Comet基于iframe的服务器推送(Server Push)例子

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服务器推送

Comet 应用服务器浏览器 JavaScript Chrome

服务器推送技术(Server Push)是最近Web技术中最热门的一个流行术语，它的别名叫Comet(彗星)。它是继AJAX之后又一个倍受追捧的Web技术。Comet有时也称反向 Ajax 或服务器端推技术（server-side push）。其思想很简单：将数据直接从服务器推到浏览器，而不必等到浏览器请求数据。听起来简单，但是如果熟悉 Web 应用程序，尤其是 HTTP 协议，那么您就会知道，这绝不简单。实现 Comet 风格的 Web 应用程序，同时保证在浏览器和服务器上的可伸缩性，这只是在最近几年才成为可能。目前一些主流网站都有类似的原理，例如：webQQ、开心网、白社会等等，它们中消息动态都是采用类似的技术，也许具体实现方式不一样。目前大概有三种实现方式：基于长轮询(long polling)、基于iframe“、基于流(stream)三种实现comet的方式。
下面是在Tomcat6.x的基础上实现基于iframe的comet聊天室：

index.jsp:聊天室页面
ChatServlet.java:实现了长连接的Servlet
MessageServlet.java:消息接受Servert

仅仅是一个Demo，可以从index.jsp?name=yourNickName进入，实现了上线，下线通知，群发，消息功能，性能还没有测试...
目前能够正常在IE，FireFox和Chrome下正常运行，但在Chrome下会一直加载不完，不知道有没有办法解决？还有不知道能不能在此基础之上搞一个基于iframe的Comet工具，包括前台js和后台java.

首先修改Tomcat配置文件
修改server.xml中<Connector connectionTimeout="20000" port="8080" protocol="org.apache.coyote.http11.Http11NioProtocol " redirectPort="8443"/>，底层用NIO实现的Http连接器

index.jsp

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     <%@ 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">
<mce:script type="text/javascript" src="jquery-1.4.2.min.js" mce_src="jquery-1.4.2.min.js"></mce:script>
<link rel="stylesheet" href="960.css" mce_href="960.css" />
<title>Comet Chat Demo</title>
<mce:script type="text/javascript"></mce:script>
</head>
<body>
<mce:script type="text/javascript"></mce:script>
<div class="container_12">
<div class="grid_10">
    <div>公共聊天</div>
    <div id="messageList" style="height:250px;overflow:scroll;border:solid 1px black;">

    </div>
    <br/>
    <div>个人聊天</div>
    <div id="privateMessage" style="height:150px;overflow:scroll;border:solid 1px black;">

    </div>
    <br/>
    <div>
        <select id="user" style="width:100px;overflow:scroll;">
            <option value="all">All</option>
        </select>
        <input type="text" id="message" size="40"></input>
        <input type="button" value="发言" onclick="sendAll()">
    </div>
</div>
<div class="grid_2">
    <h3>用户列表</h3>
    <ol id="userList">

    </ol>
</div>
</div>
</body>
</html>
     <%@ 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">
<mce:script type="text/javascript" src="jquery-1.4.2.min.js" mce_src="jquery-1.4.2.min.js"></mce:script>
<link rel="stylesheet" href="960.css" mce_href="960.css" />
<title>Comet Chat Demo</title>
<mce:script type="text/javascript"></mce:script>
</head>
<body>
<mce:script type="text/javascript"></mce:script>
<div class="container_12">
<div class="grid_10">
<div>公共聊天</div>
<div id="messageList" style="height:250px;overflow:scroll;border:solid 1px black;">

</div>
<br/>
<div>个人聊天</div>
<div id="privateMessage" style="height:150px;overflow:scroll;border:solid 1px black;">

</div>
<br/>
<div>
  <select id="user" style="width:100px;overflow:scroll;">
   <option value="all">All</option>
  </select>
  <input type="text" id="message" size="40"></input>
  <input type="button" value="发言" onclick="sendAll()">
</div>
</div>
<div class="grid_2">
<h3>用户列表</h3>
<ol id="userList">

