Hi,
I wonder if someone could clear up a problem for me. It seems that a
Stateless session bean cannot really use a Stateful session bean for
two reasons.
1. The stateless bean cannot call remove on the stateful, therefore can't
clean it up (see code below)
2. If the stateless bean holds onto a reference to a stateful bean to get
around creating one on each call and avoid problem 1., another problem
occurs. The Stateless bean can be shared between concurrent transactions
(see quote from spec below), therefore the stateful beans transactional
scope is indeterminate (cause nasty blocking or even overlapping
transactions?)
One reason you might want to use a Stateful bean from a Stateless is to
do SessionSyncronization on a non transactional datasouce for example.
--------- Code example for problem 1. --------------------------------------
/**
* For readability, this example uses xdoclet code, if you don't use it,
* you might want to check it out!
*/
class StatelessBean extends SessionBean
{
/**
* @ejb:interface-method
*/
public void transferMoney(long account1,long account2,double amount)
{
StatefulEJBLocal stateful = StatefulEJBUtil.getLocalhome().create();
stateful.someMethod(accountNumber1,amount);
// stateful.remove(); <-- Can't do this, RemoveException
// (7.5.7 p79 ejb2 spec)
}
}
------------------------------------------------------------------------------
Quote from Section 7.8, p87 of ejb2 spec
Because all instances of a stateless session bean are equivalent, the
container can choose to delegate a client-invoked method to any available
instance. This means, for example, that the Container may delegate the
requests from the same client within the same transaction to different
instances, and that the Container may interleave requests from multiple
transactions to the same instance.
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