监听器相关知识汇总

监听器：监听对象的状态变化的组件。

监听器的相关要素：

1.事件源：被监听的对象，如request，session，servletContext

2.监听器：监听时间源对象，事件源对象的状态的变化都会触发监听器

3.注册监听器：将监听器与事件源进行绑定

4.响应行为：监听器监听到事件源的状态变化时，所触发的相关行为。

监听器的划分：

1.按照被监听的对象：

a.ServletRequest

b.HttpSession

c.ServletContext

2.按照监听的状态分：

a.监听域对象的创建与销毁

b.监听域对象的属性变化

监听器demo：

1.创建自定义监听器，实现ServletContextListener接口

public class MyServletContextListener implements ServletContextListener {    /**     * Default constructor.      */    public MyServletContextListener() {          }/**     * @see ServletContextListener#contextDestroyed(ServletContextEvent)     */    public void contextDestroyed(ServletContextEvent arg0)  {     System.out.println("contextDestroyed...");    }/**     * @see ServletContextListener#contextInitialized(ServletContextEvent)     */    public void contextInitialized(ServletContextEvent arg0)  {     System.out.println("contextInitialized...");    }}

2.在web.xml中配置监听器

  <listener>    <listener-class>com.milan.listener.MyServletContextListener</listener-class>  </listener>

ServletContextListener的主要作用：

a.对象的初始化，如加载数据库驱动，连接池等

b.配置文件的初始化，如spring的相关配置文件

c.定时器，如Timer/TimerTask

属性监听器demo：

创建自定义的属性监听器，实现ServletContextAttributeListener

public class MyServletContextAttributeListener implements ServletContextAttributeListener {    /**     * Default constructor.      */    public MyServletContextAttributeListener() {    }/**     * @see ServletContextAttributeListener#attributeAdded(ServletContextAttributeEvent)     */    public void attributeAdded(ServletContextAttributeEvent arg0)  {          System.out.println("attributeAdded...");         System.out.println("attributeAdded..."+arg0.getName());         System.out.println("attributeAdded..."+arg0.getValue());         }/**     * @see ServletContextAttributeListener#attributeRemoved(ServletContextAttributeEvent)     */    public void attributeRemoved(ServletContextAttributeEvent arg0)  {     System.out.println("attributeRemoved。。。");    }/**     * @see ServletContextAttributeListener#attributeReplaced(ServletContextAttributeEvent)     */    public void attributeReplaced(ServletContextAttributeEvent arg0)  {     System.out.println("attributeReplaced...");    }}

web.xml中配置属性监听器：

  <listener>    <listener-class>com.milan.listener.MyServletContextAttributeListener</listener-class>  </listener>

编写操作属性的Servlet：

public class TestServletContextAttributeListener extends HttpServlet {private static final long serialVersionUID = 1L;           /**     * @see HttpServlet#HttpServlet()     */    public TestServletContextAttributeListener() {        super();        // TODO Auto-generated constructor stub    }/** * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response) */protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {request.getServletContext().setAttribute("name", "kaka");request.getServletContext().setAttribute("name", "milan");request.getServletContext().removeAttribute("name");}/** * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response) */protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {// TODO Auto-generated method stubdoGet(request, response);}}

控制台输出如下：

attributeAdded...
attributeAdded...name
attributeAdded...kaka
attributeReplaced...name
attributeRemoved...name

绑定解绑监听器：此监听器无需再web.xml中进行配置

Person类上绑定HttpSessionBindingListener

public class Person implements HttpSessionBindingListener{private String username;private int age;public Person(String username, int age) {super();this.username = username;this.age = age;}@Overridepublic String toString() {return "Person [username=" + username + ", age=" + age + "]";}public String getUsername() {return username;}public void setUsername(String username) {this.username = username;}public int getAge() {return age;}public void setAge(int age) {this.age = age;}@Overridepublic void valueBound(HttpSessionBindingEvent arg0) {System.out.println("person:valueBound");}@Overridepublic void valueUnbound(HttpSessionBindingEvent arg0) {System.out.println("person:valueUnbound");}}

测试监听器的绑定与解绑的类TestPersonBinding

public class TestPersonBinding extends HttpServlet {private static final long serialVersionUID = 1L;           /**     * @see HttpServlet#HttpServlet()     */    public TestPersonBinding() {        super();        // TODO Auto-generated constructor stub    }/** * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response) */protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {HttpSession session = request.getSession();Person p = new Person("milan", 1988);session.setAttribute("person", p);session.removeAttribute("person");}/** * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response) */protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {// TODO Auto-generated method stubdoGet(request, response);}}

运行后，测试结果如下：控制台打印了

person:valueBound
person:valueUnbound

钝化活化监听器：

创建Student类，实现Serializable,HttpSessionActivationListener

public class Student implements Serializable,HttpSessionActivationListener{private String username;private int age;public Student(String username, int age) {super();this.username = username;this.age = age;}@Overridepublic String toString() {return "Student [username=" + username + ", age=" + age + "]";}public String getUsername() {return username;}public void setUsername(String username) {this.username = username;}public int getAge() {return age;}public void setAge(int age) {this.age = age;}@Overridepublic void sessionDidActivate(HttpSessionEvent arg0) {System.out.println("Student：活化");}@Overridepublic void sessionWillPassivate(HttpSessionEvent arg0) {System.out.println("Student：钝化");}}

创建测试类TestStudentActivation

public class TestStudentActivation extends HttpServlet {private static final long serialVersionUID = 1L;           /**     * @see HttpServlet#HttpServlet()     */    public TestStudentActivation() {        super();        // TODO Auto-generated constructor stub    }/** * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response) */protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {HttpSession session = request.getSession();Student s = new Student("milan", 1988);session.setAttribute("student", s);System.out.println("student存入session");}/** * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response) */protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {doGet(request, response);}}

运行Tomcat：控制台输出如下

contextInitialized...

地址栏输入：http://localhost:8081/Tomcat/TestStudentActivation，控制台输出如下

student存入session

关闭tomcat，控制台输出如下

Student：钝化
contextDestroyed...

启动tomcat：控制台输出如下

contextInitialized...

Student：活化

此时可以访问session中的Student的相关属性