10_Request域监听器

桃扇骨 2023-09-27 15:37 81阅读 0赞

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

定义监听器类

package com.msb.listener;
    import javax.servlet.*;
    /**
     * @Author: Ma HaiYang
     * @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);
        }
    }

![427195130d3413e5a9d3bcb7fdb62b4b.gif][]

![4edc44bb457b7980a4fc157e54d3f12f.gif][]

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.msb.listener.MyRequestListener</listener-class>
        </listener>
    </web-app>

![96d90143a9282b825c55fbc5375150a5.gif][]

![ee9e59279baa80532186f0fe679ddb5f.gif][]

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");
        }
    }

![a4cf717b4c7f634669db4065c0e066ff.gif][]

![a3413f92260146120ccef0da908adf76.gif][]

[427195130d3413e5a9d3bcb7fdb62b4b.gif]: https://img-blog.csdnimg.cn/img_convert/427195130d3413e5a9d3bcb7fdb62b4b.gif
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[96d90143a9282b825c55fbc5375150a5.gif]: https://img-blog.csdnimg.cn/img_convert/96d90143a9282b825c55fbc5375150a5.gif
[ee9e59279baa80532186f0fe679ddb5f.gif]: https://img-blog.csdnimg.cn/img_convert/ee9e59279baa80532186f0fe679ddb5f.gif
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