Question

I came across some .xhtml files where for some components the expression language used was like rendered="#{empty from}", rendered="#{empty create}" etc.

I know that empty is an operator in EL, used to check whether a value is null or empty, but I did not understand the meaning of above mentioned ELs.

Can somebody explain to me what above EL’s mean?

Answer 1

The rendered attribute is a signal whether JSF should generate HTML for the component or not. If it evaluates false, then it won’t generate HTML for the component (nor for its children). The #{empty form} will evaluate false when the #{form} is not null nor empty.

Simple as that. You can find another examples of boolean expressions here: Conditionally displaying JSF components