web监听器与session管理技术详解-优快云博客

转: [url]http://gaojiewyh.iteye.com/blog/1759566[/url]
监听器的主要作用就是监听，当目标发生变化的时候就会触发一定的方法，这也就是所谓的事件触发机制。在这种机制中要有三个要素，也就是事件，事件源，处理事件的方法。这三要素之间是相互制约的。一旦事件处理方法被触发必定有事件发生，也就可以得到触发的事件，通过事件也就可以得到事件源，也就谁触发了事件，这样据可以将这三个要素联系在一起了。一个事件源可以有多个触发事件，而一个触发事件的发生将有多个方法来调用，这也就是所谓的一对多关系，通过一对多关系我们很容易从多端得到一端，相反从一端无法得到多端，这个道理大家都是很清楚的，所以也就可以很好的理解事件处理方法可以得到事件对象，事件对象又可以得到事件源。

1. web监听器的开发步骤

首先建立一个类实现listenner接口
Java代码

public class ContextTestListener implements ServletContextListener {  

        public void contextInitialized(ServletContextEvent sce) {  
                    //具体实现类  
            }  

        public void contextDestroyed(ServletContextEvent sce) {  
               //具体实现类   
           }  
    }

其次，在web.xml中配置监听器
Xml代码

<listener>  
      <listener-class>com.jason.listener.ContextTestListener</listener-class>  
    </listener>

2. web监听器的分类，如图所示，目前分如下几种监听器 ServletContext，Session，Request的

3. 各种监听器的详细介绍及用法示例

(1) 与ServletContext相关的监听器接口为ServletContextListener，ServletContextAttributeListener，该监听器针对的是整个web应用程序的生命周期，其范围最大的。一般用来在应用程序初始化时读取数据库连接对象，初始化应用程序程序的配置等。其接口定义如下：
Java代码

 public interface ServletContextListener {  
        public void contextInitialized(ServletContextEvent sce)；  
        public void contextDestroyed(ServletContextEvent sce)；  
    }

典型应用：需求统计一个网页请求的访问量，该web应用停止时，将访问量数值写到配置文件中，改应用程序重新启动，数值从上次访问量开始。

<1> 实现ServletContextListener接口，在初始化话方法中读取配置文件中访问量的信息，在销毁方法中存储访问量的信息。因为在应用程序启动时，会调用contextInitialized方法，在应用程序停止时，会调用contextDestroyed方法。该例子应用了properties的操作，不熟悉properties请google下用法,特别注意读取文件和存储文件的写法，代码实现如下:
Java代码

public class ContextTestListener implements ServletContextListener {  

        private static final String COUNT_NAME = "count";  

        private static final String PROPERTIES_NAME = "WEB-INF/count.properties";  

        /* 
         * (non-Javadoc) 
         *  
         * @see 
         * javax.servlet.ServletContextListener#contextInitialized(javax.servlet 
         * .ServletContextEvent) 
         */  
        public void contextInitialized(ServletContextEvent sce) {  

            ServletContext context = sce.getServletContext();  
            InputStream inputstream = context.getResourceAsStream(PROPERTIES_NAME);  

            Properties prop = new Properties();  
            try {  
                prop.load(inputstream);  
            } catch (IOException e) {  
                throw new RuntimeException(e);  
            }  

            int count = Integer.parseInt(prop.getProperty(COUNT_NAME));  
            context.setAttribute(COUNT_NAME, count);  
        }  

        /* 
         * (non-Javadoc) 
         *  
         * @see javax.servlet.ServletContextListener#contextDestroyed(javax.servlet. 
         * ServletContextEvent) 
         */  
        public void contextDestroyed(ServletContextEvent sce) {  

            ServletContext context = sce.getServletContext();  
            Object countAttr = context.getAttribute(COUNT_NAME);  
            if(countAttr != null){  
                int count = (Integer) context.getAttribute(COUNT_NAME);  

                InputStream inputstream = context.getResourceAsStream(PROPERTIES_NAME);  
                Properties prop = new Properties();  
                try {  
                    prop.load(inputstream);  
                    prop.setProperty(COUNT_NAME, String.valueOf(count));  
                } catch (IOException e) {  
                    throw new RuntimeException(e);  
                }  

