package com; import javax.servlet.ServletContextEvent;import javax.servlet.ServletContextListener;import javax.servlet.annotation.WebListener; /** * Application Lifecycle Listener implementation class MyContexxtLis * */@WebListenerpublic class CountListen implements ServletContextListener {   /**   * Default constructor.    */  public CountListen() {    // TODO Auto-generated constructor stub  }  /**   * @see ServletContextListener#contextInitialized(ServletContextEvent)   */  public void contextInitialized(ServletContextEvent arg0) {    arg0.getServletContext().setAttribute("count",100);  }  /**   * @see ServletContextListener#contextDestroyed(ServletContextEvent)   */  public void contextDestroyed(ServletContextEvent arg0) {      // TODO Auto-generated method stub  } }

package com; import javax.servlet.annotation.WebListener;import javax.servlet.http.HttpSessionAttributeListener;import javax.servlet.http.HttpSessionBindingEvent;import javax.servlet.http.HttpSessionEvent;import javax.servlet.http.HttpSessionListener;  @WebListenerpublic class SessionListen implements HttpSessionListener, HttpSessionAttributeListener {   public SessionListen() {    // TODO Auto-generated constructor stub  }   public void attributeRemoved(HttpSessionBindingEvent arg0) {    System.out.println("remove"+"\t"+arg0.getName()+arg0.getValue());  }   public void attributeAdded(HttpSessionBindingEvent arg0) {    System.out.println("add"+"\t"+arg0.getName()+arg0.getValue());  }   public void attributeReplaced(HttpSessionBindingEvent arg0) {    System.out.println("replace"+"\t"+arg0.getName()+arg0.getValue());  }   public void sessionCreated(HttpSessionEvent arg0) {    System.out.println("session create"); Integer i=(Integer)arg0.getSession().getServletContext().getAttribute("count"); i++; arg0.getSession().getServletContext().setAttribute("count", i);   }   public void sessionDestroyed(HttpSessionEvent arg0) {  Integer i=(Integer)arg0.getSession().getServletContext().getAttribute("count"); i--; arg0.getSession().getServletContext().setAttribute("count", i); System.out.println("session destroy"+i);   } }

<%@ page language="java" contentType="text/html; charset=UTF-8"  pageEncoding="UTF-8"%><%session.setMaxInactiveInterval(3); %>当前在线人数:${count}