javaee学习之路(七)Servlet监听器

时间：2021-01-14 17:34:51

例1、基本的监听实例。
第一步、编写监听类.

package cn.itcast.listener;
import *;
/**
 * servletContext对象上下文的监听
 * @author Administrator
 *
 */
public class MyServletContextListener implements ServletContextListener {
/**
 * 当servletContext对象被创建时调用
 */
public void contextInitialized(ServletContextEvent sce) {
        System.out.println("servletContext对象被创建 contextInitialized()");
//map中放置系统共有的信息
        Map map=new HashMap();
        map.put("mary", "xxxxxxxxxxxx");
        ServletContext sc=sce.getServletContext();
        System.out.println("sc "+sc);
        sc.setAttribute("map", map);
    }
/**
 * 当servletContext对象销毁时调用
 */
public void contextDestroyed(ServletContextEvent sce) {
        System.out.println("servletContext对象销毁 contextDestroyed() ");
    }
}

第二步、在web.xml中注册监听器
……

 <listener>
<listener-class>cn.itcast.listener.MyServletContextListener</listener-class>
</listener>

……
第三步、编写测试servlet. TestSrvlet.java

package cn.itcast.web;
import *;
public class TestServlet extends HttpServlet {
public void doGet(HttpServletRequest request, HttpServletResponse response) throws Exception {
        request.setCharacterEncoding("UTF-8");
        response.setCharacterEncoding("UTF-8");
        response.setContentType("text/html;charset=UTF-8");
        PrintWriter out = response.getWriter();
//获取上下文
        ServletContext sc = this.getServletContext();
        System.out.println("servlet中的sc "+sc);
        Map map = (Map)sc.getAttribute("map");
        System.out.println(map.get("mary"));
    }
public void doPost(HttpServletRequest request, HttpServletResponse response) throws  Exception {
        doGet(request, response);
    }
}

第四步、运行，观察结果：启动tomcat并在IE中键入：
http://localhost:8080/day18ServletListener/servlet/TestServlet
……
servletContext对象被创建 contextInitialized()
sc org.apache.catalina.core.ApplicationContextFacade@1735f84
……
信息: Server startup in 1851 ms
servlet中的sc org.apache.catalina.core.ApplicationContextFacade@1735f84
xxxxxxxxxxxx

重启服务器，可以看到：
……
servletContext对象销毁 contextDestroyed()
……
2012-10-24 19:22:44 org.apache.catalina.core.StandardContext addApplicationListener
信息: The listener “com.sun.faces.application.WebappLifecycleListener” is already configured for this context. The duplicate definition has been ignored.
servletContext对象被创建 contextInitialized()
sc org.apache.catalina.core.ApplicationContextFacade@f7ce53

例2、ServletSessionListener监听
javaee学习之路(七)Servlet监听器
第一步、编写监听类 MyHttpSessionListener.java

package cn.itcast.listener;
import *;
/**
 * HttpSessionListener接口用于监听HttpSession对象的创建和销毁
 */
public class MyHttpSessionListener implements HttpSessionListener {
/**
 * 创建一个Session时
 */
public void sessionCreated(HttpSessionEvent se) {
        System.out.println("创建一个Session时 sessionCreated ");
/*
 * Map map=new HashMap();
 map.put("mary", "xxxxxxxxxxxx");
 ServletContext sc=sce.getServletContext();
 System.out.println("sc "+sc);
 sc.setAttribute("map", map);
 */
//获取ServletContext对象
        ServletContext sc = se.getSession().getServletContext();
        Map map=(Map)sc.getAttribute("map");
        System.out.println("HttpSessionListener "+map.get("mary"));
    }
/**
 * 销毁一个Session时
 */
public void sessionDestroyed(HttpSessionEvent se) {
        System.out.println("销毁一个Session时 sessionDestroyed");
    }
}

第二步、在web.xml文件中注册监听器
……

<listener>
<listener-class>cn.itcast.listener.MyServletContextListener</listener-class>
</listener> 
<listener>
<listener-class>cn.itcast.listener.MyHttpSessionListener</listener-class>
</listener>

