| Q: |
What
is Session Bean?
|
| A: |
A session bean is a non-persistent object
that implements some business logic running
on the server. One way to think of a session
object is as a logical extension of the
client program that runs on the server.
Session beans are used to manage the interactions
of entity and other session beans,access
resources, and generally perform tasks on
behalf of the client.
There are two basic kinds of session bean:
stateless and stateful.
Stateless session beans are made up of business
methods that behave like procedures; they
operate only on the arguments passed to
them when they are invoked. Stateless beans
are called stateless because they are transient;
they do not maintain business state between
method invocations.Each invocation of a
stateless business method is independent
from previous invocations. Because stateless
session beans are stateless, they are easier
for the EJB container to manage, so they
tend to process requests faster and use
less resources.
Stateful session beans encapsulate business
logic and state specific to a client. Stateful
beans are called "stateful" because
they do maintain business state between
method invocations, held in memory and not
persistent. Unlike stateless session beans,
clients do not share stateful beans. When
a client creates a stateful bean, that bean
instance is dedicated to service only that
client. This makes it possible to maintain
conversational state, which is business
state that can be shared by methods in the
same stateful bean. |
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