JavaServer Pages, 3rd Edition

Developing Simple Tag Handlers

The simple tag handler is new as of JSP 2.0. Don’t be fooled by the name; a simple tag handler can implement complex behavior for a custom action, such as conditional evaluation of its body, iteration over its body any number of times, and processing of the body evaluation result. The name refers to the implementation task, which is indeed much simpler than it was for the type of tag handlers supported in previous versions of the JSP specification.

The simplifications are made possible by prohibiting the use of scripting elements (Java code) in the custom action’s body. This would have been met with a great deal of resistance not too long ago, but with the introduction of the EL and JSTL, you rarely (if ever) need to use scripting elements. If this restriction is not acceptable for your application, you must implement the custom action using a classic tag handler instead.

A simple tag handler implements the javax.servlet.jsp.tagext.SimpleTag interface. This interface has five methods, but most tag handlers just extend a base class named javax.servlet.jsp.tagext.SimpleTagSupport and inherit implementations of all but one method: doTag( ) . In addition, the tag handler must implement standard JavaBeans setter methods for all of its custom action attributes (if it has any, of course).

As you may recall, a tag library is a collection of custom actions. For instance, all custom actions used in this book are packaged as one tag library. Besides the tag-handler ...