19监听器Listener

1. 监听器概述

servlet和filter及listener 并称servlet三大技术。

a. listener主要功能是实现对某一个事件的监听，一旦触发了监听事件，则监听器就会做出对应的操作。

2. 监听器的种类

一共可以分为三类，八种监听器。

a. 监听域的创建和销毁的监听器。

request

session

servletContext

ServletRequestListener

HttpSessionListener

ServletContextListener

为什么没有监听pageContext域的，因为这个就是页面，我们可以直接查看，无需监听。

代码实现:

1.监听request域

package cn.tedu.listener;

import javax.servlet.ServletRequestEvent;
import javax.servlet.ServletRequestListener;
//监听request域创建于销毁的监听器
public class RequestListenerDemo1 implements ServletRequestListener {

    //请求销毁时触发
    public void requestDestroyed(ServletRequestEvent sre) {
        System.out.println("请求结束.."+sre.getServletRequest());
    }

    //请求创建时触发
    public void requestInitialized(ServletRequestEvent sre) {
        System.out.println("请求开始.."+sre.getServletRequest());
    }

}

web配置文件

  <!-- request域监听器 -->
  <listener>
      <listener-class>cn.tedu.listener.RequestListenerDemo1</listener-class>
  </listener>

2.监听session域

package cn.tedu.listener;

import javax.servlet.http.HttpSessionEvent;
import javax.servlet.http.HttpSessionListener;
//监听session域的创建于销毁的监听器
public class SessionListenerDemo1 implements HttpSessionListener {

    //监听session域的创建
    public void sessionCreated(HttpSessionEvent se) {
        System.out.println("session域创建..."+se.getSession());
    }

    //监听session域的销毁
    public void sessionDestroyed(HttpSessionEvent se) {
        System.out.println("session域销毁..."+se.getSession());
    }

}

配置文件

 <!-- session域监听器 -->
  <listener>
      <listener-class>cn.tedu.listener.SessionListenerDemo1</listener-class>
  </listener>

jsp页面有个配置指令默认session是true也就是当访问该jsp页面的时候会自动创建一个session对象

3.监听servletContext域

package cn.tedu.listener;

import javax.servlet.ServletContextEvent;
import javax.servlet.ServletContextListener;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletRequestWrapper;
//监听servletContext域的创建与销毁
public class ServletContextListenerDemo1 implements ServletContextListener {

    public void contextInitialized(ServletContextEvent sce) {
        
        System.out.println("day15开始.."+sce.getServletContext());
    }

    public void contextDestroyed(ServletContextEvent sce) {
        System.out.println("day15结束.."+sce.getServletContext());
    }

}

配置文件

  <!-- ServletContext域监听器 -->
  <listener>
      <listener-class>cn.tedu.listener.ServletContextListenerDemo1</listener-class>
  </listener>

在当前这一类监听器中，需要先创建一个监听器的类，在添加监听器相关配置。

监听域中属性创建修改删除的监听器

代码实现

                package cn.tedu.listener;
                
                import javax.servlet.ServletContextAttributeEvent;
                import javax.servlet.ServletContextAttributeListener;
                //servletcontext域属性监听器
                public class SCListenerDemo1 implements ServletContextAttributeListener {
                
                        //在属性创建时触发
                        public void attributeAdded(ServletContextAttributeEvent scab) {
                                System.out.println("ServletContext属性："+scab.getName()+"创建"+scab.getValue());
                        }
                
                        //在属性删除时触发
                        public void attributeRemoved(ServletContextAttributeEvent scab) {
                                System.out.println("ServletContext属性："+scab.getName()+"删除"+scab.getValue());
                        }
                
                        //在属性修改时触发
                        public void attributeReplaced(ServletContextAttributeEvent scab) {
                                System.out.println("ServletContext属性："
                                        +scab.getName()+"替换"+scab.getValue()+"替换后"+scab.getServletContext().getAttribute("name"));  //替换后获取的是当前域中对象
                        }
                
