c:out Action Tag with EL Expressions

JSP Tutorials - Herong's Tutorial Examples

∟c:out Action Tag with EL Expressions

This section provides a tutorial example of using EL expressions in the c:out JSTL Core tag.

The <c:out> action tag is probably the best tag to show how EL (Expression Language) expression can be used in JSTL tags. Here is a JSP page example, ExpExampleTag.jspx:

<?xml version="1.0"?>
<jsp:root xmlns:jsp="http://java.sun.com/JSP/Page"
   xmlns:c="http://java.sun.com/jsp/jstl/core" version="2.3">
<!-- ExpExampleTag.jspx
 - Copyright (c) 2006 HerongYang.com. All Rights Reserved.
-->
<jsp:directive.page contentType="text/html"/>
<html><body>
<p>JSTL EL Expression Examples:</p>
<c:out value="1. ${1+1==2}"/><br/>
<c:out value="2. ${1+1}"/><br/>
<c:out value="3. ${1/3}"/><br/>
<c:out value="4. ${1.0/3.0}"/><br/>
<c:out value="5. ${quantity*price lt 100.0 and country=='USA'}"/><br/>
<c:set var="message" value="Hi there!"/>
<c:out value="6. ${message}"/><br/>
<c:out value="7. ${'message'}"/><br/>
<c:out value="10. ${pageContext.request.method}"/><br/>
<c:out value="11. ${pageContext.request[method]}"/><br/>
<c:out value="12. ${pageContext.request['method']}"/><br/>
<!-- c:out value="13. ${pageContext.request.'method'}"/><br/ -->
<!-- c:out value="14. ${pageContext.'request'.method}"/><br/ -->
<c:out value="15. ${pageContext['request']['method']}"/><br/>
<c:out value="16. ${pageContext['request'].method}"/><br/>
<!-- c:out value="20. ${pageContext.request.cookies.length}"/><br/ -->
<c:out value="21. ${pageContext.request.cookies[0].name}"/><br/>
<c:out value="22. ${pageContext.request.cookies[0].value}"/><br/>
<c:out value="23. ${pageContext.request.cookies[0]}"/><br/>
<!-- c:out value="24. ${pageContext.request.cookies.0}"/><br/ -->
<!-- c:out value="25. ${pageContext.request.cookies.0.name}"/><br/ -->
<c:out value="26. ${pageContext.request.cookies['0']}"/><br/>
<jsp:scriptlet>double pi = 3.14159;</jsp:scriptlet>
<c:out value="30. ${pi}"/><br/>
<jsp:scriptlet>
   double[] list = new double[3];
   list[0] = 9.99;
</jsp:scriptlet>
<c:out value="31. ${list[0]}"/><br/>
<!-- c:out value="32. ${pageContext.request.class.name}"/><br/ -->
<!-- c:out value="33. ${pageContext[request[class[name]]]}"/><br/ -->
<!-- c:out value="34. ${out.class.name}"/><br/ -->
<!-- c:out value="35. ${pageContext.out.class.name}"/><br/ -->
<c:out value="36. ${sessionScope.now}"/><br/>
<jsp:scriptlet>
   session.setAttribute("now", new java.util.Date());
</jsp:scriptlet>
<c:out value="37. ${sessionScope.now.time}"/><br/>
</body></html>
</jsp:root>

Note that:

Tests 13, 14, 20, 24 and 25 are commented out, because they are invalid EL expressions.
Tests 32, 33, 34, and 35 are commented out, because Object.getClass().getName() methods are not considered as property getter methods in JSP 2.1 and higher.

If you visit the ExpExampleTag.jspx page for the first time, you will get:

JSTL EL Expression Examples:

1. true
2. 2
3. 0.3333333333333333
4. 0.3333333333333333
5. false
6. Hi there!
7. message
10. GET
11.
12. GET
15. GET
16. GET
21.
22.
23.
26.
30.
31.
36.
37. 1353078652164

If you visit the ExpExampleTag.jspx page again, you will get:

JSTL EL Expression Examples:

1. true
2. 2
3. 0.3333333333333333
4. 0.3333333333333333
5. false
6. Hi there!
7. message
10. GET
11.
12. GET
15. GET
16. GET
21. JSESSIONID
22. 669C0B7624702AF8209AF2B672ED9BFA
23. javax.servlet.http.Cookie@4c2b5e
26. javax.servlet.http.Cookie@4c2b5e
30.
31.
36. Sun Jul 1 10:10:52 EST 2012
37. 1152816698019

Note that:

Tests 21, 22, 23, and 26 have values now, because the second HTTP request included the JSESSIONID cookie that was created by the first page visit.
Test 36 also has a value now, because attribute "now" saved in the "sessionScope" from the first page visit is maintained by the server.