The "Struts-EL" library contains a set of tag libraries, all of whose classes are derived from classes in the Struts tag libraries. The Struts-EL tags all implement the same attributes as their counterparts in the base Struts tag libraries. The difference provided by Struts-EL is that the tag attribute values are not evaluated as run-time scriptlets (sometimes called "rtexprvalue"s), but are instead evaluated by the expression language engine in the JavaServer Pages Standard Tag Library (often called the JSTL).
The Struts-EL library is intended to be used alongside the Struts library, and with the JSTL. In the development of the Struts-EL library, each tag in the Struts tag libraries was examined to see if all of its functionality is covered in an existing tag in the JSTL. If this was the case, then it was decided to not include a version of this tag in the Struts-EL library. The tags that were "ported" to Struts-EL were deemed to have functionality which the JSTL could not directly cover.
The rest of this package description will briefly review the Struts tags which were not ported to the Struts-EL library (or which were "on the bubble", and why. The detailed package descriptions for each section of the library (html-el, logic-el, and bean-el) will demonstrate in detail the usage of the Struts-EL tags, focusing on attribute value evaluation issues. Details of the operation of these tags in the Struts framework can be learned from the package descriptions and documentation for the base Struts library.
The following table lists the "struts-logic" tags which were not ported to the "struts-logic-el" tag library, including which JSTL elements or features will provide that functionality. Examples after the table will demonstrate these.
| Struts-Logic tag | JSTL tags or feature |
|---|---|
| empty | c:if, c:when, EL |
| equal | c:if, c:when, EL |
| greaterEqual | c:if, c:when, EL |
| greaterThan | c:if, c:when, EL |
| lessEqual | c:if, c:when, EL |
| lessThan | c:if, c:when, EL |
| notEmpty | c:if, c:when, EL |
| notEqual | c:if, c:when, EL |
The following are some examples of "Before" and "After", where the first example is pure Struts usage, and the second example will be pure JSTL usage, not involving Struts-EL at all.
Struts Example:
<logic:empty name="foo" property="stuff">
Some stuff
</logic:empty>
JSTL Version:
<c:if test="${empty foo.stuff}">
Some stuff
</c:if>
Struts Example:
<logic:notEmpty name="foo" property="stuff">
Some stuff
</logic:notEmpty>
JSTL Version:
<c:if test="${!empty foo.stuff}">
Some stuff
</c:if>
Struts Example:
<logic:equal name="foo" property="stuff" value="<%=thing.getStuff()%>">
Some stuff
</logic:equal>
JSTL Version:
<%-- Assumes "thing" is a scoped variable --%>
<c:if test="${foo.stuff eq thing.stuff}">
Some stuff
</c:if>
Struts Example:
<logic:greaterThan name="foo" property="stuff" value="<%=thing.getStuff()%>">
Some stuff
</logic:empty>
JSTL Version:
<%-- Assumes "thing" is a scoped variable --%>
<c:if test="${foo.stuff ge thing.stuff}">
Some stuff
</c:if>
Struts Example:
<logic:present cookie="shoppingCart">
Some stuff
</logic:present>
JSTL Version:
<c:if test='${!empty cookie["shoppingCart"]}">
Some stuff
</c:if>
Struts Example:
<logic:present header="User-Agent">
Some stuff
</logic:present>
JSTL Version:
<c:if test='${!empty header["User-Agent"]}">
Some stuff
</c:if>
The following table lists the "struts-bean" tags which were not ported to the "struts-bean-el" tag library, including which JSTL elements or features will provide that functionality. Examples after the table will demonstrate these.
| Struts-Bean tag | JSTL tags or feature |
|---|---|
| cookie | c:set, EL |
| define | c:set, EL |
| header | c:set, EL |
| include | c:import |
| parameter | c:set, EL |
| write | c:out |
Note that the "bean:resource" Struts tag is similar, at least superficially, to the functionality of the "c:import" tag, but "bean:resource" was ported to the Struts-EL library. This is because resources requested through the "c:import" tag may be processed through a mapped servlet, preventing direct access to the resource. The "bean:resource" tag allows direct access to the resource, without an intervening servlet. For instance, if it is desired to obtain the raw text of a JSP page, using "c:import" will not work, because the JSP page will be processed by the JSP servlet. However, using "bean:resource" will retrieve just the text of the JSP page, if that is desired.
Also note that some functionality of the "bean:include" tag, which was not ported to the Struts-EL library, is not available in the JSTL. This includes the ability to specify the name of a Struts forward, and the ability to include the current transaction control token. These features will be addressed in a future minor release of Struts-EL.
The following are some examples of "Before" and "After", where the first example is pure Struts usage, and the second example will be pure JSTL usage, not involving Struts-EL at all.
Struts Example:
<bean:cookie id="cookieVal" name="stuff"/>
JSTL Version:
<c:set var="cookieVal" value='${cookie["stuff"]}'/>
Struts Example:
<bean:define id="thing" name="foo" property="stuff"/>
JSTL Version:
<c:set var="thing" value="${foo.stuff}"/>
Struts Example:
<bean:header id="headerVal" name="stuff"/>
JSTL Version:
<c:set var="headerVal" value='${header["stuff"]}'/>
Struts Example:
<bean:include id="stuffOut"
href="http://somewhere.com/stuff.jsp"/>
JSTL Version:
<c:import var="stuffOut"
value="http://somewhere.com/stuff.jsp"/>
Struts Example:
<bean:parameter id="parameterVal" name="stuff"/>
JSTL Version:
<c:set var="parameterVal" value='${param["stuff"]}'/>