| Q: |
What
is Entity Bean?
|
| A: |
The entity bean is used to represent data
in the database. It provides an object-oriented
interface to data that would normally be
accessed by the JDBC or some other back-end
API. More than that, entity beans provide
a component model that allows bean developers
to focus their attention on the business
logic of the bean, while the container takes
care of managing persistence,transactions,
and access control.
There are two basic kinds of entity beans:
container-managed ersistence (CMP) andbean-managed
persistence (BMP).
Container-managed persistence beans are
the simplest for the bean developer to create
and the most difficult for the EJB server
to support. This is because all the logic
for synchronizing the bean's state with
the database is handled automatically by
the container. This means that the bean
developer doesn't need to write any data
access logic, while the EJB server is
supposed to take care of all the persistence
needs automatically. With CMP, the container
manages the persistence of the entity bean.
Vendor tools are used to map the entity
fields to the database and absolutely no
database access code is written in the bean
class.
The bean-managed persistence (BMP) enterprise
bean manages synchronizing its state with
the database as directed by the container.
The bean uses a database API to read and
write its fields to the database, but the
container tells it when to do each synchronization
operation and manages the transactions for
the bean automatically. Bean-managed persistence
gives the bean developer the flexibility
to perform persistence operations that are
too complicated for the container or to
use a data source that is not supported
by the container. |
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