XML - Managing Data Exchange/JSTL

XML - Managing Data Exchange

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The JavaServer Pages Standard Tag Library (Short Form: JSTL) is a collection of four custom-tag libraries which extend the JSP specification. As a component it is allocated in the Java EE Web application development platform. The JSTL is administrated in the setting of the Java Community Process (JCP) 052. Within the Jakarta-Project there are reference implementations to these specifications.

Components

In version 1.1 the following libraries were intended:

core: iterative, conditional, URL-specific and general Tags
xml: Tags from the field XML and XML-transformation
sql: Tags for direct data base administration
i18n: Tags for formatting and internationalization

History

In its original Version 1.0 an „Expression Language“ was intended in comparison to Version 1.1. With JSP 2.0 JSP-EL was taken up in the JSP-specifications itself. Therefore the primary goal of JSTL 1.1 is the adaption of the libraries to the JSP-EL for JSP 2.0. With the libraries in version 1.2 the JSTL is up to date concerning the unification of the Expression Language by the JSP 2.1 and JSF-1.2-specifications. Furthermore the JSTL in Version 1.2 is part of the Java-EE-5-Platform.

Usage of JSTL 1.1

As for the use of JSTL 1.1 the JSP-EL is required, a servlet-container has to be conform to at least the JSP-2.0 specifications in order to be be used on this. The reference implementation is made up of two JAR – archives „standard.jar“ and „jstl.jar“. In most containers they usually need to be located in the lib-path of the web application only. To ensure backwards compatibility the JSTL 1.1 is referenced by the URI „http://java.sun.com/jsp/jstl/fmt“ whereas „http://java.sun.com/jstl/fmt“ is used for JSTL 1.0.

Example JSP-page in XML-notation (JSPX):

<?xml version="1.0" encoding="utf-8" ?>
<jsp:root
  xmlns:jsp="http://java.sun.com/JSP/Page"
  xmlns:c="http://java.sun.com/jsp/jstl/core"
  xmlns:fmt="http://java.sun.com/jsp/jstl/fmt"
version="2.0">

<html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en">
<head>
  <title>JSTL 1.1</title>
</head>
<body>

<h1>Iteration</h1>
<ul>
  <c:forEach var="num" begin="1" end="10">
    <li>Number<c:out value="${num}"/></li>
  </c:forEach>
</ul>

<h1>Formatting</h1>
<p>
  Currency: <fmt:formatNumber value="10000" type="currency" currencyCode="EUR" />
</p>

</body>
</html>
</jsp:root>

Code-Explanations:

In the jsp:root – element the usage of the basis- und the I18N-Taglibs (core and fmt) from the JSTL is indicated and linked to the according XML-namespace. Under the headline Iteration the forEach-Tag from the core-library is used: It displays the tag-body (i.e., the content of the Tag) ten times. In this loop with ${num} you can find JSP – Expression. With every loop cycle the current data from num is displayed here. Under the headline Formatting the formatNumber-tag from the fmt – library of JSTL is used. Depending on the adjusted language (this can be set by fmt:setLocale for example) the number 10000 will be formatted (e.g. in German as „EUR 10.000,00“ and in English as „EUR 10,000.00“)

Alternatives to the JSTL

Struts vs. JSTL: There are in fact many instances where a Struts tag and JSTL tag will perform equivalent functions. Unlike the Struts-Framework the JSTL is not linked to a certain architecture–paradigm, like the Model–View–Controller separation. JSTL tags are more powerful compared to struts tags, because JSTL is a more standard part of the J2EE specification, while at the same time many options are available like condition checking, comparing strings, triming white spaces, converting upper case or lower case, etc. Both libraries own tags with identical name. So if these libraries are mixed in applications, what is possible, it needs to be attended to use unique prefixes(JSP) or namespaces (JSPX).

Example Applications & Tutorials

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