DWR实现服务器端向客户端推送消息

1.简介

DWR（Direct Web Remoting）是一个用于改善web页面与Java类交互的远程服务器端Ajax开源框架，可以帮助开发人员开发包含AJAX技术的网站。它可以允许在浏览器里的代码使用运行在WEB服务器上的JAVA函数，就像它就在浏览器里一样。

它包含两个主要的部分:允许JavaScript从WEB服务器上一个遵循了AJAX原则的Servlet中获取数据.另外一方面一个JavaScript库可以帮助网站开发人员轻松地利用获取的数据来动态改变网页的内容.

DWR采取了一个类似AJAX的新方法来动态生成基于JAVA类的JavaScript代码。这样WEB开发人员就可以在JavaScript里使用Java代码，就像它们是浏览器的本地代码(客户端代码)一样；但是Java代码运行在WEB服务器端而且可以自由访问WEB
服务器的资源。出于安全的理由，WEB开发者必须适当地配置哪些Java类可以安全的被外部使用。[1]

这个从JAVA到JavaScript的远程功能方法给DWR的用户带来非常像传统的RPC机制,就像RMI或者SOAP一样,而且拥有运行在WEB上但是不需要浏览器插件的好处.

DWR不认为浏览器/WEB服务器协议是重要的,而更乐于保证编程界面的简单自然.对此最大的挑战就是把AJAX的异步特性和正常JAVA方法调用的同步特性相结合.在异步模式下,结果数据在开始调用之后的一段时间之后才可以被异步访问获取到.DWR允许WEB开发人员传递一个回调函数,来异步处理Java函数调用过程.
以上是百度百科中copy的废话,下面来看步骤

2.前提条件:

2.1 dwr.jar 此包可以到官网下载:http://directwebremoting.org/dwr/downloads/index.htm(必须)

2.2 commons-logging-xxxx.jar(官网说需要)

3.eclipse中new >> Dynamic Web Project 复制dwr.jar到lib目录下会自动build path

4.打开web.xml编辑:

<?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"
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>dwrDemo</display-name>
<welcome-file-list>
<welcome-file>login.jsp</welcome-file>
<welcome-file>index.jsp</welcome-file>
</welcome-file-list>
<servlet>
<display-name>LoginServlet</display-name>
<servlet-name>LoginServlet</servlet-name>
<servlet-class>com.yun.study.servlet.LoginServlet</servlet-class>
</servlet>
<servlet-mapping>
<servlet-name>LoginServlet</servlet-name>
<url-pattern>/loginServlet</url-pattern>
</servlet-mapping>

<servlet>
<servlet-name>dwr-invoker</servlet-name>
<servlet-class>org.directwebremoting.servlet.DwrServlet</servlet-class>
<init-param>
<param-name>crossDomainSessionSecurity</param-name>
<param-value>false</param-value>
</init-param>
<init-param>
<param-name>allowScriptTagRemoting</param-name>
<param-value>true</param-value>
</init-param>
<init-param>
<param-name>classes</param-name>
<param-value>java.lang.Object</param-value>
</init-param>
<init-param>
<param-name>activeReverseAjaxEnabled</param-name>
<param-value>true</param-value>
</init-param>
<init-param>
<param-name>initApplicationScopeCreatorsAtStartup</param-name>
<param-value>true</param-value>
</init-param>
<init-param>
<param-name>maxWaitAfterWrite</param-name>
<param-value>3000</param-value>
</init-param>
<init-param>
<param-name>debug</param-name>
<param-value>true</param-value>
</init-param>
<init-param>
<param-name>logLevel</param-name>
<param-value>WARN</param-value>
</init-param>
</servlet>

<!--此处必须要有 不然前端js不能自动引入-->
<servlet-mapping>
<servlet-name>dwr-invoker</servlet-name>
<url-pattern>/dwr/*</url-pattern>
</servlet-mapping>
</web-app>

以上具体的 init-param可以到官网查查文档什么的搞定

5.在web.xml同级目录下新建一个文件 dwr.xml

<?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="MessagePush">
<param name="class" value="com.yun.study.service.MessagePush" />
</create>
<create creator="new" javascript="TestPush">
<param name="class" value="com.yun.study.service.Test" />
</create>
</allow>
</dwr>

