user manual

136 BES Developer’s Guide
Container-Managed Persistence in Borland Enterprise Server
deployer maps this persistence schema to the database and creates any other
necessary classes for the beans' maintenance.
Information on J2EE 1.3 entity beans and CMP 2.0 is found in the Chapter 16,
“Using BES Properties for CMP 2.x”.
BES CMP engine's CMP 1.1 implementation
While you don't have to be an expert on all aspects of the Borland CMP
engine to use it effectively, it is helpful to have some knowledge of certain
areas. This section provides information on the areas that users of the CMP
engine should understand. In particular, it focuses on the deployment
descriptor file and the XML statements contained within the file.
Before continuing, there are some key things to note in the implementation of
an entity bean that uses 1.1 container-managed persistence:
■
The entity bean has no implementations for finder methods. The EJB
Container provides the finder method implementations for entity beans with
container-managed persistence. Rather than providing the implementation
for finder methods in the bean's class, the deployment descriptor contains
information that enables the container to implement these finder methods.
■
The entity bean declares all fields public that are managed by the container
for the bean. The CheckingAccount bean declares name and balance to be
public fields.
■
The entity bean class implements the seven methods declared in the
EntityBean interface: ejbActivate(), ebjPassivate(), ejbLoad(), ejbStore(),
ejbRemove(), setEntityContext(), and unsetEntityContext(). However, the
entity bean is required to provide only skeletal implementations of these
methods, though it is free to add application-specific code where
appropriate. The CheckingAccount bean saves the context returned by
setEntityContext() and releases the reference in unsetEntityContext().
Otherwise, it adds no additional code to the EntityBean interface methods.
■
There is an implementation of the ejbCreate() method (because this entity
bean allows callers of the bean to create new checking accounts), and the
implementation initializes the instance's two variables, account name and
balance amount, to the argument values. The ejbCreate() method returns a
null value because, with container-managed persistence, the container
creates the appropriate reference to return to the client.
■
The entity bean provides the minimal implementation for the ejbPostCreate()
method, though this method could have performed further initialization work
if needed. For beans with container-managed persistence, it is sufficient to
provide just the minimal implementation for this method because
ejbPostCreate() serves as a notification callback. Note that the same rule
applies to the methods inherited from the EntityBean interface as well.