监听器

来源：互联网发布：社会经济数据编辑：程序博客网时间：2024/05/20 08:26

1.1 概述

监听器：主要是用来监听特定对象的创建或销毁、属性的变化的！

是一个实现特定接口的普通java类！

对象：

自己创建自己用 (不用监听)

别人创建自己用（需要监听）

Servlet中哪些对象需要监听？

request / session / servletContext

分别对应的是request监听器、session相关监听器、servletContext监听器

监听器(listener)

监听器接口：

一、监听对象创建/销毁的监听器接口

InterfaceServletRequestListener 监听request对象的创建或销毁

InterfaceHttpSessionListener 监听session对象的创建或销毁

InterfaceServletContextListener 监听servletContext对象的创建或销毁

二、监听对象属性的变化

InterfaceServletRequestAttributeListener 监听request对象属性变化: 添加、移除、修改

InterfaceHttpSessionAttributeListener 监听session对象属性变化: 添加、移除、修改

InterfaceServletContextAttributeListener 监听servletContext对象属性变化

三、session相关监听器

InterfaceHttpSessionBindingListener 监听对象绑定到session上的事件

InterfaceHttpSessionActivationListener(了解) 监听session序列化及反序列化的事件

404(路径写错)

500(服务器错误，调试)

1.2 生命周期监听器

声明周期监听器：监听对象的创建、销毁的过程！

监听器开发步骤：

1. 写一个普通java类，实现相关接口；

2. 配置(web.xml)

A.ServletRequestListener

监听request对象的创建或销毁。

MyRequestListener.java

package cn.itcast.a_life;import javax.servlet.ServletRequestEvent;import javax.servlet.ServletRequestListener;/** *  监听request对象的创建或销毁 */public class MyRequestListener implements ServletRequestListener{// 对象销毁@Overridepublic void requestDestroyed(ServletRequestEvent sre) {// 获取request中存放的数据Object obj = sre.getServletRequest().getAttribute("cn");System.out.println(obj);System.out.println("MyRequestListener.requestDestroyed()");}// 对象创建@Overridepublic void requestInitialized(ServletRequestEvent sre) {System.out.println("MyRequestListener.requestInitialized()");}}

Web.xml

<!-- 监听request对象创建、销毁 -->    <listener>        <listener-class>cn.itcast.a_life.MyRequestListener</listener-class>    </listener>

listener_test.jsp

<%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%><%@page import="cn.itcast.c_session.Admin"%><!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"><html>  <head>        <title>My JSP 'index.jsp' starting page</title><meta http-equiv="pragma" content="no-cache"><meta http-equiv="cache-control" content="no-cache"><meta http-equiv="expires" content="0">      </head>    <body>  test!        <% request.setAttribute("cn","China"); %> </body></html>

B. HttpSessionListener

监听session对象的创建或销毁。

C. ServletContextListener

监听servletContext对象的创建或销毁。

MyServletContextListener.java

package cn.itcast.a_life;import javax.servlet.ServletContextEvent;import javax.servlet.ServletContextListener;/** * 监听ServletContext对象创建或销毁 */public class MyServletContextListener implements ServletContextListener{@Overridepublic void contextDestroyed(ServletContextEvent sce) {System.out.println("MyServletContextListener.contextDestroyed()");}@Overridepublic void contextInitialized(ServletContextEvent sce) {System.out.println("1..........MyServletContextListener.contextInitialized()");}}

MySessionListener.java

package cn.itcast.a_life;import javax.servlet.http.HttpSessionEvent;import javax.servlet.http.HttpSessionListener;/** * 监听Session对象创建、销毁 */public class MySessionListener implements HttpSessionListener{// 创建@Overridepublic void sessionCreated(HttpSessionEvent se) {System.out.println("MySessionListener.sessionCreated()");}// 销毁@Overridepublic void sessionDestroyed(HttpSessionEvent se) {System.out.println("MySessionListener.sessionDestroyed()");}}

listener_test.jsp

<%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%><%@page import="cn.itcast.c_session.Admin"%><!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"><html>  <head>        <title>My JSP 'index.jsp' starting page</title><meta http-equiv="pragma" content="no-cache"><meta http-equiv="cache-control" content="no-cache"><meta http-equiv="expires" content="0">      </head>    <body>  test!  <%    //request.setAttribute("cn","China");  //session.invalidate();  //销毁session    //session.setAttribute("userName","Jack");  //session.removeAttribute("userName");  //session.setAttribute("userName","Jack_new");    session.setAttribute("userInfo",new Admin());  session.removeAttribute("userInfo");  %>  </body></html>

