In JSF an component can be rendered or not using the EL empty operator
rendered="#{not empty myBean.myList}"
As I've understood the operator works both as null-check, but also check checks if the list is empty.
I want to do empty checks on some objects of my own custom class, which interface(s) or parts of interfaces do I need to implement? Which interface is the empty operator compatible with?
From EL 2.2 specification (get the one below "Click here to download the spec for evaluation"):
1.10 Empty Operator -
empty A
The
empty
operator is a prefix operator that can be used to determine if a value is null or empty.To evaluate
empty A
- If
A
isnull
, returntrue
- Otherwise, if
A
is the empty string, then returntrue
- Otherwise, if
A
is an empty array, then returntrue
- Otherwise, if
A
is an emptyMap
, returntrue
- Otherwise, if
A
is an emptyCollection
, returntrue
- Otherwise return
false
So, considering the interfaces, it works on Collection
and Map
only. In your case, I think Collection
is the best option. Or, if it's a Javabean-like object, then Map
. Either way, under the covers, the isEmpty()
method is used for the actual check. On interface methods which you can't or don't want to implement, you could throw UnsupportedOperationException
.