java 统计在线人数

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通过web.xml配置session的监听,每当监听到一个新的session,则计数加1。

反之当程序失去一个session则计数减1.

OnlineCounter类，这个类需要实现HttpSessionListener, HttpSessionAttributeListener, HttpSessionBindingListener三个接口:

/**
* OnlineCounter.java
*
* Copyright 2008. All Rights Reserved.
*/
package com.cosmow.online;

import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpSessionAttributeListener;
import javax.servlet.http.HttpSessionBindingEvent;
import javax.servlet.http.HttpSessionBindingListener;
import javax.servlet.http.HttpSessionEvent;
import javax.servlet.http.HttpSessionListener;

/**
* TODO OnlineCounter 记录在线人数
*
* Revision History
*
* 2008-8-11,Cosmo,created it
*/
public class OnlineCounter extends HttpServlet implements HttpSessionListener,
        HttpSessionAttributeListener, HttpSessionBindingListener {

    private static final long serialVersionUID = 1L;

    private static int sessionCounter = 0;
    private static int attributeCounter = 0;

    public void sessionCreated(HttpSessionEvent event) {
        sessionCounter++;
        System.out.println("session created");
    }

    public void sessionDestroyed(HttpSessionEvent event) {
        sessionCounter--;
        System.out.println("session destroied");
    }

    public void attributeAdded(HttpSessionBindingEvent event) {
        attributeCounter++;
        System.out.println("attribute added");
    }

    public void attributeRemoved(HttpSessionBindingEvent event) {
        attributeCounter--;
        System.out.println("attribute removed");
    }

    public void attributeReplaced(HttpSessionBindingEvent event) {
        System.out.println(event.getName() + " replaced");
    }

    public void valueBound(HttpSessionBindingEvent event) {
        System.out.println(event.getName() + " bound " + event.getValue());
    }

    public void valueUnbound(HttpSessionBindingEvent event) {
        System.out.println(event.getName() + " unbound " + event.getValue());
    }

    // 获取当前在线人数
    public static int getOnlineSession() {
        return sessionCounter;
    }

    public static int getOnlineAttribute() {
        return attributeCounter;
    }

}

web.xml:

<?xml version="1.0" encoding="UTF-8"?>
<web-app version="2.4" xmlns="http://java.sun.com/xml/ns/j2ee"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="http://java.sun.com/xml/ns/j2ee
    http://java.sun.com/xml/ns/j2ee/web-app_2_4.xsd">

    <listener>
        <listener-class>com.cosmow.online.OnlineCounter</listener-class>
    </listener>

    <welcome-file-list>
        <welcome-file>index.jsp</welcome-file>
    </welcome-file-list>
</web-app>