Using JSTL with Struts | Struts: The Complete Reference, 2nd Edition

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Using JSTL with Struts is as simple as adding the JSTL .jar files (jstl.jar and standard.jar) to your Web application's library directory (/WEB-INF/lib) and then referencing the Tag Library Descriptors (.tlds) from your JSPs. There are two ways that you can reference JSTL .tlds in your JSPs. First, you can use an absolute URI to Sun's site, as shown next:

<%@ taglib prefix="c" uri="http://java.sun.com/jstl/core" %>

Second, you can employ the approach used by the Struts tag libraries: an entry is made in the web.xml file and then the URI assigned in the file is used by JSPs. If you choose to take this route, you need to copy the JSTL .tld files into your Web application's WEB-INF directory so that you can reference them.

The following table lists the absolute URI for each of the libraries, should you choose to reference the .tlds in that way.

Library	Prefix	URI
Core	c	http://java.sun.com/jstl/core
Format	fmt	http://java.sun.com/jstl/fmt
SQL	sql	http://java.sun.com/jstl/sql
XML	x	http://java.sun.com/jstl/xml

Struts-EL

As previously mentioned, with the advent of JSTL, the Struts tag library tags should now be used only when there is not a JSTL equivalent tag to replace them. This ensures that JSPs are as portable as possible and shields your application from being too heavily tied to Struts-specific facilities. The following table lists each of the Struts tag library tags that can be replaced by JSTL tags and their corresponding replacements.

Struts Tag Library	Tag	JSTL Replacement
Bean	cookie	c:set
Bean	define	c:set
Bean	header	c:set
Bean	include	c:import
Bean	parameter	c:set
Bean	write	c:out
Logic	empty	c:if, c:when
Logic	equal	c:if, c:when
Logic	greaterEqual	c:if, c:when
Logic	greaterThan	c:if, c:when
Logic	iterate	c:forEach
Logic	lessEqual	c:if, c:when
Logic	lessThan	c:if, c:when
Logic	notEmpty	c:if, c:when
Logic	notEqual	c:if, c:when

As you can see, JSTL can be used in lieu of many of the Struts tag library tags. However, you may have noticed that none of the tags from the Struts HTML Tag Library has an equivalent JSTL tag. JSTL does not have a tag library for rendering HTML form elements, thus the absence of Struts tag replacements. For the HTML tags and all the tags in the Bean and Logic tag libraries that do not have JSTL replacements, a project called Struts-EL was created. Struts-EL was created by David Karr and is currently distributed with Struts in the distribution's contrib folder. It is likely that Struts-EL will eventually become part of the Struts core.

The Struts-EL project is an extension to Struts that provides a JSTL expression language-enabled version of each Struts tag for which no JSTL replacement exists. Most of the base Struts tag library tags' attributes accept values represented as scriptlet expressions. This allows the tags to have dynamic attribute values. For example, the Bean Tag Library's message tag accepts scriptlet expressions for its key attribute, as shown here:

<bean:message key="<%=messageKey%>"/>

This example uses the value of the messageKey JSP scripting variable as the value for the message tag's key attribute. Notice that the JSP scripting variable had to be specified within the scriptlet expression identifiers <%= and %>.

The following example shows the Struts-EL equivalent of the previous example using a JSTL expression to specify a dynamic value for the key attribute:

<bean-el:message key="${messageKey}"/>

As you can see, the JSTL expression syntax is a little shorter and is cleaner looking.

As mentioned, the basic concepts of using JSTL expressions apply to all the Struts-EL tags in the same way. Any tag attribute that accepts a scriptlet expression with the base tags will accept a JSTL expression with the Struts-EL tags.

JSTL Replacement Examples

The following sections provide examples for replacing Struts tag library tags with their JSTL equivalents. Remember that not all the Bean, HTML, and Logic tags can be replaced by JSTL tags.