……
第三步、session.jsp

<%@ page language="java" import="java.util.*" pageEncoding="UTF-8" contentType="text/html;charset=UTF-8"%>
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
<head>
<title>My JSP 'session.jsp' starting page</title> 
</head>
<%
 //session.setMaxInactiveInterval(3);3秒后消亡
 System.out.println("创建一个Session时 sessionCreated ");
 %>
<body>
    This is my JSP page. <br>
</body>
</html>

第四步、执行结果：
1、启动tomcat
……
servletContext对象被创建 contextInitialized()
sc org.apache.catalina.core.ApplicationContextFacade@10948cf
……
信息: Server startup in 1561 ms
2、在IE中键入：
http://localhost:8080/day18ServletListener/session.jsp 执行结果：
创建一个Session时       sessionCreated
HttpSessionListener      xxxxxxxxxxxx
创建一个Session时      sessionCreated
例3、ServletRequestListener监听器
第一步、编写监听器类MyServletRequestListener.java

package cn.itcast.listener;
import *;
public class MyServletRequestListener implements ServletRequestListener {
/**
 * 销毁一个ServletRequest对象时
 */
public void requestDestroyed(ServletRequestEvent sre) {
        System.out.println("销毁一个ServletRequest对象时 requestDestroyed");
        System.out.println("ServletRequestListener监听中的"+sre.getServletRequest());
    }
/**
 * 创建一个ServletRequest对象时
 */
public void requestInitialized(ServletRequestEvent sre) {
        System.out.println("创建一个ServletRequest对象时 requestInitialized ");
    }
}

第二步、在web.xml中注册(注释掉前面的监听器)

<listener>
<listener-class>cn.itcast.listener.MyServletRequestListener</listener-class>
</listener>

第三步、request.jsp

<%@ page language="java" import="java.util.*" pageEncoding="UTF-8" contentType="text/html;charset=UTF-8"%>
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
<head>
<title>My JSP 'session.jsp' starting page</title> 

</head>
<%
 System.out.println("jsp页面中的request:"+request);
 %>
<body>
    This is my JSP page. <br>
</body>
</html>

第四步、启动tomcat并在IE中键入：http://localhost:8080/day18ServletListener/request.jsp
得到如下结果：
javaee学习之路(七)Servlet监听器

例4、域对象中属性的变更的事件监听器之ServletContextAttributeListener
javaee学习之路(七)Servlet监听器
第一步、编写监听器类MyServletContextAttributeListener.java

package cn.itcast.listener;
import *;
public class MyServletContextAttributeListener implements
ServletContextAttributeListener {
/**
 * web容器调用
 * 在servletContext中增加属性时，调用
 */
public void attributeAdded(ServletContextAttributeEvent scab) {
        System.out.println("servletContext增加属性 attributeAdded*****************");
        System.out.println("属性的key："+scab.getName()+":属性的value："+scab.getValue());
    }
/**
 * web容器调用
 * 在servletContext中删除属性时，调用
 */
public void attributeRemoved(ServletContextAttributeEvent scab) {
        System.out.println("servletContext删除属性 attributeRemoved*****************");
        System.out.println("属性的key："+scab.getName()+":属性的value："+scab.getValue());
    }
/**
 * web容器调用
 * 在servletContext中替换属性时，调用
 */
public void attributeReplaced(ServletContextAttributeEvent scab) {
        System.out.println("servletContext替换属性 attributeReplaced******************");
        System.out.println("属性的key："+scab.getName()+":属性的value："+scab.getValue());
    }
}

第二步、在web.xml中注册

<listener>
<listener-class>cn.itcast.listener.MyServletContextAttributeListener</listener-class>
</listener>

第三步、applicationAttr.jsp

<%@ page language="java" import="java.util.*" pageEncoding="UTF-8" contentType="text/html;charset=UTF-8"%>
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
<head>
</head>
<%
 application.setAttribute("username","zhang");
 application.setAttribute("username","zhang1");
 application.removeAttribute("username");
 %>
<body>
    This is my JSP page. <br>
</body>
</html>

