JSTL - Core Library

JSTL (JSP Standard Tag Library) is a collection of pre-built tags created by SUN Microsystems. Instead of writing Java code inside JSP pages, developers can use these standard tags to perform common tasks.

Main objective of JSTL: Remove Java code from JSP.

While EL (Expression Language) removes simple expressions, JSTL removes procedural Java code like conditions and loops.

JSTL is divided into 5 sub-libraries:

• Core Library — conditions, loops, variable management, URL handling
• SQL Library — database operations
• Functions Library — string manipulation
• FMT (Formatting) Library — number/date formatting for internationalization
• XML Library — reading and writing XML data

By default, JSTL is not available to JSP pages. You must add two JAR files to your application:

Where to place the JARs: It is recommended to place these files at the server level (e.g., D:\Tomcat 7.0\lib) instead of the application level, so all web applications can use them.

Taglib directive — To use the core library in a JSP page:

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

The core library is divided into 4 categories based on functionality:

The <c:out> tag writes expressions and template text to the JSP output. It supports three attributes:

Form 1 — Simple output:

<c:out value="durga" />               <!-- Prints: durga -->
<c:out value="${param.user}" />      <!-- Prints the request parameter "user" -->

Form 2 — With default value:

<c:out value="${param.user}" default="Guest" />
<!-- If "user" parameter is missing, prints: Guest -->

The <c:set> tag sets attributes in any scope, or sets bean/map properties.

Form 1 — Set an attribute:

<c:set var="name" value="attributeValue" scope="request" />

The scope attribute is optional — default is page scope.

Form 2 — Set a bean or map property:

<c:set target="customer" property="name" value="pavan" />

Example:

<%@ taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core" %>
<c:set var="x" value="10" scope="request" />
<c:set var="y" value="20" scope="request" />
<c:set var="sum" value="${x + y}" scope="session" />
<h1>The result is: <c:out value="${sum}" /></h1>

Attributes of c:set:

The <c:remove> tag removes an attribute from a specified scope.

<c:remove var="x" scope="session" />

Attributes:

If scope is not specified, the container searches through page → request → session → application scopes in order.

Example:

<%@ taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core" %>
<c:set var="x" value="10" scope="page" />
<c:set var="y" value="60" scope="page" />
<c:set var="sum" value="${x + y}" scope="session" />

<h1>
  The result is: <c:out value="${sum}" /><br>
  <c:remove var="x" />
  <c:remove var="y" />
  <c:remove var="sum" />
  The result is: <c:out value="${sum}" default="1000" />
</h1>

The <c:catch> tag catches exceptions within the JSP instead of forwarding to an error page. Place risky code inside the tag body:

<c:catch>
  Risky Code
</c:catch>

If an exception is raised, this tag suppresses it and the rest of the JSP executes normally.

To capture the exception, use the var attribute:

<c:catch var="e">
  <%
    int age = Integer.parseInt(request.getParameter("uage"));
  %>
  Age: ${param.uage}<br>
</c:catch>

<c:if test="${e != null}">
  Oops... Exception raised: ${e}<br>
</c:if>

Behavior:

• With valid input (uage=47): displays the age normally
• With invalid input (uage=ten): catches the NumberFormatException and shows the error message

Summary of General Purpose Tags:

The <c:if> tag implements the core Java if statement. There are two forms:

Form 1 — Without body (evaluates condition and stores result):

<c:if test="test_condition" var="x" scope="session" />

Both test and var are mandatory. scope is optional (default: page). The test result is stored in variable x for later use.

Form 2 — With body (executes body if condition is true):

<c:if test="test_condition">
  Body executes only if test_condition is true
</c:if>

Both var and scope are optional. The test attribute is mandatory.

Example:

<%@ taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core" %>
<c:set var="x" value="10" scope="request" />

<c:if test="${x eq '10'}">
  <h1>x value is equal to 10</h1>
</c:if>

These tags implement if-else and switch statements. JSTL has no standalone "else" tag.

If-Else pattern:

<c:choose>
  <c:when test="test_condition">
    Action 1 (executes if true)
  </c:when>
  <c:otherwise>
    Action 2 (executes if false)
  </c:otherwise>
</c:choose>

Switch pattern:

<c:choose>
  <c:when test="${s == 1}">Sunday</c:when>
  <c:when test="${s == 2}">Monday</c:when>
  <c:when test="${s == 3}">Tuesday</c:when>
  <c:when test="${s == 4}">Wednesday</c:when>
  <c:when test="${s == 5}">Thursday</c:when>
  <c:otherwise>Select between 1 and 5</c:otherwise>
</c:choose>

Rules:

• <c:choose> must contain at least one <c:when>
• <c:otherwise> is optional and must be the last child
• Every <c:when> implicitly contains a break statement — no fall-through
• <c:choose> and <c:otherwise> take no attributes
• <c:when> takes one mandatory attribute: test

The <c:import> tag includes the response of another page at request processing time (dynamic include).

Form 1 — Basic import:

<c:import url="second.jsp" />

Form 2 — Cross-context import (from another web application):

<c:import url="/second.jsp" context="/webapp2" />

Both url and context must use absolute paths (start with /).

Form 3 — Store result in a variable (reusable without re-importing):

<c:import url="second.jsp" var="x" scope="request" />
${x}<br>   <!-- Use the stored result multiple times -->

Form 4 — Store as Reader (alternative to var):

<c:import url="second.jsp" varReader="r" scope="page" />

Form 5 — Pass parameters to the target page:

<c:import url="second.jsp">
  <c:param name="c1" value="JAVA" />
  <c:param name="c2" value="PHP" />
</c:import>

The <c:redirect> tag redirects the request to another page. It is equivalent to sendRedirect() of ServletResponse.

Form 1 — Basic redirect:

<c:redirect url="second.jsp" />

The url can be relative or absolute.

Form 2 — Cross-context redirect:

<c:redirect url="/second.jsp" context="/webapp2" />

Form 3 — Redirect with parameters:

<c:redirect url="second.jsp">
  <c:param name="c1" value="Java" />
  <c:param name="c2" value="PHP" />
</c:redirect>

The <c:url> tag rewrites URLs to append session information (for session tracking) and form parameters.

Form 1 — Basic URL rewrite:

<c:url value="second.jsp" var="x" scope="request" />
<h1>The modified URL: ${x}</h1>

The encoded URL with session ID is stored in variable x.

Form 2 — Cross-context URL:

<c:url value="/second.jsp" context="/webapp2" var="x" scope="request" />

Form 3 — URL with parameters:

<c:url value="second.jsp" var="x">
  <c:param name="c1" value="JAVA" />
  <c:param name="c2" value="PHP" />
</c:url>

<a href="${x}">Click Here to go to Next Page</a>

Complete Core Library Summary: