HttpSessionListener监听器实战

本文链接： https://blog.csdn.net/chengqiuming/article/details/100586954

一定义监听器

package lee;

import javax.servlet.*;
import javax.servlet.annotation.*;
import javax.servlet.http.*;import java.util.*;
@WebListener
public class OnlineListener
    implements HttpSessionListener
{
    // 当用户与服务器之间开始session时触发该方法
    public void sessionCreated(HttpSessionEvent se)
    {
        HttpSession session = se.getSession();
        ServletContext application = session.getServletContext();
        // 获取session ID
        String sessionId = session.getId();
        // 如果是一次新的会话
        if (session.isNew())
        {
            String user = (String)session.getAttribute("user");
            // 未登录用户当游客处理
            user = (user == null) ? "游客" : user;
            Map<String , String> online = (Map<String , String>)
                application.getAttribute("online");
            if (online == null)
            {
                online = new Hashtable<String , String>();
            }
            // 将用户在线信息放入Map中
            online.put(sessionId , user);
            application.setAttribute("online" , online);
        }
    }
    // 当用户与服务器之间session断开时触发该方法
    public void sessionDestroyed(HttpSessionEvent se)
    {
        HttpSession session = se.getSession();
        ServletContext application = session.getServletContext();
        String sessionId = session.getId();
        Map<String , String> online = (Map<String , String>)
            application.getAttribute("online");
        if (online != null)
        {
            // 删除该用户的在线信息
            online.remove(sessionId);
        }
        application.setAttribute("online" , online);
    }
}

二测试JSP

<%@ page contentType="text/html; charset=GBK" language="java" errorPage="" %>
<%@ page import="java.util.*" %>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
    "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
    <title> 用户在线信息 </title>
    <meta name="website" content="http://www.crazyit.org" />
</head>
<body>
在线用户：
<table width="400" border="1">
<%
Map<String , String> online = (Map<String , String>)application
    .getAttribute("online");
for (String sessionId : online.keySet())
{%>
<tr>
    <td><%=sessionId%>
    <td><%=online.get(sessionId)%>
</tr>
<%}%>
</body>
</html>

三测试结果

HttpSessionListener监听器实战

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