                String filepath = context.getRealPath("/");  
                FileOutputStream fos = null;  
                try {  
                    fos = new FileOutputStream(filepath + PROPERTIES_NAME);  
                } catch (FileNotFoundException e) {  
                    throw new RuntimeException(e);  
                }  

                try {  
                    prop.store(fos, "add the count");  
                } catch (IOException e) {  
                    throw new RuntimeException(e);  
                } finally {  
                    if (fos != null) {  
                        try {  
                            fos.close();  
                        } catch (IOException e) {  
                            System.err.println("Cant close stream :" + e.getMessage());  
                        }  
                    }  
                }  
            }  
        }  
    }

<2> 定义TestCountServlet，作为请求访问网页的请求URL，其实现代码如下，记录方法量，同时做跳转到访问量页面，代码如下：
Java代码

package com.jason.servlet;  

    import java.io.IOException;  

    import javax.servlet.ServletContext;  
    import javax.servlet.ServletException;  
    import javax.servlet.http.HttpServlet;  
    import javax.servlet.http.HttpServletRequest;  
    import javax.servlet.http.HttpServletResponse;  

    /** 
     * Servlet implementation class TestAccountServlet 
     */  
    public class TestAccountServlet extends HttpServlet {  
        private static final long serialVersionUID = 1L;  

        /** 
         * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response) 
         */  
        protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {  
            // TODO Auto-generated method stub  
            doPost(request,response);  
        }  

        /** 
         * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response) 
         */  
        protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {  
            // TODO Auto-generated method stub  
            ServletContext context = request.getSession().getServletContext();  
            Integer count = (Integer) context.getAttribute("count");  
            if(count == null){  
                count = 1;  
            }else{  
                count ++;  
            }  
            context.setAttribute("count",count);  
            // do other things  
            response.sendRedirect(request.getContextPath() + "/count.jsp");  
        }  
    }

<3>webxml中的配置，webxml中配置了监听器，servlet及welcoen页面，内容如下：
Java代码收藏代码

<?xml version="1.0" encoding="UTF-8"?>  
    <web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://java.sun.com/xml/ns/javaee" xmlns:web="http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd" xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd" id="WebApp_ID" version="2.5">  
      <display-name>WebListener</display-name>  
      <listener>  
        <listener-class>com.jason.listener.ContextTestListener</listener-class>  
      </listener>  
      <welcome-file-list>  
        <welcome-file>index.jsp</welcome-file>  
      </welcome-file-list>  
      <servlet>  
        <description></description>  
        <display-name>TestAccountServlet</display-name>  
        <servlet-name>TestAccountServlet</servlet-name>  
        <servlet-class>com.jason.servlet.TestAccountServlet</servlet-class>  
      </servlet>  
      <servlet-mapping>  
        <servlet-name>TestAccountServlet</servlet-name>  
        <url-pattern>/TestAccountServlet</url-pattern>  
      </servlet-mapping>  
    </web-app>

<4> 在WEB-INF 目录下，建立count.properties，内容如下：
Java代码收藏代码

count=0

<5>建立index和count页面，index页面如下：
Java代码

<%@ page language="java" contentType="text/html; charset=UTF-8" pageEncoding="UTF-8"%>  
    <%@ taglib uri="http://java.sun.com/jsp/jstl/core" prefix="c" %>  
    <!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">  
    <html>  
    <head>  
    <meta http-equiv="Content-Type" content="text/html; charset= UTF-8">  
    <title>index page</title>  
    </head>  
    <body>  
        <a href="${pageContext.request.contextPath}/TestAccountServlet">visit it to test </a>  
    </body>  
    </html>

在index页面中注意${pageContext.request.contextPath}，在jsp页面调用servlet的URL时，如果没设定basepath，前面一定要加上contextpath的路径，否则，servlet的地址是不对的。或者也可以直接用<c：out value=“/TestAccountServlet”/〉，因为jstl 中该标签直接在其前面添加contextpath路径。count页面的内容如下：
Html代码

<%@ page language="java" contentType="text/html; charset=UTF-8"  
        pageEncoding="UTF-8"%>  
    <!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">  
    <html>  
    <head>  
    <meta http-equiv="Content-Type" content="text/html; charset= UTF-8">  
    <title>count here </title>  
    </head>  
    <body>  
        visit count：${applicationScope.count}  
        <%  
        System.out.println(application.getAttribute("count"));  
        %>   
    </body>  
    </html>

利用${applicationScope.count}获取数值，该程序运行，每点击访问一次count页面，其访问量加1.

