JavaServer Pages, 3rd Edition

Web Application Deployment Descriptor

A very important file is the WEB-INF/web.xml file. It is the application deployment descriptor that contains all configuration information for the application. If your application consists only of JSP and HTML files, you typically don’t need to worry about this file at all. But if the application also contains servlets or uses the container provided security mechanisms, you often need to define some configuration information in the web.xml file.

The deployment descriptor is an XML file. Starting with Servlet 2.3 and JSP 2.0, the elements it can contain and how they must be arranged are controlled by a number of XML Schema documents.^[1] The main XML Schema document, which includes the others, is available online at http://java.sun.com/xml/ns/j2ee/web-app_2_4.xsd. This XML Schema document must be referenced in the root element of the deployment description, as shown in Example F-1.

Example F-1. Java Web Application Descriptor root element

<web-app xmlns="http://java.sun.com/xml/ns/j2ee"
  xmlns:xsi="http://www.w3c.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>
  ...
</web-app>

If you’re not familiar with the intricate details of XML Schema and namespace declarations, just accept the fact that you need to enclose all other elements in the deployment descriptor within a <web-app> element exactly as shown in Example F-1.

Within the <web-app> element body, top-level ...