What is the difference between <c:if> and <c:when>?

Question

I've noticed usages of <c:if ...> in one place of JSP code and <c:when ...> in the other. The things they do look the same for me. Are these two commands just aliases?

Answer 1

<c:if is a simple if-clause. <c:when> has options for multiple if-clauses and an else clause. Compare:

<c:if test="${foo == 'bar'}">...</c:if> 

with

<c:choose>    <c:when test="${foo == 'bar'}">...</c:when>    <c:when test="${foo == 'baz'}">...</c:when>    <c:otherwise>...</c:otherwise> </c:choose> 

Answer 2

<c:if> doesn't support any kind of "else" or "else if" functionality. <c:when> does. So if you need something analogous to

if (some_condition) {     // ... } 

then use <c:if>. If you need something analogous to

if (some_condition) {     // ... } else if (some_other_condition) {     // ... } else {     // ... } 

then use <c:choose> with <c:when> and (optionally) <c:otherwise>.