`@Component` vs `@Service` vs `@Repository` — what’s the difference?

Deep dive

All three annotations are meta-annotated with `@Component`, so they are discovered by component scanning and registered as beans. The difference is mostly **semantic** (communicating intent), but `@Repository` also enables a practical feature: **persistence exception translation** into Spring’s `DataAccessException` hierarchy.

• `@Component`: generic stereotype for “a Spring-managed component”.
• `@Service`: service/business layer (often where you place use-cases and transactions).
• `@Repository`: persistence/DAO layer (JPA/JDBC) + exception translation.

Why the semantics matter

• Encourages clean layering (controller → service → repository).
• Makes AOP pointcuts clearer (e.g., aspects on `@Service` only).

Example

@Repository
class UserDao {
  // JPA/JDBC calls
}

@Service
class UserService {
  private final UserDao dao;
  UserService(UserDao dao) { this.dao = dao; }
}

Common pitfalls

• Putting business logic into repositories.
• Assuming `@Service` changes scope/lifecycle (scope is configured separately).
• Missing `@Repository` on persistence classes and losing consistent exception types.