The 'web.xml' file describes the web app. The empty file looks like:

<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">
    <session-config>
        <session-timeout>
            30
        </session-timeout>
    </session-config>

</web-app>