DWR的原理爲：把JAVA類注入JS從且達到可以在JS中調用JAVA類中的方法，實現了異步調用。
同GWT相比DWR的優點有一、ＤＷＲ可以同ＪＳ和ＨＴＭＬ同步調用，從且解決ＧＷＴ中頁面美工排
版的困難。二、dwr是把ＪＡＶＡ類注入ＪＳ中，而不需要學習新的技術。
web.xml文件配置如下：
<?xml version="1.0" encoding="UTF-8"?>
<web-app version="2.4" xmlns="http://java.sun.com/xml/ns/j2ee"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://java.sun.com/xml/ns/j2ee
http://java.sun.com/xml/ns/j2ee/web-app_2_4.xsd">
<servlet>
<servlet-name>dwr-invoker</servlet-name>
<servlet-class>
org.directwebremoting.servlet.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>
</web-app>
dwr文件配置如下：
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE dwr PUBLIC "-//GetAhead Limited//DTD Direct Web Remoting 2.0//EN" "http://www.getahead.ltd.uk/dwr/dwr20.dtd">
<dwr>
<allow>
<create creator="new" javascript="service">
<param name="class" value="cn.epem.admin.Service" />
</create>
</allow>
</dwr>
test.jsp
<%@ page language="java" pageEncoding="UTF-8"%>
<html>
<head>
<title>My JSP 'first_dwr.jsp' starting page</title>
<script type="text/javascript" src="<%=request.getContextPath()%>/loadreport.js"></script>
<script type="text/javascript" src="<%=request.getContextPath()%>/dwr/engine.js"></script>
<script type="text/javascript" src="<%=request.getContextPath()%>/dwr/util.js"></script>
<script type='text/javascript' src='<%=request.getContextPath()%>/dwr/interface/service.js'> </script>
</head>
<body>
<input type="button" name="button" value="測試" οnclick="firstDwr()">
</body>
</html>
loadreport.js
function firstDwr(){
service.sayHello("Jorwen",callBackHello);
}
function callBackHello(data){
alert(data);
}
Service.java
package cn.epem.admin;
public class Service {
public String sayHello(String yourName) {
System.out.println(yourName);
return "Hello World " + yourName;
}
}