以上可以看出 我的class有两个

com.yun.study.service.MessagePush

com.yun.study.service.Test

属性javascript的值表示是在js中用到该类的时候引用的名字

6.新建的java类如下:

bean:

package com.yun.study.model;

public class User {
private String userId;

public String getUserId() {
return userId;
}

public void setUserId(String userId) {
this.userId = userId;
}
}

package com.yun.study.servlet;

import javax.servlet.ServletException;
import javax.servlet.http.HttpSession;

import org.directwebremoting.Container;
import org.directwebremoting.ServerContextFactory;
import org.directwebremoting.WebContextFactory;
import org.directwebremoting.event.ScriptSessionEvent;
import org.directwebremoting.event.ScriptSessionListener;
import org.directwebremoting.extend.ScriptSessionManager;
import org.directwebremoting.servlet.DwrServlet;

import com.yun.study.model.User;

public class DwrScriptSessionManagerUtil extends DwrServlet {
private static final long serialVersionUID = 109326676726848212L;

public void init() throws ServletException {

try {
Container container = ServerContextFactory.get().getContainer();
ScriptSessionManager manager = container
.getBean(ScriptSessionManager.class);
ScriptSessionListener listener = new ScriptSessionListener() {
public void sessionCreated(ScriptSessionEvent ev) {
HttpSession session = WebContextFactory.get().getSession();
String userId = ((User) session.getAttribute("userinfo"))
.getUserId() + "";
System.out.println("======>>>a ScriptSession is created,userId="+userId);
ev.getSession().setAttribute("userId", userId);
}

public void sessionDestroyed(ScriptSessionEvent ev) {
String userId = (String) ev.getSession().getAttribute("userId");
System.out.println("======>>>userId="+userId+" ScriptSession is distroyed");
}
};
manager.addScriptSessionListener(listener);
} catch (Exception e) {
e.printStackTrace();
}
}
}

package com.yun.study.service;

import javax.servlet.ServletException;

import org.directwebremoting.ScriptSession;
import org.directwebremoting.WebContextFactory;

import com.yun.study.servlet.DwrScriptSessionManagerUtil;

public class MessagePush {
public void onPageLoad(String userId) {
System.out.println("=====>>>>MessagePush onPageLoad invoke begin!");
ScriptSession scriptSession = WebContextFactory.get().getScriptSession();

scriptSession.setAttribute("userId", userId);

DwrScriptSessionManagerUtil dwrScriptSessionManagerUtil = new DwrScriptSessionManagerUtil();

try {

dwrScriptSessionManagerUtil.init();
System.out.println("=====>>>>MessagePush onPageLoad invoke end!");

} catch (ServletException e) {

e.printStackTrace();

}

}

}

package com.yun.study.service;

import java.text.SimpleDateFormat;
import java.util.Collection;
import java.util.Date;

import org.directwebremoting.Browser;
import org.directwebremoting.ScriptBuffer;
import org.directwebremoting.ScriptSession;
import org.directwebremoting.ScriptSessionFilter;

public class Test {
SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
public void sendMessageAuto(String userid) {
System.out.println("======>>>sendMessageAuto invoke begin!");
final String userId = userid;
final String sendMessage = "长江长江,我是黄河,收到请回答!当前时间是:"+sdf.format(new Date());
Browser.withAllSessionsFiltered(new ScriptSessionFilter() {
public boolean match(ScriptSession session) {
if (session.getAttribute("userId") == null)
return false;
else
return (session.getAttribute("userId")).equals(userId);
}
}, new Runnable() {

private ScriptBuffer script = new ScriptBuffer();

public void run() {
System.out.println("====>>>invoke client browser task run.......");
script.appendCall("showMessage", sendMessage);

Collection<ScriptSession> sessions = Browser.getTargetSessions();

for (ScriptSession scriptSession : sessions) {
System.out.println("===>>>loop execute sessions userId:"+scriptSession.getAttribute("userId"));
scriptSession.addScript(script);
}
}
});
System.out.println("======>>>sendMessageAuto invoke end!");
}
}

package com.yun.study.servlet;

import java.io.IOException;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import com.yun.study.model.User;

/**
* Servlet implementation class ServerPushMessageServlet
*/
public class LoginServlet extends HttpServlet {
private static final long serialVersionUID = 1L;

/**
* @see HttpServlet#HttpServlet()
*/
public LoginServlet() {
super();
// TODO Auto-generated constructor stub
}

/**
* @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response)
*/
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
doPost(request, response);
}

