servlet监听器实现监听用户在线情况

效果图：

登陆前输入用户名：

登陆后：

点击返回：

控制台输出：

代码：

index.jsp:

<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
  <head>
    <title>$Title$</title>
  </head>
  <body>
  <form action="showUser.jsp" method="post">
    <input type="text" name="user">
    <input type="submit" value="登录">
  </form>
  </body>
</html>

showUser.jsp:

<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<head>
    <title>Title</title>
</head>
<body>
    <%
        UserInfoList userInfoList = UserInfoList.getInstance();
        UserInfoTrace userInfoTrace = new UserInfoTrace();
        String user = request.getParameter("user");
        userInfoTrace.setUser(user);
        session.setAttribute("list", userInfoTrace);
        userInfoList.addUserInfo(userInfoTrace.getUser());
        session.setMaxInactiveInterval(10);
    %>

    <textare>
        <%
            Vector<String> vector = userInfoList.getList();
            if(vector != null && vector.size()>0){
                for(int i=0; i<vector.size(); i++){
                    out.print(vector.elementAt(i)+"登陆成功");
                }
            }
        %>
    </textare>

    <a href="index.jsp">返回</a>
</body>
</html>

src目录下：

cn.test.UserInfoList.java

package cn.test;

import java.util.Vector;

public class UserInfoList {
    private static UserInfoList user = new UserInfoList();
    private Vector<String> vector = null;

    public UserInfoList(){
        this.vector = new Vector<>();
    }

    //外界使用的instance对象
    public static UserInfoList getInstance(){
        return user;
    }

    //增加用户
    public boolean addUserInfo(String user){
        if(user != null){
            this.vector.add(user);
            return true;
        }else{
            return false;
        }
    }

    //获取用户列表
    public Vector<String> getList() {
        return vector;
    }

    //移除用户
    public void removeUserInfo(String user){
        if(user != null){
            vector.removeElement(user);
        }
    }
}

cn.test.UserInfoTrace.java

package cn.test;

import javax.servlet.http.HttpSessionBindingEvent;
import javax.servlet.http.HttpSessionBindingListener;

public class UserInfoTrace implements HttpSessionBindingListener {
    private String user;
    private UserInfoList container = UserInfoList.getInstance();

    public UserInfoTrace(){
        user = "";
    }

    public void setUser(String user) {
        this.user = user;
    }

    public String getUser() {
        return this.user;
    }

    @Override
    public void valueBound(HttpSessionBindingEvent httpSessionBindingEvent) {
        System.out.println(this.user+"上线");
    }

    @Override
    public void valueUnbound(HttpSessionBindingEvent httpSessionBindingEvent) {
        System.out.println(this.user+"下线");
        container.removeUserInfo(user);
    }
}

cn.test.MyContentListener.java

package cn.test;

import javax.servlet.ServletContextEvent;
import javax.servlet.ServletContextListener;

public class MyContentListener implements ServletContextListener {
    @Override
    public void contextInitialized(ServletContextEvent servletContextEvent) {

    }

    @Override
    public void contextDestroyed(ServletContextEvent servletContextEvent) {

    }
}

web.xml

<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns="http://xmlns.jcp.org/xml/ns/javaee"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee http://xmlns.jcp.org/xml/ns/javaee/web-app_4_0.xsd"
         version="4.0">
    
    <listener>
        <listener-class>cn.test.MyContentListener</listener-class>
    </listener>
</web-app>

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