maven SVN Convention
.......................................................................................................................................

79.1 Maven SVN Convention
This document describes how developers should use SVN, our SCM.

79.1.1 Subversion Configuration
Before committing files in subversion repository, you need to read the Committer Subversion Access
document and you must set your svn client with this properties file: svn-eol-style.txt

79.1.2 Commit Message Template
Commits should have a message that follows this template:

[issue1, issue2] <<comment>>
Submitted by: (when it was a patch, put that persons name there)
o some comments

Where:

• issue can be omitted if there was no relevant JIRA issue, though it is strongly encouraged to
create one for significant changes.
• Submitted by only needs to be specified when a patch is being applied for a non-committer.
• comments some words about the commits.

79.2 eg:
[MNG-1456] Added the foo to the bar
Submitted by: Baz Bazman
o applied without change

79.2.1 Apply User Patch
By default, the committer should apply the patch without any major modifications. In a second step,
the committer could apply any changes as usual.

79.2.2 Edit Commit Message
If you want to edit a commit message, you could call:

svn pe svn:log --revprop -r XXX

where XXX is the wanted version

79.2.3 Other useful Subversion commands while developing
If you've done a chunk of work and you would like ditch your changes and start from scratch use this
command to revert to the original checkout:
$ svn revert -R .
The -R argument means that the command will recurse down all directories and revert all changes.


79 Maven SVN Convention 325

Before committing code to the Subversion repository we always set the svn:ignore property on the
directory to prevent some files and directories to be checked in. We always exclude the IDE project
files and the target/ directory. Instead of keeping all of the excludes in mind all the time it's useful
to put them all in a file and reference the file with the -F option:
$ svn propset svn:ignore -F ~/bin/svnignore .
An example svnignore file:
target
*~
*.log
.classpath
.project
*.ipr
*.iws
*.iml


80 Making GPG Keys 326

80 Making GPG Keys
.......................................................................................................................................

80.1 Introduction
You need to add your GPG keys in https://svn.apache.org/repos/asf/maven/project/KEYS before a
release. Here are some useful GnuPG commands to generate your Keys.



80.1.1 gpg --gen-key

>gpg --gen-key
gpg (GnuPG) 1.4.5; Copyright (C) 2006 Free Software Foundation, Inc.
This program comes with ABSOLUTELY NO WARRANTY.
This is free software, and you are welcome to redistribute it
under certain conditions. See the file COPYING for details.
gpg: keyring `C:/Documents and Settings/Siveton Vincent/Application Data/gnupgsecri
created
gpg: keyring `C:/Documents and Settings/Siveton Vincent/Application Data/gnupgpubri
created
Please select what kind of key you want:
(1) DSA and Elgamal (default)
(2) DSA (sign only)
(5) RSA (sign only)
Your selection? 1
DSA keypair will have 1024 bits.
ELG-E keys may be between 1024 and 4096 bits long.
What keysize do you want? (2048) 2048
Requested keysize is 2048 bits
Please specify how long the key should be valid.
0 = key does not expire
<n> = key expires in n days
<n>w = key expires in n weeks
<n>m = key expires in n months
<n>y = key expires in n years
Key is valid for? (0) 0
Key does not expire at all
Is this correct? (y/N) y
You need a user ID to identify your key; the software constructs the user ID
from the Real Name, Comment and Email Address in this form:
"Heinrich Heine (Der Dichter) <heinrichh@duesseldorf.de>"
Real name: Vincent Siveton
Email address: vsiveton@apache.org
Comment:
You selected this USER-ID:
"Vincent Siveton <vsiveton@apache.org>"
Change (N)ame, (C)omment, (E)mail or (O)kay/(Q)uit? O
You need a Passphrase to protect your secret key.
You don't want a passphrase - this is probably a *bad* idea!
I will do it anyway. You can change your passphrase at any time,
using this program with the option "--edit-key".
We need to generate a lot of random bytes. It is a good idea to perform
some other action (type on the keyboard, move the mouse, utilize the
disks) during the prime generation; this gives the random number
generator a better chance to gain enough entropy.
++++++++++++++++++++.++++++++++..+++++++++++++++++++++++++++++++++++++++++++++++
+++.+++++++++++++++.++++++++++++++++++++..+++++++++++++++>++++++++++............
.........................+++++
We need to generate a lot of random bytes. It is a good idea to perform
some other action (type on the keyboard, move the mouse, utilize the
disks) during the prime generation; this gives the random number
generator a better chance to gain enough entropy.
.+++++++++++++++..++++++++++++++++++++....+++++.++++++++++.++++++++++.++++++++++
+++++.+++++++++++++++++++++++++++++++++++.+++++.++++++++++++++++++++++++++++++>+
+++++++++>+++++>+++++......................................................>++++
+......<.+++++........................+++++^^^
gpg: C:/Documents and Settings/Siveton Vincent/Application Data/gnupgtrustdb.gpg: t
© 2 0 0 9createda c h e S o f t w a r e F o u n d a t i o n • A L L R I G H T S R E S E R V E D .
, The Ap

