Comet基于iframe的服务器推送(Server Push)例子

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：

     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

<%@ 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

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 IframePrintWriter 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 chromeif (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 IOExceptionif (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());}}}}}}}

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Comet基于iframe的服务器推送(Server Push)例子

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