标签：pack ppi _id pattern xtend 取数 extends exp text
礼悟：
好好学习多思考，尊师重道存感恩。叶见寻根三二一，江河湖海同一体。
虚怀若谷良心主，愿行无悔给最苦。读书锻炼强身心，诚劝且行且珍惜。
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
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。
JavaWeb基础 ServletContext getAttribute 读取不存在的数据时返回null
标签：pack ppi _id pattern xtend 取数 extends exp text
原文地址：http://www.cnblogs.com/jizuiku/p/7706859.html
