JSTL Core Tags c:choose, c:when, c:otherwise Example

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Last Updated on 31 August 2019   |   Print  Email


In this post, you will learn how to use the <c:choose>, <c:when> and <c:otherwise> tags in the JSTL core tags library.

You know, the tags <c:choose>, <c:when> and <c:otherwise> works together to form conditional logic. Using these tags we can implement ‘if-else’ logic and to provide alternate execution.

 

JSTL <c:choose>, <c:when> and <c:otherwise> Syntax:

<c:choose>
    <c:when test="<boolean>"/>
        ...
    </c:when>
    <c:when test="<boolean>"/>
        ...
    </c:when>
    ...
    ...
    <c:otherwise>
        ...
    </c:otherwise>
</c:choose>

 

Attributes for tag <c:when>

Name

Required

Type

Description

test

True

boolean

The test expression which determines whether the body of the tag is executed or not.

 

The tags <c:choose> and <c:otherwise> does not have any attributes.

The <c:when>tag has an attribute ‘test’ to indicate test expression. If the expression evaluates to true then the proceeding statements in the <c:when> will be executed. If the test evaluates to false, the code in the <c:otherwise> will be executed.

 

JSTL <c:choose>, <c:when>, <c:otherwise> Example:

To demonstrate the usage of <c:choose>, <c:when> and <c:otherwise> let’s build a miniature color selector. We will have a JSP which contains few radio buttons to represent colors and user can select a particular color and click on submit. The selected color will be reflected in the sample HTML table we create. The following is the code for the JSP page.

<%@ page language="java" contentType="text/html; charset=ISO-8859-1"
    pageEncoding="ISO-8859-1"%>
<%@ taglib uri="http://java.sun.com/jsp/jstl/core" prefix="c" %>    
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" 
"http://www.w3.org/TR/html4/loose.dtd">
<html>
    <head>
        <meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1">
        <title>&lt;c:choose&gt;, &lt;c:when&gt;, &lt;c:otherwise&gt; Demo</title>
    </head>
    <body>
       <h1>&lt;c:choose&gt;, &lt;c:when&gt;, &lt;c:otherwise&gt; Demo</h1>
       <c:choose>
       <c:when test="${param.colorField == 'red'}">
         <table border="0" width="150" height="50" bgcolor="#ff0000">
           <tr><td>&nbsp;</td></tr>
         </table>
      </c:when>
     <c:when test="${param.colorField == 'blue'}">
       <table border="0" width="150" height="50" bgcolor="#0000ff">
         <tr><td>&nbsp;</td></tr>
      </table>
    </c:when>
    <c:when test="${param.colorField == 'green'}">
        <table border="0" width="150" height="50" bgcolor="#00ff00">
          <tr><td>&nbsp;</td></tr>
       </table>
    </c:when>
    <c:when test="${param.colorField == 'yellow'}">
        <table border="0" width="150" height="50" bgcolor="#ffff00">
         <tr><td>&nbsp;</td></tr>
        </table>
     </c:when>
  <c:otherwise>
    <table border="0" width="150" height="50" bgcolor="#000000">
      <tr><td>&nbsp;</td></tr>
     </table>
  </c:otherwise>
</c:choose>
<br/>
     <form name="conditionalForm" 
        action="${pageContext.request.contextPath}/tag-types/core/choose-when-otherwise.jsp" 
        method="POST">
           Select one color and click submit 
           (if you click submit without selecting color, default color is shown): <br/>
           red <input type="radio" name="colorField" value="red"/><br/>
           blue <input type="radio" name="colorField" value="blue"/><br/>
           green <input type="radio" name="colorField" value="green"/><br/>
           yellow <input type="radio" name="colorField" value="yellow"/><br/>
        <input type="submit" value="submit"/> 
    </form>
  </body>
</html>

In the above sample code, you can see that user selected color is captured from request parameter and conditional checking is performed to render the selected color using <c:choose>,<c:when> and <c:otherwise> tags. Also note that <c:otherwise> tag is used to specify the default color when no other color is selected.

We can have any number of alternate conditions with <c:when> tags, however there should only one default execution with <c:otherwise>. The <c:otherwise> is a way to specify default execution if none of the conditions were true.

Please note that tags <c:choose> and <c:otherwise> do not have any attributes.



 

Output:

Couple of sample runs by selecting red and blue as our color choices. The following screen demonstrates the sample runs.

choose-when-otherwise-demo

 

Recommended Usage of JSTL <c:choose>, <c:when> and <c:otherwise> tags:

The combination of these tags is especially useful in scenarios where multiple conditions are to be evaluated. We use <c:otherwise> to provide default functionality where all the conditions specified in <c:when> are evaluated to false.

 

Other JSTL Core Tags:

if |  catch  |  choose   |  forEach  |  forTokens   |  import   |  out   |  param  |  redirect  |  remove   |  set  |  url


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