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The point of the PrePassivate callback is to give the bean a chance to prepare for serialization This may include copying nonserializable variable values into Serializable variables and clearing unneeded data out of those variables to save total disk space needed to store the bean Most often the prepassivation step consists of releasing heavy-duty resources such as open database, messaging server, and socket connections that cannot be serialized A well-behaved bean should ensure that heavy-duty resources are both closed and explicitly set to null before passivation takes place From the perspective of a bean instance, there isn t much of a difference between being passivated and being destroyed In both cases, the current instance in memory would cease to exist As a result, in most cases you ll find that the same actions are performed for both the PreDestroy and PrePassivate callbacks, as we do in listing 32.

Pretty much the same applies for the PostConstruct PostActivate pair For both callbacks, the bean needs to do whatever is necessary to make itself ready to service the next incoming request Nine times out of ten, this means getting hold of resources that either are not instantiated or were lost during the serialization/deserialization process Again, listing 32 is a good example since the javasqlConnection object cannot be serialized and must be reinstantiated during activation Destroying a stateful session bean In listing 32, the cancelAccountCreation and createAccount methods are marked with the @Remove annotation Beyond the obvious importance of these methods in implementing vital workflow logic, they play an important role in maintaining application server performance Calling business methods marked with the @Remove annotation signifies a desire by the client to end the session As a result, invoking these methods triggers immediate bean destruction.

The recipe describes how to test for rollbacks for both BMT and CMT beans. Beanmanaged transaction beans should use the methods from the UserTransaction instance being used, and container-managed transaction beans should use the methods of their EJBContext instance. The recipe demonstrates in both cases an attempt to recover from exceptions thrown within the current transaction. The ability to acquire the status of a transaction and to mark it for rollback gives you more control over your transactions in both BMT and CMT beans. For BMT bean methods containing many steps, the transaction rollback control shown in the recipe allows you to test the transaction after each significant step in the method. After each step, you can attempt recovery or begin a rollback. For CMT beans, you have only one transaction per method, but you can mark the transaction for rollback without throwing an exception to the container. In both cases, testing the transaction allows you to skip the remaining code in a method if you plan to roll back the transaction. This can be important for improving performance. In addition, BMT beans could use the rollback() method to immediately force a rollback of the current transaction.

To gain an appreciation for this feature, consider what would happen if it did not exist If remove methods were not an option, the client would have no way of telling the container when a session should be ended As a result, every stateful bean instance ever created would always have to be timed out to be passivated (if the container implementation supports passivation) and timed out again to be finally destroyed In a highly concurrent system, this could have a drastic performance impact The memory footprint for the server would.

constantly be artificially high, not to mention how there would be wasted CPU cycles and disk space used in the unnecessary activation/passivation process. This is why it is critical that you remove stateful bean instances when the client is finished with its work instead of relying on the container to destroy them when they time out. Believe it or not, these are the only few stateful bean specific features that we needed to talk about! Before concluding this section on stateful beans, we ll briefly summarize the differences between stateful and stateless session beans as a handy reference in table 3.2.