Spring Boot Data Transactions

Question Variations

"Why is a transaction normally placed on a service method?"
"Why can self-invocation bypass `@Transactional`?"
"Which exceptions trigger rollback by default?"

Why This Is Asked

Transactions expose whether a candidate understands atomic business operations beyond repository method calls.

Key Concepts

@Transactional defines a transaction boundary around a service operation.
Runtime exceptions roll back by default; checked exceptions need explicit configuration.
Transaction proxies apply only to calls that pass through the Spring proxy.
Keep transactions short and avoid remote calls inside them.

Question Variations

“Why is a transaction normally placed on a service method?”
“Why can self-invocation bypass @Transactional?”
“Which exceptions trigger rollback by default?”

Answers by Technology

+ Add Variant

Spring BootImprove this answer ✏️

Expected Answer (Spring Boot 4.1.0 / Java 17+)

Put @Transactional on a service method that represents one atomic business operation. Spring opens and commits or rolls back the transaction through a proxy when an external caller invokes that bean method. Runtime exceptions trigger rollback by default; configure rollback behavior explicitly for checked exceptions when needed. Keep the transaction short and avoid network calls while database locks may be held.

Why It Matters

Correct transaction boundaries prevent partial business updates and reduce lock contention.

Code Example

@Service
class TransferService {
  @Transactional
  void transfer(Account from, Account to, BigDecimal amount) {
    from.debit(amount); to.credit(amount);
  }
}

Common Mistakes

Calling a transactional method from the same instance: The proxy is bypassed and no transaction is started.
Wrapping remote calls in a long transaction: Locks and failures propagate unnecessarily.

Follow-up Questions

Why service-level transactions? (Answer: They align with business operations across repositories.)
What rolls back by default? (Answer: Unchecked exceptions.)