JavaServer Pages, 3rd Edition

Processing the Action Body as an Executable Fragment

An action element’s body can contain other actions, EL expressions, and template text. The body can be used for input values spanning multiple lines; the JSTL database actions described in Chapter 12 use the body this way. The SQL statement is often large, so it’s cleaner to let the page author write it in the action body instead of as an attribute value. A similar example is an action that processes the body content in one way or another before it’s added to the response. Chapter 15 shows how the JSTL <x:transform> action processes its XML body using the XSL stylesheet specified as an attribute.

Some actions do not really use the body as input but process it in other ways. One example is a conditional custom action, such as the JSTL <c:if> action, which only passes the body through if a runtime condition is met. A custom action that processes the dynamic elements in the body a number of times, like the JSTL <c:forEach> action, is another example.

You can use simple tag handlers to implement all these types of custom actions. The key to unlocking this magic lies in what’s called a JSP fragment and a SimpleTag method I haven’t told you about so far:

public void setJspBody(JspFragment body)

The container calls this method with a reference to a JSP fragment representing the custom action body before calling doTag( ). If the custom action doesn’t have a body, this method is not called at all.

A JSP fragment is an internal representation ...