不同版本的Servlet的web.xml的头部文件

Servlet 3.1

对应JDK7.0和Tomcat8.0，Tomcat8.5

<?xml version="1.0" encoding="UTF-8"?>  
<web-app 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"  
        version="3.1">  

</web-app>

Servlet 3.0

对应JDK6.0和Tomcat7.0

<?xml version="1.0" encoding="UTF-8"?>  
<web-app 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"  
          version="3.0">  

</web-app>

Servlet 2.5

对应JDK5.0和Tomcat6.0

<?xml version="1.0" encoding="UTF-8"?>  
<web-app 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"  
          version="2.5">  

</web-app>

Servlet 2.4

对应JDK1.4和Tomcat5.5

<?xml version="1.0" encoding="UTF-8"?>  
<web-app 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"  
          version="2.4">  

</web-app>

Servlet 2.3

对应JDK1.3和Tomcat4.1

<!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>