gpg: key 07DDB702 marked as ultimately trusted
public and secret key created and signed.
gpg: checking the trustdb


80.1.2 gpg --list-sigs

>gpg --list-sigs "Vincent Siveton" && gpg --armor --export "Vincent Siveton"
pub 1024D/07DDB702 2006-10-10
uid Vincent Siveton <vsiveton@apache.org>
sig 3 07DDB702 2006-10-10 Vincent Siveton <vsiveton@apache.org>
sub 2048g/D2814A59 2006-10-10
sig 07DDB702 2006-10-10 Vincent Siveton <vsiveton@apache.org>
-----BEGIN PGP PUBLIC KEY BLOCK-----
Version: GnuPG v1.4.5 (MingW32)
mQGiBEUrnAsRBACQDiYGc1IQmkENLO9iznBg8otGPEbzqQozT5tsip5mB30f6Mc/
uuLxJkLdna7Ul3goIXDtCeLJq38gHvruNtVNR6S+juJFkd5sLEH8UJ18PbKuo/9I
KGlzjtCYUUDC48czRr0efhqd54NH8ydNdpaZ76NGPPYfpXtk7kKgH/nPiwCgxozK
IG2frMuWIvdFafbqdAl7y/sD/1Csf0r9jtHEeXOuyhm8jCGrSwzLbHUGKPUQP37P
ajECHoWp6HnvHEEEpgVl+UjfZvrcVhzUoP+3r5HAugqERfkzK8AWc7qjIRjf64kU
sjvto31G2KYz17Y8K9y4LkRkUspu8uw903pKnW/QELg4vvPVaEYpVVIdS6+cUreu
V0hOA/4tW7T/GpzSbQmjvnIRQ7GVHbQeXsANwrS6NmGYIxafN9P9dfHV+eUieTu6
rvMP9coOhTYyEKZksrXw2MmXx5SzgxsXT0g4wDXbwxPYFfIdGUzFMobnVXiZ3G8l
JEl9cML0cg3ZL1SoDmVf2iG3e3Yxxsne4AE1SU+0bbq0t7rqALQlVmluY2VudCBT
aXZldG9uIDx2c2l2ZXRvbkBhcGFjaGUub3JnPohgBBMRAgAgBQJFK5wLAhsDBgsJ
CAcDAgQVAggDBBYCAwECHgECF4AACgkQhPTUcAfdtwLP3gCbB/V1afp8hzxgirCS
d2r6zCkJQ2IAoLKD/RIkkerNintYzrubJliJKBsRuQINBEUrnBgQCAD1+Sx+sBDL
1XCDtxQGsrZmMnJJVK/w4TPa/8weJkuZ1GSpINOjInmqESuehvCLoOoyfcuDVXlR
PUZhKZLPEKfJlFptGNK19oTO/CoQN+SJLwR41FoumsBaf1YSSRpAukyx2J6cUxqf
uWrK/T8PmgDw4YzmY96tev//41eZ5tSOxpoUM8ypnTaShtS9pjgHijEG0b7wBqeU
e1OGOiLHgKyjEJUmlTaLm1SxJ84eq0uAvYb+rb/QoWWLpjvr2/mo1kzUvCPgo3fh
kgOxCxsC9QD836Mi5HFK6CRYU3yAFu5+/jM+LJzELy3u7uMuOSP6yuiK8WXopdbN
WHOiJQfdc2gTAAMFCADdljjAG7L+8de6JzsEduKErKqWlTEWa99n1knaGKzdUUOP
WrKxwqgI6PAJbxOfG4vBdDa6M6+nySJDMybQsOCFyNx91/7jYkgkmv8Jkt8CTW4z
P4HKlFYMAFpU95ftpTAAMAlr+t+nZRTHi94/VHMv4yLGzB/xapbzToHKuUt1Yqom
Ncio5px7RVoicn13/i/GeY72fIdC2LRGo6PXlmmDQemoAnUw0RJoEtzapb0j/tWd
BdAtQQX/Ks7qhk4aDDHGgO+CdHAB8PLHDpMpUX5Zc9JX1xhyJcS8d/LPUpXtt9WN
eekqDpx+jNmySJr6os7rPAkjx6jDUvHPiuKdT4aviEkEGBECAAkFAkUrnBgCGwwA
CgkQhPTUcAfdtwJL9ACgmLuDxE+oZaMhyFSmXWN0fM36Bd8AoLYrvwydB9+nNnhJ
85TjkMPTgjp9
=Hg4C
-----END PGP PUBLIC KEY BLOCK-----

