监听器 在线人数统计

package com.fz.servlet;
import java.util.ArrayList;
import java.util.List;

import javax.servlet.annotation.WebListener;
import javax.servlet.http.HttpSession;
import javax.servlet.http.HttpSessionAttributeListener;
import javax.servlet.http.HttpSessionBindingEvent;
import javax.servlet.http.HttpSessionEvent;
import javax.servlet.http.HttpSessionListener;

@WebListener
public class Observers implements HttpSessionListener, HttpSessionAttributeListener{

    //在线总人数
    public static int count;
    //会员在线人数
    public static List<String> vipnums = new ArrayList<>();
    @Override
    public void sessionCreated(HttpSessionEvent e) {
        count++;
        System.out.println("有人上线");
        
    }

    @Override
    public void sessionDestroyed(HttpSessionEvent e) {
        count--;
        System.out.println("有人下线");
        
    }

    @Override
    public void attributeAdded(HttpSessionBindingEvent e) {
        // session.setAttribute() 执行时
        HttpSession session = e.getSession();
        System.out.println(session);//session地址
        System.out.println(session.getId());//session id
        System.out.println(e.getName());//session名
        System.out.println(e.getValue());//session值
        System.out.println(session.getAttribute(e.getName()));//session值
        
        String nameString = (String) e.getValue();
        vipnums.add(nameString);
    }

    @Override
    public void attributeRemoved(HttpSessionBindingEvent e) {
        // session.removeAttribute() 执行时
        vipnums.remove(e.getValue().toString());
    }

    @Override
    public void attributeReplaced(HttpSessionBindingEvent e) {
        // session.setAttribute()
        // session.setAttribute();第二次执行时（重新登录时执行）
    }

}

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