</ol>
</div>
</div>
</body>
</html>

ChatServlet.java

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package demo;
import java.io.IOException;
import java.io.InputStream;
import java.io.PrintWriter;
import java.util.HashMap;
import java.util.Map;
import java.util.Map.Entry;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import org.apache.catalina.CometEvent;
import org.apache.catalina.CometProcessor;
/**
*
* @author Aries Zhao
*
*/
public class ChatServlet extends HttpServlet implements CometProcessor {
    private static final long serialVersionUID = -3667180332947986301L;
    // <用户,长连接>
    protected static Map<String, HttpServletResponse> connections = new HashMap<String, HttpServletResponse>();
    // 消息推送线程
    protected static MessageSender messageSender = null;
    public void init() throws ServletException {
        // 启动消息推送线程
        messageSender = new MessageSender();
        Thread messageSenderThread = new Thread(messageSender, "MessageSender["
                + getServletContext().getContextPath() + "]");
        messageSenderThread.setDaemon(true);
        messageSenderThread.start();
    }
    public void destroy() {
        connections.clear();
        messageSender.stop();
        messageSender = null;
    }
    public void event(CometEvent event) throws IOException, ServletException {
        HttpServletRequest request = event.getHttpServletRequest();
        HttpServletResponse response = event.getHttpServletResponse();
        // 昵称
        String name = request.getParameter("name");
        if (name == null) {
            return;
        }
        if (event.getEventType() == CometEvent.EventType.BEGIN) {
            // Http连接空闲超时
            event.setTimeout(Integer.MAX_VALUE);
            log("Begin for session: " + request.getSession(true).getId());
            // 创建Comet Iframe
            PrintWriter writer = response.getWriter();
            writer
                    .println("<!doctype html public \"-//w3c//dtd html 4.0 transitional//en\">");
            writer
                    .println("<html><head><mce:script type=\"text/javascript\"></mce:script></head><body>");
            writer.println("<mce:script type=\"text/javascript\"></mce:script>");
            writer.flush();
            // for chrome
            if (request.getHeader("User-Agent").contains("KHTML")) {
                for (int i = 0; i < 100; i++) {
                    writer.print("<input type=hidden name=none value=none>");
                }
                writer.flush();
            }
            // 欢迎信息
            writer.print("<mce:script type=\"text/javascript\"></mce:script>");
            writer.flush();
            // 通知其他用户有新用户登陆
            if (!connections.containsKey(name)) {
                messageSender.login(name);
            }
            // 推送已经登陆的用户信息
            for (String user : connections.keySet()) {
                if (!user.equals(name)) {
                    writer.print("<mce:script type=\"text/javascript\"></mce:script>");
                }
            }
            writer.flush();
            synchronized (connections) {
                connections.put(name, response);
            }
        } else if (event.getEventType() == CometEvent.EventType.ERROR) {
            log("Error for session: " + request.getSession(true).getId());
            synchronized (connections) {
                connections.remove(name);
            }
            event.close();
        } else if (event.getEventType() == CometEvent.EventType.END) {
            log("End for session: " + request.getSession(true).getId());
            messageSender.logout(name);
            synchronized (connections) {
                connections.remove(name);
            }
            PrintWriter writer = response.getWriter();
            writer.println("</body></html>");
            event.close();
        } else if (event.getEventType() == CometEvent.EventType.READ) {
            InputStream is = request.getInputStream();
            byte[] buf = new byte[512];
            do {
                int n = is.read(buf); // can throw an IOException
                if (n > 0) {
                    log("Read " + n + " bytes: " + new String(buf, 0, n)
                            + " for session: "
                            + request.getSession(true).getId());
                } else if (n < 0) {
                    return;
                }
            } while (is.available() > 0);
        }
    }
    // 发送消息给所有人
    public static void send(String message) {
        messageSender.send("*", message);
    }
    // 向某个连接发送消息
    public static void send(String name, String message) {
        messageSender.send(name, message);
    }
    public class MessageSender implements Runnable {
        protected boolean running = true;
        protected Map<String, String> messages = new HashMap<String, String>();
        public MessageSender() {
        }
        public void stop() {
            running = false;
        }
        // 新用户登陆
        public void login(String name) {
            synchronized (messages) {
                messages.put("Login", name);
                messages.notify();
            }
        }
        // 用户下线
        public void logout(String name) {
            synchronized (messages) {
                messages.put("Logout", name);
                messages.notify();
            }
        }
        // 发送消息
        public void send(String user, String message) {
            synchronized (messages) {
                messages.put(user, message);
