Nested JSTL tags

Question

I am facing a problem in implementing JSTL in my jsp pages :
In my A.jsp page I am creating session variables as under:
<%
pageContext.setAttribute ("pageType1", "user_admin", pageContext.SESSION_SCOPE);
pageContext.setAttribute ("pageType2", "user", pageContext.SESSION_SCOPE);
//(I am creating these variables n the fly but for simplicity i have defined it as under)
pageContext.setAttribute ("user_admin_preferences", "Hello world", pageContext.SESSION_SCOPE);
pageContext.setAttribute ("user_preferences", "Hello Java", pageContext.SESSION_SCOPE);
%>
on the other page B.jsp:
I am supposed to concat the two String parts of a variable and access the session variables :
But following solutions a re not working:
Solution 1:
var Name : <c:out value="${<%=session.getAttribute('pageType1').toString()%>_preferences}" />
Solution 2:
var Name : <c:out value="${<c:out value="${pageType1}"/>_preferences}" />
Can any one help me fix this problem? Or any other alernative solution will do??
Thanks in advance.

Answer 1

Is it generating the <c: > tags into the HTML when you view source?
Check: you have imported the tag library at the top. -
Which version of JSTL are you using 1.0 or 1.1?
Note that the taglib URIs changed between JSTL1.0 and JSTL1.1
1.0 = http://java.sun.com/jstl/core
1.1 = http://java.sun.com/jsp/jstl/core
Make sure you are using the right URI when importing the taglib.
JSTL 1.1 only works with a JSP2.0 compliant container (Tomcat 5)
If you are using 1.0, then the previous code won't work, as it relies on the container evaluating EL outside of tags.
Consider the following example, which will more limited does basically the same thing.
<%   
session.setAttribute("pageType1", "user_admin");   
session.setAttribute("pageType2", "user"); 
session.setAttribute("user_admin", "The value of user_admin");   
session.setAttribute("user", "The value of user");   
session.setAttribute("user_admin_preferences", "Hello world");   
session.setAttribute("user_preferences", "Hello Java");
%>
<c:out value="${sessionScope.pageType1}"/><BR>
<c:out value="${sessionScope[pageType1]}"/><BR>
<c:out value="${sessionScope.pageType2}"/><BR>
<c:out value="${sessionScope[pageType2]}"/><BR>
<c:set var="foo" value="${sessionScope.pageType1}_preferences"/>
<c:out value="${foo}"/><BR>
<c:out value="${sessionScope[foo]}"/><BR>Which results in :
user_admin
The value of user_admin
user
The value of user
user_admin_preferences
Hello worldIn EL a.b gets evaluated as a["b"] which is different from a[b]
ie
${sessionScope.pageType1} = ${sessionScope["pageType1"]} = "user_admin"
${sessionScope[pageType1]} = ${sessionScope["user_admin"]} = "The value of user_admin"
Cheers,
evnafets