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dwr 后台推送技术

2016-07-08 15:47 330 查看

实例分为两个页面

sendMsg.jsp页面，发送一段消息给后台，然后后台将消息推送到showMsg.jsp页面

web.xml配置

[html] view
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<?xml version="1.0" encoding="UTF-8"?>

<web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://java.sun.com/xml/ns/javaee" xmlns:web="http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd" xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd" id="WebApp_ID" version="2.5">

  <display-name>dwr3</display-name>

  <welcome-file-list>

    <welcome-file>index.jsp</welcome-file>

  </welcome-file-list>

    <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>

         

         <init-param>

          <param-name>pollAndCometEnabled</param-name>

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

         </init-param>

         <load-on-startup>1</load-on-startup>

    </servlet>

    <servlet-mapping>

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

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

    </servlet-mapping>

</web-app>

sendMsg.java 推送类

[java] view
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package com.zf.dwr;



import java.util.Collection;



import org.directwebremoting.ScriptBuffer;

import org.directwebremoting.ScriptSession;

import org.directwebremoting.WebContext;

import org.directwebremoting.WebContextFactory;

import org.directwebremoting.proxy.dwr.Util;



public class SendMsg {



    @SuppressWarnings("deprecation")

    public void sendMsg(String msg){

        //得到上下文

        WebContext contex = WebContextFactory.get();



        //得到要推送到的页面  dwr3为项目名称，一定要加上。

        Collection<ScriptSession> sessions = contex.getScriptSessionsByPage("/dwr3/showMsg.jsp");



        //不知道该怎么解释这个，

        Util util = new Util(sessions);



        //下面是创建一个javascript脚本，相当于在页面脚本中添加了一句  show(msg);

        ScriptBuffer sb = new ScriptBuffer();

        sb.appendScript("show(");

        sb.appendData(msg);

        sb.appendScript(")");



        //推送

        util.addScript(sb);

    }

}

dwr.xml配置

[html] view
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<?xml version="1.0" encoding="UTF-8"?>

<!DOCTYPE dwr PUBLIC

    "-//GetAhead Limited//DTD Direct Web Remoting 3.0//EN"

    "http://getahead.org/dwr/dwr30.dtd">

  <dwr>

        <allow>

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

                <param name="class">com.zf.dwr.SendMsg</param>

            </create>

        </allow>

  </dwr>

sendMsg.jsp

[html] view
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<%@ page language="java" contentType="text/html; charset=utf-8"

    pageEncoding="utf-8"%>

<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">

<html>

<head>

<meta http-equiv="Content-Type" content="text/html; charset=utf-8">

<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/SendMsg.js"></script>

<script type="text/javascript" src="jquery-1.7.1.js"></script>

<script type="text/javascript">

    $(function(){

        dwr.engine.setActiveReverseAjax(true);

        $("#but").click(function(){

            SendMsg.sendMsg($("#msg").val());

        });

    });

</script>

<title>Insert title here</title>

</head>

<body>

    <input type="text" id="msg"  />

    <input type="button" value="发送" id="but" />

</body>

</html>

showMsg.jsp

[html] view
plain copy

<%@ page language="java" contentType="text/html; charset=utf-8"

    pageEncoding="utf-8"%>

<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">

<html>

<head>

<meta http-equiv="Content-Type" content="text/html; charset=utf-8">

<script type="text/javascript" src="dwr/util.js"></script>

<script type="text/javascript" src="dwr/engine.js"></script>

<script type="text/javascript" src="jquery-1.7.1.js"></script>

<script type="text/javascript">

    $(function(){

        //这句话千万不能少，表示允许使用推送技术

        dwr.engine.setActiveReverseAjax(true);

    });

    //这个函数是提供给后台推送的时候  调用的

    function show(msg){

        $("#message").text(msg);

    }

</script>

<title>Insert title here</title>

</head>

<body>

    <div id="message" style="width: 200px;height: 200px;border: 1px solid red ; text-align: center; padding: 5px;"></div>

</body>

</html>

使用dwr推送技术时需要有WebContext 对象，但是 WebContext 对象需要通过 WebContextFactory.get();获取，而WebContextFactory.get(); 方法只有当页面请求某个java方法时，在该方法中调用WebContextFactory.get(); 才能得到值。否则是取不到值的。

然后通过WebContext 获取指定的页面。再向页面推送消息。

有一个问题是当后来又新开了页面，却收不到消息。

可以使用一个线程，去定时的更新Collection<ScriptSession> 对象

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