Letting Actions Cooperate
Now that you’ve seen how to develop basic tag handlers, let’s discuss some more advanced features. In this section, we look at tag handlers that let a page author use custom actions that cooperate with each other.
You have seen examples of this throughout this book. For instance, in
Chapter 9, various types of value actions are
nested within the body of an
<ora:sqlQuery>
action to set the
values of place holders in the SQL statement. Another example is the
<ora:encodeURL>
action with nested
<ora:param>
actions, which are used in Chapter 8:
<ora:encodeURL url="product1.jsp"> <ora:param name="id" value="<%= product.getId( )%>" /> </ora:encodeURL>
How does the <ora:param>
action tell the
enclosing <ora:encodeURL>
action about the
parameter it defines? The answer to this question lies in a couple of
Tag
interface methods and a utility method
implemented by the TagSupport
class that I skipped
earlier.
The Tag
interface methods are
setParent( )
and
getParent( )
, implemented like this by the
TagSupport
class:
... private Tag parent; ... public void setParent(Tag t) { parent = t; } public Tag getParent( ) { return parent; }
These two methods are standard accessor methods for the
parent
instance
variable. For a nested action element, the setParent( )
method is always called on the tag handler with the value
of the enclosing Tag
as its value. This way, a nested tag handler always has a reference to its parent. So a tag handler at any nesting level can ask ...
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