JavaServer Pages, 3rd Edition

Developing Classic Tag Handlers

Classic tag handler is the designation used in the JSP 2.0 specification for the original version of the tag handler API, to distinguish it from the new, easier-to-use API. Given that a simple tag handler is so much easier to implement than a classic tag handler and can do exactly the same things, why bother with the classic tag handler at all? The answer is “you shouldn’t,” unless one of the following is true:

• The tag library must work with JSP 1.1 or 1.2 as well as 2.0

• The page author must be able to use Java code (scripting elements) in the custom action bodies

• The tag handler instance is very expensive to create or initialize

It is hard to do anything about the first reason; if the tag library must work with JSP versions prior to 2.0, you have no choice but to use classic tag handlers.

Scripting code is rarely needed nowadays, so the second reason should be looked at with suspicion. I suggest that you think long and hard about other solutions, such as using JSTL, more custom actions, and EL expressions instead.

The third reason is related to the fact that simple tag handlers cannot be reused; the container creates a new instance for every invocation. A container is, however, allowed to reuse classic tag handlers for multiple custom action invocations, as long as the strict rules (described later) are followed. While this may sound like a great performance boost, benchmarks have shown that it has very little effect in reality when using a modern Java ...