（2）与Session相关的监听器有有个四个HttpSessionListener，HttpSessionAttributeListener ，HttpSessionBindListener和HttpSessionActivationListener

<1>HttpSessionListener 是生命周期监听器，如果想对Session对象创建或结束时，做相应的动作可实现HttpSessionListener，该接口的定义如下：
Java代码

public interface HttpSessionListener {  
        public void sessionCreated(HttpSessionEvent se) ；  
        public void sessionDestroyed(HttpSessionEvent se) ；  
    }

关于该监听器的用法，例如我们防止用户重新登录时，常常在数据库中定义字段状态，来表明该用户是否登录，在注销时，我们将其状态修改，但好多情况下，我们直接关闭浏览器，造成数据库状态没法更新，同时，用户登录session也有存活期限，此时我们希望在session销毁时，改变数据库状态，我们可以在HttpSessionListener监听器的sessionDestroyed（se）方法中在session中获取该用户，操作数据库，将该用户的登录状态设置为未登录。
Java代码

/** 
     * Application Lifecycle Listener implementation class OnlinePepoleListener 
     * 
     */  
    public class OnlinePepoleListener implements HttpSessionListener {  

        /** 
         * @see HttpSessionListener#sessionCreated(HttpSessionEvent) 
         */  
        public void sessionCreated(HttpSessionEvent se) {  
            // TODO Auto-generated method stub  
        }  

        /** 
         * @see HttpSessionListener#sessionDestroyed(HttpSessionEvent) 
         */  
        public void sessionDestroyed(HttpSessionEvent se) {  
            // TODO Auto-generated method stub  
            HttpSession session = se.getSession();  
            String user = (String)session.getAttribute("login");  
            //修改数据库用户登录状态为未登录  
        }  
    }

典型应用：统计当前用户在线数

（1）index页面
Java代码

<%@ page language="java" contentType="text/html; charset=utf-8"  
        pageEncoding="utf-8"%>  
    <!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">  
    <html>  
    <head>  
    <meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1">  
    <title>Insert title here</title>  
    </head>  
        <body>  
            <form action="login.jsp" method="post">  
               userName：<input type="text" name="username" />  
                <br />  
                <input type="submit" value="login" />  
            </form>  
        </body>  
    </html>

2.login页面
Html代码

<%@ page language="java" contentType="text/html; charset=utf-8" pageEncoding="utf-8"%>  
    <%@ page import="java.util.*"%>  
    <!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">  
    <html>  
    <head>  
    <meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1">  
    <title>Insert title here</title>  
    </head>  
        <body>  
        <%  
            request.setCharacterEncoding("UTF-8");  
            // 取得登录的用户名  
            String username = request.getParameter("username");  
            // 把用户名保存进session  
            session.setAttribute("username", username);  
            // 把用户名放入在线列表  
            List onlineUserList = (List) application.getAttribute("onlineUserList");  
            // 第一次使用前，需要初始化  
            if (onlineUserList == null) {  
                onlineUserList = new ArrayList();  
                application.setAttribute("onlineUserList", onlineUserList);  
            }  
            onlineUserList.add(username);  
            // 成功  
            response.sendRedirect("result.jsp");  
        %>  
        </body>  
    </html>

3.result页面
Html代码

<%@ page language="java" contentType="text/html; charset=utf-8" pageEncoding="utf-8"%>  
    <%@ page isELIgnored="false"%>  
    <%@page import="java.util.List"%>  
    <!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">  
    <html>  
    <head>  
    <meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1">  
    <title>Insert title here</title>  
    </head>  
    <body>  
        <h3>您好：${username} [<a href="logout.jsp">注销</a>]</h3>  
        当前在线用户：  
        <table>  
        <%  
           List onlineUserList = (List) application.getAttribute("onlineUserList");  
           for (int i = 0; i < onlineUserList.size(); i++) {  
           String onlineUsername = (String) onlineUserList.get(i);  
        %>  
           <tr>  
               <td><%=onlineUsername%></td>  
           </tr>  
        <%  
        }  
        %>  
        </table>  
    </body>  
    </html>