                messages.notify();
            }
        }
        public void run() {
            while (running) {
                if (messages.size() == 0) {
                    try {
                        synchronized (messages) {
                            messages.wait();
                        }
                    } catch (InterruptedException e) {
                        // Ignore
                    }
                }
                synchronized (connections) {
                    synchronized (messages) {
                        // 推送消息队列中的消息
                        for (Entry<String, String> message : messages
                                .entrySet()) {
                            if (message.getKey().equals("Login")) {// 新用户登陆
                                log(message.getValue() + " Login");
                                for (HttpServletResponse response : connections
                                        .values()) {
                                    try {
                                        PrintWriter writer = response
                                                .getWriter();
                                        writer
                                                .print("<mce:script type=\"text/javascript\"></mce:script>");
                                        writer.flush();
                                    } catch (IOException e) {
                                        log("IOExeption execute command", e);
                                    }
                                }
                            } else if ("Logout".equals(message.getKey())) {// 用户退出
                                log(message.getValue() + " Logout");
                                for (HttpServletResponse response : connections
                                        .values()) {
                                    try {
                                        PrintWriter writer = response
                                                .getWriter();
                                        writer
                                                .print("<mce:script type=\"text/javascript\"></mce:script>");
                                        writer.flush();
                                    } catch (IOException e) {
                                        log("IOExeption execute command", e);
                                    }
                                }
                            } else if ("*".equals(message.getKey())) {// 群发消息
                                log("Send message: " + message.getValue()
                                        + " to everyone.");
                                for (HttpServletResponse response : connections
                                        .values()) {
                                    try {
                                        PrintWriter writer = response
                                                .getWriter();
                                        writer
                                                .print("<mce:script type=\"text/javascript\"></mce:script>");
                                        writer.flush();
                                    } catch (IOException e) {
                                        log("IOExeption execute command", e);
                                    }
                                }
                            } else {// 向某人发信息
                                try {
                                    HttpServletResponse response = connections
                                            .get(message.getKey());
                                    PrintWriter writer = response.getWriter();
                                    writer
                                            .print("<mce:script type=\"text/javascript\"></mce:script>");
                                    writer.flush();
                                } catch (IOException e) {
                                    log("IOExeption sending message", e);
                                }
                            }
                            // 从消息队列中删除消息
                            messages.remove(message.getKey());
                        }
                    }
                }
            }
        }
    }
}
package demo;
import java.io.IOException;
import java.io.InputStream;
import java.io.PrintWriter;
import java.util.HashMap;
import java.util.Map;
import java.util.Map.Entry;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import org.apache.catalina.CometEvent;
import org.apache.catalina.CometProcessor;
/**
*
* @author Aries Zhao
*
*/
public class ChatServlet extends HttpServlet implements CometProcessor {
private static final long serialVersionUID = -3667180332947986301L;
// <用户,长连接>
protected static Map<String, HttpServletResponse> connections = new HashMap<String, HttpServletResponse>();
// 消息推送线程
protected static MessageSender messageSender = null;
public void init() throws ServletException {
  // 启动消息推送线程
  messageSender = new MessageSender();
  Thread messageSenderThread = new Thread(messageSender, "MessageSender["
    + getServletContext().getContextPath() + "]");
  messageSenderThread.setDaemon(true);
  messageSenderThread.start();
}
public void destroy() {
  connections.clear();
  messageSender.stop();
  messageSender = null;
}
public void event(CometEvent event) throws IOException, ServletException {
  HttpServletRequest request = event.getHttpServletRequest();
  HttpServletResponse response = event.getHttpServletResponse();
