is a process of transferring an enterprise bean
from secondary storage to memory.
Stateful session beans maintain sessions between
method invocations, this is called conversational
state because it represents the continuing conversation
with the stateful session beanís client . The
integrity of this conversational state needs
to be maintained for the life of the beanís
service to the client. But stateful session
bean does not participate in instance pooling
like stateless session beans and entity beans,
instead activation is used with stateful session
beans to conserve resources. When an EJB server
needs to conserve resources, it can evict stateful
session beans from memory. This reduces the
number of instances maintained by the system.
To passivate the bean and preserve its conversational
state, the beans state is serialized to a secondary
storage and maintained relative to its EJB object.
When a client invokes a method on the EJB object,
a new stateful instance is instantiated and
populated from the passivated secondary storage.
a bean is the act of restoring a stateful bean
instanceís state relative to its EJB object.
When a method on the passivated EJB object is
invoked , the container automatically instantiates
a new instance and sets it fields equal to the
data stored during passivation.
activation process is supported by the state
management call methods ejbActivate () and ejbPassivate
() methods which notify the stateful session
bean that it is about to be activated or passivated
respectively. The ejbActivate () method is called
immediately following the successful activation
of a bean instance and can be used to reset
transient fields to an initial value if necessary.
beans do not have conversational state that
needs to be serialized like stateful beans;
instead the state of entity bean instance is
persisted directly to the data base. Entity
beans do, however, leverage the activation callback
methods ejbActivate () and ejbPassivate () to
notify the instance when it si about to be swapped
in or out of the instance pool. The ejbActivate
() method is invoked immediately after the bean
instance is swapped into the EJB object and
the ejbPassivate () method is invoked just before
the instance is swapped out of the instance