《Head First Servlets & JSP》-6-会话管理-listener etc. demo

工程结构

上下文参数示例

示例程序展示了如何从上下文读取参数，并在上下文监听器中生成属性对象和在上下文中设置属性。

  • 建立一个简单的JavaBean对象作为属性：Dog.java
  1. package com.example.entities;
  3. /**
  4.  * Created by LTN on 2016/11/2.
  5.  */
  6. public class Dog {
  7.     private String breed;
  9.     public Dog(String breed) {
  10.         this.breed = breed;
  11.     }
  13.     public String getBreed() {
  14.         return breed;
  15.     }
  17. }
  • 建立一个servlet上下文监听器DogServletContextListener.java
  1. package com.example.listener;
  3. import com.example.entities.Dog;
  5. import javax.servlet.ServletContext;
  6. import javax.servlet.ServletContextEvent;
  8. /**
  9.  * Created by LTN on 2016/11/2.
  10.  */
  11. public class DogServletContextListener implements javax.servlet.ServletContextListener {
  12.     public void contextInitialized(ServletContextEvent event) {
  13.         ServletContext sc = event.getServletContext();
  14.         String dogBreed = sc.getInitParameter("breed");
  15.         Dog d = new Dog(dogBreed);
  16.         sc.setAttribute("dog", d);
  17.     }
  19.     public void contextDestroyed(ServletContextEvent event) {
  20.         //do nothing.
  21.     }
  22. }
  • 建立Servlet进行测试ContextListenerTester.java
  1. package com.example.servlet;
  3. import com.example.entities.Dog;
  5. import javax.servlet.ServletException;
  6. import javax.servlet.http.HttpServlet;
  7. import javax.servlet.http.HttpServletRequest;
  8. import javax.servlet.http.HttpServletResponse;
  9. import java.io.IOException;
  10. import java.io.PrintWriter;
  12. /**
  13.  * Created by LTN on 2016/11/2.
  14.  */
  15. public class ContextListenerTester extends HttpServlet {
  16.     public void doGet(HttpServletRequest request, HttpServletResponse response) throws IOException, ServletException {
  17.         response.setContentType("text/html");
  18.         PrintWriter out = response.getWriter();
  19.         out.println("test context attributes set by listener<br>");
  20.         out.println("<br>");
  22.         Dog dog = (Dog) getServletContext().getAttribute("dog");
  23.         out.println("Dog's breed is: " + dog.getBreed());
  24.     }
  25. }
  • 在DD（web.xml）中配置上下文参数、监听器和servlet映射关系
  1. <web-app>
  3.   <display-name>Archetype Created Web Application</display-name>
  5.   <context-param>
  6.     <param-name>breed</param-name>
  7.     <param-value>Great Dane</param-value>
  8.   </context-param>
  10.   <servlet>
  11.     <servlet-name>ListenerTester</servlet-name>
  12.     <servlet-class>com.example.servlet.ContextListenerTester</servlet-class>
  13.   </servlet>
  14.   <servlet-mapping>
  15.     <servlet-name>ListenerTester</servlet-name>
  16.     <url-pattern>/ListenTest.do</url-pattern>
  17.   </servlet-mapping>
  19.   <listener>
  20.     <listener-class>com.example.listener.DogServletContextListener</listener-class>
  21.   </listener>
  23. </web-app>
  1. test context attributes set by listener
  3. Dog's breed is: Great Dane