You need to append this result to https://svn.apache.org/repos/asf/maven/project/KEYS.
You also need to upload your key to the public server: http://pgp.mit.edu/ by copying the same you
appended in the text field and submit. You can ensure by searching your email in key search engine.
You can read more about Checksums And Signatures.


81 Release Process 329

81 Release Process
.......................................................................................................................................

81.1 Releasing A Maven Project
What follows is a description of releasing a Maven project to a staging repository, whereupon it is
scrutinized by the community, approved, and transferred to a production repository.

81.1.1 Prerequisites
Be sure that:

• you have all Maven servers defined in your settings.xml. For more information, please refer to
Committer settings.
• you have created your GPG keys. For more information, please refer to Making GPG Keys.
• you have a GPG client installed and on your shell's path. See http://www.gnupg.org/.
• you have a Subversion 1.5+ client installed and on your shell's path. See http://
subversion.tigris.org/.
• you have a Java 1.4.2 JDK installed and on your shell's path. See http://java.sun.com/j2se/1.4.2/
download.html.
• you have set the environment variable MAVEN_OPTS=-Xmx512m
• you are using Maven 2.0.x (or 2.2.x), as Maven 2.1.x is known to produce wrong gpg pom
signatures (see MGPG-14).
Formerly, a release profile was required in the ${user.home}/.m2/settings.xml to define
the staging repository. As of inheritance from the Apache parent POM version 5, a repository
manager will automatically handle staging (see below for details). Hence, configuration of
deploy.altRepository is no longer necessary and should be removed from your existing
release profile.
Here's what your release profile might look like in your ${user.home}/.m2/settings.xml:

<settings>
...
<profiles>
<profile>
<id>apache-release</id>
<properties>
<gpg.passphrase>  </gpg.passphrase>
</properties>
</profile>
</profiles>
...
</settings>

Everything that you need to release has been configured in the POM all Maven projects inherit from.
The release plugin configuration being used is the following:


<plugin>
<configuration>
<useReleaseProfile>false</useReleaseProfile>
<goals>deploy</goals>
<arguments>-Papache-release</arguments>
</configuration>
</plugin>

And the profile being used for releases is the following:


<profile>
<id>apache-release</id>
<build>
<plugins>

<plugin>
<artifactId>maven-gpg-plugin</artifactId>
<configuration>
<passphrase>${gpg.passphrase}</passphrase>
</configuration>
<executions>
<execution>
<goals>
<goal>sign</goal>
</goals>
</execution>
</executions>
</plugin>

<plugin>
<artifactId>maven-deploy-plugin</artifactId>
<configuration>
<updateReleaseInfo>true</updateReleaseInfo>
</configuration>
</plugin>
<plugin>
<artifactId>maven-source-plugin</artifactId>
<executions>
<execution>
<id>attach-sources</id>
<goals>
<goal>jar</goal>
</goals>
</execution>
</executions>
</plugin>
<plugin>
<artifactId>maven-javadoc-plugin</artifactId>
<configuration>
<encoding>${project.build.sourceEncoding}</encoding>
</configuration>
<executions>
<execution>
<id>attach-javadocs</id>
<goals>
<goal>jar</goal>
</goals>
</execution>
</executions>
</plugin>
</plugins>
</build>
</profile> S o f t w a r e F o u n d a t i o n • A L L R I G H T S R E S E R V E D .
©2009, The Apache