4、logout页面
Html代码

<%@ page language="java" contentType="text/html; charset=utf-8" pageEncoding="utf-8"%>  
    <%@ page import="java.util.*"%>  
    <!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">  
    <html>  
    <head>  
    <meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1">  
    <title>Insert title here</title>  
    </head>  
    <body>  
    <%  
        // 取得登录的用户名  
        String username = (String) session.getAttribute("username");  
        // 销毁session  
        session.invalidate();  
        // 从在线列表中删除用户名  
        List onlineUserList = (List) application.getAttribute("onlineUserList");  
        onlineUserList.remove(username);  
        // 成功  
        response.sendRedirect("index.jsp");  
    %>  
    </body>  
    </html>

5、监听器代码
Java代码

package com.jason.listener;  

    import java.util.List;  

    import javax.servlet.ServletContext;  
    import javax.servlet.http.HttpSession;  
    import javax.servlet.http.HttpSessionEvent;  
    import javax.servlet.http.HttpSessionListener;  

    /** 
     * Application Lifecycle Listener implementation class OnlineUserListener 
     * 
     */  
    public class OnlineUserListener implements HttpSessionListener {  

        public void sessionCreated(HttpSessionEvent event) {  

            System.out.println("新建session:"+event.getSession().getId());  
        }  

        public void sessionDestroyed(HttpSessionEvent event) {  

            HttpSession session = event.getSession();  
            ServletContext application = session.getServletContext();  
            // 取得登录的用户名  
            String username = (String) session.getAttribute("username");  
            // 从在线列表中删除用户名  
            List onlineUserList = (List) application.getAttribute("onlineUserList");  
            onlineUserList.remove(username);  
            System.out.println(username+"已经退出！");  
        }  

    }

6 web的配置
Html代码

<?xml version="1.0" encoding="UTF-8"?>  
    <web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://java.sun.com/xml/ns/javaee" xmlns:web="http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd" xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd" id="WebApp_ID" version="2.5">  
      <display-name>OnlinePepoleListener</display-name>  
      <welcome-file-list>  
        <welcome-file>index.jsp</welcome-file>  
      </welcome-file-list>  
      <listener>  
        <listener-class>com.jason.listener.OnlineUserListener</listener-class>  
      </listener>  
    </web-app>

一旦监听器发现调用了sessionDestoryed方法就会把其用户从在线人数中delete，在下面两种情况下会发生sessionDestoryed事件

a.执行session.invalidate()方法时

logout.jsp中调用了 session.invalidate()方法

b.session会话超时

session的默认超时事件是30分钟，30分钟后自动销毁session

2、HttpSessionBindingListener

HttpSessionBindingListener虽然叫做监听器，但使用方法与HttpSessionListener完全不同。我们实际看一下它是如何使用的。新建类OnlineUserBindingListener，实现HttpSessionBindingListener接口，构造方法传入username参数，HttpSessionBindingListener内有两个方法valueBound(HttpSessionBindingEvent event)和valueUnbound(HttpSessionBindingEvent event)，前者为数据绑定，后者为取消绑定所谓对session进行数据绑定，就是调用session.setAttribute()把HttpSessionBindingListener保存进session中。

在login.jsp中做这一步：
Java代码

<%@page import="com.test.OnlineUserBindingListener"%>  
    <%@ page contentType="text/html;charset=utf-8"%>  
    <%@ page import="java.util.*"%>  
    <%  
        request.setCharacterEncoding("UTF-8");  
        // 取得登录的用户名  
        String username = request.getParameter("username");  
           // 把用户名放入在线列表  
        session.setAttribute("onlineUserBindingListener", new OnlineUserBindingListener(username));  
        // 成功  
        response.sendRedirect("result.jsp");  
    %>