1.3 属性监听器

监听:request/session/servletContext对象属性的变化！

ServletRequestAttributeListener

HttpSessionAttributeListener

ServletContextAttributeListener

总结：先写类，实现接口；再配置

MySessionAttrListener.java

package cn.itcast.b_attr;import javax.servlet.http.HttpSession;import javax.servlet.http.HttpSessionAttributeListener;import javax.servlet.http.HttpSessionBindingEvent;/** * 监听session对象属性的变化 */public class MySessionAttrListener implements HttpSessionAttributeListener {// 属性添加@Overridepublic void attributeAdded(HttpSessionBindingEvent se) {// 先获取session对象HttpSession session = se.getSession();// 获取添加的属性Object obj = session.getAttribute("userName");// 测试System.out.println("添加的属性：" + obj);}// 属性移除@Overridepublic void attributeRemoved(HttpSessionBindingEvent se) {System.out.println("属性移除");}// 属性被替换@Overridepublic void attributeReplaced(HttpSessionBindingEvent se) {// 获取sesison对象HttpSession session = se.getSession();// 获取替换前的值Object old = se.getValue();System.out.println("原来的值：" + old);// 获取新值Object obj_new = session.getAttribute("userName");System.out.println("新值：" + obj_new);}}

listener_test.jsp

<%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%><%@page import="cn.itcast.c_session.Admin"%><!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"><html>  <head>        <title>My JSP 'index.jsp' starting page</title><meta http-equiv="pragma" content="no-cache"><meta http-equiv="cache-control" content="no-cache"><meta http-equiv="expires" content="0">      </head>    <body>  test!  <%    //request.setAttribute("cn","China");  //session.invalidate();  //销毁session    //session.setAttribute("userName","Jack");  //session.removeAttribute("userName");  //session.setAttribute("userName","Jack_new");    session.setAttribute("userInfo",new Admin());  session.removeAttribute("userInfo");  %>  </body></html>

web.xml

<?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"><!-- session的最大活跃时间 --><session-config><session-timeout>60</session-timeout></session-config><!-- 监听request对象创建、销毁 --><listener><listener-class>cn.itcast.a_life.MyRequestListener</listener-class></listener><!-- 监听session对象创建、销毁 --><listener><listener-class>cn.itcast.a_life.MySessionListener</listener-class></listener><!-- 监听servletContext对象创建、销毁 --><listener><listener-class>cn.itcast.a_life.MyServletContextListener</listener-class></listener><!-- 属性监听器 --><listener><listener-class>cn.itcast.b_attr.MySessionAttrListener</listener-class></listener><welcome-file-list><welcome-file>index.jsp</welcome-file></welcome-file-list></web-app>

1.4 其他监听器： session相关监听器

HttpSessionBindingListener

监听对象绑定/解除绑定到sesison上的事件!

步骤：

对象实现接口；再把对象绑定/解除绑定到session上就会触发监听代码。

作用：

(上线提醒！)

Admin.java

package cn.itcast.c_session;import javax.servlet.http.HttpSessionBindingEvent;import javax.servlet.http.HttpSessionBindingListener;/** * 监听此对象绑定到session上的过程，需要实现session特定接口 */public class Admin implements HttpSessionBindingListener {private int id;private String name;public Admin() {super();}public Admin(int id, String name) {super();this.id = id;this.name = name;}// 构造函数public int getId() {return id;}public void setId(int id) {this.id = id;}public String getName() {return name;}public void setName(String name) {this.name = name;}// 对象放入session@Overridepublic void valueBound(HttpSessionBindingEvent event) {System.out.println("Admin对象已经放入session");}// 对象从session中移除@Overridepublic void valueUnbound(HttpSessionBindingEvent event) {System.out.println("Admin对象从session中移除！");}}

1.4 案例

需求：做一个在线列表提醒的功能!

