Build Java Web Application Using Apache Struts

An Introduction to
Building Web Application Using
Jakarta Struts Framework
Presented to Indianapolis Java User Group

10/30/2002

Wei Li

Challenge from Building Web
Applications
• Stateless protocol
• Multiple tiers
• …

Building Web Application with
Java - Why it is good
• Build once, run everywhere (platform-
independent, vendor-independent)
• Build it in an object-oriented way
• Reusable components
• Flexible and easy to be maintained and extended

Building Web Application with
Java - choices
• Pure Java Servlets (control + presentation)
• Java Servlets (control) + template engine
(presentation) (Velocity, WebMacro, Tea)
• Java Servlets (control) + XML and XSLT
(presentation)
• JSP (presentation + control) + Java Beans
(control+model) (Model 1)
• JSP(presentation) + Java Servlets (control)+ Java
Beans (model) (Model 2)

Problems with Pure Java
Servlets - sample code
public void printHTMLReport(PrintWriter out, Results results) {
println(out, "Poll: " + poll.getId() + " ");
println(out, "Question: " + poll.getQuestion() + " ");
out.print("Candidates: ");
this.printCandidates(out);
println(out, " ");
println(out, " ");
println(out, "The winner is... " + results.getWinner() + "! ");
println(out, " ");
println(out, "Round-by-round summary: ");
…
…
}

Problems with Pure Java
Servlets
• Servlets have to take care of presentation - which
is not a good thing for it to do
• HTML tags in the Java code
• Hard to maintain and extend (every content
change requires the compilation of Java classes)
• Frustration of Java developers who are good at
writing Java code but not HTML

Problems with JSPs + Java Beans
(Model 1)
No controller - each page is responsible to direct control to the
next page.

request

JSP Java EIS
response
Beans

Problems with JSPs + Java Beans
(Model 1)
• Java code in HTML tags
• Hard to maintain and change also
• Frustration of content developer

MVC and Model II
• Aim to separate the flow control, business logic
and presentation

MVC and Model II
• Model - this is you data in the system. Such as a poll, the
profile of a poll administrator.
• View - how data is represented to the user. For instance
the view in a web application could be an HTML page, an
image or other media.
• Controller - is the glue between the model and the view.
It is responsible for controlling the flow as well as
processing updates from the model to the view and visa
versa

MVC and Model II
• Model II - uses a controller

Web container
1. request
Controller
2

3 Model EIS
4
5. response
View

MVC and Model II

• Controller - Java servelts
• Model - Java Beans (domain objects, value
objects)
• View - JSP, XML + XSLT ….

MVC and Model II

• Many implementations available for choice
• Expresso
• Barracuda
• Cocoon
• WebWork
• Velocity, Tea, WebMacro
• ….

MVC and Model II

• And of course, you can build your own
• But, Why? Regardless how you implement, you
probably will end up with something similar or
close to Struts.

Break 1

A good scientist is a person with original ideas. A
good engineer is a person who makes a design that
works with as few original ideas as possible.

--- Freeman Dyson

Jakarta Struts - What is it?
• A flexible control layer based on standard technologies
like Java Servlets, JavaBeans, ResourceBundles, and
Extensible Markup Language (XML).
• An implementation of MVC Model II
• A standardized and extensible web application
design/implementation framework

Jakarta Struts - General Info
• Craig McClanahan created the original framework and
donated it to Apache Software Foundation (ASF) in 2000.
• Current stable release - 1.0.2.
• 1.1 is in beta release.
• The framework provides 9 package with 250 classes

Jakarta Struts - Features
• An Model II implementation of MVC
• Big base packages and classes ready to use
• Rich Custom Tag Libraries ready to use
• Easy support for internationalization (I18N)

Jakarta Struts - the whole picture
configuration configuration
Struts-config.xml
request ActionServlet Message Bundle

Controller
action
action
action
EIS
Model

response View
Java Beans,
JSP, Tag Library
EJB, ...
….

Jakarta Struts - the controller

• ActionServlet - Responsible for flow of control - 1.
receive all requests, 2. route/delegate request to Action for
handling, 3. return response
• One instance per web application
• Uses a configuration file called struts-config.xml to read
mapping data, which specify control flow information
• Provided by the framework already. Ready to use but can
also be extended

Jakarta Struts - the controller
• Action - the actual class which processes the
request relevant to the business operation. Based
on action mappings defined in an XML
configuration file, the controller dispatches a call
to the perform method of the appropriate Action
Class.
• Command pattern
• Framework provides some actions. You need to
implement you own action class for business
purpose.

