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大数据必学Java基础（一百一十四）：Requet域监听器

2023-02-18 16:39:21 时间

​Requet域监听器

一、认识Requet域监听器

Requet域共有两个监听器接口,分别是

ServletRequestListener

ServleRequestAttributeListener

接下来我们就认识一些每个接口和接口中每个方法的用处

二、定义监听器类

package com.lanson.listener;
import javax.servlet.*;
/**
 * @Author: Lansonli
 * @Description: MircoMessage:Mark_7001
 */
public class MyRequestListener implements ServletRequestListener, ServletRequestAttributeListener {
    @Override
    public void requestDestroyed(ServletRequestEvent sre) {
        // 监听HttpServletRequest对象的销毁  项目中任何一个Request对象的销毁都会触发该方法的执行
        ServletRequest servletRequest = sre.getServletRequest();
        System.out.println("request"+servletRequest.hashCode()+"对象销毁了");
    }
    @Override
    public void requestInitialized(ServletRequestEvent sre) {
        // 监听HttpServletRequest对象的创建并初始化 项目中任何一个Request对象的创建并初始化都会触发该方法的执行
        ServletRequest servletRequest = sre.getServletRequest();
        System.out.println("request"+servletRequest.hashCode()+"对象初始化");
    }
    @Override
    public void attributeAdded(ServletRequestAttributeEvent srae) {
        // 任何一个Request对象中调用 setAttribute方法增加了数据都会触发该方法
        ServletRequest servletRequest = srae.getServletRequest();
        String name = srae.getName();
        Object value = srae.getValue();
        System.out.println("request"+servletRequest.hashCode()+"对象增加了数据:"+name+"="+value);
    }
    @Override
    public void attributeRemoved(ServletRequestAttributeEvent srae) {
       // 任何一个Request对象中调用 removeAttribute方法移除了数据都会触发该方法
        ServletRequest servletRequest = srae.getServletRequest();
        String name = srae.getName();
        Object value = srae.getValue();
        System.out.println("request"+servletRequest.hashCode()+"对象删除了数据:"+name+"="+value);
    }
    @Override
    public void attributeReplaced(ServletRequestAttributeEvent srae) {
        // 任何一个Request对象中调用 setAttribute方法修改了数据都会触发该方法
        ServletRequest servletRequest = srae.getServletRequest();
        String name = srae.getName();
        Object value = srae.getValue();
        Object newValue=servletRequest.getAttribute(name);
        System.out.println("request"+servletRequest.hashCode()+"对象增修改了数据:"+name+"="+value+"设置为:"+newValue);
    }
}

三、配置监听器

使用web.xml 或者通过@WebListener注解都可以

<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns="http://xmlns.jcp.org/xml/ns/javaee"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee http://xmlns.jcp.org/xml/ns/javaee/web-app_4_0.xsd"
         version="4.0">
    
    <listener>
        <listener-class>com.lanson.listener.MyRequestListener</listener-class>
    </listener>
</web-app>

四、准备Servlet

@WebServlet(urlPatterns = "/myServlet3.do")
public class MyServlet3 extends HttpServlet {
    @Override
    protected void service(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        req.setAttribute("name", "zhangsan");
        req.setAttribute("name", "lisi");
        req.removeAttribute("name");
    }
}

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