web server - Borland Technical Publications

Handling of EJB exceptions
Options for continuing a transaction
When a transaction is not marked for rollback, then the client has three options:
■
■
Rollback the transaction.
Pass the responsibility by throwing a checked exception or re-throwing the original
exception.
■
Retry and continue the transaction. This can entail retrying portions of the
transaction.
When a client receives a checked exception for a transaction not marked for rollback,
its safest course is to rollback the transaction. The client does this by either marking
the transaction as “rollback only” or, if the client has actually started the transaction,
calling the rollback method to actually rollback the transaction.
The client can also throw its own checked exception or re-throw the original exception.
By throwing an exception, the client lets other programs further up the transaction
chain decide whether or not to abort the transaction. However, in general it is
preferable for the code or program closest to the occurrence of the problem to make
the decision about saving the transaction.
Lastly, the client can continue with the transaction. The client can evaluate the
exception message and decide if invoking the method again with different parameters
is likely to succeed. However, you need to keep in mind that retrying a transaction is
potentially dangerous. You have no knowledge of nor guarantee that the enterprise
bean properly cleaned up its state.
Clients that are calling stateless session beans, on the other hand, can retry the
transaction with more confidence if they can determine the problem from the thrown
exception. Because the called bean is stateless, the client does not have the problem
of not knowing the state in which the bean left the transaction.
Chapter 19: Transaction management 181