Overview of Java Web Technologies, Part 1 - Reviewing Deployment Descriptors
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A deployment descriptor is an XML file, so you can edit it using a text editor. The deployment descriptor for an application compliant with the Servlet 2.3 specification starts with the following:
<?xml version="1.0" encoding="ISO-8859-1"?>
<!DOCTYPE web-app PUBLIC "-//Sun Microsystems, Inc.//DTD Web Application 2.3//EN"
"http://java.sun.com/dtd/web-app_2_3.dtd">
These headers indicate that the document type definition (DTD) for this deployment descriptor can be downloaded from http://java.sun.com/dtd/web-app_2_3.dtd. If you open the DTD file, you can see that the root element of a deployment descriptor is
web-app. The web-app element can have up to 23 kinds of subelements, as shown here:
<!ELEMENT web-app (icon?, display-name?, description?, distributable?, context-param*, filter*, filter-mapping*, listener*, servlet*, servlet-mapping*, session-config?, mime-mapping*, welcome-file-list?, error-page*, taglib*, resource-env-ref*, resource-ref*, security-constraint*,login-config?, security-role*, env-entry*, ejb-ref*, ejb-local-ref*)>
All of these subelements are optional, so you are not required to include any of them. The subelements preceding a question mark (?) can appear only once. Those followed by an asterisk (*) can appear many times. Additionally, some of these subelements can have subelements.
Note that in Servlet 2.4, a deployment descriptor is validated against a schema, not a DTD file. However, the elements under web-app are pretty much the same.
 Remember: This is part one of the first chapter of JavaServer Faces Programming, by Budi Kurniawan (McGraw-Hill/Osborne, ISBN 0-07-222983). Stay tuned for part 2 of "Overviews of Java Web Technologies," where we learn about JSP, JavaBeans, and Model 2.
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