Enterprise JavaBeans, Fourth Edition

The Life Cycle of a Stateful Session Bean

The biggest difference between the stateful session bean and the other bean types is that stateful session beans do not use instance pooling. Stateful session beans are dedicated to one client for their entire lives, so swapping or pooling of instances isn’t possible.^[34] When they are idle, stateful session bean instances are simply evicted from memory. The EJB object remains connected to the client, but the bean instance is dereferenced and garbage collected during inactive periods. This means that each stateful bean must be passivated before it is evicted in order to preserve the conversational state of the instance, and it must be activated to restore its state when the EJB object becomes active again.

The bean’s perception of its life cycle depends on whether it implements a special interface called javax.ejb.SessionSynchronization. This interface defines an additional set of callback methods that notify the bean of its participation in transactions. A bean that implements SessionSynchronization can cache database data across several method calls before making an update. We have not discussed transactions in detail yet; we will consider this part of the bean’s life cycle in Chapter 15. This section describes the life cycle of stateful session beans that do not implement the SessionSynchronization interface.

The life cycle of a stateful session bean has three states: Does Not Exist, Method-Ready, and Passivated. This sounds a lot ...