制作站点计数监听器

package com.utils;

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

public class CounterListener implements HttpSessionListener {

    public static int count;
    public CounterListener() {
        count = 0;
    }
    
    @Override
    public void sessionCreated(HttpSessionEvent arg0) {
        count++;
    }

    @Override
    public void sessionDestroyed(HttpSessionEvent arg0) {
        if(count > 0) {
            count--;
        }
    }
}

<?xml version="1.0" encoding="UTF-8"?>
<web-app version="2.5"
    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" >
    
    <welcome-file-list>
        <welcome-file>index.jsp</welcome-file>
    </welcome-file-list>
    <listener>
        <listener-class>com.utils.CounterListener</listener-class>
    </listener>
</web-app>