SA stateful session bean is an extension of
the client application. It performs tasks on
behalf of the client and maintains state related
to that client. This state is called conversational
state because it represents a continuing conversation
between the stateful session bean and the client.
Methods invoked on a stateful session bean can
write and read data to and from this conversational
state, which is shared among all methods in
the bean. Stateful session beans tend to be
specific to one scenario. They represent logic
that might have been captured in the client
application of a two-tier system. Session beans,
whether they are stateful or stateless, are
not persistent like entity beans. In other words,
beans are not saved to the database.
session beans offer an alternative that lies
between entity beans and stateless ses sion
beans. Stateful session beans are dedicated
to one client for the life of the bean instance;
a stateful session bean acts on behalf of a
client as its agent. They are not swapped among
EJB objects or kept in an instance pool like
entity and stateless bean instances. Once a
stateful session bean is instantiated and assigned
to an EJB object, it is dedicated to that EJB
object for its entire life cycle.
Stateful session beans maintain conversational
state, which means that the instance variables
of the bean class can cache data relative to
the client between method invocations. This
makes it possible for methods to be interdependent,
so that changes made by methods to the beanís
state can affect the result of subsequent method
invocations. In contrast, the stateless session
beans we have been talking about do not maintain
conversational state. Although stateless beans
may have instance variables, these fields are
not specific to one client. A stateless instance
is swapped among many EJB objects, so you canít
predict which instance will service a method
call. With stateful session beans, every method
call from a client is serviced by the same instance
(at least conceptually), so the bean instanceís
state can be predicted from one method invocation
to the next.
Some important points
1) Conversational State? A stateful session
bean performs tasks on behalf of the client
and maintians state related to that client.
This state is called conversional state. Because
it represents a continuing conversation between
the stateful session bean and the client.
Stateful Session beans are available only through
handle object as for as the specific bean instance
is kept alive in the EJB server.
The bean instance not swapped among EJB object.
Stateful session beans doesn't use instance
The EJB object reamins connected to the client,
but the bean instance is dereferenced and garbage
collected during inactive periods.
If ejbRemove(), Attributes of instance are wiped
clean and client still has reference to instance.