Jetty comet技术初探

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Jetty的org.mortbay.util.ajax.Continuation 接口：

suspend(long timeout) Suspend handling. // 相当于Object的wait
resume() Resume the request. // 相当于Object的notify

......

Jetty 的Streaming Comet实现：

/**
*
*/
package comet.first;

import java.io.IOException;
import java.util.Date;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import org.mortbay.util.ajax.Continuation;
import org.mortbay.util.ajax.ContinuationSupport;

/**
* Streaming Comet
*
* @author yangwm Sep 26, 2010 11:47:02 AM
*/
public class JettyCometStreaming extends HttpServlet {

   /**
   *
   */
   private static final long serialVersionUID = 8098872819945693191L;

   private static final int TIMEOUT = 3 * 1000;

   public void service(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
       // handle the time request

       // get the jetty continuation
       Continuation con = ContinuationSupport.getContinuation(req, null);

       // set the header
       resp.setContentType("text/html");

       resp.getWriter().print("service begin " + new Date() + ", ");
       resp.getWriter().flush();

       // write time periodically
       while (resp.getWriter().checkError() == false) { // validity of the response's connection
           resp.getWriter().print("first... ");
           resp.getWriter().flush();

            /*
             * 每次被唤醒后恢复执行两次while循环开始到con.suspend之前的代码，
             * 因为con.suspend() equivalence con.reset() if con.isPending() is true
             * 所以timeout之后重新从service开始执行--> con.suspend() --> con.suspend之后的代码 --> 继续while循环开始到con.suspend之前的代码，
             */
           con.suspend(TIMEOUT); // suspend the response

           resp.getWriter().print("end!");
           resp.getWriter().flush();
       }
       // ...
   }

}

Jetty 的Long Polling Comet实现：

/**
*
*/
package comet.second;

import java.io.IOException;

import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import org.mortbay.util.ajax.Continuation;
import org.mortbay.util.ajax.ContinuationSupport;

/**
* Long Polling Comet
*
* @author yangwm Sep 28, 2010 11:47:02 AM
*/
public class JettyCometLongPolling extends HttpServlet {

    /**
    *
    */
    private static final long serialVersionUID = 8098872819945693191L;

    private static final int TIMEOUT = 30 * 1000;

    public void service(HttpServletRequest req, HttpServletResponse resp)
            throws IOException {
        // handle the time request

        // get the jetty continuation
        Continuation con = ContinuationSupport.getContinuation(req, null);
        JettyContinuationManager.add("yangwm", con); // id is yangwm

        // set the header
        resp.setContentType("text/html");

        // write continuation resume
        if(con.suspend(TIMEOUT)) {
            System.out.println(con + ", get data: " + con.getObject());
            resp.getWriter().write(con + ", get data: " + con.getObject());
            resp.getWriter().flush();
        } else {
            System.out.println(con + ", timeout");

            resp.getWriter().write(con + ", timeout");
            resp.getWriter().flush();

            JettyContinuationManager.clear("yangwm"); // id is yangwm
        }

        // ...
    }

}

/**
*
*/
package comet.second;

import java.io.IOException;
import java.util.Date;

import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import org.mortbay.util.ajax.Continuation;

/**
* Notify Comet
*
* @author yangwm Sep 28, 2010 11:47:02 AM
*/
public class JettyCometNotify extends HttpServlet {

    /**
    *
    */
    private static final long serialVersionUID = 8098872819945693191L;

    public void service(HttpServletRequest req, HttpServletResponse resp)
            throws IOException {
        // handle the time request

        Continuation con = JettyContinuationManager.get("yangwm"); // id is yangwm

        System.out.println(con + ", resume: ");
        resp.getWriter().write(con + ", resume: ");
        resp.getWriter().flush();

        if (con != null) {
            con.setObject(new Date() + ", it works!");
            con.resume();
        }

        // ...
    }

}

package comet.second;

import java.util.concurrent.ConcurrentHashMap;
import java.util.concurrent.ConcurrentMap;

import org.mortbay.util.ajax.Continuation;

/**
* Continuation Manager
*
* @author yangwm Sep 28, 2010 11:47:02 AM
*/
public class JettyContinuationManager {

    private static ConcurrentMap<String, Continuation> map = new ConcurrentHashMap<String, Continuation>();

    public static void add(String key, Continuation con) {
        map.put(key, con);
    }

    public static void clear(String key) {
        map.remove(key);
    }

    public static Continuation get(String key){
        return map.get(key);
    }

}

Jetty 的Streaming Comet与Long Polling实现的配置：

web.xml:

<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns="http://java.sun.com/xml/ns/javaee" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
   xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd"
   version="2.5">

   <display-name>Welcome to testcomet</display-name>
   <description>
        Welcome to testcomet
    </description>

   <servlet>
        <servlet-name>CometStreaming</servlet-name>
        <servlet-class>comet.first.JettyCometStreaming</servlet-class>
   </servlet>
   <servlet-mapping>
        <servlet-name>CometStreaming</servlet-name>
        <url-pattern>/stream</url-pattern>
   </servlet-mapping>

   <servlet>
        <servlet-name>CometLongPolling</servlet-name>
        <servlet-class>comet.second.JettyCometLongPolling</servlet-class>
   </servlet>
   <servlet-mapping>
        <servlet-name>CometLongPolling</servlet-name>
        <url-pattern>/longPoll</url-pattern>
   </servlet-mapping>
   <servlet>
        <servlet-name>CometNotify</servlet-name>
        <servlet-class>comet.second.JettyCometNotify</servlet-class>
   </servlet>
   <servlet-mapping>
        <servlet-name>CometNotify</servlet-name>
        <url-pattern>/notify</url-pattern>
   </servlet-mapping>
</web-app>

部署到jetty容器中。

1.Streaming方式:

D:/>curl http://127.0.0.1:8080/testcomet/stream

service begin Tue Sep 28 11:55:08 CST 2010, first... service begin Tue Sep 28 11:55:10 CST 2010, first... end!first...

第一次输出为：service begin Tue Sep 28 11:55:08 CST 2010, first...，也就是从service方法开始执行并不会执行suspend之后的代码。

之后输出为：service begin Tue Sep 28 11:55:10 CST 2010, first... end!first...，也就是从service方法开始执行并会执行suspend之后的代码。

2.Long Polling方式:

D:/>curl http://127.0.0.1:8080/testcomet/longPoll
RetryContinuation@9876930, get data: Tue Sep 28 11:57:04 CST 2010, it works

D:/>curl http://127.0.0.1:8080/testcomet/notify
RetryContinuation@9876930,pending,parked, resume:

先http://127.0.0.1:8080/testcomet/longPoll访问，再访问http://127.0.0.1:8080/testcomet/notify。

学习参考资料：

TimYang的comet server之java实现:asyncweb,jetty,tomcat，http://hi.baidu.com/jabber/blog/item/f556c7fcbaa76286b801a042.html

Cometd & Jetty Continuations:http://geeklu.com/2010/07/cometd-jetty-continuations/

jetty javadoc: http://jetty.codehaus.org/jetty/jetty-6/apidocs/index.html

Comet (programming) - Wikipedia, the free encyclopedia:http://en.wikipedia.org/wiki/Comet_%28programming%29

Continuations - Jetty - Codehaus:http://docs.codehaus.org/display/JETTY/Continuations

Cometd (aka Bayeux) - Jetty - Codehaus:http://docs.codehaus.org/display/JETTY/Cometd+%28aka+Bayeux%29

Welcome to CometD Project @ The Dojo Foundation | cometd.org:http://www.cometd.org/