建立和使用一个RequestAttribute监听者（Head first servlet+Jsp）（实验三）

package com.example;

import java.io.IOException;
import java.io.PrintWriter;

import javax.servlet.ServletException;
import javax.servlet.ServletRequestAttributeEvent;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

/**
 * Servlet implementation class TestServletContextType
 */
@WebServlet("/TestServletContextType")
public class TestServletContextType extends HttpServlet {
    private static final long serialVersionUID = 1L;
       
    /**
     * @see HttpServlet#HttpServlet()
     */
    public TestServletContextType() {
        super();
        // TODO Auto-generated constructor stub
    }

    /**
     * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response)
     */
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        request.setAttribute("a","b");
        request.setAttribute("a", "c");
        request.removeAttribute("a");
    }
    

    /**
     * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response)
     */
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        // TODO Auto-generated method stub
        doGet(request, response);
    }

}

监听者类：

package com.example;

import javax.servlet.ServletRequestAttributeEvent;
import javax.servlet.ServletRequestAttributeListener;

public class MyservletAttributeListen implements ServletRequestAttributeListener {

    @Override
    public void attributeAdded(ServletRequestAttributeEvent ev) {
        System.out.println("A:"+ev.getName()+"->"+ev.getValue());

    }

    @Override
    public void attributeRemoved(ServletRequestAttributeEvent ev) {
        System.out.println("M:"+ev.getName()+"->"+ev.getValue());

    }

    @Override
    public void attributeReplaced(ServletRequestAttributeEvent ev) {
        System.out.println("P:"+ev.getName()+"->"+ev.getValue());

    }

}

web.xml文件

<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://xmlns.jcp.org/xml/ns/javaee" xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee http://xmlns.jcp.org/xml/ns/javaee/web-app_3_1.xsd" id="WebApp_ID" version="3.1">
  <display-name>FirstListener</display-name>
  <servlet>
    <servlet-name>ListenerTest</servlet-name>
    <servlet-class>com.example.ListenerTest</servlet-class>
  </servlet>
  <servlet-mapping>
    <servlet-name>ListenerTest</servlet-name>
    <url-pattern>/ListenTest.do</url-pattern>
  </servlet-mapping>
  
  <servlet>
    <servlet-name>TestServletContextType</servlet-name>
    <servlet-class>com.example.TestServletContextType</servlet-class>
  </servlet>
  <servlet-mapping>
    <servlet-name>TestServletContextType</servlet-name>
    <url-pattern>/testtype.do</url-pattern>
  </servlet-mapping>
  
  <servlet>
    <servlet-name>TestServletContextType2</servlet-name>
    <servlet-class>com.example.TestServletContextType2</servlet-class>
  </servlet>
  <servlet-mapping>
    <servlet-name>TestServletContextType2</servlet-name>
    <url-pattern>/testtype1.do</url-pattern>
  </servlet-mapping>
  
  <context-param>
    <param-name>breed</param-name>
    <param-value>Greet Dane</param-value>
  </context-param>
  <listener>
    <listener-class>com.example.MyservletAttributeListen</listener-class>
  </listener>
</web-app>

测试结果：

注：如果属性被替换，getValue方法返回的是原来的属性。