Version matching of JSP, JSTL and Servlet

Working with JSP, JSTL, Servlet and Container is not an easy job if you download and configure every part by yourself. The most important problem is version matching. Also web.xml must be correctly configured to make use of the right version of Servlet/JSP.

Web app descriptor (web.xml)
To make use of correct version of JSP/JSTL/EL, you should read following posts which give detailed information you need to know to write web.xml:
http://faq.javaranch.com/java/ServletsWebXml

Some useful resources I found:
http://faq.javaranch.com/java/ElOrJstlNotWorkingAsExpected
http://forum.springframework.org/archive/index.php/t-19866.html
http://blog.csdn.net/eviliw/archive/2007/12/17/1944270.aspx
http://faq.javaranch.com/java/JstlTagLibDefinitions

On Sun's website, it is so hard to find a download link for JSTL 1.2. Usually you will be directed to the JSTL spec site.
You can download JSTL 1.2 from here: https://maven-repository.dev.java.net/repository/jstl/jars/.
Note for JSTL 1.2 there is just one jar file instead of two.
In JSTL 1.1/1.0, there are two jars : jstl.jar and standard.jar.
You can download JSTL 1.1 from here http://jakarta.apache.org/site/downloads/downloads_taglibs-standard.cgi and JSTL 1.0 from http://jakarta.apache.org/site/downloads/downloads_taglibs-standard.cgi.

Version match
JSTL 1.0 : Servlet 2.3 : JSP 1,2 (tomcat 4)
JSTL 1.1 : Servlet 2.4 : JSP 2.0 (tomcat 5)
JSTL 1.2 : Servlet 2.5 : JSP 2.1 (tomcat 6)
In old versions of JSP, EL is not enabled by default!! You can enable EL manually by using JSP page directory.
JSTL  jars are not included in tomcat distributions so far. You need to download and deploy JSTL by yourself.

JSTL 1.0 specifies a set of custom tag libraries based on the JSP 1.2 API. There are four separate tag libraries, each containing custom actions targeting a specific functional area. This table lists each library with its recommended tag prefix and default URI:

Description	Prefix	Default URI
Core	c	http://java.sun.com/jstl/core
XML Processing	x	http://java.sun.com/jstl/xml
I18N & Formatting	fmt	http://java.sun.com/jstl/fmt
Database Access	sql	http://java.sun.com/jstl/sql

JSTL 1.1 specifies a set of custom tag libraries based on the JSP 2.0 API. There are five separate tag libraries, each containing custom actions targeting a specific functional area. This table lists each library with its recommended tag prefix and default URI:

Description	Prefix	Default URI
Core	c	http://java.sun.com/jsp/jstl/core
XML Processing	x	http://java.sun.com/jsp/jstl/xml
I18N & Formatting	fmt	http://java.sun.com/jsp/jstl/fmt
Database Access	sql	http://java.sun.com/jsp/jstl/sql

One missed tag in the table is "functions".
It seems that you also can use tag URI like this: http://java.sum.com/jstl/core_rt. And it works in my application. However, I have not investigated what's going on behind the scene. So this may or may not work generally. Instead, you should always use the new tag URI.

Prefixes and URL of JSTL 1.2 Tag Libraries are the same as that of JSTL 1.1.

Troubleshooting
(1) If you get following error "According  to TLD or attribute directive in tag file, attribute test does not accept any expressions", it is possible that you don't specify tag prefix and URI correctly. You may be using JSTL 1.2 while you specify tag URI of JSTL 1.0 wrongly. Take Core as an example, tag URI in JSTL 1.1/1.2 is http://java.sun.com/jsp/jstl/core while tag URI in JSTL 1.0 is http://java.sun.com/jstl/core.
(2) If your EL/JSP is displayed directly without evaluation. it is highly possible that your web.xml file specifies wrong JSP version. See this post http://faq.javaranch.com/java/ServletsWebXml.