web.xml 各版本的 Schema 头部声明

<?xml version="1.0" encoding="UTF-8"?>  
<!DOCTYPE web-app PUBLIC  
 "-//Sun Microsystems, Inc.//DTD Web Application 2.3//EN"  
 "http://java.sun.com/dtd/web-app_2_3.dtd" >  
  
<web-app>  
  <display-name>Servlet 2.3 Web Application</display-name>  
</web-app>

<?xml version="1.0" encoding="UTF-8"?>  
<web-app version="2.4" 
    xmlns="http://java.sun.com/xml/ns/j2ee"  
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"  
    xsi:schemaLocation="http://java.sun.com/xml/ns/j2ee  
    http://java.sun.com/xml/ns/j2ee/web-app_2_4.xsd">  
</web-app>

<?xml version="1.0" encoding="UTF-8"?>  
<web-app version="2.5" 
    xmlns="http://java.sun.com/xml/ns/javaee"  
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"  
    xsi:schemaLocation="http://java.sun.com/xml/ns/javaee  
    http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd">  
</web-app>

<?xml version="1.0" encoding="UTF-8"?>
<web-app version="3.0" 
    xmlns="http://java.sun.com/xml/ns/javaee"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="http://java.sun.com/xml/ns/javaee
    http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd">
</web-app>

<?xml version="1.0" encoding="UTF-8"?>
<web-app version="3.1" 
    xmlns="http://xmlns.jcp.org/xml/ns/javaee"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee
    http://xmlns.jcp.org/xml/ns/javaee/web-app_3_1.xsd">
</web-app>

<?xml version="1.0" encoding="UTF-8"?>
<web-app version="4.0" 
  xmlns="http://xmlns.jcp.org/xml/ns/javaee"
  xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
  xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee　　　    　 　　
  http://xmlns.jcp.org/xml/ns/javaee/web-app_4_0.xsd">
</web-app>

web.xml 各版本的 Schema 头部声明

原文：https://www.cnblogs.com/wumz/p/10716512.html