1. 监听器

时间 2019-12-06

标签监听器繁體版

原文原文链接

1. 什么是监听器html

监听器也叫Listener，是Servlet的监听器，它能够监听客户端的请求、服务端的操做等。经过监听器，能够自动激发一些操做，好比监听在线的用户的数量。
所谓的监听器，是指对整个web环境的监听，当被见识的对象发生变化时，当即调用相应的方法进行处理。

2.监听器最多见的应用场景：java

Java SE GUI编程；
Android 手机开发编程。

3. 监听器术语web

事件源：被监听对象。(目标对象)；
监听器对象：用于监听"事件源"的对象；
注册(绑定)：将"监听器对象"注册给"事件源"。当"事件源"发生某些行为时，监听对象将被执行；
事件：事件源行为的称呼；
事件对象：在“监听器对象”中得到“事件源”。

4. 监听器的编写流程编程

编写监听器实现类，须要实现指定的接口；
在web.xml文件配置监听器(部分监听不须要配置);

5. JavaEE规范规定了8个监听器接口用于监听不一样的web对象服务器

监听域对象建立与销毁
监听域对象属性变动(添加、替换、删除)
监听session做用域特殊Javabean

6. 域对象监听器session

ServletRequestListener
HttpSessionListener
ServletContext

7. 域对象属性监听器（app

4大域对象：ServletContext 、Request、Session、PageContextide

7.1 做用域属性操做编码

　　setAttribute(k,v)　　　　getAttribute(k)　　　　removeAttribute(k)spa

7.2 域对象属性变动监听器

ServletRequestAttributeListener
HttpSessionAttributeListener
ServletContextAttributeListener

　　7.3 特殊的Javabean监听器(Session做用域）

HttpSessionBindingListener
HttpSessionActivationListener（钝化和活化)

前面六个监听器须要在web.xml中配置，最后的两个监听器不须要再web.xml中配置

8. 实例

　　8.1 ServletRequestListener

　　监听request对象建立或销毁，其中request对象的特色以下：

类型：Javax.servlet.http.HttpServletRequest
描述：来自客户端的请求经Servlet容器处理后，由request对象进行封装。注：客户端和服务器的一次通讯就是一次请求（发送请求或获得相应）。
做用域：request。说明，此次请求结束后，它的生命周期就结束了。
举例：
- 建立ServletRequestListener实现类MyServletRequestListener；

 1 package com.eagle.listener;
 2 
 3 import javax.servlet.ServletRequestEvent;
 4 import javax.servlet.ServletRequestListener;
 5 
 6 public class MyServletRequestListener implements ServletRequestListener {
 7 
 8     public MyServletRequestListener() {
 9         super();
10         System.out.println("request对象的构造方法");
11     }
12 
13     public void requestInitialized(ServletRequestEvent sre) {
14         System.out.println("request建立了！");
15     }
16 
17     public void requestDestroyed(ServletRequestEvent sre) {
18         System.out.println("request对象销毁了！");
19     }
20 
21 }

MyServletRequestListener

- 在web.xml文件配置监听器。

1   <listener>
2     <listener-class>com.eagle.listener.MyServletRequestListener</listener-class>
3   </listener>

web.xml

服务器启动就先构造了request对象，而后每一个页面请求都会触发

MyServletRequestListener.requestInitialized(ServletRequestEvent sre)方法和

MyServletRequestListener.requestDestroyed(ServletRequestEvent sre)方法

　　8.2 HttpSessionListener

类型：Javax.servlet.http.HttpSession
描述：表示一个会话，用来保存用户信息，以便跟踪每一个用户的状态。（不要用来保存业务数据，request）
定义：是指在一段时间内客户端和服务器之间的一连串的相关的交互过程。
做用域：session。
举例
- 建立MyHttpSessionListener

 1 package com.eagle.listener;
 2 
 3 import javax.servlet.http.HttpSessionEvent;
 4 import javax.servlet.http.HttpSessionListener;
 5 
 6 public class MyHttpSessionListener implements HttpSessionListener {
 7 
 8     public MyHttpSessionListener() {
 9 
10         super();
11         System.out.println("session对象构造方法");
12     }
13 
14     public void sessionCreated(HttpSessionEvent arg0) {
15         System.out.println("建立session对象");
16     }
17 
18     public void sessionDestroyed(HttpSessionEvent arg0) {
19         System.out.println("销毁session对象");
20     }
21 
22 }

