• 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>
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  • 原文地址:https://www.cnblogs.com/xuwangqi/p/11383280.html
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