servlet web.xml samples

Servlet 2.3 

<!DOCTYPE web-app PUBLIC
 "-//Sun Microsystems, Inc.//DTD Web Application 2.3//EN"
 "http://java.sun.com/dtd/web-app_2_3.dtd" >
 
  <display-name>Servlet 2.3 Web Application</display-name>
</web-app>

Servlet 2.4 

<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>

Servlet 2.5 

<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">

  <display-name>Servlet 2.5 Web Application</display-name>
</web-app>

Servlet 3.0 

<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">

  <display-name>Servlet 3.0 Web Application</display-name>
</web-app>

Ref:

http://en.wikipedia.org/wiki/Java_Servlet

http://docs.oracle.com/cd/E14571_01/web.1111/e13712/web_xml.htm