Using c:out in a jsp:include

Question

In a template, I refer to the "body", which is a String in request scope.
All operates as desired if a scriptlet is used, but fails if I attempt to replace the scriptlet with
a c:out tag.
Here is the source :
<jsp:useBean id="body" scope="request" type="java.lang.String" />
<%-- This succeeds : --%>
<jsp:include page='<%= body %>' flush="true"/>
<%-- This fails: --%>
<jsp:include page='<c:out value="${body}"/>' flush="true" />
Why?

Answer 1

You can't use a custom tag as an attribute to another tag.
They only accept runtime expressions. That is why the <%= %> tag works.
This is true for ALL tags.
A <jsp:getProperty> tag wouldn't work either
ie this is also illegal:
<jsp:include page='<jsp:getProperty .... />' flush="true"/>
For this reason, a lot of the JSTL tags have an alternative syntax that let you use the body.
ie
instead of:
<c:set var="test" value="<fmt:formatDate var="${myDate}"/>" />
you can do
<c:set var="test>
<fmt:formatDate var="${myDate}"/>
</c:set>
ok its a bad example of tags you want to mix, but you get the idea hopefully.
That is also why struts has a special taglib for using EL as attributes.
If you have a JSP2.0 container like Tomcat5, you can use the EL expression tags instead of the regular expression tags
ie <jsp:include page='${body}' flush="true"/>
Hope this helps,
evnafets