Prentice Hall and Sun Microsystems. Personal use only; do not redistribute.

14.1 The Components That Make Up a Tag Library

313

The JSP File

Once you have a tag handler implementation and a tag library description,

you are ready to write a JSP file that makes use of the tag. Listing 14.3 gives

an example. Somewhere before the first use of your tag, you need to use the

taglib

 directive. This directive has the following form:

<%@ taglib uri="..." prefix="..." %>

The required 

uri

 attribute can be either an absolute or relative URL

referring to a tag library descriptor file like the one shown in Listing 14.2.

To complicate matters a little, however, Tomcat 3.1 uses a 

web.xml

 file that

maps an absolute URL for a tag library descriptor to a file on the local sys 

tem. I don't recommend that you use this approach, but you should be

aware of it in case you look at the Apache examples and wonder why it

works when they specify a nonexistent URL for the 

uri

 attribute of the

taglib

 directive.

The 

prefix

 attribute, also required, specifies a prefix that will be used in

front of whatever tag name the tag library descriptor defined. For example, if

the TLD file defines a tag named 

tag1

 and the 

prefix

 attribute has a value

of 

test

, the actual tag name would be 

test:tag1

. This tag could be used in

either of the following two ways, depending on whether it is defined to be a

container that makes use of the tag body:

Arbitrary JSP

or just

To illustrate, the descriptor file of Listing 14.2 is called 

csa 

jsp taglib.tld

, and resides in the same directory as the JSP file shown in

Listing 14.3. Thus, the 

taglib

 directive in the JSP file uses a simple relative

URL giving just the filename, as shown below.

<%@ taglib uri="csajsp taglib.tld" prefix="csajsp" %>

Furthermore, since the 

prefix

 attribute is 

csajsp

 (for Core Servlets and

JavaServer Pages), the rest of the JSP page uses 

csajsp:example

 to refer to

the 

example

 tag defined in the descriptor file. Figure 14 1 shows the

result. 

Second edition of this book: www.coreservlets.com; Sequel: www.moreservlets.com.

Servlet and JSP training courses by book's author: courses.coreservlets.com.