Spring and DWR

Spring and DWRFrameworks for Rich Web Enterprise Application

Thomas Wiradikusumathomas@wiradikusuma.com

www.wiradikusuma.com

Presentation to the 20th Java User Group Meet Up (JaMU), May 20, 2006

Objective

• To introduce Spring, an application framework for developing enterprise applications.

• To introduce DWR, an Ajax framework for developing Rich Internet Application (RIA).

• To show Spring+DWR integration to get the best of both worlds.

Agenda

• Intro to Spring

• Spring wiring

• Spring step-by-step

• Intro to DWR

• DWR configuration

• DWR step-by-step

• Spring and DWR integration

Typical JavaEE App Development

• Usually developing web applications that serve many users and access (possibly many, heterogeneous) enterprise resources.

• EJB is used because we want some of its features.

• EJB is complicated, for a reason.

• Testing is tedious.

• Is there an easier way?

Here Comes Spring!

• An open source Java/JavaEE application framework.

• Codes originally came from Rod Johnson’s book “Expert One-on-One: J2EE Design and Development”, Wrox Press, 2002.

• Enables POJOs to achieve things that were previously only possible with EJBs.

Spring Mission Statement

• JavaEE should be easier to use.• OO design is more important than any

implementation technology, such as JavaEE.

• Testability is essential, and a framework such as Spring should help make your code easier to test.

• Spring should not compete with good existing solutions (Hibernate, Struts, etc), but should foster integration.

Spring Described

• Lightweight

• Inversion of control

• Aspect-oriented

• Container

• Framework

Spring Modules

Some Spring Usage Scenarios

Some Spring Usage Scenarios - 2

Inversion of Control

• Dependency injection– Beans define their dependencies through

constructor arguments or properties– The container provides the injection at

runtime• “Don’t talk to strangers,” also known

as the Hollywood principle, “Don’t call me I’ll call you.”

• Decouples object creators and locators from application logic

• Easy to maintain and reuse• Testing is easier

Spring Bean Definition• The bean class is the actual implementation of the bean

being described by the BeanFactory. • Bean examples: DAO, DataSource, Transaction Manager,

Persistence Manager, Service objects, etc.• Spring config contains implementation classes while your

code should program to interfaces.• Bean behaviors include:

– Singleton or prototype– Autowiring– Spring-aware interfaces– Initialization and destruction methods

• init-method• destroy-method

• Beans can be configured to have property values set. • Can read simple values, collections, maps, references to

other beans, etc.

Simple Spring Bean Example<bean id="orderBean" class="example.OrderBeanImpl"

init-method="init"><property name=“maxOrder">10</property><property name="orderDAO"> <ref bean="orderDAO"/></property>

</bean>

public class OrderBeanImpl implements OrderBean {// ...

public void setMaxOrder(double maxOrder){ this.maxOrder = maxOrder;

} public void setOrderDAO(OrderDAO orderDAO){

this.orderDAO = orderDAO; }

// ...}

Spring BeanFactory

• BeanFactory is core to the Spring framework– Lightweight container that loads bean

definitions and manages your beans.– Configured declaratively using an XML file,

or files, that determine how beans can be referenced and wired together.

– Knows how to serve and manage a singleton or prototype defined bean

– Responsible for lifecycle methods.– Injects dependencies into defined beans

when served

• Avoids the use of singletons and factories

Spring ApplicationContext• A Spring ApplicationContext allows you to get

access to the objects that are configured in a BeanFactory in a framework manner.

• ApplicationContext extends BeanFactory– Adds services such as international messaging

capabilities.– Add the ability to load file resources in a generic

fashion.• Several ways to configure a context:

– XMLWebApplicationContext – Configuration for a web application.

