The placement of the @Transactional annotation in Spring applications is a critical decision that affects the transaction management and overall architecture of the application. Based on the best practices and recommendations from various sources, the @Transactional annotation should ideally be placed on service layer methods.
Service Layer Placement
The service layer is considered the most appropriate place for the @Transactional annotation for several reasons:
Transaction Boundaries: The service layer typically encapsulates the business logic and defines clear transaction boundaries. Placing @Transactional here ensures that the entire business operation is covered by a single transaction, which is crucial for maintaining data integrity and consistency[2][5][7][8].
Propagation of Transactions: When @Transactional is used at the service layer, it helps in managing transaction propagation across different methods that might be called within the same business process. This is important for ensuring that all parts of the transaction are committed or rolled back together[2][5].
Avoiding Premature Transactions: Using @Transactional in the service layer prevents premature database interactions that might occur if placed in the DAO or repository layer. This placement ensures that transactions are started only when all necessary business rules and validations are satisfied[2][5][8].
Technical Considerations
Proxy Behavior: Spring uses proxies for managing transactions, which means that the transactional proxy intercepts calls to the @Transactional methods. If @Transactional is placed on a method within the same class that calls another @Transactional method, the inner method call does not pass through the proxy, and thus, does not participate in the transaction management. This is known as the self-invocation issue, which further supports the use of @Transactional at the service layer rather than deeper layers like DAOs[3][4][11].
Interface vs. Class Annotation: It is recommended to annotate concrete classes rather than interfaces with @Transactional. This is because me...
