Evaluate empty or null JSTL c tags

Question

How can I validate if a String is null or empty using the c tags of JSTL?

I have a variable of name var1 and I can display it, but I want to add a comparator to validate it.

<c:out value="${var1}" /> 

I want to validate when it is null or empty (my values are strings).

Answer 1

How can I validate if a String is null or empty using the c tags of JSTL?

You can use the empty keyword in a <c:if> for this:

<c:if test="${empty var1}">     var1 is empty or null. </c:if> <c:if test="${not empty var1}">     var1 is NOT empty or null. </c:if> 

Or the <c:choose>:

<c:choose>     <c:when test="${empty var1}">         var1 is empty or null.     </c:when>     <c:otherwise>         var1 is NOT empty or null.     </c:otherwise> </c:choose> 

Or if you don't need to conditionally render a bunch of tags and thus you could only check it inside a tag attribute, then you can use the EL conditional operator ${condition? valueIfTrue : valueIfFalse}:

<c:out value="${empty var1 ? 'var1 is empty or null' : 'var1 is NOT empty or null'}" /> 

To learn more about those ${} things (the Expression Language, which is a separate subject from JSTL), check here.

See also:

• How does EL empty operator work in JSF?