1. 監聽器

時間 2019-12-06

標籤監聽器简体版

原文原文鏈接

1. 什麼是監聽器html

監聽器也叫Listener，是Servlet的監聽器，它能夠監聽客戶端的請求、服務端的操做等。經過監聽器，能夠自動激發一些操做，好比監聽在線的用戶的數量。
所謂的監聽器，是指對整個web環境的監聽，當被見識的對象發生變化時，當即調用相應的方法進行處理。

2.監聽器最多見的應用場景：java

Java SE GUI編程；
Android 手機開發編程。

3. 監聽器術語web

事件源：被監聽對象。(目標對象)；
監聽器對象：用於監聽"事件源"的對象；
註冊(綁定)：將"監聽器對象"註冊給"事件源"。當"事件源"發生某些行爲時，監聽對象將被執行；
事件：事件源行爲的稱呼；
事件對象：在「監聽器對象」中得到「事件源」。

4. 監聽器的編寫流程編程

編寫監聽器實現類，須要實現指定的接口；
在web.xml文件配置監聽器(部分監聽不須要配置);

5. JavaEE規範規定了8個監聽器接口用於監聽不一樣的web對象服務器

監聽域對象建立與銷燬
監聽域對象屬性變動(添加、替換、刪除)
監聽session做用域特殊Javabean

6. 域對象監聽器session

ServletRequestListener
HttpSessionListener
ServletContext

7. 域對象屬性監聽器（app

4大域對象：ServletContext 、Request、Session、PageContextide

7.1 做用域屬性操做編碼

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

7.2 域對象屬性變動監聽器

ServletRequestAttributeListener
HttpSessionAttributeListener
ServletContextAttributeListener

　　7.3 特殊的Javabean監聽器(Session做用域）

HttpSessionBindingListener
HttpSessionActivationListener（鈍化和活化)

前面六個監聽器須要在web.xml中配置，最後的兩個監聽器不須要再web.xml中配置

8. 實例

　　8.1 ServletRequestListener

　　監聽request對象建立或銷燬，其中request對象的特色以下：

類型：Javax.servlet.http.HttpServletRequest
描述：來自客戶端的請求經Servlet容器處理後，由request對象進行封裝。注：客戶端和服務器的一次通訊就是一次請求（發送請求或獲得相應）。
做用域：request。說明，此次請求結束後，它的生命週期就結束了。
舉例：
- 建立ServletRequestListener實現類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對象的構造方法");
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對象銷燬了！");
19     }
20 
21 }

MyServletRequestListener

- 在web.xml文件配置監聽器。

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

web.xml

服務器啓動就先構造了request對象，而後每一個頁面請求都會觸發

MyServletRequestListener.requestInitialized(ServletRequestEvent sre)方法和

MyServletRequestListener.requestDestroyed(ServletRequestEvent sre)方法

　　8.2 HttpSessionListener

類型：Javax.servlet.http.HttpSession
描述：表示一個會話，用來保存用戶信息，以便跟蹤每一個用戶的狀態。（不要用來保存業務數據，request）
定義：是指在一段時間內客戶端和服務器之間的一連串的相關的交互過程。
做用域：session。
舉例
- 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對象構造方法");
12     }
13 
14     public void sessionCreated(HttpSessionEvent arg0) {
15         System.out.println("建立session對象");
16     }
17 
18     public void sessionDestroyed(HttpSessionEvent arg0) {
19         System.out.println("銷燬session對象");
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("服務器已經存在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文件中配置監聽器

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

web.xml

　　8.3 servletContextListener

類型：javax.servlet.ServletContext
描述：從servlet配置對象得到的servlet上下文
做用域：application
這個對象的生命週期是最長的。服務器啓動的時候就會建立application對象。從服務器存在到服務器終止，都一直存在，且只保留一個對象，全部用戶共享一個application。不是很經常使用。
舉例：
- 建立MyServletContextListener監聽器

 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對象構建！");
10     }
11 
12     public void contextInitialized(ServletContextEvent sce) {
13         System.out.println("ServletContext對象初始化！");
14     }
15     
16     public void contextDestroyed(ServletContextEvent sce) {
17         System.out.println("ServletContext對象銷燬！");
18     }
19 }

MyServletContextListener

- 在web.xml文件中配置監聽器

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

web.xml

./shutdown.sh 　　//中止Apache服務

　　8.4 ServletRequestAttributeListener

編寫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         // 編碼
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

編寫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對象添加了新屬性！");
15     }
16 
17     public void attributeRemoved(ServletRequestAttributeEvent sre) {
18         System.out.println("reqeust對象移除了屬性！");
19     }
20 
21     public void attributeReplaced(ServletRequestAttributeEvent sre) {
22         System.out.println("request修改了屬性！");
23     }
24 
25 }

MyRequestAttribute

配置web.xml。

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

web.xml

　　8.5 HttpSessionAttributeListener

編寫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

編寫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 添加了新屬性！");
15     }
16 
17     public void attributeRemoved(HttpSessionBindingEvent hbe) {
18         System.out.println("sessionAttributeListener 移除了屬性！");
19     }
20 
21     public void attributeReplaced(HttpSessionBindingEvent hbe) {
22         System.out.println("sessionAttributeListener 修改了屬性！");
23     }
24 
25 }

MySessionAttributeListener

配置web.xml

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

web.xml

注：設置session引起request屬性修改監聽器

　　8.6 ServletContextAttributeListener

編寫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

編寫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對象構造！");
11     }
12 
13     public void attributeAdded(ServletContextAttributeEvent sce) {
14         System.out.println("ServletContextAttributeListener對象添加屬性！");
15     }
16 
17     public void attributeReplaced(ServletContextAttributeEvent sce) {
18         System.out.println("ServletContextAttributeListener對象修改屬性！");
19     }
20 
21     public void attributeRemoved(ServletContextAttributeEvent sce) {
22         System.out.println("ServletContextAttributeListener對象移除屬性！");
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

編寫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

編寫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對象初始化");
11     }
12 
13     public void valueBound(HttpSessionBindingEvent hse) {
14         System.out.println("httpSessionBindingListening對象綁定！");
15     }
16 
17     public void valueUnbound(HttpSessionBindingEvent hse) {
18         System.out.println("httpSessionBindingListening對象解綁！");
19     }
20 
21 }

MyHttpSessionBindingListener

　　8.8 HttpSessionActivationListener

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

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