JavaServer Pages Pocket Reference

Developing Custom Actions

A custom action—actually, a tag handler class for a custom action—is basically a bean, with property setter methods corresponding to the custom action element’s attributes. In addition, the tag handler class must implement one of two Java interfaces defined by the JSP specification.

All the interfaces and classes you need to implement a tag handler are defined in the javax.servlet.jsp.tagext package. The two primary interfaces are named Tag and BodyTag. The Tag interface defines the methods you need to implement for any action. The BodyTag interface extends the Tag interface and adds methods used to access the body of an action element. To make it easier to develop a tag handler, two support classes are defined by the API: TagSupport and BodyTagSupport (shown in Figure 1-4). These classes provide default implementations for the methods in the corresponding interfaces.

Figure 1-4. The primary tag-extension interfaces and support classes

The specification defines interfaces as well as the support classes that implement them to cover all the bases. If you already have a class with functionality that you want to access as a custom action, you can specify that your class implements the appropriate interface and add the few methods defined by that interface. In practice, though, I recommend that you implement your tag handlers as extensions of the support classes. ...