Chapter 21. Advanced Custom Tag Library Features
In the previous chapter, you learned how to develop basic tag handlers, such as conditional and iteration actions, with and without access to the element body. But there’s a lot more that you can do. In this chapter we look at some more advanced features: how actions can cooperate, how to verify that actions are used correctly, how to bundle listener classes with a tag library, and how to convert text attribute values into types more appropriate for the tag handler.
Developing Cooperating Actions
It’s often necessary
to develop custom actions so
that they can be combined with other actions, letting them cooperate
in some fashion. You have seen examples of this throughout this book.
For instance, in Chapter 11,
<sql:param> action elements are nested
within the body of a <sql:query> action to
set the values of placeholders in the SQL statement. Another example
of cooperation is how the <c:forEach> action
can use the query result produced by the
<sql:query> action. In this section, we take
a look at the cooperation techniques demonstrated by these two
examples: explicit cooperation between a parent element and elements
nested in its body and implicit cooperation through objects exposed
as scoped variables.
Using Explicit Parent-Child Cooperation
One example of
explicit parent-child cooperation is
the <ora:forward>
action with nested <ora:param> actions used
in Chapter 10:
<ora:forward page="product1.jsp"> <ora:param name="id" value="${product.id}" ...Get JavaServer Pages, Second Edition now with the O’Reilly learning platform.
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