How does the @Transactional annotation work in Spring? How is it implemented within the framework?

The @Transactional annotation in Spring is used for declarative transaction management. It allows for automatically starting, committing, or rolling back a transaction around a method.

Within Spring, this is implemented using AOP (Aspect-Oriented Programming):

• When a method annotated with @Transactional is called, a proxy is created that wraps the call.
• The proxy begins a transaction via PlatformTransactionManager before executing the method.
• If the method completes without exceptions, the transaction is committed.
• If an exception occurs (by default RuntimeException), the transaction is rolled back.

Example:

@Service
public class UserService {

    @Transactional
    public void createUser(User user) {
        userRepository.save(user);
        // other operations that should be atomic
    }
}

Thus, developers do not need to manually manage transactions — Spring takes care of it, ensuring data consistency and simplifying the code.