The Java EE 5 Tutorial (PDF) - Oracle Software Downloads

To use a custom tag in a JSP page, you must
■ Declare the tag library containing the tag
■ Make the tag library implementation available to the web application
See Chapter 8, “Custom Tags in JSP Pages,” for detailed information on the different types of
tags and how to implement tags.
DeclaringTag Libraries
To declare that a JSP page will use tags defined in a tag library, you include a taglib directive in
the page before any custom tag from that tag library is used. If you forget to include the taglib
directive for a tag library in a JSP page, the JSP compiler will treat any invocation of a custom tag
from that library as static data and will simply insert the text of the custom tag call into the
response.
The prefix attribute defines the prefix that distinguishes tags defined by a given tag library
from those provided by other tag libraries.
If the tag library is defined with tag files (see “Encapsulating Reusable Content Using Tag Files”
on page 231), you supply the tagdir attribute to identify the location of the files. The value of
the attribute must start with /WEB-INF/tags/. A translation error will occur if the value points
to a directory that doesn’t exist or if it is used in conjunction with the uri attribute.
The uri attribute refers to a URI that uniquely identifies the tag library descriptor (TLD), a
document that describes the tag library (see “Tag Library Descriptors” on page 245).
Tag library descriptor file names must have the extension .tld. TLD files are stored in the
WEB-INF directory or subdirectory of the WAR file, or in the META-INF directory or subdirectory
of a tag library packaged in a JAR. You can reference a TLD directly or indirectly.
The following taglib directive directly references a TLD file name:
This taglib directive uses a short logical name to indirectly reference the TLD:
Using CustomTags
The iterator example defines and uses a simple iteration tag. The JSP pages use a logical name
to reference the TLD.
Chapter 5 • JavaServer PagesTechnology 171