javaweb监听器（统计在线人数：统计session）

1、创建监听器，重写里面的方法

package com.xiaocong.listener;

import javax.servlet.ServletContext;
import javax.servlet.http.HttpSessionEvent;
import javax.servlet.http.HttpSessionListener;

//统计在线人数：统计session
public class OnlineCountListener implements HttpSessionListener {
    //创建Session监听
    public void sessionCreated(HttpSessionEvent httpSessionEvent) {
        ServletContext sc = httpSessionEvent.getSession().getServletContext();
        Integer onlineCount = (Integer) sc.getAttribute("OnlineCount");

        if(onlineCount==null){
            onlineCount=new Integer(1);
        }else{
            int count=onlineCount.intValue();
            onlineCount=new Integer(count+1);
        }

        sc.setAttribute("OnlineCount",onlineCount);
    }
    //销毁Session监听
    public void sessionDestroyed(HttpSessionEvent httpSessionEvent) {
        ServletContext sc = httpSessionEvent.getSession().getServletContext();
        System.out.println(httpSessionEvent.getSession().getId());
        Integer onlineCount = (Integer) sc.getAttribute("OnlineCount");
        httpSessionEvent.getSession().invalidate();

        if(onlineCount==null){
            onlineCount=new Integer(0);
        }else{
            int count=onlineCount.intValue();
            onlineCount=new Integer(count-1);
        }

        sc.setAttribute("OnlineCount",onlineCount);

    }
}

2、在web.xml中注册

    
        com.xiaocong.listener.OnlineCountListener
    

    
        60
    

3、在网页上显示出来

<%@ page contentType="text/html;charset=UTF-8" language="java" %>

  
    
  
  
  当前有<%=this.getServletConfig().getServletContext().getAttribute("OnlineCount")%>人在线