经过Servlet3.0添加对异步的支持实现后台推送

本例参考：http://blog.csdn.NET/chenxiang0207/article/details/14054681/

http://blog.csdn.net/u010497228/article/details/43387575   

感谢上面的两位大佬，转载只是为了方便浏览。

我按照上面博文的思路从新走了一遍

项目结构以下图

 /**
  * AsyncServlet
  *
  * 支持异步处理的Servlet
  * 页面中隐藏的iframe经过访问此Servlet来创建HTTP长链接
  * 从然后台能实时的推送javascript代码给页面调用
  *
  */
 @WebServlet(urlPatterns = "/Async", asyncSupported = true)
 public class AsyncServlet extends HttpServlet {

     private static final long serialVersionUID = 822178713133426493L;
     private final static int DEFAULT_TIME_OUT = 10 * 60 * 1000;

     @Override
     protected void doGet(HttpServletRequest req, HttpServletResponse res) {
         AsyncContext actx = req.startAsync();
         actx.setTimeout(DEFAULT_TIME_OUT);
         actx.addListener(new AsyncListener() {

             @Override
             public void onComplete(AsyncEvent arg0) throws IOException {
                 // TODO Auto-generated method stub
                 ClientComet.getInstance().removeAsyncContext(actx);
                 System.out.println("AsyncListener-->onComplete");
             }

             @Override
             public void onError(AsyncEvent arg0) throws IOException {
                 // TODO Auto-generated method stub
                 ClientComet.getInstance().removeAsyncContext(actx);
                 System.out.println("AsyncListener-->onError");
             }

             @Override
             public void onStartAsync(AsyncEvent arg0) throws IOException {
                 // TODO Auto-generated method stub
                 System.out.println("AsyncListener-->onStartAsync");
             }

             @Override
             public void onTimeout(AsyncEvent arg0) throws IOException {
                 // TODO Auto-generated method stub
                 ClientComet.getInstance().removeAsyncContext(actx);
                 System.out.println("AsyncListener-->onTimeout");
             }

         });
         ClientComet.getInstance().addAsyncContext(actx);
     }
 }

 /**
  * ClientComet
  *
  * 管理用户的AsyncContext(添加、删除)
  *
  * 经过开启一个线程来不断地从mesgQueue获取javascript 并遍历用户的AsyncContext来吧javascript推送给每一个用户
  *
  */
 public class ClientComet {
     private static ClientComet instance;
     private ConcurrentLinkedQueue<AsyncContext> actxQueue;
     private LinkedBlockingQueue<Javascript> mesgQueue;

     private ClientComet() {
         actxQueue = new ConcurrentLinkedQueue<AsyncContext>();
         mesgQueue = new LinkedBlockingQueue<Javascript>();
         new ClientCometThread().start();
     }

     public static ClientComet getInstance() {
         if (instance == null) {
             instance = new ClientComet();
         }
         return instance;
     }

     public void addAsyncContext(AsyncContext actx) {
         actxQueue.add(actx);
     }

     public void removeAsyncContext(AsyncContext actx) {
         actxQueue.remove();
     }

     public void callClient(Javascript javascript) {
         mesgQueue.add(javascript);
     }

     protected class ClientCometThread extends Thread {

         @Override
         public void run() {
             while (true) {
                 try {
                     Javascript javascript = mesgQueue.take();
                     for (AsyncContext actx : actxQueue) {
                         PrintWriter writer = actx.getResponse().getWriter();
                         writer.write(javascript.getScript());
                         writer.flush();
                         System.out
                                 .println("ClientCometThread-->sendJavaScript");
                     }
                 } catch (InterruptedException | IOException e) {
                     // TODO Auto-generated catch block
                     e.printStackTrace();
                 }

             }
         }
     }

 }

 /**
  * Javascript
  *
  * 提供将javascript的方法调用补全到一个script标签中的功能
  */
 public class Javascript {
     private String script;

     public Javascript(String func) {
         script = "<script type='text/javascript'>" + "\n" + "window.parent."
                 + func + "\n" + "</script>" + "\n";
     }

     public String getScript() {
         return script;
     }
 }

 /**
  * TestServlet
  *
  * 访问此Servlet可以给ClientComet的mesgQueue添加对象
  *
  */
 @WebServlet(urlPatterns = "/Test")
 public class TestServlet extends HttpServlet {

     private static final long serialVersionUID = -7817902387051107187L;

     @Override
     protected void doGet(HttpServletRequest req, HttpServletResponse res) {
         int times = 5;
         while (--times >= 0) {
             try {
                 Thread.sleep(5000);
                 ClientComet.getInstance().callClient(
                         new Javascript("append(" + "\'"
                                 + new Date().toGMTString() + "\'" + ")"));
                 System.out.println("TestServlet-->callClient");
             } catch (InterruptedException e) {
                 // TODO Auto-generated catch block
                 e.printStackTrace();
             }
         }
     }
 }

 Comet.jsp

 <%@ 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">
 <title>Comet Test</title>
 <script type='text/javascript'>
     function append(str) {
         var textField = document.getElementById("textField");
         textField.innerHTML = textField.innerHTML + str + "<br/>";
     };
 </script>
 </head>
 <body>
     <!-- textField——用来显示服务器推送的内容 -->
     <p id="textField"></p>
     <!-- cometFrame——隐藏的iframe，用来访问AsyncServlet,创建长链接(注意，这样作window.onload的函数将失效，或直到此链接断开才执行) -->
     <iframe id="cometFrame" style="display: none;" src="/CometTest/Async"></iframe>
 </body>
 </html>

开启Tomcat

开启一个页面A先访问http://localhost:8080/CometTest/Comet.jsp

再打开一个新的页面B访问http://localhost:8080/CometTest/Test

此时可以看到A的内容不断的增长

PS:若想让onload函数不失效能够把对iframe的src的赋值操做放在onload中，而一开始src为空

项目打包:http://download.csdn.net/detail/u010497228/8415545