– ClassPathXMLApplicationContext – standalone XML application context

– FileSystemXmlApplicationContext• Allows you to avoid writing Service Locators

XMLWebApplicationContext<context-param>

<param-name>contextConfigLocation</param-name> <param-value> /WEB-INF/applicationContext.xml</param-value>

</context-param>

<listener> <listener-class> org.springframework.web.context.ContextLoaderListener</listener-class>

</listener>

Spring MVC

Sample Spring Application

• DEMOApplicationContext factory = new

ClassPathXmlApplicationContext(“config.xml");

• index.jsp<%@ taglib

uri="http://java.sun.com/jsp/jstl/core" prefix="c" %>

<c:redirect url="something.htm"/>

• Spring Bind Tag<%@taglib

uri="http://www.springframework.org/tags" prefix="spring"%>

<spring:bind path="command.property">

Web is All Around

• History of dynamic web applications

• Web 2.0 and Ajax

• The DWR approach to Ajax

• Tools and widgets

Ajax – Not a Football Team

• Not one technology, several technologies:– XHTML and CSS– Document Object Model (DOM)– XML (and XSLT)– XMLHttpRequest (XHR)– JavaScript

Ajax Approach to Web

Ajax Approach to Web - 2

Issues in Ajax

• Browser incompatibilities

• Back button and browser history

• Working with XML in JavaScript

• Accessibility

Ajax Frameworks

• DWR• Echo2• JSON-RPC• Sajax• Many more…

• Why DWR?– Mostly used framework– Integrates best with Spring

DWR Described

• Open source Java library

• Allows code in a web browser to use Java functions running on a web server as if it was in the browser

• Two main parts:– Java Servlet– JavaScript

• Dynamically generates JavaScript code based on Java classes

Sample DWR Configuration

• web.xml:<servlet>

<servlet-name>dwr-invoker</servlet-name>

<servlet-class>

uk.ltd.getahead.dwr.DWRServlet

</servlet-class>

<init-param>

<param-name>debug</param-name>

<param-value>true</param-value>

</init-param>

</servlet>

<servlet-mapping>

<servlet-name>dwr-invoker</servlet-name>

<url-pattern>/dwr/*</url-pattern>

</servlet-mapping>

Sample DWR Configuration - 2

• dwr.xml:<!DOCTYPE dwr PUBLIC "-//GetAhead Limited//DTD

Direct Web Remoting 1.0//EN" "http://www.getahead.ltd.uk/dwr/dwr10.dtd">

<dwr>

<allow>

<create creator="new" javascript="myDate">

<param name="class" value="java.util.Date"/>

</create>

</allow>

</dwr>

DWR Step-by-step

1. Install the DWR JAR file2. Edit the config files3. Go to the following URL:

http://localhost:8080/[YOUR-WEBAPP]/dwr/ 4. Put this in your JSP:

<script src='/[YOUR-WEBAPP]/dwr/interface/[YOUR-SCRIPT].js'></script>

<script src='/[YOUR-WEBAPP]/dwr/engine.js'></script>

<script src='/[YOUR-WEBAPP]/dwr/util.js'></script>

Spring+DWR Integration

• Check list:1. Use the latest DWR. The Spring

creator has changed so it is well worth checking that you have the latest download.

2. Make sure DWR and Spring each are working OK in your application.

3. Configure DWR to work with Spring.

4. Check result in the debug pages: http://localhost:8080/[YOUR-WEBAPP]/dwr/

Spring+DWR Integration - 2

• The SpringCreator:<create creator="spring" javascript="test"> <param name="beanName" value="test"/> </create>

• Find the Spring configuration:– ContextLoaderListener

<context-param><param-name>contextConfigLocation</param-name><param-value>/WEB-INF/classes/beans.xml</param-value></context-param>

<listener><listener-class>org.springframework.web.context.ContextLoaderListener</listener-class></listener>

– Or by “location*” parameters<create creator="spring" javascript="test"><param

name="beanName" value="test"/><param name="location" value="beans.xml"/></create>

– Or by setting the BeanFactory DirectlySpringCreator.setOverrideBeanFactory(BeanFactory)

Resources

• Spring Website: www.springframework.org

• The Spring Reference Manual.• Walls, Craig and Ryan Breidenbach.

Spring in Action. Manning. 2003. • Johnson, Rod and Jurgen Hoeller.

J2EE without EJB. Wrox. 2004.• DWR Website:

http://www.getahead.ltd.uk/dwr