MyHttpSessionListener

- 建立servlet CreateSession

 1 package com.eagle.web;
 2 
 3 import java.io.IOException;
 4 import javax.servlet.ServletException;
 5 import javax.servlet.http.HttpServlet;
 6 import javax.servlet.http.HttpServletRequest;
 7 import javax.servlet.http.HttpServletResponse;
 8 import javax.servlet.http.HttpSession;
 9 
10 public class CreateSession extends HttpServlet {
11 
12     private static final long serialVersionUID = 1L;
13 
14     public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
15         request.setCharacterEncoding("utf-8");
16         response.setContentType("text/html;charset=utf-8"); 
17         HttpSession httpSession = request.getSession();
18         httpSession.setMaxInactiveInterval(10);
19         String id = httpSession.getId();
20         if(httpSession.isNew()) {
21             httpSession.setAttribute("name", "狼");        
22             String name = (String) httpSession.getAttribute("name");
23             response.getWriter().print("恭喜session建立成功，sessionid="+id+";name="+name);
24         }else {
25             String name = (String) httpSession.getAttribute("name");
26             response.getWriter().print("服务器已经存在session了，sessionid="+id+";name="+name);
27         }
28     }
29 
30     public void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
31         doGet(request, response);
32     }
33 }

CreateSession

- web.xml文件中配置监听器

1   <listener>
2     <listener-class>com.eagle.listener.MyHttpSessionListener</listener-class>
3   </listener>

web.xml

　　8.3 servletContextListener

类型：javax.servlet.ServletContext
描述：从servlet配置对象得到的servlet上下文
做用域：application
这个对象的生命周期是最长的。服务器启动的时候就会建立application对象。从服务器存在到服务器终止，都一直存在，且只保留一个对象，全部用户共享一个application。不是很经常使用。
举例：
- 建立MyServletContextListener监听器

 1 package com.eagle.listener;
 2 
 3 import javax.servlet.ServletContextEvent;
 4 import javax.servlet.ServletContextListener;
 5 
 6 public class MyServletContextListener implements ServletContextListener {
 7 
 8     public MyServletContextListener() {
 9         System.out.println("ServletContext对象构建！");
10     }
11 
12     public void contextInitialized(ServletContextEvent sce) {
13         System.out.println("ServletContext对象初始化！");
14     }
15     
16     public void contextDestroyed(ServletContextEvent sce) {
17         System.out.println("ServletContext对象销毁！");
18     }
19 }

MyServletContextListener

- 在web.xml文件中配置监听器

1  <listener>
2       <listener-class>com.eagle.listener.MyServletContextListener</listener-class>
3   </listener>

web.xml

./shutdown.sh 　　//中止Apache服务

　　8.4 ServletRequestAttributeListener

编写servlet 　　ServletRequestAttribute；

 1 package com.eagle.web;
 2 
 3 import java.io.IOException;
 4 import javax.servlet.ServletException;
 5 import javax.servlet.http.HttpServlet;
 6 import javax.servlet.http.HttpServletRequest;
 7 import javax.servlet.http.HttpServletResponse;
 8 
 9 public class ServletRequestAttribute extends HttpServlet {
10 
11     private static final long serialVersionUID = 1L;
12 
13     public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
14         // 编码
15         request.setCharacterEncoding("utf-8");
16         response.setContentType("text/html;charset=utf-8");
17         request.setAttribute("name", "first");
18         String name = (String) request.getAttribute("name");
19         response.getWriter().print("name="+name);
20         request.removeAttribute("name");
21     }
22 
23     public void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
24         doGet(request, response);
25     }
26 }

ServletRequestAttribute

编写ServletRequestAttributeListener；

 1 package com.eagle.listener;
 2 
 3 import javax.servlet.ServletRequestAttributeEvent;
 4 import javax.servlet.ServletRequestAttributeListener;
 5 
 6 public class MyRequestAttribute implements ServletRequestAttributeListener {
 7 
 8     public MyRequestAttribute() {
 9         super();
10         System.out.println("requestattribute初始化！");
11     }
12 
13     public void attributeAdded(ServletRequestAttributeEvent sre) {
14         System.out.println("request对象添加了新属性！");
15     }
16 
17     public void attributeRemoved(ServletRequestAttributeEvent sre) {
18         System.out.println("reqeust对象移除了属性！");
19     }
20 
21     public void attributeReplaced(ServletRequestAttributeEvent sre) {
22         System.out.println("request修改了属性！");
23     }
24 
25 }

MyRequestAttribute

配置web.xml。

<listener>
    <listener-class>com.eagle.listener.MyRequestAttribute</listener-class>
  </listener>

web.xml

　　8.5 HttpSessionAttributeListener

编写servlet

 1 package com.eagle.web;
 2 
 3 import java.io.IOException;
 4 import javax.servlet.ServletException;
 5 import javax.servlet.http.HttpServlet;
 6 import javax.servlet.http.HttpServletRequest;
 7 import javax.servlet.http.HttpServletResponse;
 8 import javax.servlet.http.HttpSession;
 9 
10 public class SessionAttribute extends HttpServlet {
11 
12     private static final long serialVersionUID = 1L;
13 
14     public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
15         HttpSession session = request.getSession();
16         session.setAttribute("name", "first");
17         session.setAttribute("name", "second");
18         session.getAttribute("name");
19         session.removeAttribute("name");
20         response.getWriter().write("hello haohao...");
21     }
22 
23     public void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
24         doGet(request, response);
25     }
26 }