第四步、观察运行结果：
1、启动tomcat
javaee学习之路(七)Servlet监听器
例5、域对象中属性的变更的事件监听器之HttpSessionAttributeListener
第一步、编写监听器类MyHttpSessionAttributeListener.java

package cn.itcast.listener;
import javax.servlet.http.HttpSessionAttributeListener;
import javax.servlet.http.HttpSessionBindingEvent;
public class MyHttpSessionAttributeListener implements
HttpSessionAttributeListener {
/**
 * web容器调用
 * 在session中增加属性时，调用
 */
public void attributeAdded(HttpSessionBindingEvent se) {
        System.out.println("httpSession增加属性 attributeAdded***********************");
        System.out.println("属性的key："+se.getName()+":属性的value："+se.getValue());

    }
/**
 * web容器调用
 * 在session中删除属性时，调用
 */
public void attributeRemoved(HttpSessionBindingEvent se) {
        System.out.println("httpSession删除属性 attributeAdded***********************");
        System.out.println("属性的key："+se.getName()+":属性的value："+se.getValue());
    }
/**
 * web容器调用
 * 在session中替换属性时，调用
 */
public void attributeReplaced(HttpSessionBindingEvent se) {
        System.out.println("httpSession替换属性 attributeAdded***********************");
        System.out.println("属性的key："+se.getName()+":属性的value："+se.getValue());
    }
}

第二步、注册

<listener>
<listener-class>cn.itcast.listener.MyHttpSessionAttributeListener</listener-class>
</listener>

第三步、session.jsp

<%@ page language="java" import="java.util.*" pageEncoding="UTF-8" contentType="text/html;charset=UTF-8"%>
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
<head>
</head>
<%
 session.setAttribute("username","zhang");
 session.setAttribute("username","zhang1");
 session.removeAttribute("username");
 %>
<body>
    This is my JSP page. <br>
</body>
</html>

第四步、运行，启动tomcat在IE中键入：
http://localhost:8080/day18Listener/sessionAttr.jsp得到结果：
httpSession增加属性 attributeAdded***********************
属性的key：username:属性的value：zhang
httpSession替换属性 attributeAdded***********************
属性的key：username:属性的value：zhang
httpSession删除属性 attributeAdded***********************
属性的key：username:属性的value：zhang1

例6、域对象中属性的变更的事件监听器之ServletRequestAttributeListener 同例5
例7、感知session绑定的事件监听器之HttpSessionBindingListener。
第一步、编写javabean User.java

package cn.itcast.listener;
import javax.servlet.http.HttpSessionBindingEvent;
import javax.servlet.http.HttpSessionBindingListener;
public class User implements HttpSessionBindingListener{
private String name;
private String psw;
public String getName() {
return name;
    }
public void setName(String name) {
this.name = name;
    }
public String getPsw() {
return psw;
    }
public void setPsw(String psw) {
this.psw = psw;
    }
/**由web容器调用
 * 在session中放置javabean
 */
public void valueBound(HttpSessionBindingEvent event) {
        System.out.println("valueBound************************");
        System.out.println("HttpSessionBinding session"+event.getSession());
        String name=event.getName();
        User user = (User)event.getValue();
if(user!=null){
            System.out.println("属性的key:"+name+" 属性的value:"+user.getName()+" "+user.getPsw());
        }

    }
/**
 * 在session中删除javabean
 */
public void valueUnbound(HttpSessionBindingEvent event) {
        System.out.println("valueUnbound***********************");
        String name=event.getName();
        User user = (User)event.getValue();
if(user!=null){
            System.out.println("属性的key:"+name+" 属性的value:"+user.getName()+" "+user.getPsw());
        }else{
            System.out.println("user==null");
        }
    }
}

第二步、sessionBing.jsp

<%@ page language="java" import="java.util.*" pageEncoding="UTF-8" contentType="text/html;charset=UTF-8"%>
<%@ page import="cn.itcast.listener.*"%>
……
<%
 User user=new User();
 user.setName("zhang");
 session.setAttribute("user",user);
 //上一行代码，web容器会调用valueBound方法,
 System.out.println("jsp页面中的session:"+session);
 User user1=new User();
 user1.setName("zhangfeng");
 session.setAttribute("user",user1);
 session.removeAttribute("user");
 %>
<body>
    This is my JSP page. <br>
</body>
</html>

