Chapter 18. The Standard Tag LibraryChapter 17 covered what might be considered the outer layers of Tomcat. These included issues related to the way Tomcat offers and secures incoming requests, as well as how Tomcat can make global resources available to individual Web applications. There is another view of Tomcat from the inner layers: the APIs and data structures that Tomcat offers to developers of Web applications. The most important of these APIs are the Servlet 2.4 and JavaServer Pages 2.0 specification. These APIs are large and complex, and covering them in full would require an entire book on each. One of the most important features of JSP is the ability to create tags, code that may be invoked from pages using a196-like syntax. Such code has access to parameters passed from the page, chunks of text on the page that may include other tags, and the entire application environment. Initially, after the tag functionality was introduced, almost everyone using tags developed their own set. This entailed a great deal of overlap and needless duplication of effort, so it was natural that a standard tag library would eventually be defined. This tag library is a separate standard from the Servlet and JSP specifications, but it rests on top of features introduced in JSP 2.0. It therefore is a natural enhancement to Tomcat, which at the time of this writing is the only application server that fully supports these features.
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