不同版本(2.3,2.4,2.5) web.xml 的web-app头信息

Servlet 2.3  
<?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>
    ...
</web-app>


Servlet 2.4  
<?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   "
            version="2.4">
    ...
</web-app>

Servlet 2.5  
<?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>

<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>

see here:http://www.mkyong.com/web-development/the-web-xml-deployment-descriptor-examples/