不同版本的web.xml的头表信息

<?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/j2ee"       
xmlns:web="http://java.sun.com/xml/ns/j2ee/web-app_2_4.xsd" 
xsi:schemaLocation="http://java.sun.com/xml/ns/j2ee [http://java.sun.com/xml/ns/j2ee/web-app_2_4.xsd](http://java.sun.com/xml/ns/j2ee/web-app_2_4.xsd) "        
version="2.4"> 
</web-app>

<?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>

<?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>