JSP EL variables

EL Variables come from one of two places:

implicit variable

pageContext
pageScope
requestScope
sessionScope
applicationScope
param
paramValues
header
headerValues
cookie
initParam

pageContext.findAttribute(varname)
which is like getting the first of:

page.getAttribute(varname)
request.getAttribute(varname)
session.getAttribute(varname)
application.getAttribute(varname)

So if you have a variable like:

<% boolean a = true; %>

you have to store it as an attribute to make it available as an EL variable:

<% 
  boolean b = true; 
  pageContext.setAttribute("b",new Boolean(b));
%>

<c:if test="${b}">
b is TRUE
</c:if>

Here is an example that shows this a bit more:

Making values available as JSP EL variables

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

  boolean b = true; 
  pageContext.setAttribute("b",new Boolean(b));

  boolean c = false; 
  pageContext.setAttribute("c",new Boolean(c));

  boolean param = true;
  pageContext.setAttribute("param",new Boolean(param));
%>
 
<%-- 
  this is false because 'a' is not findable by
  pageContext.findAttribute(varname)
--%>
<c:if test="${'${'}a}">
a is TRUE
</c:if>

<c:if test="${'${'}b}">
b is TRUE
</c:if>

<%-- this is false because 'c' was set to false --%>
<c:if test="${'${'}c}">
c is TRUE
</c:if>


<%-- 
  This is false because 'param' is an implicit variable
  which is used instead of pageContext.findAttribute("param")
--%>
<c:if test="${'${'}param}">
param is TRUE
</c:if>

b is TRUE