import javax.servlet.ServletContext;

 import javax.servlet.ServletContextEvent;

 import javax.servlet.ServletContextListener;

 import javax.servlet.ServletRequest;

 import javax.servlet.ServletRequestEvent;

 import javax.servlet.ServletRequestListener;

 import javax.servlet.http.HttpServletRequest;

 import javax.servlet.http.HttpSession;

 import javax.servlet.http.HttpSessionEvent;

 import javax.servlet.http.HttpSessionListener;

 public class Global implements ServletContextListener, HttpSessionListener,

         ServletRequestListener {

     @Override

     public void contextInitialized(ServletContextEvent sce) {

         // TODO Auto-generated method stub

         System.out.println("网站启动");

         ServletContext application = sce.getServletContext();

         application.setAttribute("count", 10);

     }

     @Override

     public void contextDestroyed(ServletContextEvent sce) {

         // TODO Auto-generated method stub

         ServletContext application = sce.getServletContext();

         application.setAttribute("count", 0);

         System.out.println("网站停止");

     }

     @Override

     public void requestInitialized(ServletRequestEvent arg0) {

         // TODO Auto-generated method stub

         System.out.println("服务器接收一个请求");

         ServletRequest request = arg0.getServletRequest();

         if (request instanceof HttpServletRequest) {

             HttpServletRequest httpRequest = (HttpServletRequest) request;

             String url = httpRequest.getRequestURI();

             System.out.println(url);

         }

     }

     @Override

     public void requestDestroyed(ServletRequestEvent arg0) {

         // TODO Auto-generated method stub

         System.out.println("服务器销毁一个请求");

     }

     @Override

     public void sessionCreated(HttpSessionEvent arg0) {

         // TODO Auto-generated method stub

         System.out.println("服务器创建一个会话");

         HttpSession session = arg0.getSession();

         session.setAttribute("count", 10);

         ServletContext application = session.getServletContext();

         Object obj = application.getAttribute("count");

         if (obj instanceof Integer) {

             Integer appCount = (Integer) obj;

             appCount += 1;

             application.setAttribute("count", appCount);

         }

     }

     @Override

     public void sessionDestroyed(HttpSessionEvent arg0) {

         // TODO Auto-generated method stub

         System.out.println("服务器销毁一个会话");

         HttpSession session = arg0.getSession();

         ServletContext application = session.getServletContext();

         Object obj = application.getAttribute("count");

         if (obj instanceof Integer) {

             Integer appCount = (Integer) obj;

             appCount -= 1;

             application.setAttribute("count", appCount);

         }

     }

 }

 <?xml version="1.0" encoding="UTF-8"?>

 <web-app version="2.5" xmlns="http://java.sun.com/xml/ns/javaee"

  xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://java.sun.com/xml/ns/javaee   http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd">

  <listener>

   <listener-class>Global</listener-class>

  </listener>

 </web-app>