Java

Resources/tutorials:

• Official JavaServer Pages Standard Tag Library 1.1 Tag Reference
• Biblioteca Padrão de Tags JSP: a good introductory article with examples (PT);
• JSTL Examples
• Mixing JSTL and JSF in Web Applications

Examples:

choose

the choose tag (only one clause will be outputted):

<c:choose>
    <c:when test="${cart.numberOfItems > 1}">
        <p>Your shopping cart contains ${cart.numberOfItems} items.</p>
    </c:when>
    <c:when test="${cart.numberOfItems == 1}">
        <p>Your shopping cart contains ${cart.numberOfItems} item.</p>
    </c:when>
    <c:otherwise>
        <p>Your shopping cart is empty.</p>
    </c:otherwise>
</c:choose>

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set

the set tag using choose to set the value (note how the var "value" is accesses trough EL in the anchor below the set tag):

<c:set var="value">
    <c:choose>
        <c:when test="${!empty selectedCategory}">
            category
        </c:when>       
        <c:otherwise>
            index.jsp
        </c:otherwise>
    </c:choose>
</c:set>
<a href="${value}">continue shopping</a>

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url

<c:url var="url" value="chooseLanguage">
    <c:param name="language" value="en"/>
</c:url>
<div class="bubble"><a href="${url}">english</a></div>

The link will have a url with a query string: "chooseLanguage?language=en"
The url jstl tag is used in order to properly encode the request URL in the event that URL rewriting is used as a means for session tracking (when the client has cookies disabled).

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fn library (JSTL functions)

See the complete fn list
You can use JSTL's functions (i.e., fn) library to perform string operations.

<%@taglib prefix="fn" uri="http://java.sun.com/jsp/jstl/functions" %>
(...)
<%-- Test if servlet path contains '/confirmation'--%>
<c:if test="${!fn:contains(pageContext.request.servletPath,'/confirmation')}">
</c:if>

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