CMP and
BMP entity beans can declare home
methods
that perform operations related to the
EJB component but that are not specific to an entity bean instance. A
home method must have a matching implementation in the bean class
with the signature
ejbHome<
METHOD-NAME
>( )
.
For example, the Cruise EJB might define a home method that calculates the total revenue in bookings for a specific Cruise:
public interface CruiseHomeLocal extends javax.ejb.EJBLocalHome {
public CruiseLocal create(String name, ShipLocal ship);
public double totalReservationRevenue(CruiseLocal cruise);
}
Every home method declared by the home interfaces must have a
corresponding
ejbHome<
METHOD-NAME
>( )
in the bean class. For example, the
CruiseBean
class would have an
ejbHomeTotalReservationRevenue( )
method, as shown
in the following code:
public abstract class CruiseBean implements javax.ejb.EntityBean { public Integer ejbCreate(String name, ShipLocal ship) { setName(name); } ... public double ejbHomeTotalReservationRevenue(CruiseLocal cruise) { Set reservations = ejbSelectReservations(cruise); Iterator it = reservations.iterator( ); double total = 0; while(it.hasNext( )) { ReservationLocal res = (ReservationLocal)it.next( ); total += res.getAmount( ); } return total; } public abstract ejbSelectReservations(CruiseLocal cruise); ... }
The ejbHome( )
methods execute without an identity
within the instance pool. This is why
ejbHomeTotalReservationRevenue( )
required that a
CruiseLocal
EJB object reference be passed in to
the method. This makes sense once you realize that the caller is
invoking the home method on the entity bean’s EJB
home object and not an entity bean reference directly. The EJB home
(local or remote) is not specific to any one entity identity.
The bean developer may implement home methods in both bean-managed
and container-managed persistence implementations. The
ejbHome( )
methods of CMP entities typically rely
on ejbSelect( )
methods, while the
ejbHome( )
methods of BMP implementations
frequently use direct database access and find methods to query data
and apply changes.