黑马day14 监听器&监听三大域对象

监听三大域对象主要监听域对象的创建和销毁。因此域对象的创建和销毁一定要知道。

1.ServletContext域对象的监听

package cn.itheima.listener;import java.io.InputStream;import java.net.MalformedURLException;import java.net.URL;import java.util.Enumeration;import java.util.Set;import javax.servlet.RequestDispatcher;import javax.servlet.Servlet;import javax.servlet.ServletContext;import javax.servlet.ServletContextEvent;import javax.servlet.ServletContextListener;import javax.servlet.ServletException;public class ApplicationListener implements ServletContextListener {/** * 当ServletContext初始化的时候加载,即当应用一加载的时候就会触发这个事件 */public void contextInitialized(ServletContextEvent sce) {System.out.println("ServletContext对象被创建了...."+sce.getServletContext());}/** * 当ServletContext对象被销毁的时候会触发这个事件 */public void contextDestroyed(ServletContextEvent sce) {System.out.println("ServletContext对象被销毁了..."+sce.getServletContext());}}

web.xml文件中的配置：

<!-- 配置ServletContext对象的监听器 -->  <listener>  <listener-class>cn.itheima.listener.ApplicationListener</listener-class>  </listener>

运行结果分析：

启动和关闭应用的时候会打印：

2.Session域对象的监听

package cn.itheima.listener;import javax.servlet.http.HttpSessionEvent;import javax.servlet.http.HttpSessionListener;public class SessionListener implements HttpSessionListener {//session 被创建的时候触发这个事件public void sessionCreated(HttpSessionEvent se) {System.out.println("session对象被创建了..."+se.getSession());}//session 被销毁的时候会触发这个事件public void sessionDestroyed(HttpSessionEvent se) {System.out.println("session对象被销毁了..."+se.getSession());}}

web.xml注册监听器

<!-- 配置Session对象的监听器 -->  <listener>  <listener-class>cn.itheima.listener.SessionListener</listener-class>  </listener>

分别写一个Servlet创建session..另一个Servlet销毁session...

创建session的servlet

package cn.itheima.servlet;import java.io.IOException;import javax.servlet.ServletException;import javax.servlet.http.HttpServlet;import javax.servlet.http.HttpServletRequest;import javax.servlet.http.HttpServletResponse;import javax.servlet.http.HttpSession;public class SessionDemo extends HttpServlet {public void doGet(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException {//创建session对象HttpSession session = request.getSession();session.setAttribute("name", "李卫康");}public void doPost(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException {doGet(request, response);}}

销毁session的servlet

package cn.itheima.servlet;import java.io.IOException;import javax.servlet.ServletException;import javax.servlet.http.HttpServlet;import javax.servlet.http.HttpServletRequest;import javax.servlet.http.HttpServletResponse;public class SessionDemo2 extends HttpServlet {public void doGet(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException {response.setContentType("text/html;charset=utf-8");String name = (String) request.getSession().getAttribute("name");response.getWriter().write(name);//session自杀了request.getSession().invalidate();}public void doPost(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException {doGet(request, response);}}

首先访问Demo会打印创建session触发的事件中的函数...然后访问Demo2会销毁session...会打印销毁session触发的事件

解释：session有三种死法,我演示的是自杀式的死法即调用invalidate()方法，会瞬间杀死session..

三种死法：

自杀：invalidate()

超出session的生命周期的时间默认是30分钟...会自动死亡

非正常关闭服务器...如果正常关闭服务器只是会出现session的钝化...当再打开服务器的时候就会session的活化

以上三种死法都会触发销毁session的事件，我就不演示了..

3.request对象的创建和销毁

package cn.itheima.listener;import javax.servlet.ServletRequestEvent;import javax.servlet.ServletRequestListener;public class RequestListener implements ServletRequestListener {//request对象创建的时候会触发public void requestDestroyed(ServletRequestEvent sre) {System.out.println("request对象被创建了..."+sre.getServletRequest());}//request销毁的时候会触发public void requestInitialized(ServletRequestEvent sre) {System.out.println("request对象被销毁了..."+sre.getServletRequest());}}

配置文件：

 <!-- 配置request对象的监听器 -->  <listener>  <listener-class>cn.itheima.listener.RequestListener</listener-class>  </listener>

运行结果：