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Chapter 7: Web Application Confi guration As you can see, the name of the extension is referenced in each entry. This is suffixed by a specific attribute name describing the extension. The name of the extension in this file is an alias for the extension s name as defined in the jarfile. Thus, the declaration of the extension s alias is accomplished by simply prefixing it to the attribute names; it does not need to be explicitly defined. The extension s proper name is referred to in the first entry. The server will investigate the contents of each jar file installed on it and check packages to determine whether the names match. The specifications and implementation version numbers are self-explanatory, as should be the vendor name that is specified in the Implementation-Vendor attribute. The vendor should be a globally unique ID. The custom of including the reversed host name is common. In the preceding example, this is com.wrox. Finally, the Implementation-URL should be provided, giving the location of additional information and often download instructions. For our purpose, this is the most useful line. If the extension is not installed, the URL should provide enough information to ensure that it is made available to the Web application by other means. The manifest file is typically generated automatically when a Web application is packaged as a Web archive ( .war) file. Packaging Web applications for distribution as .war files is described in Chapter 2 . The Context File The context file (context.xml) contains the configuration for the Web applications Context . As you saw in Chapter 4 , the Context represents a Web application, and has all the configurable elements for it. This is not the only place where the Web applications Contextis defined: Chapter 5 describes this in greater detail, and lists all the places where the Web application Context can be configured. Understanding the Deployment Descriptor (web.xml) A deployment descriptor is an XML file that contains configuration information used by the Web application for execution on the Servlet engine. The deployment descriptor for a Web application is the /webapps//WEB-INF/web.xml file. There is another web.xml file that is applicable for all Web applications deployed in the servlet Engine, and this is located under /conf. This section examines application-specific deployment only. However, the configuration-related information is valid for all deployment descriptors. The Servlet 2.5 specification uses a schema for the deployment descriptor older specifications (Servlet 2.3 and earlier) still use a Document Type Definition (DTD). Both are still supported for backward compatibility with existing Web applications. Because you might need to support existing Web applications, this chapter covers both the older Servlet 2.3 style web.xmland the schema-based versions. The first few lines of the deployment descriptor indicate whether it is the Servlet 2.4/2.5 schema-based web.xmlor the older DTD-based version.

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