DWR3实现服务器端向客户端精确推送消息
??????? 研究了一天半，终于模拟出了这个功能，网上DWR的资料不少，但是真正实现客户端向服务器端精确推送消息的只有两篇文章。但是代码都只有一部分，向我这种刚开始学习DWR的人来说要看懂真的蛮难。不过即便如此，http://www.blogjava.net/stevenjohn/archive/2012/07/07/382447.html这片文章还是给了我很大帮助，再次表示感谢，下面我将这两天的研究详细记录下来备忘，也希望能帮助到像我一样的人。只写过程，不写原理（不是不写，而是有些地方我也不太懂），下面开始：
???????? 第一、在项目中引入dwr.jar，然后在web.xml中进行配置，配置如下：
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<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>
?? 第二：在web.xml的同级目录下新建dwr.xml文件，内容如下
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<!DOCTYPE dwr PUBLIC "-//GetAhead Limited//DTD Direct Web Remoting 3.0//EN" "http://getahead.org/dwr/dwr30.dtd"><dwr> <alow> <create creator="new" javascript="MessagePush"> <param name="class" value="com.huatech.messageremind.service.MessagePush"/> </create> <create creator="new" javascript="TestPush"> <param name="class" value="com.huatech.messageremind.service.Test"/> </create> </alow></dwr>
?? 这个是dwr的基本配置，MessagePush在页面的javascript中使用，这个是对被推送页面开放的java类，Test是对推送页面开放的java类。场景：管理员后台登陆，发布一条消息，通过Test推送到后台，后台通过MessagePush推送给指定的用户，当然，至于怎么找到指定的用户，下面会说。
???? 第三，被推送的页面代码
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<%@ page language="java" import="java.util.*" pageEncoding="utf-8"%><%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>DWR DEMO</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"> </head> <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/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.humanid}'; MessagePush.onPageLoad(userId); } //推送信息 function showMessage(autoMessage){alert(autoMessage);} </script> <body onload="onPageLoad();dwr.engine.setActiveReverseAjax(true);dwr.engine.setNotifyServerOnPageUnload(true);;"> This is my DWR DEOM page. <hr> <br> <div id="DemoDiv">demo</div> </body></html>??? 以上代码的简单解释：
???? 页面页面onload的3个函数都是必须的，后两个是dwr的，第一个是将登录用户的userid与对应?? 的scriptSession进行处理，以便精确推送的时候能找到推送对象
第四 MessagePush类中实现的方法如下：
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public void onPageLoad(String userId) { ScriptSession scriptSession = WebContextFactory.get().getScriptSession(); scriptSession.setAttribute(userId, userId); DwrScriptSessionManagerUtil dwrScriptSessionManagerUtil = new DwrScriptSessionManagerUtil(); try { dwrScriptSessionManagerUtil.init(); System.out.println("cacaca"); } catch (ServletException e) { e.printStackTrace(); } }?
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里面对应的DwrScriptSessionManagerUtil 对应如下：
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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;public class DwrScriptSessionManagerUtil extends DwrServlet{ private static final long serialVersionUID = -7504612622407420071L; public void init()throws ServletException { 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")).getHumanid()+""; System.out.println("a ScriptSession is created!"); ev.getSession().setAttribute("userId", userId); } public void sessionDestroyed(ScriptSessionEvent ev) { System.out.println("a ScriptSession is distroyed"); } }; manager.addScriptSessionListener(listener); }}?第五 推送页面代码：
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<%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%><%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 'MyJsp.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="<%=request.getContextPath() %>/js/jquery-1.5.1.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 msg = document.getElementById("msgId").value;//msg = {msgId: '1', context: $("#msgContext").val()};TestPush.sendMessageAuto(msg,"哈哈哈");}</script> </head> <body> id : <input type="text" name="msgId" id="msgId" /> <br /> <input type="button" value="Send" onclick="test()" /> </body></html>?第六：精确推送要实现的代码：
?public class Test{ public void sendMessageAuto(String userid, String message){ final String userId = userid; final String autoMessage = message; 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(){ script.appendCall("showMessage", autoMessage); Collection<ScriptSession> sessions = Browser .getTargetSessions(); for (ScriptSession scriptSession : sessions){ scriptSession.addScript(script); } } }); }}?至此?? 这个例子的代码都已经贴出来了，应该是可以跑通的，有问题的话可以给我留言。当然，要自己写个登录，然后把userId放到session里面，这个比较简单，就不贴代码了，有问题可以在http://download.csdn.net/detail/luojia_wang/5275588上下载原项目。我只是简单的做了一个能实现功能的例子，还有很多地方要研究，比如跟spring整合，还可能有很多优化，等我继续学习一下再说.
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