What is JSTL (JavaServer Pages Standard Tag Library)…

JSTL is a set of standard tag libraries for JavaServer Pages (JSP). It provides ready-to-use tags for common tasks such as iterating over collections, conditional execution, data formatting, and interaction with XML, which helps separate presentation logic (JSP) from business logic (Java).

Main functional areas of JSTL:

Core Tags: Conditional operators (<c:if>, <c:choose>, <c:when>, <c:otherwise>), loops (<c:forEach>, <c:forTokens>), working with variables (<c:set>, <c:remove>, <c:catch>), redirection (<c:redirect>), import (<c:import>), URL handling (<c:url>).
Formatting Tags: Number and date formatting (<fmt:formatNumber>, <fmt:formatDate>), internationalization (<fmt:setLocale>, <fmt:bundle>, <fmt:message>).
XML Tags: Parsing and transforming XML documents (<x:parse>, <x:transform>), working with XPath (<x:out>, <x:set>, <x:if>, <x:forEach>).
SQL Tags: (Considered deprecated for production applications, prefer using separate data access layers) Executing SQL queries (<sql:query>, <sql:update>).
Functions: A set of built-in functions available in EL (Expression Language) for working with strings, collections, and XML.

Advantages of JSTL:

Separation of Concerns (SoC): Reduces Java code (scriptlets) in JSP, making pages cleaner and easier for designers to maintain.
Improved Readability: Using tags more clearly describes presentation logic than embedding Java code.
Performance Enhancement: Some processing done by JSTL can be more efficient than similar code in scriptlets, thanks to standard implementation.
Standardization: Provides a unified approach to common tasks in JSP.

Example of using the <c:forEach> tag:

<%@ taglib uri="http://java.sun.com/jsp/jstl/core" prefix="c" %>
<html>
<head><title>Item List</title></head>
<body>
    <h1>Items:</h1>
    <ul>
        <c:forEach var="item" items="${myItems}">
            <li>${item}</li>
        </c:forEach>
    </ul>
</body>
</html>

In this example, the <c:forEach> tag iterates over the collection myItems, available in the page context (e.g., from request or session attribute), and displays each item as a list element.

JSTL is an important tool for developing web applications based on JSP, contributing to creating more structured, maintainable, and readable presentation code.

What is JSTL (JavaServer Pages Standard Tag Library) and what is it used for?