經過Servlet3.0添加對異步的支持實現後臺推送

本例參考：http://blog.csdn.NET/chenxiang0207/article/details/14054681/

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

感謝上面的兩位大佬，轉載只是爲了方便瀏覽。

我按照上面博文的思路從新走了一遍

項目結構以下圖

 /**
  * AsyncServlet
  *
  * 支持異步處理的Servlet
  * 頁面中隱藏的iframe經過訪問此Servlet來創建HTTP長鏈接
  * 從然後臺能實時的推送javascript代碼給頁面調用
  *
  */
 @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
  *
  * 管理用戶的AsyncContext(添加、刪除)
  *
  * 經過開啓一個線程來不斷地從mesgQueue獲取javascript 並遍歷用戶的AsyncContext來吧javascript推送給每一個用戶
  *
  */
 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
  *
  * 提供將javascript的方法調用補全到一個script標籤中的功能
  */
 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
  *
  * 訪問此Servlet可以給ClientComet的mesgQueue添加對象
  *
  */
 @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——用來顯示服務器推送的內容 -->
     <p id="textField"></p>
     <!-- cometFrame——隱藏的iframe，用來訪問AsyncServlet,創建長鏈接(注意，這樣作window.onload的函數將失效，或直到此鏈接斷開才執行) -->
     <iframe id="cometFrame" style="display: none;" src="/CometTest/Async"></iframe>
 </body>
 </html>

開啓Tomcat

開啓一個頁面A先訪問http://localhost:8080/CometTest/Comet.jsp

再打開一個新的頁面B訪問http://localhost:8080/CometTest/Test

此時可以看到A的內容不斷的增長

PS:若想讓onload函數不失效能夠把對iframe的src的賦值操做放在onload中，而一開始src爲空

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