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 "

        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 "

        version="2.5">

  ...

</web-app>