用户--à 登陆

---à 显示登陆信息，列表展示。(list.jsp)

--à 显示在线用户列表 (list.jsp)

-à 列表点击进入“在线列表页面” onlineuser.jsp

实现：

1. 先增加退出功能；再把session活跃时间1min;

2. 写监听器，监听servletContext对象的创建：初始化集合(onlineuserlist)

3. 登陆功能：用户登陆时候，把数据保存到servletContext中

4. List.jsp 增加超链接，点击时候提交直接跳转到online.jsp

5. 写监听器：监听session销毁，把当前登陆用户从onlineuserlist移除！

Admin.java

package cn.itcast.entity;/** * 1. 管理员实体类开发 */public class Admin {private int id; private String userName;private String pwd;public int getId() {return id;}public void setId(int id) {this.id = id;}public String getUserName() {return userName;}public void setUserName(String userName) {this.userName = userName;}public String getPwd() {return pwd;}public void setPwd(String pwd) {this.pwd = pwd;}}

Employee.java

package cn.itcast.entity;/** * 1. 员工 */public class Employee {private int empId;private String empName;private int dept_id;public int getEmpId() {return empId;}public void setEmpId(int empId) {this.empId = empId;}public String getEmpName() {return empName;}public void setEmpName(String empName) {this.empName = empName;}public int getDept_id() {return dept_id;}public void setDept_id(int deptId) {dept_id = deptId;}}

IAdminDao.java

package cn.itcast.dao;import cn.itcast.entity.Admin;/** * 2. 管理员数据访问层接口设计 */public interface IAdminDao {/** * 根据用户名密码查询 * @param admin * @return */Admin findByNameAndPwd(Admin admin);}

IEmployeeDao.java

package cn.itcast.dao;import java.util.List;import cn.itcast.entity.Employee;/** * 2. 员工数据访问层接口设计 */public interface IEmployeeDao {/** * 查询所有的员工 * @return */List<Employee> getAll();}

AdminDao.java

package cn.itcast.dao.impl;import java.sql.SQLException;import org.apache.commons.dbutils.handlers.BeanHandler;import cn.itcast.dao.IAdminDao;import cn.itcast.entity.Admin;import cn.itcast.utils.JdbcUtils;public class AdminDao implements IAdminDao {@Overridepublic Admin findByNameAndPwd(Admin admin) {try {String sql = "select * from admin where userName=? and pwd=?";return JdbcUtils.getQueryRuner()//.query(sql, new BeanHandler<Admin>(Admin.class),admin.getUserName(),admin.getPwd());} catch (SQLException e) {throw new RuntimeException(e);}}}

EmployeeDao.java

package cn.itcast.dao.impl;import java.sql.SQLException;import java.util.List;import org.apache.commons.dbutils.handlers.BeanListHandler;import cn.itcast.dao.IEmployeeDao;import cn.itcast.entity.Employee;import cn.itcast.utils.JdbcUtils;public class EmployeeDao implements IEmployeeDao {@Overridepublic List<Employee> getAll() {String sql = "select * from employee";try {return JdbcUtils.getQueryRuner()//.query(sql, new BeanListHandler<Employee>(Employee.class));} catch (SQLException e) {throw new RuntimeException(e);}}}

IAdminService.java

package cn.itcast.service;import cn.itcast.entity.Admin;/** * 3. 管理员业务逻辑层 */public interface IAdminService {/** * 根据用户名密码查询 * @param admin * @return */Admin findByNameAndPwd(Admin admin);}

IEmployeeService.java

package cn.itcast.service;import java.util.List;import cn.itcast.entity.Employee;/** * 2. 员工业务逻辑层 */public interface IEmployeeService {/** * 查询所有的员工 * @return */List<Employee> getAll();}

AdminService.java

package cn.itcast.service.impl;import cn.itcast.dao.IAdminDao;import cn.itcast.dao.impl.AdminDao;import cn.itcast.entity.Admin;import cn.itcast.service.IAdminService;public class AdminService implements IAdminService{// 创建dao对象private IAdminDao adminDao = new AdminDao();@Overridepublic Admin findByNameAndPwd(Admin admin) {try {return adminDao.findByNameAndPwd(admin);} catch (Exception e) {throw new RuntimeException(e);}}}

EmployeeService.java

package cn.itcast.service.impl;import java.util.List;import cn.itcast.dao.IEmployeeDao;import cn.itcast.dao.impl.EmployeeDao;import cn.itcast.entity.Employee;import cn.itcast.service.IEmployeeService;public class EmployeeService implements IEmployeeService {private IEmployeeDao employeeDao = new EmployeeDao();@Overridepublic List<Employee> getAll() {try {return employeeDao.getAll();} catch (Exception e) {throw new RuntimeException(e);}}}

