Spring introduction

Spring Overview
• Spring is an open source layered Java/J2EE application
framework
• Created by Rod Johnson
• Based on book “Expert one-on-one J2EE Design and
Development” (October, 2002)
• Current version 2.0.6 (released on 2007-06-18)
• The Spring Framework is licensed under the terms of the
Apache License, Version 2.0 and can be downloaded at:
• http://www.springframework.org/download
• Philosophy: J2EE should be easier to use,
“Lightweight Container” concept
A software framework is a re-usable
design for a software system.

What are Lightweight Frameworks?
• Non-intrusive
• No container requirements
• Simplify application development
• Remove re-occurring pattern code
• Productivity friendly
• Unit test friendly
• Very pluggable
• Usually open source
• Examples:
• Spring, Pico, Hivemind
• Hibernate, IBatis, Castor
• WebWork
• Quartz
• Sitemesh

Spring Mission Statement
• J2EE should be easier to use
• It's best to program to interfaces, rather than classes. Spring reduces
the complexity cost of using interfaces to zero.
• JavaBeans offer a great way of configuring applications
• OO design is more important than any implementation technology,
such as J2EE
• Checked exceptions are overused in Java. A framework shouldn't
force you to catch exceptions you're unlikely to be able to recover
from.
• Testability is essential, and a framework such as Spring should help
make your code easier to test
• Spring should be a pleasure to use
• Your application code should not depend on Spring APIs
• Spring should not compete with good existing solutions, but should
foster integration. (For example, JDO and Hibernate are great O/R
mapping solutions. Don't need to develop another one).

Modules of the Spring Framework
The Spring Framework can be considered as a collection
of frameworks-in-the-framework:
• Core - Inversion of Control (IoC) and Dependency Injection
• AOP - Aspect-oriented programming
• DAO - Data Access Object support, transaction management,
JDBC-abstraction
• ORM - Object Relational Mapping data access, integration
layers for JPA, JDO, Hibernate, and iBatis
• MVC - Model-View-Controller implementation for web-
applications
• Remote Access, Authentication and Authorization, Remote
Management, Messaging Framework, Web Services, Email,
Testing, …

Overview of the Spring Framework
Very loosely coupled, components widely reusable and
separately packaged.

Spring Details
• Spring allows to decouple software layers by injecting a component’s
dependencies at runtime rather than having them declared at compile time via
importing and instantiating classes.
• Spring provides integration for J2EE services such as EJB, JDBC, JNDI,
JMS, JTA. It also integrates several popular ORM toolkits such as Hibernate
and JDO and assorted other services as well.
• One of the highly touted features is declarative transactions, which allows the
developer to write transaction-unaware code and configure transactions in
Spring config files.
• Spring is built on the principle of unchecked exception handling. This also
reduces code dependencies between layers. Spring provides a granular
exception hierarchy for data access operations and maps JDBC, EJB, and
ORM exceptions to Spring exceptions so that applications can get better
information about the error condition.
• With highly decoupled software layers and programming to interfaces, each
layer is easier to test. Mock objects is a testing pattern that is very useful in
this regard.

Advantages of Spring Architecture
• Enable you to write powerful, scalable applications using POJOs
• Lifecycle – responsible for managing all your application
components, particularly those in the middle tier container sees
components through well-defined lifecycle: init(), destroy()
• Dependencies - Spring handles injecting dependent components
without a component knowing where they came from (IoC)
• Configuration information - Spring provides one consistent way of
configuring everything, separate configuration from application
logic, varying configuration
• In J2EE (e.g. EJB) it is easy to become dependent on container and
deployment environment, proliferation of pointless classes
(locators/delegates); Spring eliminates them
• Cross-cutting behavior (resource management is cross-cutting
concern, easy to copy-and-paste everywhere)
• Portable (can use server-side in web/ejb app, client-side in swing app,
business logic is completely portable)

Spring Solutions
• Solutions address major J2EE problem areas:
• Web application development (MVC)
• Enterprise Java Beans (EJB, JNDI)
• Database access (JDBC, iBatis, ORM)
• Transaction management (JTA, Hibernate, JDBC)
• Remote access (Web Services, RMI)
• Each solution builds on the core architecture
• Solutions foster integration, they do not re-invent
the wheel

How to Start Using Spring
• Download Spring from www.springframework.org, e.g.
spring-framework-2.0.6-with-dependencies.zip
• Unzip to some location, e.g.
C:toolsspring-framework-2.0.6
• Folder C:toolsspring-framework-2.0.6dist
contains Spring distribution jar files
• Add libraries to your application classpath
and start programming with Spring

Inversion of Control (IoC)
• Central in the Spring is its Inversion of Control container
• Based on “Inversion of Control Containers and the
Dependency Injection pattern” (Martin Fowler)
• Provides centralized, automated configuration, managing and
wiring of application Java objects
• Container responsibilities:
• creating objects,
• configuring objects,
• calling initialization methods
• passing objects to registered callback objects
• etc
• All together form the object lifecycle which is one of the most
important features
Java objects that are managed
by the Spring IoC container are
referred to as beans

Dependency Injection – Non-IoC
public class MainBookmarkProcessor implements BookmarkProcessor{
private PageDownloader pageDownloader;
private RssParser rssParser;
public List<Bookmark> loadBookmarks()
{
// direct initialization
pageDownloader = new ApachePageDownloader();
rssParser = new JenaRssParser();
// or factory initialization
// pageDownloader = PageDownloaderFactory.getPageDownloader();
// rssParser = RssParserFactory.getRssParser();
// use initialized objects
pageDownloader.downloadPage(url);
rssParser.extractBookmarks(fileName, resourceName);
// ...
}

Dependency Injection - IoC
• Beans define their dependencies through constructor arguments or
properties
• Container resolves (injects) dependencies of components by setting
implementation object during runtime
• BeanFactory interface - the core that
loads bean definitions and manages beans
• Most commonly used implementation
is the XmlBeanFactory class
• Allows to express the objects that compose
application, and the interdependencies
between such objects, in terms of XML
• The XmlBeanFactory takes this XML
configuration metadata and uses it to create a fully configured system

Non-IoC versus IoC
Non Inversion of Control
approach
Inversion of Control
approach

IoC Basics
• Basic JavaBean pattern:
• include a “getter” and “setter” method for each field:
• Rather than locating needed resources, application components
provide setters through which resources are passed in during
initialization
• In Spring Framework, this pattern is used extensively, and
initialization is usually done through configuration file rather than
application code
class MyBean {
private int counter;
public int getCounter()
{ return counter; }
public void setCounter(int counter)
{ this.counter = counter; }
}

IoC Java Bean
public class MainBookmarkProcessor implements BookmarkProcessor{
private PageDownloader pageDownloader;
private RssParser rssParser;
public List<Bookmark> loadBookmarks()
{
pageDownloader.downloadPage(url);
rssParser.extractBookmarks(fileName, resourceName);
// ...
}
public void setPageDownloader(PageDownloader pageDownloader){
this.pageDownloader = pageDownloader;
}
public void setRssParser(RssParser rssParser){
this.rssParser = rssParser;
}

References
• Spring Home:
http://www.springframework.org
• Inversion of Control Containers and the Dependency
Injection pattern
http://www.martinfowler.com/articles/injection.html
• Spring IoC Container:
http://static.springframework.org/spring/docs/2.0.x/referenc
e/beans.html
• Introduction to the Spring Framework by Rod Johnson
http://www.theserverside.com/tt/articles/article.tss?
l=SpringFramework

Spring introduction

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