Red Hat Application Server, Manual

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80 Chapter 8. Developing Entity Beans
•
Bean-Managed Persistence : the bean provider writes the database access operations (JDBC code)
in the methods of the enterprise bean that are specified for data creation, load, store, retrieval, and
remove operations (
ejbCreate
,
ejbLoad
,
ejbStore
,
ejbFind
...,
ejbRemove
).
Currently, the platform handles persistence in relational storage systems through the JDBC interface.
For both container-managed and bean-managed persistence, JDBC connections are obtained from an
object provided at the EJB server level, the DataSource . The DataSource interface is defined in the
JDBC 2.0 standard extensions (see http://java.sun.com/products/jdbc/). A DataSource object identifies
a database and a means to access it via JDBC (a JDBC driver). An EJB server may propose access to
several databases and thus provides the corresponding DataSource objects. DataSources are described
in more detail in Chapter 4 Configuring JDBC DataSources .
8.2. The Home Interface
In addition to “home business methods,” the Home interface is used by any client application to cre-
ate, remove, and retrieve instances of the Entity Bean. The bean provider needs to provide only the
desired interface; the container will automatically provide the implementation. If it is remote, the in-
terface must extend the
javax.ejb.EJBHome
interface; if it is local, the interface must extend the
javax.ejb.EJBLocalHome
interface. The methods of a remote home interface must follow the rules
for Java RMI. The signatures of the
create
and
find
... methods should match the signatures of the
ejbCreate
and
ejbFind
... methods that will be provided later in the Enterprise Bean implementa-
tion class (the same number and types of arguments, but different return types).
8.2.1. create Methods
•
The return type is the Enterprise Bean’s component interface.
•
The exceptions defined in the
throws
clause must include the exceptions defined for the
ejbCreate and ejbPostCreate methods, and must include
javax.ejb.CreateException
and
java.rmi.RemoteException
(the latter is only for a remote interface).
8.2.2. remove Methods
•
The interfaces for these methods must not be defined—they are inherited from
EJBHome
or
EJBLocalHome
.
•
The method is
void remove
, taking as an argument the primary key object or the handle (for a
remote interface).
•
The exceptions defined in the throws clause should be
javax.ejb.RemoveException
and
java.rmi.RemoteException
for a remote interface.
•
The exceptions defined in the
throws
clause should be
javax.ejb.RemoveException
and
java.ejb.EJBException
for a local interface.
8.2.3. finder Methods
Finder methods are used to search for an EJB object or a collection of EJB objects. The arguments
of the method are used by the Entity Bean implementation to locate the requested entity objects.
For bean-managed persistence, the bean provider is responsible for developing the corresponding
ejbFinder methods in the bean implementation. For container-managed persistence, the bean provider
does not write these methods; they are generated at deployment time by the platform tools; the de-
scription of the method is provided in the deployment descriptor, as defined in Section 8.7 Configuring