JavaServer Pages, Second Edition

Mixing Action Elements and Scripting Elements

Even when you use custom actions and the JSTL, you may occasionally want to use small amounts of scripting code. One case is for setting attribute values to dynamic values for an action that doesn’t support EL expressions. Another is for a quick fix or prototyping, when creating a custom action seems like overkill.

Using an Expression Element to Set an Attribute

In all examples so far, dynamic action attribute values are set using EL expressions, but that isn’t always possible. None of the JSP standard actions (those with prefix jsp) support EL expressions in JSP 1.2. Custom actions may support EL expressions, but to do so, they must incorporate code that evaluates the expression, as described in Chapter 22. It’s expected that the EL will be included in the next JSP specification version, allowing EL expressions to be used for attribute values in all standard actions as well as in all custom actions (without requiring special evaluation code in the tag handlers), so this is likely a temporary problem.

Until the JSP specification includes the EL , you must use a JSP expression to set a dynamic attribute value for actions that don’t support EL expressions. A JSP expression used this way is called a request-time attribute value . Here is an example of how it can be used to set the value attribute of the standard <jsp:param> action:

<jsp:forward page="prodInfo.jsp"> <jsp:param name="id" value='<%= request.getParameter("prodId") %>' /> </jsp:forward> ...