Question

I am trying learn more about JSP expression evaluations. How and which variables are determined to be in scope for access by expressions?

I have a simple JSP (ELEvaluator is a convenience wrapper)

<% String foo = "bar"; %>
<%= ELEvaluator.evaluate("${foo}", request, pageContext) %> //-> blank
<%= ELEvaluator.evaluate("${1 + 1}", request, pageContext %> // -> 2

Do these vars/objs have to exist on the request obj? or be registered with the pageContext/Evaluator?

Thanks

Answer 1

${foo} means

• find a page-scope attribute named “foo” and, if not found
• find a request-scope attribute named “foo” and, if not found
• find a session-scope attribute named “foo” and, if not found
• find an application-scope attribute named “foo”

So, if you want some object to be available to the EL, store it in the appropriate scope:

pageContext.setAttribute("foo", theObject);
// or
request.setAttribute("foo", theObject);
// or
session.setAttribute("foo", theObject);
// or
servletContext.setAttribute("foo", theObject);