                }

添加web.xml信息

<!-- ServletContext域属性监听器 -->
  <listener>
      <listener-class>cn.tedu.listener.SCListenerDemo1</listener-class>
  </listener>

c. 监听javabean在session域中变化的监听器

HttpSessionBindingListener

HttpSessionActivationListener

此类监听器在使用时，直接在javabean身上实现对应的接口，不需要添加相关配置信息。

HttpSessionActivationListener 让javabean自己感知到自己随着session被钝化和活化

i. HttpSessionBindingListener

让javabean自己感知到自己被存入或移除出session的状态变化的监听器

此监听器不需要单独开发类，也不需要在web.xml中进行配置，而是直接让需要监听的JavaBean实现即可。

                package cn.tedu.domain;
                
                import java.io.Serializable;
                
                import javax.servlet.http.HttpSessionBindingEvent;
                import javax.servlet.http.HttpSessionBindingListener;
                
                public class Person implements HttpSessionBindingListener{ 
                        private String name;
                        private int age;
                        private String gender;
                        
                        public Person(){
                                
                        }
                        public Person(String name, int age, String gender) {
                                super();
                                this.name = name;
                                this.age = age;
                                this.gender = gender;
                        }
                        public String getName() {
                                return name;
                        }
                        public void setName(String name) {
                                this.name = name;
                        }
                        public int getAge() {
                                return age;
                        }
                        public void setAge(int age) {
                                this.age = age;
                        }
                        public String getGender() {
                                return gender;
                        }
                        public void setGender(String gender) {
                                this.gender = gender;
                        }
                        //javabean进入session域时触发
                        public void valueBound(HttpSessionBindingEvent event) {
                                System.out.println("javabean进入session"+name);
                        }
                        
                        //javabean移除session域时触发
                        public void valueUnbound(HttpSessionBindingEvent event) {
                                System.out.println("javabean离开session"+name);
                        }
                        
                        
                
                }

项目中的使用

package com.easymall.listener;

import javax.servlet.ServletRequestEvent;
import javax.servlet.ServletRequestListener;
import javax.servlet.http.HttpServletRequest;

public class RequestListener implements ServletRequestListener{

    public void requestDestroyed(ServletRequestEvent sre) {
//        1.获取请求对象
        HttpServletRequest request = (HttpServletRequest) sre.getServletRequest();
        //2.获取请求对象的参数。ip。url
        String url = request.getRequestURL().toString();
        String ip = request.getRemoteAddr();
        String username = request.getParameter("username");
        if(username == null){
            username = "游客";
        }
        System.out.println("用户【"+username+"】访问地址【"+url+"】客户机ip【"+ip+"】请求结束");
        
    }

    public void requestInitialized(ServletRequestEvent sre) {
//        1.获取请求对象
        HttpServletRequest request = (HttpServletRequest) sre.getServletRequest();
        //2.获取请求对象的参数。ip。url
        String url = request.getRequestURL().toString();
        String ip = request.getRemoteAddr();
        String username = request.getParameter("username");
        if(username == null){
            username = "游客";
        }
        System.out.println("用户【"+username+"】访问地址【"+url+"】客户机ip【"+ip+"】请求开始");
    }

}

package com.easymall.listener;

import javax.servlet.ServletRequestEvent;
import javax.servlet.ServletRequestListener;
import javax.servlet.http.HttpServletRequest;

public class RequestListener implements ServletRequestListener{

    public void requestDestroyed(ServletRequestEvent sre) {
//        1.获取请求对象
        HttpServletRequest request = (HttpServletRequest) sre.getServletRequest();
        //2.获取请求对象的参数。ip。url
        String url = request.getRequestURL().toString();
        String ip = request.getRemoteAddr();
        String username = request.getParameter("username");
        if(username == null){
            username = "游客";
        }
        System.out.println("用户【"+username+"】访问地址【"+url+"】客户机ip【"+ip+"】请求结束");
        
    }

    public void requestInitialized(ServletRequestEvent sre) {
//        1.获取请求对象
        HttpServletRequest request = (HttpServletRequest) sre.getServletRequest();
        //2.获取请求对象的参数。ip。url
        String url = request.getRequestURL().toString();
        String ip = request.getRemoteAddr();
        String username = request.getParameter("username");
        if(username == null){
            username = "游客";
        }
        System.out.println("用户【"+username+"】访问地址【"+url+"】客户机ip【"+ip+"】请求开始");
    }

}

<!--SerlvetContextlistener -->



-<listener>

<listener-class>com.easymall.listener.SCListener</listener-class>

</listener>


-<listener>

<listener-class>com.easymall.listener.RequestListener</listener-class>

</listener>