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

朱雀 2021-10-26 22:22 169阅读 0赞

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：

![678688-20170516142731760-67962405.png][]

注：如果属性被替换，getValue方法返回的是原来的属性。

转载于:https://www.cnblogs.com/zoeyqq/p/6861211.html

[678688-20170516142731760-67962405.png]: /images/20211026/5cb9716ae0d24eccabb76dbda60936b3.png