Posted in Java/Android onMarch 17, 2022
HttpSessionListener监听器
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);
}
}
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>
测试结果
HttpSessionListener监听器应用场景
应用场景：用来统计当前在线人数
实现HttpSessionListener
import javax.servlet.ServletContext;
import javax.servlet.http.HttpSession;
import javax.servlet.http.HttpSessionEvent;
import javax.servlet.http.HttpSessionListener;
public class MyHttpSessionListener implements HttpSessionListener {
@Override
public void sessionCreated(HttpSessionEvent httpSessionEvent) {
System.out.println("httpsession被创建");
}
@Override
public void sessionDestroyed(HttpSessionEvent httpSessionEvent) {
System.out.println("httpsession被销毁");
}
}
登陆界面去创建HttpSessionListenter
<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<head>
<title>$Title$</title>
</head>
<body>
<%
<%-- 创建HttpSessionListenter--%>
request.getSession();
%>
</body>
</html>
登出销毁HttpSessionListenter
<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<head>
<title>$Title$</title>
</head>
<body>
<%
<%-- 销毁HttpSessionListener--%>
request.getSession().invalidate();
%>
<h1>已退出</h1>
</body>
</html>
实现统计登陆人数（多线程并发）
web.xml中配置监听
<?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>MyHttpSessionListener</listener-class>
</listener>
<listener>
<listener-class>myServletContextListener</listener-class>
</listener>
</web-app>
统计人数实在最大ServletContextListener这个域当中
因为HttpSessionListener监听器只在当前会话中有效
（1）创建ServletContextListener监听器并设置初始值为0
import javax.servlet.ServletContext;
import javax.servlet.ServletContextEvent;
import javax.servlet.ServletContextListener;
public class myServletContextListener implements ServletContextListener {
@Override
public void contextInitialized(ServletContextEvent servletContextEvent) {
ServletContext sc = servletContextEvent.getServletContext();
sc.setAttribute("count", 0);
}
@Override
public void contextDestroyed(ServletContextEvent servletContextEvent) {
}
}
2）变更在线人数
import javax.servlet.ServletContext;
import javax.servlet.http.HttpSession;
import javax.servlet.http.HttpSessionEvent;
import javax.servlet.http.HttpSessionListener;
public class MyHttpSessionListener implements HttpSessionListener {
@Override
public void sessionCreated(HttpSessionEvent httpSessionEvent) {
System.out.println("httpsession被创建");
countPersion( httpSessionEvent.getSession().getServletContext(), true);
}
@Override
public void sessionDestroyed(HttpSessionEvent httpSessionEvent) {
System.out.println("httpsession被销毁");
countPersion(httpSessionEvent.getSession().getServletContext(), false);
}
/*
* 变更在线的人数
* */
public void countPersion(ServletContext sc, boolean isAdd) {
// 为了防止多线程并发问题加锁
synchronized (sc) {
// 获得当前的在线人数
Integer count = (Integer) sc.getAttribute("count");
if(isAdd) {
sc.setAttribute("count", ++count);
} else {
sc.setAttribute("count", --count);
}
}
}
}
（3）前端页面上去获取显示
<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<head>
<title>$Title$</title>
</head>
<body>
<%
<%-- 创建HttpSessionListenter--%>
request.getSession();
%>
<h1>欢迎登陆</h1>
<hr>
当前的在线人数 ${count}
<a href="logout.jsp" rel="external nofollow" >退出</a>
</body>
</html>
以上为个人经验，希望能给大家一个参考，也希望大家多多支持三水点靠木。
使用HttpSessionListener监听器实战
- Author -
chengqiuming- Original Sources -
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