Javadoc
The rollback operation will terminate the transaction and return
normally if it succeeded, while throwing an appropriate exception if it
didn't. If there is no transaction associated with the invoking thread
then WrongStateException is thrown. If the coordinator is not aware of the
current transaction UnknownTransactionException is thrown. If any other error
occurs a SystemException is thrown. When complete, this operation disassociates
the transaction from the current thread such that it becomes associated with no
transaction.