JSTL fmt:param tag question

Question

<%@taglib uri="http://java.sun.com/jstl/fmt" prefix="fmt"%>
<fmt:message key="result_display">
     <fmt:param value="${resultBean.sourceNumber}"/>
     <fmt:param value="${resultBean.resultValue}"/>
</fmt:message>
As far as I can tell, the "value" attribute of the <fmt:param> tag is capable of taking an EL. And yet, the code above does not compile. I get the error message "According to TLD or attribute directive in tag file, attribute value does not accept any expressions". If I use the <fmt_rt:param> tag, everything works fine. Am I reading the spec wrong?

Answer 1

You're not reading the spec wrong, but I think you are using the wrong version of JSTL. Are you using Tomcat 5? (Or another JSP2.0 container?)
If so, you should be using JSTL1.1
It has a uri of "http://java.sun.com/jsp/jstl/fmt"
Note the extra /jsp in there.
Tomcat 5 treats ${  } as runtime expressions. To a JSP2.0 container, they ARE runtime expressions. Thus in JSTL 1.1, the fmt:param tag does accept runtime expressions.
In JSTL1.0 because the ${  } expressions WEREN'T understood by the container, they made the tags so as not to accept runtime expressions, and called their custom evaluator.
You are using the 1.0 uri, which specifies that it doesn't accept runtime expressions. It is complaining that ${ } is a runtime expression - so you must be using a JSP2.0 container.
In short: You probably have a JSP2.0 container, and should be using JSTL1.1 uri: <%@taglib uri="http://java.sun.com/jsp/jstl/fmt" prefix="fmt"%>
Cheers,
evnafets