Question

I often want to declare conditional CSS style-classes for components if a certain condition is met. If the condition is not met, then no style should be added. I usually do it like this (which has worked fine so far):

<some:tag styleClass="#{someCondition ? 'SomeClass' : null}" />

Is this OK, or are there any dangerous pitfalls to having null there?

Answer 1

There are no dangerous pitfalls. #{null} is perfectly fine as EL won’t emit anything to the response (it evaluates basically to an empty string).

You also sometimes see this style:

<some:tag styleClass="#{someCondition ? 'SomeClass' : ''}" />

This is the style which is usually used in plain Java code as follows:

System.out.println(someCondition ? "SomeClass" : "");

In plain Java code converting null to String would result in "null", not "", which may be undesireable. For ones not so familiar with EL, the above style is actually more self-documenting. Otherwise you get questions like Doesn’t it print “null” then?