第三步、启动tomcat并在IE中键入：
javaee学习之路(七)Servlet监听器
例8、感知session绑定的事件监听器之HttpSessionBindingListener。
第一步、

package cn.itcast.listener;
import *;
public class User implements HttpSessionActivationListener,java.io.Serializable{
private String name;
private String psw;
public String getName() {
return name;
    }
public void setName(String name) {
this.name = name;
    }
public String getPsw() {
return psw;
    }
public void setPsw(String psw) {
this.psw = psw;
    }
/**
 * 把session对象保存到硬盘上(要序列化)
 */
public void sessionWillPassivate(HttpSessionEvent se) {
        System.out.println("钝化******************************");
    }
/**
 * 把session对象从硬盘上读取(要序列化)
 */
public void sessionDidActivate(HttpSessionEvent se) {
        System.out.println("活化******************************");
    }
}

第二步、sessionBing.jsp

<%
       User user=new User();
       user.setName("zhang");
       session.setAttribute("user",user);
       //上一行代码，web容器会调用valueBound方法,
       // System.out.println("jsp页面中的session:"+session);
       // User user1=new User();
       //user1.setName("zhangfeng");
       //session.setAttribute("user",user1);
       //session.removeAttribute("user");
   %>

第三步、运行观察结果：
1. 启动tomcat，在IE中键入：http://localhost:8080/day18Listener1/sessionBing.jsp
2. 关闭tomcat可以看到：
……
钝化********************
……
此时打开C:\apache-tomcat-6.0.20\work\Catalina\localhost\day18Listener1
可以看到钝化的结果：将session写入到了硬盘上面！！！
3. 启动tomcat:
……
信息: Starting Servlet Engine: Apache Tomcat/6.0.20
活化********************
……
信息: Server startup in 2072 ms
C:\apache-tomcat-6.0.20\work\Catalina\localhost\day18Listener1中的session文件消失：读入到了文件中了！（活化的结果）

注意:sessionBing.jsp中注释部分一定要注释，否则出错！！！
实例：网站的在线人数统计
javaee学习之路(七)Servlet监听器
javaee学习之路(七)Servlet监听器
javaee学习之路(七)Servlet监听器
1、User.java

package cn.itcast.bean;
/**
 * 用户类
 * @author Administrator
 *
 */
public class User {
private String username;
private String psw;
    ……
}

2、SessionUser.java

package cn.itcast.bean;
import *;
public class SessionUser extends User implements HttpSessionBindingListener{
private String ip;//登录用户和游客的IP
public String getIp() {
return ip;
    }
public void setIp(String ip) {
this.ip = ip;
    }
public void valueBound(HttpSessionBindingEvent event) {
//System.out.println("valueBound******************");
//这里的this(SessionUser对象)与login.jsp中新建的SessionUser一样
//1.获取session
        HttpSession session=event.getSession();
//2.获取sessionid
        String sessionid=session.getId();
//3.获取上下文对象
        ServletContext sc=session.getServletContext();
//4.从上下文对象中获取onlinemap(Map)
        Map<String,SessionUser> map = (Map)sc.getAttribute("onlinemap");
//5.放置sessionUser对象到Map中
        map.put(sessionid, this);
    }
public void valueUnbound(HttpSessionBindingEvent event) {}
}

3、MyServletContextListener.java

package cn.itcast.listener;
import *;
/*
 * 上下文监听
 */
public class MyServletContextListener implements ServletContextListener {
/**
 * 服务器启动时调用，执行顺序最先执行
 */
public void contextInitialized(ServletContextEvent sce) {
//System.out.println("contextInitialized");
//初始化集合
        Map<String,SessionUser> map=new HashMap<String,SessionUser>();
//获取servletContext
        ServletContext sc=sce.getServletContext();
if(sc!=null){
//System.out.println("map***********************");
            sc.setAttribute("onlinemap", map);
        }
    }
public void contextDestroyed(ServletContextEvent sce) {
    }
}

4、login.jsp

<%
 //获取客户端IP
String ip=request.getRemoteAddr();
 System.out.println(ip);
 //创建SessionUser对象
 SessionUser sessionUser=new SessionUser();
 sessionUser.setIp(ip);
 //用户名为空null
 //放置到Session中
 session.setAttribute("userInfo",sessionUser);
 %>
<body>
<h2>登陆页面游客可以访问login.jsp</h2>
<form action="${pageContext.request.contextPath}/servlet/LoginServlet" method="post">
           用户名：<input type="text" name="username"/>
           密码：<input type="password" name="psw"/>
<input type="submit" value="登录"/>
</form>
<hr>
<a href="">中俄建交十周年</a>
</body>
</html>