81.1.2 Verify you are using JDK 1.4.2
Maven 2.0.X and its plugins should be built with JDK 1.4.2.

>mvn --version
...
Maven version: 2.0.X
Java version: 1.4.2_18

81.1.3 Release Process for Part Of Maven

1 Prepare your POMs for release:
a Make sure there are no snapshots in the POMs to be released.
b Check that your POMs will not lose content when they are rewritten during the release
process.
• Verify that all pom.xml files have an SCM definition.
• mvn release:prepare -DdryRun=true
• Diff the original file pom.xml with the one called pom.xml.tag to see if the license
or any other info has been removed. This has been known to happen if the starting
<project> tag is not on a single line. The only things that should be different
between these files are the <version> and <scm> elements. Any other changes, you
must backport yourself to the original pom.xml file and commit before proceeding
with the release.
2 Publish a snapshot:

>mvn deploy
...
[INFO] [deploy:deploy]
[INFO] Retrieving previous build number from apache.snapshots.https
...

If you experience an error during deployment like a HTTP 401 check your settings for the
required server entries as outlined in the Prerequisites.
Note: Be sure that the generated artifacts respect the Apache release rules: NOTICE and
LICENSE files should be present in the META-INF directory within the jar. For -sources
artifacts, be sure that your POM does not use the maven-source-plugin:2.0.3 which is broken.
The recommended version at this time is 2.0.4.
Note: You should verify the deployment under Maven Snapshot repository on Apache.

https://repository.apache.org/content/repositories/snapshots/org/apache/maven/pl
3 Prepare the release

mvn release:clean
mvn release:prepare

Note: Preparing the release will create the new tag in SVN, automatically checking in on your
behalf.
4 Stage the release for a vote

mvn release:perform



The release will automatically be inserted into a temporary staging repository for you. See the
Nexus staging documentation for full details.
5 Close the staging repository
Login to https://repository.apache.org using your Apache SVN credentials. Click
on "Staging". Then click on "org.apache.maven" in the list of repositories. In the panel below
you should see an open repository that is linked to your username and ip. Right click on this
repository and select "Close". This will close the repository from future deployments and make it
available for others to view. If you are staging multiple releases together, skip this step until you
have staged everything.
See the image below for details.

Closing the repository
6 Verify the Staged artifacts
If you click on your repository, a tree view will appear below. You can then browse the contents
to ensure the artifacts are as you expect them. Pay particular attention to the existence of *.asc
(signature) files. If the you don't like the content of the repository, right click your repository and
choose "Drop". You can then rollback your release and repeat the process.
Note the repository URL, you will need this in your vote email.



Validating the artifacts
7 Stage the latest documentation
The plugin parent POM is configured to stage the documentation in a "versioned" directory such
as /plugins/maven-XXX-plugin-Y.Z.

a Stage the documentation for the current release version (not the new snapshot).

cd target/checkout
mvn site:stage-deploy -Preporting

Note: It requires Maven 2.1.0 or higher to successfully deploy to people.apache.org
via SSH. Older Maven versions will fail due to com.jcraft.jsch.JSchException:
Algorithm negotiation fail.
Note: You should verify the deployment of the site on the Maven website (you need to wait
the sync).

http://maven.apache.org/plugins/maven-XXX-plugin-Y.Z/



Some developers have reported problems with the site:stage-deploy goal. In that
case, you can stage the site locally and upload it manually:

mvn site:stage -Preporting
scp -r target/staging/people.apache.org/www/maven.apache.org/plugins/maven-X
b Verify/change folder permissions to 0775 and files permissions to 0664. Log on to
people.apache.org and change to the directory above the staging directory. That would
be /www/maven.apache.org/plugins for a plugin. Then run these commands:

find . -type d -exec chmod a+rx,g+w {} ;
find . -type f -exec chmod 664 {} ;
8 Propose a vote on the dev list with the closed issues, the issues left, the staging repository and the
staging site. For instance:

To: "Maven Developers List" <dev@maven.apache.org>
Subject: [VOTE] Release Maven XXX plugin version Y.Z
Hi,
We solved N issues:
http://jira.codehaus.org/secure/ReleaseNote.jspa?projectId=XXX&styleName=Html&ve
There are still a couple of issues left in JIRA:
http://jira.codehaus.org/secure/IssueNavigator.jspa?reset=true&pid=XXX&status=1
Staging repo:
https://repository.apache.org/content/repositories/maven-staging-[YOUR REPOSITOR
Staging site:
http://maven.apache.org/plugins/maven-XXX-plugin-Y.Z/
Guide to testing staged releases:
http://maven.apache.org/guides/development/guide-testing-releases.html
Vote open for 72 hours.
[ ] +1
[ ] +0
[ ] -1

To get the JIRA release notes link, browse to the plugin's JIRA page, select the Road Map link,
and use the link to Release Notes that is next to the version being released.
To get the list of issues left in JIRA, browse to the plugin's JIRA page, and from the Preset
Filters on the right, use the link for Outstanding issues.
9 Check the vote results
Copied from Votes on Package Releases.

Votes on whether a package is ready to be released follow a format similar to ma
-- except that the decision is officially determined solely by whether at least
+1 votes were registered. Releases may not be vetoed. Generally the community wi
vote to release if anyone identifies serious problems, but in most cases the ult
once three or more positive votes have been garnered, lies with the individual s
release manager. The specifics of the process may vary from project to project,
'minimum of three +1 votes' rule is universal.

The list of binding voters is available at http://people.apache.org/~jim/projects.html#maven-pmc
Once a vote is successful, post the result to the dev list and cc the PMC. For instance:



To: "Maven Developers List" <dev@maven.apache.org>
CC: "Maven Project Management Committee List" <private@maven.apache.org>
Subject: [RESULT] [VOTE] Release Maven XXX plugin version Y.Z
Hi,
The vote has passed with the following result :
+1 (binding): <<list of names>>
+1 (non binding): <<list of names>>
I will promote the artifacts to the central repo.

If the vote is unsuccessful, the process will need to be restarted. Be sure to drop your staging
repository as described above.
10Promote the release
Once the release is deemed fit for public consumption it can be transfered to a production
repository where it will be available to all users.
Login to https://repository.apache.org with your Apache SVN credentials. Click
on "Staging" and then on the repository with id "maven-staging". Find your closed staging
repository, right click on it and choose "Promote". Select the "Releases" repository and click
"Promote".
See image below.

Promote the artifacts

Next click on "Repositories", select the "Releases" repository and validate that your artifacts
exist as you expect them.
11Deploy the current website
Note: Be sure to generate and deploy the site using the same version of the release. Typically,
you need to check out the tag (or go to target/checkout)

cd targetcheckout
mvn site-deploy -Preporting

Note: You can not just copy the documentation from Step 7 into the released documentation as
the links are not identical. See the email thread http://www.nabble.com/forum/ViewPost.jtp?
post=24018250&framed=y
12Review the website
Wait for the files to arrive at



http://maven.apache.org/plugins/maven-XXX-plugin

or for a shared component at

http://maven.apache.org/shared/maven-XXX

The wait is necessary to allow the site to be rsync'ed into production.
13Update the maven site
Check out the maven site project: https://svn.apache.org/repos/asf/maven/site/
trunk
If this is a plugin release, update the version number for the plugin on the src/site/apt/plugins/
index.apt page.
If this is a shared component release, update the version number for the component on the src/
site/apt/shared/index.apt page.
Commit your changes.
14Update JIRA
For a plugin, go to Admin section in JIRA for the maven-XXX-plugin project and mark the
Y.Z version as released. Create version Y.Z+1, if that hasn't already been done.
If this is a shared component, go to Admin section in JIRA for the MSHARED project and
mark the maven-XXX-Y.Z version as released. Create version maven-XXX-Y.Z+1, if that hasn't
already been done.
15Create an announcement. For instance:
Note: You must send this email from your apache email account, e.g.
YOUR_APACHE_USERNAME@apache.org otherwise the email to
announce@maven.apache.org will bounce.

From: YOUR_APACHE_USERNAME@apache.org
To: announce@maven.apache.org, users@maven.apache.org
Cc: dev@maven.apache.org
Subject: [ANN] Maven XXX Plugin Y.Z Released
The Maven team is pleased to announce the release of the Maven XXX Plugin, versi
This plugin (insert short description of the plugin's purpose).
http://maven.apache.org/plugins/maven-XXX-plugin/
You should specify the version in your project's plugin configuration:
<plugin>
<version>Y.Z</version>
</plugin>
Release Notes - Maven 2.x XXX Plugin - Version Y.Z
(Copy Here Release Notes in Text Format from JIRA)
Enjoy,
-The Maven team
16Add the release to the next board report, in the private subversion area.
This is a PMC activity. If you are not a PMC member then email the "Maven Developers
List" <dev@maven.apache.org> with a request to update this file for your release.