这就是HttpSessionBindingListener和HttpSessionListener之间的最大区别：HttpSessionListener只需要设置到web.xml中就可以监听整个应用中的所有session。HttpSessionBindingListener必须实例化后放入某一个session中，才可以进行监听。从监听范围上比较，HttpSessionListener设置一次就可以监听所有session，HttpSessionBindingListener通常都是一对一的。正是这种区别成就了HttpSessionBindingListener的优势，我们可以让每个listener对应一个username，这样就不需要每次再去session中读取username，进一步可以将所有操作在线列表的代码都移入listener，更容易维护。
Java代码

package com.test;  

    import java.util.ArrayList;  
    import java.util.List;  
    import javax.servlet.ServletContext;  
    import javax.servlet.http.HttpSession;  
    import javax.servlet.http.HttpSessionBindingEvent;  
    import javax.servlet.http.HttpSessionBindingListener;  

    public class OnlineUserBindingListener implements HttpSessionBindingListener {  
        String username;  

        public OnlineUserBindingListener(String username){  
            this.username=username;  
        }  

        public void valueBound(HttpSessionBindingEvent event) {  
            HttpSession session = event.getSession();  
            ServletContext application = session.getServletContext();  
            // 把用户名放入在线列表  
            List onlineUserList = (List) application.getAttribute("onlineUserList");  
            // 第一次使用前，需要初始化  
            if (onlineUserList == null) {  
                onlineUserList = new ArrayList();  
                application.setAttribute("onlineUserList", onlineUserList);  
            }  
            onlineUserList.add(this.username);  
        }  

        public void valueUnbound(HttpSessionBindingEvent event) {  
            HttpSession session = event.getSession();  
            ServletContext application = session.getServletContext();  

            // 从在线列表中删除用户名  
            List onlineUserList = (List) application.getAttribute("onlineUserList");  
            onlineUserList.remove(this.username);  
            System.out.println(this.username + "退出。");  
        }  
    }

这里可以直接使用listener的username操作在线列表，不必再去担心session中是否存在username。

valueUnbound的触发条件是以下三种情况：

a.执行session.invalidate()时。

b.session超时，自动销毁时。

c.执行session.setAttribute("onlineUserListener", "其他对象");或session.removeAttribute("onlineUserListener");将listener从session中删除时。

因此，只要不将listener从session中删除，就可以监听到session的销毁。

典型事例：强行把用户踢出例子

1、监听器代码如下：
Java代码

package com.jason.listener;  

    import java.util.HashMap;  
    import java.util.Map;  

    import javax.servlet.ServletContext;  
    import javax.servlet.http.HttpSession;  
    import javax.servlet.http.HttpSessionAttributeListener;  
    import javax.servlet.http.HttpSessionBindingEvent;  

    import com.jason.domain.User;  

    /** 
     * Application Lifecycle Listener implementation class SessionAttributeListener 
     * 
     */  
    public class SessionAttributeListener implements HttpSessionAttributeListener {  

        /** 
         * @see HttpSessionAttributeListener#attributeRemoved(HttpSessionBindingEvent) 
         */  
        public void attributeRemoved(HttpSessionBindingEvent arg0) {  
            // TODO Auto-generated method stub  
        }  

        /** 
         * @see HttpSessionAttributeListener#attributeAdded(HttpSessionBindingEvent) 
         */  
        public void attributeAdded(HttpSessionBindingEvent se) {  
            // TODO Auto-generated method stub  
            System.out.println("start");  
            Object obj = se.getValue();  
            if(obj instanceof User){  
                HttpSession session = se.getSession();  
                ServletContext application = session.getServletContext();  
                Map map = (Map) application.getAttribute("userMap");  
                if(map == null){  
                   map = new HashMap();  
                   application.setAttribute("userMap", map);  
                }  
                User user = (User) obj;  
                map.put(user.getUserName(), session);  
            }  
        }  

        /** 
         * @see HttpSessionAttributeListener#attributeReplaced(HttpSessionBindingEvent) 
         */  
        public void attributeReplaced(HttpSessionBindingEvent arg0) {  
            // TODO Auto-generated method stub  
        }  

