JavaServer Pages, 3rd Edition

Generating an XML Response

XML is a set of syntax rules for how to represent structured data using markup elements represented by an opening tag (optionally with attributes), a body, and a closing tag:

<employee id="123">
  <first-name>Hans</first-name>
  <last-name>Bergsten</last-name>
  <telephone>310-555-1212</telephone>
</employee>

This XML example contains four elements: <employee>, <first-name>, <last-name>, and <telephone>.

By selecting sensible element names, an XML file may be understandable to a human, but to make sense to a program, it must use only a restricted set of elements in which each element has a well-defined meaning. This is known as an XML application (the XML syntax applied to a certain application domain). A couple of examples are the Wireless Markup Language (WML) used for browsers in cellular phones and other small devices, and XHTML, which is HTML 4.0 reformulated as an XML application. Another example is the web application deployment descriptor, used to configure various aspects of a standard Java web application, as you have seen in the previous chapters.

As I mentioned in Chapter 3 and Chapter 5, everything in a JSP page that is not a JSP element is template text. In all examples so far, I have used HTML as the template text, but it can be any markup, for instance XHTML or WML XML elements. Example 15-1 shows a JSP page that sends a simple phone book to a wireless device, using the XML elements defined by the WML specification as the template text.

Example 15-1. WML ...