Creating the Tag Library Descriptor
Now you have a good idea about what the Java classes for tag library functions and both simple and classic tag handlers looks like. When the JSP container processes a page, it converts EL functions and custom action elements into code that creates and calls the correct classes. To do this, it needs information about which tag handler implements which custom action element, and which Java method corresponds to an EL function. It gets this information from the Tag Library Descriptor (TLD). As you will see in Chapter 22, 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 and
functions in a library. A JSP page that uses a custom tag library
must identify the corresponding TLD and the namespace prefix used for
the actions and functions in the page with the
taglib
directive:
<%@ taglib prefix="ora" uri="orataglib" %> ... <ora:addCookie name="userName" value="${param.userName}" /> ... ${ora:toCelsius(param.f)}
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 and functions included in the library.
The JSP container then uses the TLD to find the information it needs to generate code for invoking the correct class when it encounters action elements and functions with a matching prefix.
Example 21-13 shows a part ...
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