监听器

监听器： 主要是用来监听特定对象的创建或销毁、属性的变化的！ 是一个实现特定接口的普通java类！

对象：

         自己创建自己用 (不用监听)

         别人创建自己用 （需要监听）

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Servlet中哪些对象需要监听？

         request / session / servletContext

         分别对应的是request监听器、session相关监听器、servletContext监听器

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监听器(listener)

监听器接口：

一、监听对象创建/销毁的监听器接口

         Interface ServletRequestListener     监听request对象的创建或销毁

         Interface HttpSessionListener        监听session对象的创建或销毁

         Interface ServletContextListener     监听servletContext对象的创建或销毁

二、监听对象属性的变化

         Interface ServletRequestAttributeListener 监听request对象属性变化: 添加、移除、修改

         Interface HttpSessionAttributeListener    监听session对象属性变化: 添加、移除、修改

Interface ServletContextAttributeListener  监听servletContext对象属性变化

三、session相关监听器

         Interface HttpSessionBindingListener   监听对象绑定到session上的事件    

    Interface HttpSessionActivationListener(了解) 监听session序列化及反序列化的事件

404(路径写错)

500(服务器错误，调试)

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package com.loaderman.demo.a_life;

import javax.servlet.ServletRequestEvent;
import javax.servlet.ServletRequestListener;

/**
 *  监听request对象的创建或销毁
 * @author Jie.Yuan
 *
 */
public class MyRequestListener implements ServletRequestListener{

    // 对象销毁
    @Override
    public void requestDestroyed(ServletRequestEvent sre) {
        // 获取request中存放的数据
        Object obj = sre.getServletRequest().getAttribute("cn");
        System.out.println(obj);
        System.out.println("MyRequestListener.requestDestroyed()");
    }

    // 对象创建
    @Override
    public void requestInitialized(ServletRequestEvent sre) {
        System.out.println("MyRequestListener.requestInitialized()");
    }
}

package com.loaderman.demo.a_life;

import javax.servlet.ServletContextEvent;
import javax.servlet.ServletContextListener;

/**
 * 监听ServletContext对象创建或销毁
 * @author Jie.Yuan
 *
 */
public class MyServletContextListener implements ServletContextListener{

    @Override
    public void contextDestroyed(ServletContextEvent sce) {
        System.out.println("MyServletContextListener.contextDestroyed()");
    }

    @Override
    public void contextInitialized(ServletContextEvent sce) {
        System.out.println("1..........MyServletContextListener.contextInitialized()");
    }

}

package com.loaderman.demo.a_life;


import javax.servlet.http.HttpSessionEvent;
import javax.servlet.http.HttpSessionListener;

/**
 * 监听Session对象创建、销毁
 * @author Jie.Yuan
 *
 */
public class MySessionListener implements HttpSessionListener{

    // 创建
    @Override
    public void sessionCreated(HttpSessionEvent se) {
        System.out.println("MySessionListener.sessionCreated()");
    }

    // 销毁
    @Override
    public void sessionDestroyed(HttpSessionEvent se) {
        System.out.println("MySessionListener.sessionDestroyed()");
    }

}

package com.loaderman.demo.b_attr;

import javax.servlet.http.HttpSession;
import javax.servlet.http.HttpSessionAttributeListener;
import javax.servlet.http.HttpSessionBindingEvent;

/**
 * 监听session对象属性的变化
 * @author Jie.Yuan
 *
 */
public class MySessionAttrListener implements HttpSessionAttributeListener {

    // 属性添加
    @Override
    public void attributeAdded(HttpSessionBindingEvent se) {
        // 先获取session对象
        HttpSession session = se.getSession();
        // 获取添加的属性
        Object obj = session.getAttribute("userName");
        // 测试
        System.out.println("添加的属性：" + obj);
    }

    // 属性移除
    @Override
    public void attributeRemoved(HttpSessionBindingEvent se) {
        System.out.println("属性移除");
    }

    // 属性被替换
    @Override
    public void attributeReplaced(HttpSessionBindingEvent se) {
        // 获取sesison对象
        HttpSession session = se.getSession();

        // 获取替换前的值
        Object old = se.getValue();
        System.out.println("原来的值：" + old);

        // 获取新值
        Object obj_new = session.getAttribute("userName");
        System.out.println("新值：" + obj_new);

    }

}

package com.loaderman.demo.c_session;

import javax.servlet.http.HttpSessionBindingEvent;
import javax.servlet.http.HttpSessionBindingListener;

/**
 * 监听此对象绑定到session上的过程，需要实现session特定接口
 * @author Jie.Yuan
 *
 */
public class Admin implements HttpSessionBindingListener {

    private int id;
    private String name;

    public Admin() {
        super();
    }
    public Admin(int id, String name) {
        super();
        this.id = id;
        this.name = name;
    }


    // 构造函数
    public int getId() {
        return id;
    }
    public void setId(int id) {
        this.id = id;
    }
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }

    // 对象放入session
    @Override
    public void valueBound(HttpSessionBindingEvent event) {
        System.out.println("Admin对象已经放入session");
    }
    // 对象从session中移除
    @Override
    public void valueUnbound(HttpSessionBindingEvent event) {
        System.out.println("Admin对象从session中移除！");
    }

}

 <!-- session的最大活跃时间 -->
    <session-config>
        <session-timeout>60</session-timeout>
    </session-config>

    <!-- 监听request对象创建、销毁 -->
    <listener>
        <listener-class>com.loaderman.demo.a_life.MyRequestListener</listener-class>
    </listener>
    <!-- 监听session对象创建、销毁 -->
    <listener>
        <listener-class>com.loaderman.demo.a_life.MySessionListener</listener-class>
    </listener>

    <!-- 监听servletContext对象创建、销毁 -->
    <listener>
        <listener-class>com.loaderman.demo.a_life.MyServletContextListener</listener-class>
    </listener>

    <!-- 属性监听器 -->
    <listener>
        <listener-class>com.loaderman.demo.b_attr.MySessionAttrListener</listener-class>
    </listener>