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310

Chapter 14 Creating Custom JSP Tag Libraries

behavior of the two versions. However, Tomcat 3.1 uses a slightly different

directory structure, as summarized Table 14.1. 

Table 14.1  Standard Tomcat Directories

Tomcat 3.0

Tomcat 3.1

Location of startup 

install_dir

install_dir/bin

and shutdown Scripts

Standard Top Level 

install_dir/webpages/ 

install_dir/webapps/ 

Directory for Servlets 

WEB INF/classes

ROOT/WEB INF/classes

and Supporting Classes

Standard Top Level 

install_dir/webpages

install_dir/webapps/ 

Directory for HTML 

ROOT

and JSP Files

14.1 The Components That Make 

Up a Tag Library

In order to use custom JSP tags, you need to define three separate compo 

nents: the tag handler class that defines the tag's behavior, the tag library

descriptor file that maps the XML element names to the tag implementa 

tions, and the JSP file that uses the tag library. The rest of this section gives

an overview of each of these components and the following sections give

details on how to build these components for various different styles of tags.

The Tag Handler Class

When defining a new tag, your first task is to define a Java class that tells the

system what to do when it sees the tag. This class must implement the

javax.servlet.jsp.tagext.Tag

 interface. This is usually accomplished by

extending the 

TagSupport

 or 

BodyTagSupport

 class. Listing 14.1 is an

example of a simple tag that just inserts  

Custom tag example (coreserv 

lets.tags.ExampleTag)

  into the JSP page wherever the corresponding

tag is used. Don't worry about understanding the exact behavior of this class;

that will be made clear in the next section. For now, just note that it is in the

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

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