How does EL empty operator work in JSF

Question

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

User · Answer

Using BalusC s suggestion of implementing Collection i can now hide my primefaces p dataTable using not empty operator on my dataModel that extends javax faces model ListDataModel   Code sample   import java io Serializable  import java util Collection  import java util List  import javax faces model ListDataModel  import org primefaces model SelectableDataModel   public class EntityDataModel extends ListDataModel lt Entity gt  implements         Collection lt Entity gt   SelectableDataModel lt Entity gt   Serializable        public EntityDataModel List lt Entity gt  data    super data           Override     public Entity getRowData String rowKey               In a real app  a more efficient way like a query by rowKey should be            implemented to deal with huge data         List lt Entity gt  entitys    List lt Entity gt   getWrappedData            for  Entity entity   entitys                if  Integer toString entity getId    equals rowKey   return entity                    return null              Override     public Object getRowKey Entity entity            return entity getId                Override     public boolean isEmpty             List lt Entity gt  entity    List lt Entity gt   getWrappedData            return  entity    null     entity isEmpty                     other not implemented methods of Collection

User · Answer

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 is null  return true   Otherwise  if A is the empty string  then return true   Otherwise  if A is an empty array  then return true   Otherwise  if A is an empty Map  return true   Otherwise  if A is an empty Collection  return true   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

[jsf] How does EL empty operator work in JSF?

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