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sessioncontext in EJB

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Could anyone explain the reason for the following
We have setEntityContext() and unsetEntityContext() methods in Entity beans but why we have only setSessionContext() method but not unsetSessionContext() method in Session Beans.
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I agree that it would be better for symmetry to have both, but I think the reason has to do with the lifecycle differences between the bean types.
If you look at the EJB lifecycles in the spec or in an EJB book, you will see that:
A session bean calls setSessionContext in transition from DoesNotExist to MethodReady state. It also calls ejbCreate in this transition. The opposite transition from MethodReady to DoesNotExist calls ejbRemove. So if there is work to be done on these state transitions, you should put that work in ejbCreate and undo it in ejbRemove. The setSessionContext method should do nothing but set the context.
For an entity bean, there are many more states. The transitions between DoesNotExist and Pooled calls set/unset EntityContext, and ejbCreate/ejbRemove are called on the transitions between Pooled and Ready.
So if your entity needs to do "work" on the transition between DoesNotExist and Pooled, you do that in setEntityContext, and you need unsetEntityContext to "undo" that work.
Not the clearest thing in the world, but that's where the job security comes from.
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