监听器 ServletRequestAttributeListener&ServletRequestListener详解

在web开发中，监听器不仅可以对Application监听，同时还可以对seesion和request对象进行监听；

该文章主要演示的是对request对象的创建和request属性的监听。

项目结构(红叉不需要关注，是maven环境的问题，不影响我们的主线)

web.xml

<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xmlns="http://java.sun.com/xml/ns/javaee"
xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd"
id="WebApp_ID" version="3.0">
  <display-name>gzipfilter</display-name>
  <listener>
    <listener-class>request.RequestListener</listener-class>
    <listener-class>request.RequestAttrListener</listener-class>
  </listener>
  <servlet>
    <servlet-name>TestServlet</servlet-name>
    <servlet-class>web.TestServlet</servlet-class>
  </servlet>
  <servlet-mapping>
    <servlet-name>TestServlet</servlet-name>
    <url-pattern>/servlet/test</url-pattern>
  </servlet-mapping>
  <welcome-file-list>
    <welcome-file>index.jsp</welcome-file>
  </welcome-file-list>
</web-app>

pom.xml

    <dependencies>
        <dependency>
            <groupId>javax.servlet</groupId>
            <artifactId>jstl</artifactId>
            <version>1.2</version>
            <type>jar</type>
        </dependency>
        <dependency>
            <groupId>javax.servlet</groupId>
            <artifactId>servlet-api</artifactId>
            <version>2.5</version>
            <scope>provided</scope>
        </dependency>
        <dependency>
            <groupId>javax.servlet.jsp</groupId>
            <artifactId>jsp-api</artifactId>
            <version>2.1</version>
            <scope>provided</scope>
        </dependency>
    </dependencies>

RequestAttrListener

public class RequestAttrListener implements ServletRequestAttributeListener{

    public void attributeAdded(ServletRequestAttributeEvent event) {
        System.out.println("request域添加了属性:" + event.getName() + "=" + event.getValue());
    }

    public void attributeRemoved(ServletRequestAttributeEvent event) {
        System.out.println("request域删除了属性:" + event.getName() + "=" + event.getValue());
    }

    public void attributeReplaced(ServletRequestAttributeEvent event) {
        System.out.println("request域修改了属性(这里展示的是被替换的):" + event.getName() + "=" + event.getValue());
    }

}

RequestListener

public class RequestListener implements ServletRequestListener{

    public void requestDestroyed(ServletRequestEvent even) {
        System.out.println("request对象销毁了 ......");
    }

    public void requestInitialized(ServletRequestEvent even) {
        System.out.println("request对象创建了 ......");
    }

}

TestServlet

public class TestServlet extends HttpServlet {
    public void doGet(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
         request.setAttribute("a", "aaaa");
         request.setAttribute("a", "bbbb");
         request.removeAttribute("a");
         response.getOutputStream().print("over");
    }
}

index.jsp

<%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%>
<%
String path = request.getContextPath();
String basePath = request.getScheme()+"://"+request.getServerName()+":"+request.getServerPort()+path+"/";
%>
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
<head>
<base href="<%=basePath%>">
<title>My JSP 'index.jsp' starting page</title>
<meta http-equiv="pragma" content="no-cache">
<meta http-equiv="cache-control" content="no-cache">
</head>
<body>
  <a href="servlet/test">点点</a>
</body>
</html>

访问测试：

http://localhost:8080/listener/

结果解析：

这三行是http://localhost:8080/listener/生成的request对象创建了 ......
request域修改了属性(这里展示的是被替换的):org.apache.catalina.ASYNC_SUPPORTED=true
request对象销毁了 ......

//以下是点击了index.jsp页面超链接生成的
request对象创建了 ......
request域修改了属性(这里展示的是被替换的):org.apache.catalina.ASYNC_SUPPORTED=true
request域添加了属性:a=aaaa
request域修改了属性(这里展示的是被替换的):a=aaaa
request域删除了属性:a=bbbb
request对象销毁了 ......

巴特西

监听器 ServletRequestAttributeListener&ServletRequestListener详解

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