Session属性监听器

使用Session属性监听器对Session中属性进行监听，当Session属性发生增加、删除或改变时，会被该监听器捕捉。

  • 创建一个Session属性监听类DogSessionAttributeListener.java
  1. package com.example.listener;
  3. import javax.servlet.http.HttpSessionAttributeListener;
  4. import javax.servlet.http.HttpSessionBindingEvent;
  6. /**
  7.  * Created by LTN on 2016/11/2.
  8.  */
  9. public class DogSessionAttributeListener implements HttpSessionAttributeListener {
  10.     public void attributeAdded(HttpSessionBindingEvent event) {
  11.         String name = event.getName();
  12.         Object value = event.getValue();
  14.         System.out.println("Attribute added: " + name + ": " + value);
  15.     }
  17.     public void attributeRemoved(HttpSessionBindingEvent event) {
  18.         String name = event.getName();
  19.         Object value = event.getValue();
  21.         System.out.println("Attribute removed: " + name + ": " + value);
  22.     }
  24.     public void attributeReplaced(HttpSessionBindingEvent event) {
  25.         String name = event.getName();
  26.         Object value = event.getValue();
  28.         System.out.println("Attribute replaced: " + name + ": " + value);
  29.     }
  30. }
  • 建立一个Servlet测试类AttributeListenerTester.java
  1. package com.example.servlet;
  3. import javax.servlet.ServletException;
  4. import javax.servlet.http.HttpServlet;
  5. import javax.servlet.http.HttpServletRequest;
  6. import javax.servlet.http.HttpServletResponse;
  7. import javax.servlet.http.HttpSession;
  8. import java.io.IOException;
  10. /**
  11.  * Created by LTN on 2016/11/2.
  12.  */
  13. public class AttributeListenerTester extends HttpServlet {
  14.     private static int labelCounter = 0;
  16.     public void doGet(HttpServletRequest request, HttpServletResponse response) throws IOException, ServletException {
  17.         HttpSession session = request.getSession();
  18.         session.setAttribute("label", "label" + labelCounter++);
  19.     }
  20. }
  • 在DD中配置servlet和listener
  1. <servlet>
  2.   <servlet-name>AttributeListenTester</servlet-name>
  3.   <servlet-class>com.example.servlet.AttributeListenerTester</servlet-class>
  4. </servlet>
  5. <servlet-mapping>
  6.   <servlet-name>AttributeListenTester</servlet-name>
  7.   <url-pattern>/AttributeListenerTest.do</url-pattern>
  8. </servlet-mapping>
  10. <listener>
  11.   <listener-class>com.example.listener.DogSessionAttributeListener</listener-class>
  12. </listener>
  1. Attribute added: label: label0

然后连续三次刷新，后台依次打印：

  1. Attribute replaced: label: label0
  2. Attribute replaced: label: label1
  3. Attribute replaced: label: label2

注意，event.getName()和event.getValue()都是获取该事件之前的session属性的值。

统计全局活动的对话

使用HttpSessionListener进行全局活动会话的统计，类似统计在线人数功能。

  • 建立全局活动会话监听器
  1. package com.example.listener;
  3. import javax.servlet.http.HttpSessionEvent;
  4. import javax.servlet.http.HttpSessionListener;
  6. /**
  7.  * Created by LTN on 2016/11/2.
  8.  */
  9. public class GlobalCounterListener implements HttpSessionListener {
  10.     static private int activeSessions;
  12.     public static int getActiveSessions() {
  13.         return activeSessions;
  14.     }
  16.     public void sessionCreated(HttpSessionEvent event) {
  17.         activeSessions++;
  18.     }
  20.     public void sessionDestroyed(HttpSessionEvent event) {
  21.         activeSessions--;
  22.     }
  23. }
  • 建立servlet测试类GlobalCounterTester.java
  1. package com.example.servlet;
  3. import com.example.listener.GlobalCounterListener;
  5. import javax.servlet.ServletException;
  6. import javax.servlet.http.HttpServlet;
  7. import javax.servlet.http.HttpServletRequest;
  8. import javax.servlet.http.HttpServletResponse;
  9. import javax.servlet.http.HttpSession;
  10. import java.io.IOException;
  11. import java.io.PrintWriter;
  13. /**
  14.  * Created by LTN on 2016/11/2.
  15.  */
  16. public class GlobalCounterTester extends HttpServlet {
  17.     public void doGet(HttpServletRequest request, HttpServletResponse response) throws IOException, ServletException {
  18.         PrintWriter out = response.getWriter();
  20.         HttpSession session = request.getSession();
  21.         session.setAttribute("name","counter");
  22.         String name=(String)session.getAttribute("name");
  24.         int activeSessions= GlobalCounterListener.getActiveSessions();
  26.         out.println("name: "+name);
  27.         out.println("activeSessions: "+activeSessions);
  28.     }
  29. }
  • 在DD中配置servlet和listener
  1. <servlet>
  2.   <servlet-name>SessionCounterTester</servlet-name>
  3.   <servlet-class>com.example.servlet.GlobalCounterTester</servlet-class>
  4. </servlet>
  5. <servlet-mapping>
  6.   <servlet-name>SessionCounterTester</servlet-name>
  7.   <url-pattern>/CounterTest.do</url-pattern>
  8. </servlet-mapping>
  10. <listener>
  11.   <listener-class>com.example.listener.GlobalCounterListener</listener-class>
  12. </listener>
  1. name: counter
  2. activeSessions: 1

