> Now I have another doubt, in the FireBird exists the following ways
> of isolation:

First of all, you can specify your own TPB (with a limitation - no table
locking in "consistency" mode). You know how to do this
(FirebirdConnection.setTransactionParameters(int, int[]) method).

Also JayBird provides default mapping:

> "Read Commited",

default mapping for Connection.TRANSACTION_READ_COMMITTED is following TPB
isc_tpb_read_committed + isc_tpb_rec_version + isc_tpb_write + isc_tpb_wait

> "Concurrency"

default mapping for Connection.TRANSACTION_REPEATABLE_READ is
isc_tpb_concurrency + isc_tpb_write + isc_tpb_wait

> and "Consistency",

default mapping for Connection.TRANSACTION_SERIALIZABLE is
isc_tpb_consistency + isc_tpb_write + isc_tpb_wait

Roman