T - the result type@FunctionalInterface public interface TransactionCallback<T>
TransactionalOperator's
 execute method, often as anonymous class within a method implementation.
 Typically used to assemble various calls to transaction-unaware data access
 services into a higher-level service method with transaction demarcation. As an
 alternative, consider the use of declarative transaction demarcation (e.g. through
 Spring's Transactional annotation).
TransactionalOperator| Modifier and Type | Method and Description | 
|---|---|
| org.reactivestreams.Publisher<T> | doInTransaction(ReactiveTransaction status)Gets called by  TransactionalOperatorwithin a transactional context. | 
org.reactivestreams.Publisher<T> doInTransaction(ReactiveTransaction status)
TransactionalOperator within a transactional context.
 Does not need to care about transactions itself, although it can retrieve and
 influence the status of the current transaction via the given status object,
 e.g. setting rollback-only.status - associated transaction statusTransactionalOperator.transactional(reactor.core.publisher.Flux<T>)