JSTL (JSP Standard tag library) :-

JSTL (JSP Standard tag library) is a collection of JSP custom tags libraries, which provides an alternative of using Tags in place of plain old java code for web development in JSP. JSTL provide tags for almost all the JSP Scriptlet code. JSTL is a collection of several tag libraries specified by their URI,s (Uniform Resource Identifier).

Advantages of JSTL -

1- JSTL is easy to learn and understand.
2- Provides reusability of code.
3- Provide Scriptlet free coding.
4- Easier to read and understand as it uses XML like tag structure.
5- Provides formatting of numbers and strings, and internationalization (I18N) support.

Types of JSTL tag libraries -

JSTL tags can be classified into the following five categories according to their functionalities -

Tag library Description URI Prefix
Core tag library As the name indicates, it provides tags for core java functionalities like - loops, conditional statements, URL management etc. http://java.sun.com/jsp/jstl/core c
Formatting/Internationalization Tag Library Provide tags for parsing and formatting data http://java.sun.com/jsp/jstl/fmt fmt
SQL Tag Library Provide tags for sql database access. http://java.sun.com/jsp/jstl/sql sql
XML Tag Library Provide tags for accessing xml documents. http://java.sun.com/jsp/jstl/xml x
JSTL Functions Provide functions for string manipulation and to find collection length http://java.sun.com/jsp/jstl/functions fn

Syntax to include JSTL tag library in JSP -

TO include a tag library in our JSP file, we need to specify the 'uri' and 'prefix' of the desired tag library as follows -
<%@taglib prefix="tag_lib_prefix" uri="tag_lib_URI"  %>    
For Example - To include 'Core Tag Library' into JSP, you need to specify its 'URI' and 'prefix' as follows -
<%@taglib prefix="http://java.sun.com/jsp/jstl/core" uri="c"  %>    

JSTL Tag Library Jar File ('jstl1.2.jar')-

Some IDE already have the jar file required to work with JSTL tag library, whereas for others we have to download and include the required jar file in our project.
NetBeans IDE - For NetBeans IDE the required jar file is already included. So in NetBeans we can work directly with JSTL.
Eclipse IDE- For Eclipse IDE you need to download 'jstl1.2.jar' file. we can download it from here -
Download jstl1.2.jar file
After downloading it go to 'lib' folder and paste the downloaded 'jstl1.2.jar' file there, and now you will be able to work with JSTL tag library.