  // 昵称
  String name = request.getParameter("name");
  if (name == null) {
   return;
  }
  if (event.getEventType() == CometEvent.EventType.BEGIN) {
   // Http连接空闲超时
   event.setTimeout(Integer.MAX_VALUE);
   log("Begin for session: " + request.getSession(true).getId());
   // 创建Comet Iframe
   PrintWriter writer = response.getWriter();
   writer
     .println("<!doctype html public \"-//w3c//dtd html 4.0 transitional//en\">");
   writer
     .println("<html><head><mce:script type=\"text/javascript\"></mce:script></head><body>");
   writer.println("<mce:script type=\"text/javascript\"></mce:script>");
   writer.flush();
   // for chrome
   if (request.getHeader("User-Agent").contains("KHTML")) {
    for (int i = 0; i < 100; i++) {
     writer.print("<input type=hidden name=none value=none>");
    }
    writer.flush();
   }
   // 欢迎信息
   writer.print("<mce:script type=\"text/javascript\"></mce:script>");
   writer.flush();
   // 通知其他用户有新用户登陆
   if (!connections.containsKey(name)) {
    messageSender.login(name);
   }
   // 推送已经登陆的用户信息
   for (String user : connections.keySet()) {
    if (!user.equals(name)) {
     writer.print("<mce:script type=\"text/javascript\"></mce:script>");
    }
   }
   writer.flush();
   synchronized (connections) {
    connections.put(name, response);
   }
  } else if (event.getEventType() == CometEvent.EventType.ERROR) {
   log("Error for session: " + request.getSession(true).getId());
   synchronized (connections) {
    connections.remove(name);
   }
   event.close();
  } else if (event.getEventType() == CometEvent.EventType.END) {
   log("End for session: " + request.getSession(true).getId());
   messageSender.logout(name);
   synchronized (connections) {
    connections.remove(name);
   }
   PrintWriter writer = response.getWriter();
   writer.println("</body></html>");
   event.close();
  } else if (event.getEventType() == CometEvent.EventType.READ) {
   InputStream is = request.getInputStream();
   byte[] buf = new byte[512];
   do {
    int n = is.read(buf); // can throw an IOException
    if (n > 0) {
     log("Read " + n + " bytes: " + new String(buf, 0, n)
       + " for session: "
       + request.getSession(true).getId());
    } else if (n < 0) {
     return;
    }
   } while (is.available() > 0);
  }
}
// 发送消息给所有人
public static void send(String message) {
  messageSender.send("*", message);
}
// 向某个连接发送消息
public static void send(String name, String message) {
  messageSender.send(name, message);
}
public class MessageSender implements Runnable {
  protected boolean running = true;
  protected Map<String, String> messages = new HashMap<String, String>();
  public MessageSender() {
  }
  public void stop() {
   running = false;
  }
  // 新用户登陆
  public void login(String name) {
   synchronized (messages) {
    messages.put("Login", name);
    messages.notify();
   }
  }
  // 用户下线
  public void logout(String name) {
   synchronized (messages) {
    messages.put("Logout", name);
    messages.notify();
   }
  }
  // 发送消息
  public void send(String user, String message) {
   synchronized (messages) {
    messages.put(user, message);
    messages.notify();
   }
  }
  public void run() {
   while (running) {
    if (messages.size() == 0) {
     try {
      synchronized (messages) {
       messages.wait();
      }
     } catch (InterruptedException e) {
      // Ignore
     }
    }
    synchronized (connections) {
     synchronized (messages) {
      // 推送消息队列中的消息
      for (Entry<String, String> message : messages
        .entrySet()) {
       if (message.getKey().equals("Login")) {// 新用户登陆
        log(message.getValue() + " Login");
        for (HttpServletResponse response : connections
          .values()) {
         try {
          PrintWriter writer = response
            .getWriter();
          writer
            .print("<mce:script type=\"text/javascript\"></mce:script>");
          writer.flush();
         } catch (IOException e) {
          log("IOExeption execute command", e);
         }
        }
       } else if ("Logout".equals(message.getKey())) {// 用户退出
        log(message.getValue() + " Logout");
        for (HttpServletResponse response : connections
          .values()) {
         try {
          PrintWriter writer = response
            .getWriter();
          writer
            .print("<mce:script type=\"text/javascript\"></mce:script>");
          writer.flush();
         } catch (IOException e) {
          log("IOExeption execute command", e);
         }
        }
       } else if ("*".equals(message.getKey())) {// 群发消息
        log("Send message: " + message.getValue()
          + " to everyone.");
        for (HttpServletResponse response : connections
          .values()) {
         try {
          PrintWriter writer = response
            .getWriter();
          writer
            .print("<mce:script type=\"text/javascript\"></mce:script>");
          writer.flush();
         } catch (IOException e) {
          log("IOExeption execute command", e);
         }
        }
       } else {// 向某人发信息
        try {
         HttpServletResponse response = connections
           .get(message.getKey());
         PrintWriter writer = response.getWriter();
         writer
           .print("<mce:script type=\"text/javascript\"></mce:script>");
         writer.flush();
        } catch (IOException e) {
         log("IOExeption sending message", e);
        }
       }
       // 从消息队列中删除消息
       messages.remove(message.getKey());
      }
     }
    }
   }
  }
}
}