5、onlinenum.jsp
……

 <body>
  显示注册用户信息:<br/>
    <c:forEach items="${applicationScope.onlinemap}" var="sessionUser">
       <c:if test="${sessionUser.value.username!=null}">
${sessionUser.value.ip}~~~~~~~${sessionUser.value.username}~~~~~~
         <a href="${pageContext.request.contextPath}/servlet/RemoveServlet?sessionid=${sessionUser.key}">转为游客</a><br/>
       </c:if>
    </c:forEach>    
  <br/> <br/>

 显示游客信息:<br/>
    <c:forEach items="${applicationScope.onlinemap}" var="sessionUser">
       <c:if test="${sessionUser.value.username==null}">
${sessionUser.value.ip}~~~~~~~${sessionUser.value.username}<br/>
       </c:if>
    </c:forEach>

……
6、LoginServlet.java

package cn.itcast.web;
import *;
public class LoginServlet extends HttpServlet {
public void doGet(HttpServletRequest request, HttpServletResponse response) throws Exception {
        request.setCharacterEncoding("UTF-8");
        response.setCharacterEncoding("UTF-8");
        response.setContentType("text/html;charset=UTF-8");
        PrintWriter out = response.getWriter();
        String path="";
        HttpSession session=request.getSession(false);
//<input type="text" name="username"/>
        String username=request.getParameter("username");
if(session!=null){
//session.setAttribute("userInfo",sessionUser);
            User user=(User)session.getAttribute("userInfo");
            user.setUsername(username);
            path="/WEB-INF/jsp/title.jsp";
        }
        request.getRequestDispatcher(path).forward(request, response);
    }
public void doPost(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
        doGet(request, response);
    }
}

7、title.jsp
……

<body>
<h2>只有登录用户才能看到此页面</h2>
<hr>
<a href="">中俄反恐演习顺利结束！</a>

……
8、RemoveServlet.java

package cn.itcast.web;
import *;
public class RemoveServlet extends HttpServlet {
public void doGet(HttpServletRequest request, HttpServletResponse response) throws Exception {
        request.setCharacterEncoding("UTF-8");
        response.setCharacterEncoding("UTF-8");
        response.setContentType("text/html;charset=UTF-8");
        PrintWriter out = response.getWriter();
//获取Sessionid
        String sessionid=request.getParameter("sessionid");
//获取ServletContext对象
        ServletContext sc=this.getServletContext();
//从ServletContext中获取集合
        Map<String,SessionUser> onlinemap=(Map<String,SessionUser>)sc.getAttribute("onlinemap");
//从集合中找出sessionUser对象
        SessionUser sessionUser=onlinemap.get(sessionid);
//更改用户名为null
        sessionUser.setUsername(null);
    }
public void doPost(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
        doGet(request, response);
    }
}

9、MyHttpSessionListener.java

package cn.itcast.listener;
import *;
public class MyHttpSessionListener implements HttpSessionListener {
public void sessionCreated(HttpSessionEvent se) {
    }
/**web容器自动调用
 * 当session过期后或消亡的时候，才能执行该方法
 */
public void sessionDestroyed(HttpSessionEvent se) {
//1.获取session
        HttpSession session=se.getSession();
//2.获取sessionid
        String sessionid=session.getId();
//3.获取上下文
        ServletContext sc=session.getServletContext();
//4.获取集合
        Map<String,SessionUser> onlinemap=(Map<String,SessionUser>)sc.getAttribute("onlinemap");
//5.从集合中清除
        onlinemap.remove(sessionid);
//6.session中userInfo也 删除
        session.removeAttribute("userInfo");
    }
}

10、web.xml
……

<listener>
<listener-class>cn.itcast.listener.MyHttpSessionListener</listener-class>
</listener> 
<listener>
<listener-class>cn.itcast.listener.MyServletContextListener</listener-class>
</listener>

……
11.观察效果：
在浏览器中开多个窗口，访问：http://localhost:8080/day18onlineCount/login.jsp
然后在浏览器中键入：http://localhost:8080/day18onlineCount/onlinenum.jsp 即可进行后台管理
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