AdminServlet.java

package cn.itcast.servlet;import java.io.IOException;import java.util.List;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 cn.itcast.entity.Admin;import cn.itcast.service.IAdminService;import cn.itcast.service.impl.AdminService;/** * 用户管理servlet 1. 登陆 2. 退出 */public class AdminServlet extends HttpServlet {// Service实例private IAdminService adminService = new AdminService();// 跳转资源private String uri;protected void doGet(HttpServletRequest request,HttpServletResponse response) throws ServletException, IOException {// 区别不同的操作类型String method = request.getParameter("method");// 判断if ("login".equals(method)) {// 登陆操作, 调用登陆方法login(request, response);}else if ("out".equals(method)) {// 退出操作，调用推出方法out(request, response);}}// 1 登陆private void login(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException {request.setCharacterEncoding("UTF-8");// 1. 获取参数String userName = request.getParameter("userName");String pwd = request.getParameter("pwd");// 封装Admin admin = new Admin();admin.setUserName(userName);admin.setPwd(pwd);try {// 2. 调用service处理业务Admin loginInfo = adminService.findByNameAndPwd(admin);// 判断:if (loginInfo == null) {// 登陆失败uri = "/login.jsp";} else {// 登陆成功// 先，保存数据到sessionrequest.getSession().setAttribute("loginInfo", loginInfo);//【在线列表： 1. 先从servletContext中拿到在线列表集合;  (onLineUserList)//           2. 当前用户放入“在线列表集合中”】// 实现1：先得到servletContext对象ServletContext sc = getServletContext();// 实现2： 再获取在线列表集合List<Admin> onlineList = (List<Admin>) sc.getAttribute("onlineList");// 判断if (onlineList != null){// 实现3: 添加当前登陆者onlineList.add(loginInfo);//sc.setAttribute("onlineList", onlineList);  // 对象引用传递,不需要写也可以}// 再，跳转到首页显示servlet(/index)uri = "/index";}} catch (Exception e) {// 测试e.printStackTrace();// 错误uri = "/error/error.jsp";}// 3. 跳转request.getRequestDispatcher(uri).forward(request, response);}// 2 退出private void out(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException {//1. 获取sessionHttpSession session = request.getSession(false);//2.判断： if (session!=null) {// 从session中移除用户// session.removeAttribute("loginInfo");  //?// 销毁sessionsession.invalidate();}//3. 跳转(登陆)response.sendRedirect(request.getContextPath() + "/login.jsp");}protected void doPost(HttpServletRequest req, HttpServletResponse resp)throws ServletException, IOException {this.doGet(req, resp);}}

IndexServlet.java

package cn.itcast.servlet;import java.io.IOException;import java.io.PrintWriter;import java.util.List;import javax.servlet.ServletException;import javax.servlet.http.HttpServlet;import javax.servlet.http.HttpServletRequest;import javax.servlet.http.HttpServletResponse;import cn.itcast.entity.Admin;import cn.itcast.entity.Employee;import cn.itcast.service.IAdminService;import cn.itcast.service.IEmployeeService;import cn.itcast.service.impl.AdminService;import cn.itcast.service.impl.EmployeeService;public class IndexServlet extends HttpServlet {// Service实例private IEmployeeService employeeService = new EmployeeService();// 跳转资源private String uri;public void doGet(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException {try {// 调用service查询所有List<Employee> list = employeeService.getAll();request.setAttribute("listEmp", list);// 进入首页jspuri = "/list.jsp";} catch (Exception e) {e.printStackTrace();uri = "/error/error.jsp";}// 转发request.getRequestDispatcher(uri).forward(request, response);}public void doPost(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException {this.doGet(request, response);}}

JdbcUtils.java

package cn.itcast.utils;import javax.sql.DataSource;import org.apache.commons.dbutils.QueryRunner;import com.mchange.v2.c3p0.ComboPooledDataSource;/** * 工具类 * 1. 初始化C3P0连接池 * 2. 创建DbUtils核心工具类对象 */public class JdbcUtils {/** *  1. 初始化C3P0连接池 */private static  DataSource dataSource;static {dataSource = new ComboPooledDataSource();}/** * 2. 创建DbUtils核心工具类对象 */public static QueryRunner getQueryRuner(){// 创建QueryRunner对象，传入连接池对象// 在创建QueryRunner对象的时候，如果传入了数据源对象；// 那么在使用QueryRunner对象方法的时候，就不需要传入连接对象；// 会自动从数据源中获取连接(不用关闭连接)return new QueryRunner(dataSource);}}

