EL or JSTL Not Working As Expected
One of the most common causes of problems with the EL and JSTL is a configuration mismatch between the version of
JSP that you are using, the version of the JSTL that you employ, and how you have declared your web application in the deployment descriptor (web.xml).
For a JSP 2.1 container (such as
Tomcat 6),
you should be using JSTL 1.2, and you should have your web application declared as a
Servlets 2.5 web app by using the Servlets 2.5 XML Schema.
For a JSP 2.0 container (such as Tomcat 5), you should be using JSTL 1.1, and you should have your web application declared as a Servlets 2.4 web app by using the Servlets 2.4 XML Schema.
For a JSP 1.x container (such as Tomcat 4), you should be using JSTL 1.0, and you should have your web application declared as a Servlets 2.3 web app by using the Servlets 2.3 DOCTYPE.
See
ServletsWebXml for information on declaring the deployment descriptor properly. Note: even though you
can use the Servlets 2.3 DOCTYPE with a JSP 2.0 container, this will put the container into "compatibility mode" and the the EL will be disabled on the JSP pages.
See
JstlTagLibDefinitions and
SetupJstlForJsp2 for information on obtaining and declaring the correct JSTL version.
JspFaq 
