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Java Dwr3实现消息推送步骤详解

dexcoder 1年前发布
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1、在工程中引入dwr.jar，之后修改配置web.xml文件，添加配置具体代码如下： 

<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>

2、在web.xml统计目录下新增dwr.xml文件，具体内容如下： 

<!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.yoodb.service.MessagePush"/>
              </create>
	      <create creator="new" javascript="TestPush">  
                  <param name="class" value="com.yoodb.service.TestPush"/>  
              </create>
          </alow>
     </dwr>

MessagePush在页面的javascript中使用，com.yoodb.service.MessagePush实现了想要调用的方法，其中MessagePush.java对被推送页面开放的java类，Test.java是对推送页面开放的java类。在javascript中使用MessagePush.java类中实现的方法，即可在dwr中调用。

3、引入JavaScript文件，具体如下： 

<script type="text/javascript" src="<%=basepath%>dwr/engine.js"></script>
<script type="text/javascript" src="<%=basepath%>dwr/util.js"></script>
<script type="text/javascript" src="<%=basepath%>dwr/interface/MessagePush.js"></script>

注意：

1)dwr.xml配置的javascript中engine.js和util.js是必须引入的文件。

2)在任何一个用户登录的时候，都需要将其userId或者其他唯一性标识放入session中，我放的是userId，这里就以userId为唯一性标识。

3)在载入想推送的页面时，需要onload一个我在MessagePush类中实现的方法，当然了，需要使用dwr调用

被推送html页面具体内容代码如下： 

<%@ 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.userId}';  
            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>

其中MessagePush.java文件中实现方法，如下： 

public class MessagePush{  
	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();  
	       }  
	}  
}

对于onPageLoad()方法中DwrScriptSessionManagerUtil类的实现，具体如下： 

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);  
    }  
}

4、推送html页面具体内容代码如下： 

<%@ 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='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 testPush() {  
        var msg = document.getElementById("msgId").value;  
        TestPush.sendMessageAuto(msg,"www.yoodb.com");  
    }  
    </script>  
  </head>  
  <body>  
    id值: <input type="text" name="msgId" id="msgId" /> <br />  
    <input type="button" value="Send" onclick="testPush()"  />  
  </body>  
</html>

其中TeshPush.java文件，具体内容如下： 

public class TestPush{  
    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);  
                }  
            }  
        });  
    }  
}

原文：http://my.oschina.net/freelife/blog/419253

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1条评论
EM
EmmaGong 1年前
越来越多的产品都需要实时推送，自己实现又困难又麻烦。我建议使用第三方提供的推送服务，他们专注在实时推送 这个方向，所以产品也就更专业可靠！GoEasy Web实时推送就很不错，都在说几分钟就自己实现推送了，可见代码的简单易懂度，推送稳定！他们的官网是：https://goeasy.io/

dexcoder

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