换一个浏览器，输入地址，会显示activeSessions数值递增。

注意，同一个浏览器开新标签不能使得session个数增加；关闭当前浏览器再接着启动，也不能。

属性绑定监听器

当属性对象被加入session或从session删除使，对象本身可以知道。

  • 建立Session binding监听器Dog.java，该类继承了HttpSessionBindingListener，并实现valueBound和valueUnbound方法。
  1. package com.example.entities;
  3. import javax.servlet.http.HttpSessionBindingEvent;
  4. import javax.servlet.http.HttpSessionBindingListener;
  6. /**
  7.  * Created by LTN on 2016/11/2.
  8.  */
  9. public class Dog implements HttpSessionBindingListener {
  10.     private String breed;
  12.     public Dog(String breed) {
  13.         this.breed = breed;
  14.     }
  16.     public String getBreed() {
  17.         return breed;
  18.     }
  20.     public void valueBound(HttpSessionBindingEvent event) {
  21.         System.out.println("I am a dog, i know i am in a conversation now.");
  22.     }
  24.     public void valueUnbound(HttpSessionBindingEvent event) {
  25.         System.out.println("I am a dog, i know i am leaving a conversation now.");
  26.     }
  27. }
  • 建立servlet测试类EntityBindingTester.java
  1. package com.example.servlet;
  3. import com.example.entities.Dog;
  5. import javax.servlet.ServletException;
  6. import javax.servlet.http.HttpServlet;
  7. import javax.servlet.http.HttpServletRequest;
  8. import javax.servlet.http.HttpServletResponse;
  9. import javax.servlet.http.HttpSession;
  10. import java.io.IOException;
  12. /**
  13.  * Created by LTN on 2016/11/2.
  14.  */
  15. public class EntityBindingTester extends HttpServlet {
  16.     public void doGet(HttpServletRequest request, HttpServletResponse response)throws IOException,ServletException {
  18.         Dog dog = (Dog) getServletContext().getAttribute("dog");
  20.         HttpSession session = request.getSession();
  21.         session.setAttribute("dog-binding",dog);
  22.         session.invalidate();
  23.     }
  25. }
  • 在DD中配置servlet，注意，属性Dog不用/能在DD中配置
  1. <servlet>
  2.   <servlet-name>ObjectBindingTester</servlet-name>
  3.   <servlet-class>com.example.servlet.EntityBindingTester</servlet-class>
  4. </servlet>
  5. <servlet-mapping>
  6.   <servlet-name>ObjectBindingTester</servlet-name>
  7.   <url-pattern>/ObjectBindingTest.do</url-pattern>
  8. </servlet-mapping>
  1. I am a dog, i know i am in a conversation now.
  2. Attribute added: dog-binding: com.example.entities.Dog@6dbba86e
  3. I am a dog, i know i am leaving a conversation now.
  4. Attribute removed: dog-binding: com.example.entities.Dog@6dbba86e

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    posted @ 2016-12-17 16:15  ITRoad  阅读(322)  评论(0)  编辑  收藏  举报