    }

2.loginservlet
Java代码

package com.jason.servlet;  

    import java.io.IOException;  
    import java.util.ArrayList;  
    import java.util.HashMap;  
    import java.util.Map;  

    import javax.servlet.ServletContext;  
    import javax.servlet.ServletException;  
    import javax.servlet.http.HttpServlet;  
    import javax.servlet.http.HttpServletRequest;  
    import javax.servlet.http.HttpServletResponse;  
    import javax.servlet.http.HttpSession;  

    import com.jason.domain.User;  

    /** 
     * Servlet implementation class LoginServlet 
     */  
    public class LoginServlet extends HttpServlet {  

        /** 
         * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response) 
         */  
        protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {  
            // TODO Auto-generated method stub  
            doPost(request,response);  
        }  

        /** 
         * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response) 
         */  
        protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {  
            // TODO Auto-generated method stub  
            String username = request.getParameter("username");  
            String password = request.getParameter("password");  
            User user = new User();  
            user.setUserName(username);  
            user.setPassword(password);  
            HttpSession session= request.getSession();  
            session.setAttribute("user", user);  
            response.sendRedirect(request.getContextPath()+"/user.jsp");  
        }  

    }

3、kickoutServelt
Java代码

package com.jason.servlet;  

    import java.io.IOException;  
    import java.util.Map;  

    import javax.servlet.ServletException;  
    import javax.servlet.http.HttpServlet;  
    import javax.servlet.http.HttpServletRequest;  
    import javax.servlet.http.HttpServletResponse;  
    import javax.servlet.http.HttpSession;  

    /** 
     * Servlet implementation class KickUserServlet 
     */  
    public class KickUserServlet extends HttpServlet {  
        private static final long serialVersionUID = 1L;  

        /** 
         * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response) 
         */  
        protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {  
            // TODO Auto-generated method stub  
            doPost(request,response);  
        }  

        /** 
         * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response) 
         */  
        protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {  
            // TODO Auto-generated method stub  
            String username = request.getParameter("username");  
            Map map = (Map) request.getServletContext().getAttribute("userMap");  
            HttpSession session = (HttpSession) map.get(username);  
               if(session != null){  
                   session.invalidate();  
                   map.remove(username);  
               }  
               request.getRequestDispatcher("/listUser.jsp").forward(request, response);  
        }  
    }

6.index页面
Html代码

<%@ page language="java" contentType="text/html; charset=utf-8" pageEncoding="utf-8"%>  
    <!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">  
    <html>  
    <head>  
    <meta http-equiv="Content-Type" content="text/html; charset=utf-8">  
    <title>Insert title here</title>  
    </head>  
    <body>  
    <form method="post" action="${pageContext.request.contextPath }/LoginServlet">  
       用户名：<input type="text" name="username" /><br/>  
       密码: <input type="password" name="password" /><br/>  
       <input type="submit" value="登陆" /><br/>  
    </form>  
    </body>  
    </html>

2 user 页面
Java代码

<%@ page language="java" contentType="text/html; charset=utf-8"  
        pageEncoding="utf-8"%>  
    <!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">  
    <html>  
    <head>  
    <meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1">  
    <title>Insert title here</title>  
    </head>  
    <body>  
     欢迎您：${user.userName}  
    <a href="listUser.jsp" >user list</a>  
    </body>  
    </html>

3 userlist页面
Html代码

<%@ taglib uri="http://java.sun.com/jsp/jstl/core" prefix="c" %>  
    <%@ page language="java" contentType="text/html; charset=utf-8" pageEncoding="utf-8"%>  
    <%@page import="java.util.*"%>  
    <!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">  
    <html>  
    <head>  
    <meta http-equiv="Content-Type" content="text/html; charset=utf-8">  
    <title>Insert title here</title>  
    </head>  
    <body>  
    欢迎您：${user.userName}  
    <br/>  
    当前登陆用户有：<br/>  
    <%  
        Map onlineUserMap = (Map) application.getAttribute("userMap");  
        System.out.println(onlineUserMap.size());  
    %>  
    <c:forEach var="me" items="${userMap}">  
        ${me.key} <a href="${pageContext.request.contextPath}/KickUserServlet?username=${me.key}" >踢死你</a>  
    </c:forEach>  
    </body>  
    </html>