Servlet事件监听器（2）

监听三个域对象属性变化

Servlet规范定义了监听 ServletContext, HttpSession, HttpServletRequest 这三个对象中的属性变更信息事件的监听器。
这三个监听器接口分别是ServletContextAttributeListener, HttpSessionAttributeListener ServletRequestAttributeListener
这三个接口中都定义了三个方法来处理被监听对象中的属性的增加，删除和替换的事件，同一个事件在这三个接口中对应的方法名称完全相同，只是接受的参数类型不同。

attributeRemoved 方法

 

当删除被监听对象中的一个属性时，web 容器调用事件监听器的这个方法进行相应
各个域属性监听器中的完整语法定义为：
public void attributeRemoved(ServletContextAttributeEvent scae)
public void attributeRemoved (HttpSessionBindingEvent  hsbe)
public void attributeRemoved (ServletRequestAttributeEvent srae)

attributeAdded 方法

当向被监听器对象中增加一个属性时，web容器就调用事件监听器的 attributeAdded 方法进行相应，这个方法接受一个事件类型的参数，监听器可以通过这个参数来获得正在增加属性的域对象和被保存到域中的属性对象

各个域属性监听器中的完整语法定义为：
public void attributeAdded(ServletContextAttributeEvent scae)
public void attributeAdded(HttpSessionBindingEvent  hsbe)
public void attributeAdded(ServletRequestAttributeEvent srae)

attributeReplaced 方法

当监听器的域对象中的某个属性被替换时，web容器调用事件监听器的这个方法进行相应
各个域属性监听器中的完整语法定义为：
public void attributeReplaced(ServletContextAttributeEvent scae)
public void attributeReplaced (HttpSessionBindingEvent  hsbe)
public void attributeReplaced (ServletRequestAttributeEvent srae)

实现踢人功能案例

//////////////////////////实现踢人功能//////////////////////////////////////User.java//////////////////////////////////package com.hbsi.domain;public class User {  private String username;  private String password;public String getUsername() {return username;}public void setUsername(String username) {this.username = username;}public String getPassword() {return password;}public void setPassword(String password) {this.password = password;}  }///////////////////////////KickUserServlet.java/////////////package com.hbsi.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;public class KickUserServlet extends HttpServlet {public void doGet(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException {String username = request.getParameter("username");username = new String(username.getBytes("iso8859-1"),"UTF-8");Map map = (Map) this.getServletContext().getAttribute("map");HttpSession session = (HttpSession) map.get(username);if(session!=null){session.invalidate();map.remove(username);}request.getRequestDispatcher("/listuser.jsp").forward(request,response);}public void doPost(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException {doGet(request, response);}}/////////////////////////LoginServlet.java//////////////////package com.hbsi.servlet;import java.io.IOException;import javax.servlet.ServletException;import javax.servlet.http.HttpServlet;import javax.servlet.http.HttpServletRequest;import javax.servlet.http.HttpServletResponse;import com.hbsi.domain.User;public class LoginServlet extends HttpServlet {public void doGet(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException {String username = request.getParameter("username");String password = request.getParameter("password");User user = new User();user.setUsername(username);user.setPassword(password);request.getSession().setAttribute("user",user);//给session添加了属性response.sendRedirect("/Listenertest/index.jsp");}public void doPost(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException {doGet(request, response);}}/////////////////////////////CharseterEncodingFilter.java//////package com.hbsi.web.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;public class CharseterEncodingFilter implements Filter {private FilterConfig config = null;private String defaultCharset = "UTF-8";@Overridepublic void destroy() {// TODO Auto-generated method stub}@Overridepublic void doFilter(ServletRequest request, ServletResponse response,FilterChain chain) throws IOException, ServletException {String charset = config.getInitParameter("charset");if(charset==null){charset = defaultCharset;}request.setCharacterEncoding(charset);response.setCharacterEncoding("UTF-8");response.setContentType("text/html;charset="+charset);chain.doFilter(request, response);}@Overridepublic void init(FilterConfig filterConfig) throws ServletException {this.config = filterConfig;}}////////////////////////SessionListener.java/////////////////package com.hbsi.web.listener;import java.util.HashMap;import java.util.Map;import javax.servlet.http.HttpSession;import javax.servlet.http.HttpSessionAttributeListener;import javax.servlet.http.HttpSessionBindingEvent;import com.hbsi.domain.User;public class SessionListener implements HttpSessionAttributeListener {@Overridepublic void attributeAdded(HttpSessionBindingEvent arg0) {Object obj = arg0.getValue();if(obj instanceof User){User user =(User)obj;HttpSession session = arg0.getSession();Map map = (Map) session.getServletContext().getAttribute("map");if(map==null){map = new HashMap();session.getServletContext().setAttribute("map",map);}map.put(user.getUsername(),session);}}@Overridepublic void attributeRemoved(HttpSessionBindingEvent arg0) {// TODO Auto-generated method stub}@Overridepublic void attributeReplaced(HttpSessionBindingEvent arg0) {// TODO Auto-generated method stub}}

 

////////////////////////////////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"><filter>    <filter-name>CharseterEncodingFilter</filter-name>    <filter-class>com.hbsi.web.filter.CharseterEncodingFilter</filter-class>    <init-param>      <param-name>charset</param-name>      <param-value>UTF-8</param-value>    </init-param>  </filter>  <filter-mapping>    <filter-name>CharseterEncodingFilter</filter-name>    <url-pattern>/*</url-pattern>  </filter-mapping><listener>  <listener-class>com.hbsi.web.listener.SessionListener</listener-class></listener>  <servlet>    <servlet-name>LoginServlet</servlet-name>    <servlet-class>com.hbsi.servlet.LoginServlet</servlet-class>  </servlet>  <servlet>    <servlet-name>KickUserServlet</servlet-name>    <servlet-class>com.hbsi.servlet.KickUserServlet</servlet-class>  </servlet>  <servlet-mapping>    <servlet-name>LoginServlet</servlet-name>    <url-pattern>/servlet/LoginServlet</url-pattern>  </servlet-mapping>  <servlet-mapping>    <servlet-name>KickUserServlet</servlet-name>    <url-pattern>/servlet/KickUserServlet</url-pattern>  </servlet-mapping>  <welcome-file-list>    <welcome-file>index.jsp</welcome-file>  </welcome-file-list></web-app>//////////////////////////////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>  </head>    <body>  欢迎您：${user.username} <br>  </body></html>////////////////////////////////login.jsp////////////////////<%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%><!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"><html>  <head>      <title>My JSP 'login.jsp' starting page</title>   </head>    <body>  <form action="${pageContext.request.contextPath}/servlet/LoginServlet" method="post">  用户名：<input type="text" name="username"/><br/>  密码：<input type="password" name="password"/><br/>  <input type="submit" value="登陆"/>    </form>  </body></html>//////////////////////////////listuser.jsp//////////////////////////////<%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%><%@ 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 'listuser.jsp' starting page</title>   </head>    <body>  当前在线用户为：<br/>  <c:forEach items="${map}" var="me">  <c:url value="/servlet/KickUserServlet" var="url">    <c:param name="username" value="${me.key}"></c:param>  </c:url>      ${me.key}<a href="${url}">剔出去</a><br/>    </c:forEach>  </body></html>