JSTL - Iteration Tags

JSTL provides two iteration tags in the core library:

Form 1 — Simple numeric loop:

<c:forEach begin="1" end="10" step="1">
  <h1>Learning JSTL is very easy!</h1>
</c:forEach>

This prints the message 10 times.

Attributes:

Examples:

<c:forEach begin="1" end="10" step="2">    <!-- Runs 5 times -->
<c:forEach begin="4" end="0" step="-1">   <!-- INVALID: step cannot be negative -->

Form 2 — Using var to access the counter:

The <c:forEach> tag maintains an internal counter variable. Use var to access it.

<c:forEach begin="1" end="10" step="2" var="count">
  <h1>Learning JSTL is very easy!!! --- ${count}</h1>
</c:forEach>

This prints the message 5 times with counter values 1, 3, 5, 7, 9.

Note: The var variable is local to the loop — it cannot be accessed outside the loop body.

Form 3 — Iterating over arrays and collections:

<c:forEach items="collection_object" var="current_object">
  body
</c:forEach>

The items attribute accepts a Collection, Array, Map, or String. The current item is stored in the var variable.

Example — Print all elements of an array:

<%@ taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core" %>
<%
  String[] s = {"A", "B", "C", "D"};
  pageContext.setAttribute("s", s);
%>

<c:forEach items="${s}" var="obj">
  <h1>The current Object is: ${obj}</h1>
</c:forEach>

Example — Print all request headers:

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

<table border="2">
  <c:forEach items="${header}" var="hdr">
    <tr>
      <td>${hdr.key}</td>
      <td>${hdr.value}</td>
    </tr>
  </c:forEach>
</table>

Example — Print all request parameters:

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

<table border="2">
  <c:forEach items="${param}" var="p">
    <tr>
      <td>${p.key}</td>
      <td>${p.value}</td>
    </tr>
  </c:forEach>
</table>

Form 4 — Using varStatus for iteration metadata:

The varStatus attribute provides an object of type javax.servlet.jsp.core.TagLoopStatus with methods describing the current iteration state.

Example:

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

<c:forEach items="durga,pavan,ravi,shiva" varStatus="status">
  <h1>
    Is it First Iteration: ${status.first}<br>
    The current Object is: ${status.current}<br>
    Number of iterations already completed: ${status.count}<br>
    Is it Last Iteration: ${status.last}<br>
    <hr>
  </h1>
</c:forEach>

TagLoopStatus methods:

<c:forTokens> is a specialized version of <c:forEach> that splits strings by a delimiter — similar to Java's StringTokenizer.

Basic form:

<c:forTokens items="durga.pavan.shiva.ravi" delims="." var="x">
  <h1>Hello: ${x}</h1>
</c:forTokens>

With begin, end, step, and varStatus:

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

<c:forTokens items="one,two,three,four,five,six" delims="," var="x" begin="2" end="5" step="1">
  <h1>Current Token is: ${x}</h1>
</c:forTokens>

This iterates over tokens at indices 2, 3, 4, 5 (tokens: three, four, five, six).

c:forEach vs c:forTokens:

<c:forTokens> is considered a specialized version of <c:forEach> — it only works with String items.

The JSTL SQL Library provides tags for communicating with databases. Add this taglib directive to use it:

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

Important SQL tags:

Example — Select query:

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

<sql:setDataSource var="ds" driver="oracle.jdbc.OracleDriver"
  url="jdbc:oracle:thin:@localhost:1521:XE"
  user="scott" password="tiger" />

<sql:query dataSource="${ds}" var="result">
  SELECT * from Employees
</sql:query>

<h1>
  <c:forEach items="${result.rows}" var="row">
    ${row.eno} -- ${row.ename} -- ${row.esal} -- ${row.eaddr}<br>
  </c:forEach>
</h1>

Example — Insert:

<sql:update dataSource="${ds}" var="count">
  insert into employees values(500, 'Lasya', 5000, 'hyd')
</sql:update>
<h1>The number of rows inserted: ${count}</h1>

Example — Transaction:

<sql:transaction dataSource="${ds}">
  <sql:update>
    update employees set esal=esal-1000 where ename='durga'
  </sql:update>
  <sql:update>
    update employees set esal=esal+1000 where ename='sunny'
  </sql:update>
</sql:transaction>

Note: It is not recommended to use JSTL SQL Library in production JSP pages. JSP is meant for presentation logic, not business or database logic.

The JSTL Functions Library provides tags for general string manipulation. Add this taglib directive:

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

Example — String operations:

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

<c:set var="s" value="Hello Learning JSTL is Very Easy" />

<h1>
  Length: ${fn:length(s)}<br>
  In Upper Case: ${fn:toUpperCase(s)}<br>
  In Lower Case: ${fn:toLowerCase(s)}<br>
  Sub String from index 6 to 15: ${fn:substring(s, 6, 15)}<br>
  Is s contains JSTL: ${fn:contains(s, "JSTL")}<br>
  Is s starts with Hello: ${fn:startsWith(s, "Hello")}<br>
  Is s ends with Easy: ${fn:endsWith(s, "Easy")}<br>
</h1>

Example — Split and Join:

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

<c:set var="data" value="sunny,mallika,veena,reshmi,anasuya" />

<c:set var="s" value="${fn:split(data, ',')}" />
<h1>
  Result of split method:<br>
  <c:forEach items="${s}" var="s1">
    ${s1}<br>
  </c:forEach>

  <c:set var="result" value="${fn:join(s, '-')}" />
  Result of Joining: ${result}
</h1>