From: YOUR_APACHE_USERNAME@apache.org
To: dev@maven.apache.org
Subject: [PMC] Maven XXX Plugin Y.Z needs adding to board report
The Maven XXX Plugin has been released.
Can this get added to the next board report please.
17Add the release to the wiki, under the Recent Releases section of the front page and on the
Releases page.
Note: If you don't have access to edit this page email "Jason van Zyl"
<jason@maven.org>
18Celebrate :o)

81.2 Trouble Shooting

81.2.1 mvn release:prepare "commit failed" during Prepare the release
If you get an error message similar to:

[INFO] Unable to tag SCM
Provider message:
The svn tag command failed.
Command output:
svn: Commit failed (details follow):
svn: File '/repos/asf/maven/plugins/tags/maven-eclipse-plugin-2.7/src/main/java/

Then the resolution is to use a Subversion client 1.6+ and to run svn update.

81.2.2 mvn release:prepare "commit failed" during Prepare the release
If you get an error message similar to:

[ERROR] BUILD FAILURE
[INFO] ------------------------------------------------------------------------
[INFO] Unable to tag SCM
Provider message:
The svn tag command failed.
Command output:
svn: Path 'https://svn.apache.org/repos/asf/maven/plugins/tags/maven-eclipse-plugin-

Then the resolution is to delete the tag using svn del -m "re-releasing build" <svn path>


82 Deploy Maven Current References 339

82 Deploy Maven Current References
.......................................................................................................................................

82.1 Introduction
This document gives step-by-step instructions for deploying the Maven current references. The
primary audience is Maven PMC.

82.2 Prerequisite
Be sure that:

• you have all Maven servers defined in your settings.xml. For more information, please refer to
Committer settings.
• you have created your GPG keys. For more information, please refer to Making GPG Keys.

82.3 Deploy Maven Current References
1 Do a fresh check out of a release tag of Maven, for example:

$ svn checkout https://svn.apache.org/repos/asf/maven/maven-2/tags/maven-2.2.0 m
2 Execute the site goal for the maven-2.2.0 project

maven-2.2.0$ mvn site -Preporting
3 Verify the documentation before deploying
You could also use the stage goal of the Maven Site Plugin to verify the site output. For instance:

maven-2.2.0$ mvn site:stage -Preporting -DstagingDirectory=/tmp/maven-2.2.0
4 Deploy to people.apache.org

maven-2.2.0$ mvn site-deploy -Preporting

It will create a new folder 2.2.0 in /www/maven.apache.org/ref/ on the Apache server.
Note: It will take an hour or so to sync.
5 Update the current ref symlink to point the last Maven release

• Connect you to people.apache.org and go to /www/maven.apache.org/ref/ folder.
• Create a symlink from 2.2.0 folder to current if it is the newest stable release of Maven:

ref$ ln -s 2.2.0/ ./current


83 External Resources 340

83 External Resources
.......................................................................................................................................

83.1 Books on Maven

Maven: The Definitive Guide (Readable HTML and Free PDF Download)
• Covers: Maven 2.0.9+
• Published: O'Reilly (Edition 1: October 1, 2008)
• Authors: Sonatype ( Jason van Zyl, Brian Fox, John Casey, Bruce Snyder, Tim O'Brien,
Eric Redmond)
• Read Online: http://www.sonatype.com/books/maven-book/
• Buy the Book: Amazon

Better Builds with Maven (Free PDF Download)
• Covers:Maven 2.0.4
• Published: MaestroDev (March 2006)
• Authors: John Casey, Vincent Massol, Brett Porter, Carlos Sanchez
• Read Online: http://www.maestrodev.com/better-build-maven



Maven: A Developer's Notebook

• Covers:Maven 1.0.2
• Published: O'Reilly (July 2005)
• Authors: Vincent Massol, Tim O'Brien

83.2 Miscellaneous on Maven
If you're interested in testing your Maven skills, check out JavaBlackBelt's Maven exam. This
exam is being written collaboratively by the community. Feel free to add new questions, suggest
improvements, etc.

83.3 Articles on Maven
If you are writing an article on Maven we suggest contacting the developers on the mailing list as we
would be happy to provide feedback to help ensure accuracy in your article. Just ping us on the dev
mailing list to get in touch.

Title Publisher Author Published
Maven: mas que Manuel Recena June 2009
una herramienta de
construccion (in Spanish)
Introduction to m2eclipse TheServerSide Tim O'Brien, Bruce July 2008
Snyder, Eugene Kuleshov
Maven 2.x (in Turkish) Anadolu Üniversitesi Mustafa Sait Özen August 2007
Setting up the Internal The Server Side Avneet Mangat June 2007
Repository
Building Web Applications java.net Will Iverson 1 March 2007
with Maven 2
Introduction to Apache developerWorks Sing Li 19 December 2006
Maven 2
Maven - Menos mal que Universidad de Sevilla Manuel J. Recena Soto 6 November 2006
has venido (in Spanish)



FAQ for Maven 2 and Developpez.com Eric Reboisson 11 October 2006
Continuum (in French)
Keep Your Maven DevX Eric Redmond 8 September 2006
Projects Portable
Throughout the Build
Cycle
Automation for the deverloperWorks Paul Duvall 5 September 2006
people: Choosing a
Continuous Integration
server
Java Posse #070 - Java Posse Tor Norbye, Carl Quinn, 18 July 2006
Interview with Brett Porter Dick Wall, Joe Nuxoll,
of Maven Brett Porter
Continuous Integration Java.net John Ferguson Smart 30 May 2006
with Continuum
The Maven 2 POM JavaWorld Eric Redmond 29 May 2006
demystified
Maven: Building Complex Dr.Dobb's Gigi Sayfan 21 April 2006
Systems
Working with maven 2 PeopleWare Jan Dockx 13 April 2006
Maven 2.0: Compile, onjava Chris Hardin 29 March 2006
Test, Run, Deploy, and
More
Descripcion tecnica de Metaware Inc Juan Pablo Santos 13 March 2006
Maven (in Spanish) Rodríguez
Get the most out of JavaWorld John Ferguson Smart 27 February 2006
Maven 2 site generation
An introduction to Maven Developpez.com Denis Cabasson 27 January 2006
2 (in french)
Maven 2.0 - Javapolis Vincent Massol 15 December 2005
2005
An introduction to Maven JavaWorld John Ferguson Smart 5 December 2005
2
Taking the Maven 2 David DeWolf 1 October 2005
Plunge
Building J2EE Projects OnJava Vincent Massol 7 September 2005
with Maven
Maven 2.0 and Brett Porter 1 June 2005
Continuum SJUG
Presentation
Exploiting Maven in developerWorks Gilles Dodinet 24 May 2005
Eclipse
Managing WebSphere developerWorks Hinrich Boog 30 March 2005
Portal V5.1 projects
with Apache Maven and
Rational Application
Developer 6.0



Maven 1.0 Javapolis Vincent Massol 16 December 2004
Presentation
Master and Commander Oracle Julien Dubois November 2004
by Julien Dubois
installing and working with Manfred Wolff August 2004
Maven (in German)
Apache's Maven Comes internetnews.com Sean Michael Kerner 15 July 2004
of Age (Coverage of the
release of Maven 1.0)
Extending Maven OnJava Eric Pugh 17 March 2004
Through Plugins by Eric
Pugh
Maven Magic - a tutorial TheServerSide Srikanth Shenoy November 2003
on Maven and J2EE
projects.
Developing with Maven OnJava Rob Herbst 22 October 2003
by Rob Herbst
Apache Maven Simplifies DevX Dave Ford 2 September 2003
the Java Build Process
Even More Than Ant
Building J2EE TheServerSide Vincent Massol 27 June 2003
applications with
Maven (Slides from
TheServerSide
Symposium)
Maven ties together JavaWorld Jeff Linwood 11 October 2002
tools for better code
management
How to get Maven to build Astrogrid
your web service into a
WAR on AstroGrid
Some Maven FAQs on Astrogrid
AstroGrid
Some Useful Maven Astrogrid
Notes on AstroGrid
A tutorial for Maven, J2EE
projects, and MevenIDE
(in Portuguese).


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