SessionAttribute

编写HttpSessionAttributeListener

 1 package com.eagle.listener;
 2 
 3 import javax.servlet.http.HttpSessionAttributeListener;
 4 import javax.servlet.http.HttpSessionBindingEvent;
 5 
 6 public class MySessionAttributeListener implements HttpSessionAttributeListener {
 7 
 8     public MySessionAttributeListener() {
 9         super();
10         System.out.println("sessionAttributeListener初始化！");
11     }
12 
13     public void attributeAdded(HttpSessionBindingEvent hbe) {
14         System.out.println("sessionAttributeListener 添加了新属性！");
15     }
16 
17     public void attributeRemoved(HttpSessionBindingEvent hbe) {
18         System.out.println("sessionAttributeListener 移除了属性！");
19     }
20 
21     public void attributeReplaced(HttpSessionBindingEvent hbe) {
22         System.out.println("sessionAttributeListener 修改了属性！");
23     }
24 
25 }

MySessionAttributeListener

配置web.xml

1   <listener>
2     <listener-class>com.eagle.listener.MySessionAttributeListener</listener-class>
3   </listener>

web.xml

注：设置session引起request属性修改监听器

　　8.6 ServletContextAttributeListener

编写servlet

 1 package com.eagle.web;
 2 
 3 import java.io.IOException;
 4 
 5 import javax.servlet.ServletContext;
 6 import javax.servlet.ServletException;
 7 import javax.servlet.http.HttpServlet;
 8 import javax.servlet.http.HttpServletRequest;
 9 import javax.servlet.http.HttpServletResponse;
10 
11 public class ServletContextAttribute extends HttpServlet {
12 
13     private static final long serialVersionUID = 1L;
14 
15     public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
16         ServletContext servletContext = request.getServletContext();
17         servletContext.setAttribute("name", "first");
18         servletContext.setAttribute("name", "second");
19         servletContext.removeAttribute("name");
20         response.getWriter().write("hello haohao...");
21     }
22 
23     public void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
24         doGet(request, response);
25     }
26 }

ServletContextAttribute

编写ServletContextAttributeListener

 1 package com.eagle.listener;
 2 
 3 import javax.servlet.ServletContextAttributeEvent;
 4 import javax.servlet.ServletContextAttributeListener;
 5 
 6 public class MyServletContextAttributeListener implements ServletContextAttributeListener {
 7 
 8     public MyServletContextAttributeListener() {
 9         super();
10         System.out.println("ServletContextAttributeListener对象构造！");
11     }
12 
13     public void attributeAdded(ServletContextAttributeEvent sce) {
14         System.out.println("ServletContextAttributeListener对象添加属性！");
15     }
16 
17     public void attributeReplaced(ServletContextAttributeEvent sce) {
18         System.out.println("ServletContextAttributeListener对象修改属性！");
19     }
20 
21     public void attributeRemoved(ServletContextAttributeEvent sce) {
22         System.out.println("ServletContextAttributeListener对象移除属性！");
23     }
24 }

MyServletContextAttributeListener

配置web.xml

1   <listener>
2     <listener-class>com.eagle.listener.MyServletContextAttributeListener</listener-class>
3   </listener>

web.xml

　　8.7 HttpSessionBindingListener

编写servlet

 1 package com.eagle.web;
 2 
 3 import java.io.IOException;
 4 import javax.servlet.ServletException;
 5 import javax.servlet.http.HttpServlet;
 6 import javax.servlet.http.HttpServletRequest;
 7 import javax.servlet.http.HttpServletResponse;
 8 import javax.servlet.http.HttpSession;
 9 
10 import com.eagle.listener.MyHttpSessionBindingListener;
11 
12 public class ServletHttpSessionBindingListener extends HttpServlet {
13 
14     private static final long serialVersionUID = 1L;
15 
16     public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
17         MyHttpSessionBindingListener ml = new MyHttpSessionBindingListener();
18         HttpSession hs = request.getSession();
19         hs.setAttribute("ml", ml);
20         hs.invalidate();
21         response.getWriter().write("hello haohao...");
22     }
23 
24     public void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
25         doGet(request, response);
26     }
27 }

ServletHttpSessionBindingListener

编写HttpSessionBindingListener

 1 package com.eagle.listener;
 2 
 3 import javax.servlet.http.HttpSessionBindingEvent;
 4 import javax.servlet.http.HttpSessionBindingListener;
 5 
 6 public class MyHttpSessionBindingListener implements HttpSessionBindingListener {
 7 
 8     public MyHttpSessionBindingListener() {
 9         super();
10         System.out.println("httpSessionBindingListening对象初始化");
11     }
12 
13     public void valueBound(HttpSessionBindingEvent hse) {
14         System.out.println("httpSessionBindingListening对象绑定！");
15     }
16 
17     public void valueUnbound(HttpSessionBindingEvent hse) {
18         System.out.println("httpSessionBindingListening对象解绑！");
19     }
20 
21 }

MyHttpSessionBindingListener

　　8.8 HttpSessionActivationListener

　　参照：https://www.cnblogs.com/eaglesour/p/9474540.html