Question

What is the difference between Custom Tag Libraries and Core Tag Libraries in JSP?

Answer 1

Custom tag libraries are homegrown tag libraries. Core tag libraries are part of JSTL (JSP Standard Tag Library). You can find an overview of them all in the JSTL taglib documentation. It’s the JSTL core one. It just offers a set of tags which are likely to be very commonly used to control the flow/output of a JSP page. Here’s an extract of relevance:

JSTL core

---

Standard Syntax:

    <%@ taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core" %>

XML Syntax:

    <anyxmlelement xmlns:c="http://java.sun.com/jsp/jstl/core" />

---

JSTL 1.1 core library

Tag Library Information

• Display Name: JSTL core
• Version: 1.1
• Short Name: c
• URI: http://java.sun.com/jsp/jstl/core

Tag Summary

• catch Catches any Throwable that occurs in its body and optionally exposes it.

• choose Simple conditional tag that establishes a context for mutually exclusive conditional operations, marked by <when> and <otherwise>

• if Simple conditional tag, which evalutes its body if the supplied condition is true and optionally exposes a Boolean scripting variable representing the evaluation of this condition

• import Retrieves an absolute or relative URL and exposes its contents to either the page, a String in ‘var’, or a Reader in ‘varReader’.

• forEach The basic iteration tag, accepting many different collection types and supporting subsetting and other functionality

• forTokens Iterates over tokens, separated by the supplied delimeters

• out Like <%= ... >, but for expressions.

• otherwise Subtag of <choose> that follows tags and runs only if all of the prior conditions evaluated to ‘false’

• param Adds a parameter to a containing ‘import’ tag’s URL.

• redirect Redirects to a new URL.

• remove Removes a scoped variable (from a particular scope, if specified).

• set Sets the result of an expression evaluation in a ‘scope’

• url Creates a URL with optional query parameters.

• when Subtag of <choose> that includes its body if its condition evalutes to ‘true’

See also:

• Java EE 5 tutorial – Using JSTL
• Java EE 5 tutorial – Custom tags in JSP pages

Note that Java EE 6 tutorial doesn’t mention about them anywhere as JSP is considered to be “legacy”. It’s not officially deprecated though, the focus is just more put on Facelets, the successor of JSP, and the MVC framework JSF.