LoginFilter.java

package cn.itcast.filter;import java.io.IOException;import javax.servlet.Filter;import javax.servlet.FilterChain;import javax.servlet.FilterConfig;import javax.servlet.ServletException;import javax.servlet.ServletRequest;import javax.servlet.ServletResponse;import javax.servlet.http.HttpServletRequest;import javax.servlet.http.HttpServletResponse;import javax.servlet.http.HttpSession;/** * 登陆验证过滤器 *  *  http://localhost:8080/emp_sys/login.jsp   可以直接访问http://localhost:8080/emp_sys/login      可以直接访问http://localhost:8080/emp_sys/index   不能直接访问http://localhost:8080/emp_sys/list.jsp   不能直接访问 */public class LoginFilter implements Filter {private String uri;/** * 分析： * 1. 先指定放行的资源，哪些资源不需要拦截：      login.jsp   +    /login  (request对象可以获取)2. 获取session，从session中获取登陆用户3. 判断是否为空：      为空， 说明没有登陆， 跳转到登陆       不为空， 已经登陆，放行！ */@Overridepublic void doFilter(ServletRequest req, ServletResponse res,FilterChain chain) throws IOException, ServletException {//0. 转换HttpServletRequest request = (HttpServletRequest) req;HttpServletResponse response = (HttpServletResponse) res;//1. 获取请求资源，截取  String uri = request.getRequestURI();   // /emp_sys/login.jsp// 截取 【login.jsp或login】String requestPath = uri.substring(uri.lastIndexOf("/") + 1, uri.length());  //2. 判断： 先放行一些资源：/login.jsp、/loginif ("admin".equals(requestPath) || "login.jsp".equals(requestPath)) {// 放行chain.doFilter(request, response);}else {//3. 对其他资源进行拦截//3.1 先获取Session、获取session中的登陆用户(loginInfo)HttpSession session = request.getSession(false);// 判断if (session != null) {Object obj = session.getAttribute("loginInfo");//3.2如果获取的内容不为空，说明已经登陆，放行if (obj != null) {// 放行chain.doFilter(request, response);   return;} else {//3.3如果获取的内容为空，说明没有登陆； 跳转到登陆uri = "/login.jsp";}} else {// 肯定没有登陆uri = "/login.jsp";}request.getRequestDispatcher(uri).forward(request, response);}}@Overridepublic void init(FilterConfig filterConfig) throws ServletException {}@Overridepublic void destroy() {}}

OnlineAdminListener.java

package cn.itcast.listener;import java.util.ArrayList;import java.util.List;import javax.servlet.ServletContext;import javax.servlet.ServletContextEvent;import javax.servlet.ServletContextListener;import cn.itcast.entity.Admin;/** * 初始化在线列表集合监听器 */public class OnlineAdminListener implements ServletContextListener {//1. ServletContext对象创建@Overridepublic void contextInitialized(ServletContextEvent sce) {// 创建集合：存放在线用户// 每次当用户登陆后，就往这个集合中添加添加当前登陆者List<Admin> onlineList = new ArrayList<Admin>();// 放入ServletContext中sce.getServletContext().setAttribute("onlineList", onlineList);}//2. ServletContext对象销毁@Overridepublic void contextDestroyed(ServletContextEvent sce) {// 获取ServletContextServletContext sc = sce.getServletContext();// 获取在线列表Object obj = sc.getAttribute("onlineList");// 移除在线列表集合if (obj != null) {sc.removeAttribute("onlineList");}}}

SessionListener.java

package cn.itcast.listener;import java.util.List;import javax.servlet.ServletContext;import javax.servlet.http.HttpSession;import javax.servlet.http.HttpSessionEvent;import javax.servlet.http.HttpSessionListener;import cn.itcast.entity.Admin;/** * 监听Session销毁的动作： *  当服务器销毁session的时候，从在线列表集合中移除当亲的登陆用户 */public class SessionListener implements HttpSessionListener{@Overridepublic void sessionDestroyed(HttpSessionEvent se) {//1. 获取Session对象、ServletContext对象HttpSession session = se.getSession();ServletContext sc = session.getServletContext();//2. 获取Session中存储的当前登陆用户Object obj = session.getAttribute("loginInfo");//?//3. 获取ServletContext中存储的在线用户列表集合List<Admin> list = (List<Admin>) sc.getAttribute("onlineList");// 先判断if (obj != null){//4. 把“当前登陆用户”从在线列表集合中移除list.remove(obj);}}@Overridepublic void sessionCreated(HttpSessionEvent se) {}}

