JavaServer Pages, Second Edition

Creating the Tag Library Descriptor

Now you have a good idea about what the code for a tag handler looks like. But when the JSP container converts custom action elements into code that creates and calls the correct tag handler, it needs information about which tag handler implements which custom action element. It gets this information from the Tag Library Descriptor (TLD). As you will see in Chapter 21, the JSP container also uses the TLD information to verify that the attribute list for an action element is correct.

The TLD is an XML file with information about all custom actions in one library. A JSP page that uses custom actions must identify the corresponding TLD and the namespace prefix used for the actions in the page with the taglib directive:

<%@ taglib prefix="ora" uri="orataglib" %>
...
<ora:redirect page="main.jsp" />

The uri attribute identifies the TLD, in one of several ways that I describe later in this section. The prefix attribute assigns a prefix to use for the action elements included in the library.

The JSP container then uses the TLD to find the information it needs to generate code for invoking the correct tag handler class when it encounters an action element with a matching prefix.

Example 20-5 shows a part of the JSP 1.2 version of the TLD for the custom actions in this book. Some changes were made to the format of the TLD between JSP 1.1 and 1.2; I describe the differences at the end of this section. A JSP 1.2 container is required to accept a TLD in ...