ServletContext getAttribute 读取不存在的数据时返回null

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       javaEE：7           
       javaSE：1.8
          JSTL：1.2.2  
      server：tomcat 8.5
    explorer：Firefox        
             os：windows7 x64
            ide：MyEclipse 2017

工程目录结构

 

web.xml

<?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">


	<servlet>
		<servlet-name>ReadNotExistDataServletContext</servlet-name>
		<servlet-class>jizuiku.web.servlet.ReadNotExistDataServletContext</servlet-class>
	</servlet>
	<servlet-mapping>
		<servlet-name>ReadNotExistDataServletContext</servlet-name>
		<url-pattern>/ReadNotExistDataServletContext</url-pattern>
	</servlet-mapping>
	
	<context-param>
		<param-name>minNum</param-name>
		<param-value>10</param-value>
	</context-param>
	
	<context-param>
		<param-name>count</param-name>
		<param-value>100</param-value>
	</context-param>
	
	<context-param>
		<param-name>maxNum</param-name>
		<param-value>1000</param-value>
	</context-param>
	
</web-app>

 

代码

package jizuiku.web.servlet;

import java.io.IOException;

import javax.servlet.ServletContext;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

/**
 * ServletContext 读取不存在的数据
 * 
 * @author 给最苦
 * @version V17.10.21
 */
public class ReadNotExistDataServletContext extends HttpServlet {

	/**
	 * 
	 */
	private static final long serialVersionUID = 1L;

	@Override
	protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
		// TODO Auto-generated method stub
		System.out.println("读取数据");
		
		ServletContext application = this.getServletContext();
		String notExistAttributeValue = (String)application.getAttribute("notExistAttribute");
		
		if(notExistAttributeValue == null){
			System.out.println("notExistAttribute 未创建");
		} else {
			System.out.println("如果输出这个,需要检查程序的逻辑");
		}
	}
	
	@Override
	protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
		// TODO Auto-generated method stub
		super.doPost(req, resp);
	}
}

 

效果

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学习资源：itcast和itheima视频库。如果您有公开的资源，可以分享给我的话，用您的资源学习也可以。
博文是观看视频后，融入思考写成的。博文好，是老师讲得好。博文坏，是 给最苦 没认真。