使用HttpSessionListener监听器实战

使用HttpSessionListener监听器实战

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 online = (Map)

application.getAttribute("online");

if (online == null)

{

online = new Hashtable();

}

// 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 online = (Map)

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.*" %>

"http://w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">

在线用户：

<%

Map online = (Map)application

.getAttribute("online");

for (String sessionId : online.keySet())

{%>

<%}%>

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" %>

<%

<%-- 创建HttpSessionListenter--%>

request.getSession();

%>

登出销毁HttpSessionListenter

<%@ page contentType="text/html;charset=UTF-8" language="java" %>

<%

<%-- 销毁HttpSessionListener--%>

request.getSession().invalidate();

%>

实现统计登陆人数（多线程并发）

web.xml中配置监听

xmlns:xsi="http://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">

MyHttpSessionListener

myServletContextListener

xmlns:xsi="http://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">

MyHttpSessionListener

myServletContextListener

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" %>

<%

<%-- 创建HttpSessionListenter--%>

request.getSession();

%>

当前的在线人数 ${count}

退出

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