/**
* @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response)
*/
protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
String pageName = request.getParameter("pageName");
String sessionId = request.getSession().getId();
User u = new User();
u.setUserId(sessionId);
request.getSession().setAttribute("userinfo", u);
response.sendRedirect(pageName);
}

}

以下是界面:
登录:login.jsp

<?xml version="1.0" encoding="UTF-8" ?>
<%@ page language="java" contentType="text/html; charset=UTF-8"
pageEncoding="UTF-8"%>
<%
String path = request.getContextPath();
String basePath = request.getScheme() + "://"
+ request.getServerName() + ":" + request.getServerPort()
+ path + "/";
%>

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<base href="<%=basePath%>"></base>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8" />
<title>dwr test</title>

</head>
<body>

<form action="<%=basePath%>/loginServlet" method="post">
<p>请点击以下button 将会模拟登录得到一个sessionKey设置到你的session中用于表示您的身份,</p>
<p style="color: red;">界面将跳转到一个客户端页面(用于接收服务器推送消息的)!</p>
<br/><input type="hidden" name="pageName" value="index.jsp"/>
<input type="submit" value="跳转到客户端"/>
</form>
<br/><br/><br/>
<hr/>
<form action="<%=basePath%>/loginServlet" method="post">
<p>请点击以下button 将会模拟登录得到一个sessionKey设置到你的session中用于表示您的身份,</p>
<p style="color: red;">界面将跳转到一个触发服务端推送消息的界面(用于通知服务器推送消息给客户端的)!</p><br/>
<input type="hidden" name="pageName" value="clientPush.jsp"/>
<input type="submit" value="跳转到通知服务发送界面"/>
</form>

</body>
</html>

:index.jsp:

<?xml version="1.0" encoding="UTF-8" ?>
<%@ page language="java" contentType="text/html; charset=UTF-8"
pageEncoding="UTF-8"%>
<%
String path = request.getContextPath();
String basePath = request.getScheme() + "://"
+ request.getServerName() + ":" + request.getServerPort()
+ path + "/";
%>

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<base href="<%=basePath%>"></base>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8" />
<title>dwr client test</title>
<script type="text/javascript" src="<%=basePath%>/js/jquery-1.7.2.min.js"></script>
<script type="text/javascript" src="dwr/engine.js"></script>
<script type="text/javascript" src="dwr/util.js"></script>
<script type="text/javascript"
src="<%=basePath%>/dwr/interface/MessagePush.js"></script>

<script type="text/javascript">
//通过该方法与后台交互，确保推送时能找到指定用户
function onPageLoad() {
var userId = '${userinfo.userId}';
MessagePush.onPageLoad(userId);
}
//服务器向客户端推送信息的方法
function showMessage(autoMessage) {
$("#serverSay").html(autoMessage);
}
</script>
</head>
<body
onload="onPageLoad();dwr.engine.setActiveReverseAjax(true);dwr.engine.setNotifyServerOnPageUnload(true);;">
This is my DWR DEOM page.please copy this userId <span style="color: red;">${userinfo.userId}</span>
to clientPush.jsp page to trigger a event,server will send message to client......
<hr/><br/>
<div id="DemoDiv">demo</div>
<h2 style="color: red;" id="serverSay"></h2>
</body>
</html>

clientPush.jsp:

<?xml version="1.0" encoding="UTF-8" ?>
<%@ page language="java" contentType="text/html; charset=UTF-8"
pageEncoding="UTF-8"%>
<%
String path = request.getContextPath();
String basePath = request.getScheme() + "://"
+ request.getServerName() + ":" + request.getServerPort()
+ path + "/";
%>

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<base href="<%=basePath%>"></base>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8" />
<title>server push message trigger</title>
<script type="text/javascript" src="<%=basePath%>/js/jquery-1.7.2.min.js"></script>
<script type='text/javascript' src='dwr/engine.js'></script>
<script type='text/javascript' src='dwr/util.js'></script>
<script type='text/javascript' src='dwr/interface/TestPush.js'></script>

<script type="text/javascript">
function test() {
var userId = $("#userId").val();
TestPush.sendMessageAuto(userId);
}
</script>
</head>

<body>
client userId <input type="text" name="userId" id="userId" />
<br />
<input type="button" value="Send" onclick="test()" />
</body>
</html>

ok!

注意:以上测试 客户端和通知服务端的页面请使用两个不同的浏览器测试,以免session存在覆盖的问题