DWR反向Ajax技术
常规的Web应用和通常的Ajax应用都要满足“请求--响应”模型。在反向Ajax模型中，服务器的Java方法可以“直接修改”浏览器里的Web页面，改变Web页面中组件的状态，服务器可以主动将最新的信息发送给浏览器。。使用反向Ajax，要修改两个地方来启动反向Ajax：
[*]修改web.xml文件中的DwrServlet的配置，指定启动反向Ajax
[*]修改HTML页面代码，指定该页面启动反向Ajax技术
先修改web.xml文件，在DWR核心Servlet中加一个属性pollAndComeEnabled = true<?xml version="1.0" encoding="UTF-8"?><web-app version="2.5" xmlns="http://java.sun.com/xml/ns/javaee" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_2_5.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><!-- 启动反向Ajax --><init-param> <param-name>pollAndCometEnabled</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> Java处理类package com.lbx.dwr;import java.util.Collection;import org.directwebremoting.ScriptSession;import org.directwebremoting.WebContext;import org.directwebremoting.WebContextFactory;import org.directwebremoting.proxy.dwr.Util;public class DWRHelper {public void addMessage(String text) {System.out.println("客户端传来：" + text);WebContext wctx = WebContextFactory.get();String currentPage = wctx.getCurrentPage();System.out.println("currentPage:" + currentPage);// 通过scriptsession调用js函数，操作dom。就像我们给sessson中放置内容一样轻松。// 获得正在交互的浏览器上下文：ScriptSession,再得到工具UtilUtil utilThis = new Util(wctx.getScriptSession());utilThis.setValue("text", ""); // 操作客户端DOM模型！utilThis.addFunctionCall("ggg", "服务器数据！"); // 执行客户端的函数！// 获得正在访问chat.jsp所有的浏览器客户端.在服务器端直接调用操作所有客户端内容Collection<ScriptSession> sessions = wctx.getScriptSessionsByPage(currentPage);// 用户每点一次刷新就会生成新的scriptsession对象。// 所以，为了有效管理scriptsession，我们专门维护一个map.for (ScriptSession object : sessions) {System.out.println("ScriptSessionID:" + object.getId());}Util utilAll = new Util(sessions);// 调用一个客户端的js函数！utilAll.addFunctionCall("addChatMsg", text);}} dwr.xml文件的配置<!DOCTYPE dwr PUBLIC "-//GetAhead Limited//DTD Direct Web Remoting 2.0//EN" "http://getahead.org/dwr/dwr20.dtd"><dwr><allow> <create creator="new" javascript="DWRHelper"> <param name="class" value="com.lbx.dwr.DWRHelper"/> </create><!-- <create creator="new" javascript="Demo"> <param name="class" value="com.cssxt.dwr.MyTestDwr"/> </create> <convert match="com.cssxt.dwr.Person" converter="bean"></convert> javabean的转化 --> </allow></dwr> 客户端JSP代码<%@ page language="java" import="java.util.*" pageEncoding="gbk"%><%String path = request.getContextPath();String basePath = request.getScheme()+"://"+request.getServerName()+":"+request.getServerPort()+path+"/";%><!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"><html><head><base href="<%=basePath%>"><title>My JSP 'index.jsp' starting page</title><meta http-equiv="pragma" content="no-cache"><meta http-equiv="cache-control" content="no-cache"><meta http-equiv="expires" content="0"><meta http-equiv="keywords" content="keyword1,keyword2,keyword3"><meta http-equiv="description" content="This is my page"><script type='text/javascript' src='dwr/util.js'></script><script type='text/javascript' src='dwr/engine.js'></script><script type='text/javascript' src='dwr/interface/DWRHelper.js'></script><script type="text/javascript"> function sendMessage() { DWRHelper.addMessage($("text").value); } functionaddChatMsg(msg){ var d2 = document.createElement("div"); d2.innerHTML=msg; $("div1").appendChild(d2); } function ggg(g){ alert("ggg:"+g); }</script></head><body >聊天记录：<div id="div1"></div>我说：<input id="text" /><input type="button" value="Send"/></p><hr /></body></html>
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