web.xml各版本部署描述符

1. Servlet 3.1 deployment descriptor

Java EE 7 XML schema, namespace is http://xmlns.jcp.org/xml/ns/javaee/

web.xml

<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>

2. Servlet 3.0 deployment descriptor

Java EE 6 XML schema, namespace is http://java.sun.com/xml/ns/javaee

web.xml

<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>

3. Servlet 2.5 deployment descriptor

Java EE 5 XML schema, namespace is http://java.sun.com/xml/ns/javaee

web.xml

<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>

4. Servlet 2.4 deployment descriptor

J2EE 1.4 XML schema, namespace is http://java.sun.com/xml/ns/j2ee

web.xml

<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">

  <display-name>Servlet 2.4 Web Application</display-name>
</web-app>

5. Servlet 2.3 deployment descriptor

J2EE 1.3 DTDs schema. This web.xml file is too old, highly recommend you to upgrade it.
web.xml

<!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>