c3p0-config.xml

<c3p0-config>  <default-config>     <property name="driverClass">com.mysql.jdbc.Driver</property>      <property name="jdbcUrl">jdbc:mysql:///jdbc_demo</property>      <property name="user">root</property>      <property name="password">root</property>      <property name="initialPoolSize">5</property>      <property name="maxPoolSize">10</property>   </default-config>  <named-config name="oracleConfig">    <property name="driverClass">com.mysql.jdbc.Driver</property>      <property name="jdbcUrl">jdbc:mysql:///day17</property>      <property name="user">root</property>      <property name="password">root</property>      <property name="initialPoolSize">5</property>      <property name="maxPoolSize">10</property>    </named-config></c3p0-config>

index.jsp

<%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%><!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"><html>  <head>    <title>My JSP 'index.jsp' starting page</title><meta http-equiv="pragma" content="no-cache"><meta http-equiv="cache-control" content="no-cache"><meta http-equiv="expires" content="0">      </head>    <body>    This is my JSP page. <br>  </body></html>

head.jsp

<%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%><h3 align="center"> 欢迎你，${sessionScope.loginInfo.userName };  <a href="${pageContext.request.contextPath }/admin?method=out">退出</a>  <a href="${pageContext.request.contextPath }/online.jsp">在线列表展示</a></h3>

list.jsp

<%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%><!-- 引入jstl核心标签库 --><%@taglib uri="http://java.sun.com/jsp/jstl/core" prefix="c" %><!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"><html>  <head>    <title>My JSP 'index.jsp' starting page</title><meta http-equiv="pragma" content="no-cache"><meta http-equiv="cache-control" content="no-cache"><meta http-equiv="expires" content="0">      </head>    <body>    <!-- 引入头部页面 -->  <jsp:include page="/public/head.jsp"></jsp:include>    <!-- 列表展示数据 -->  <table align="center" border="1" width="80%" cellpadding="3" cellspacing="0">  <tr>  <td>序号</td>  <td>编号</td>  <td>员工名称</td>  </tr>  <c:if test="${not empty requestScope.listEmp}">  <c:forEach var="emp" items="${requestScope.listEmp}" varStatus="vs">  <tr>  <td>${vs.count }</td>  <td>${emp.empId }</td>  <td>${emp.empName }</td>  </tr>  </c:forEach>  </c:if>  </table>  </body></html>

<%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%><!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"><html>  <head>    <title>My JSP 'index.jsp' starting page</title><meta http-equiv="pragma" content="no-cache"><meta http-equiv="cache-control" content="no-cache"><meta http-equiv="expires" content="0">      </head>    <body>  <form name="frmLogin" action="${pageContext.request.contextPath }/admin?method=login" method="post">  <table align="center" border="1">  <tr>  <td>用户名</td>  <td>  <input type="text" name="userName">  </td>  </tr>  <tr>  <td>密码</td>  <td>  <input type="password" name="pwd">  </td>  </tr>  <tr>  <td>  <input type="submit" value="亲，点我登陆！">  </td>  </tr>  </table>  </form>  </body></html>

online.jsp

<%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%><!-- 引入jstl核心标签库 --><%@taglib uri="http://java.sun.com/jsp/jstl/core" prefix="c" %><!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"><html>  <head>    <title>在线用户列表</title><meta http-equiv="pragma" content="no-cache"><meta http-equiv="cache-control" content="no-cache"><meta http-equiv="expires" content="0">      </head>    <body>    <!-- 引入头部页面 -->  <jsp:include page="/public/head.jsp"></jsp:include>    <!-- 在线用户 -->  <table align="center" border="1" width="80%" cellpadding="3" cellspacing="0">  <tr>  <td colspan="2" align="center"><h3>在线列表展示：</h3></td>  </tr>  <tr>  <td>编号</td>  <td>员工名称</td>  </tr>  <c:if test="${not empty applicationScope.onlineList}">  <c:forEach var="admin" items="${applicationScope.onlineList}">  <tr>  <td>${admin.id }</td>  <td>${admin.userName }</td>  </tr>  </c:forEach>  </c:if>  </table>  </body></html>

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