Jakarta Struts - the model

• You are responsible for creating it - Java Bean,
EJB, etc.
• Should be reusable domain objects and value
objects to represent a state.
• The framework works fine with any model
implementation.

Jakarta Struts - the view

• JSP
• Custom Tag Library
• Resource Bundle

Jakarta Struts - the view

• Struts provides rich custom tag library to
dramatically reduce Java code in your jsp.

• Example: HTML, BEAN, LOGIC,
TEMPLATES,…

• We will see how handy they are in the case study

Jakarta Struts - the others

• ActionForm - encapsulate request/session data,
typically used for input forms, provides a central
point to validate form data.

Jakarta Struts - the others

• ActionMessage and ActionError

Jakarta Struts - the configuration

• Glue the system together
• web.xml and struts-config.xml


• Web.xml:
o define the controller servlet (ActionServlet)with initial parameters;
o define URL mapping to be handled by the controller servlet;
o define the Struts tag libraries.


• struts-config.xml
o Glue all components together and set the rules for the
application
o Data Source Configuration
o Form Bean Definitions
o Action Mapping Definitions
o Global Forward Definitions

Break 2
A manager, an engineer, and a developer are going down a
hill in a jeep when it suddenly loses control and goes into a
ditch. They each attempt to offer a solution to the problem.
The manager says 'Let's have a meeting to discuss a
solution'. The engineer says 'Let's disassemble the jeep,
and examine every part to find out where the problem is.'
The developer says, 'Let's push it back up the hill and try
again.

http://www.middleware-company.com/offer/patternsday1/article4.shtml

Case Study:
An Online Instant Poll
• Introduction - When I was having a hard time to define an
appropriate application to really have my hands wet with
Struts, I spotted Alex Chaffee’s JiffyPoll
(http://www.purpletech.com/irv/index.html). I like his
idea but not all his implementation. Then I began to apply
the struts framework to it and extends its functionality …

Case Study:
• What does it do?
o As a normal user - you can select and vote a poll, you
can view the results of any poll, you can also see the
information about a poll.
o As an administrator - you can create a new poll right
away. You can also disable/enable a poll owned by you.

Case Study:
• What does it do - Let us try it.

Case Study:
Flat text file
Web container as persistence
Service interface
media
request PlainTextFilePollService
controller Service DatabasePollService
factory Relational
EJBPollService Database

response
view model EJB Container

Case Study:
• Benefits of the design
o The real business logic is de-coupled from the
controller, the model and the view
o Increase of the reusability of the components - the
service is completely reusable, the model (domain
object and value object) is fully reusable also.

Case Study:
• The controller - directly use ActionServlet
provided by the framework

• The action classes - delegate to service provider
which does the real work.

Case Study:
• The real business logic - de-coupled from the
framework and stands as a independent/reusable
component

Case Study:
• The Model - reusable Java Beans, domain objects
and value objects.

Case Study:
• The view - use the data provided in the model
• Rich use of tag library provide by the framework

• Show some sample JSPs and includes

• Almost no Java code in JSPs

Case Study:
• Internationalization - easy to be implemented like
a breeze

• Demo

Jakarta Struts - Why it is good

• Promote clean separation of components


• Increase the modularity, reusability of components


• Focus on design


• Very use case driven


• What you need to do is clear
• You can really focus on the real work - the
business logic


• Easy internationalization


• Free
• Open Source
• Implemented by savvy developer/expert
• large user community

New features in 1.1 - what makes
it better
• Declarative exception handling
<action path="/login"
type="net.indyjug.weili.struts.security.LoginAction"
name="loginForm"
scope="request"
validate="true"
input="/jsp/login.jsp">
<exception
key="error.invalidlogin"
path=”/jsp/login.jsp"
scope="request"
type=”net.indyjug.weili.struts.exception.InvalidLoginException"/>
<forward name="success" path="/jsp/administration.jsp" />
<forward name="failure" path="/jsp/login.jsp" />
</action>

it better
• Dynamic Form Bean

it better
• Plug-in

it better
• Tiles

The learning curve

• Not so easy for the first time. After that life is
easy.
• Manageable
• Custom tag library may make mad at the
beginning. Do not quit. They are so handy once
you know how to use them.

Fast Track:
Getting Started
• What you need
o JDK 1.2 and above
o Web Contained compliant with Servlet API 2.2 and JSP
API 1.1
o An XML parser compliant with JAXP 1.1 or above
(this is usually provided by the web container)

Fast Track:
Getting Started
• The framework provides an application template
for you to use and extend
• Always continue on top of something which is
working.
• Build the whole structure first and leave the
concrete implementation later on (example)

Build Java Web Application Using Apache Struts

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