HttpSessionListener监听器
定义监听器
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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
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<%@ 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
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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
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<%@ 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
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<%@ 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
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<? 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
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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
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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
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<%@ 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。
原文链接：https://blog.csdn.net/chengqiuming/article/details/100586954
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