Checking attribute exists in JSP

Question

Hello,

I have some classes which extends a superclass, and in the JSP I want to show some attributes of these classes. I only want to make one JSP, but I don't know in advance if the object has an attribute or not. So I need a JSTL expression or a tag which checks that the object I pass has this attribute (similar to in operator in javascript, but in the server).

<c:if test="${an expression which checks if myAttribute exists in myObject}">
    <!-- Display this only when myObject has the atttribute "myAttribute" -->
    <!-- Now I can access safely to "myAttribute" -->
    ${myObject.myAttribute}
</C:if>

How can I get this?

Thanks.

Answer 1

Do you mean something like this:

<c:if test="${not null myObject.myAttribute}">
   <!-- Now I can access safely to "myAttribute" -->
</C:if>

or other variant

<c:if test="${myObject.myAttribute != null}">
   <!-- Now I can access safely to "myAttribute" -->
</C:if>

If it is a list you can do

<c:if test="#{not empty myObject.myAttribute}">

Answer 2

Make use of JSTL c:catch.

<c:catch var="exception">${myObject.myAttribute}</c:catch>
<c:if test="${not empty exception}">Attribute not available.</c:if>