Layered Architecture Simplified

Layered Architecture Simplified

Layered architecture = clean separation of concerns.

Most apps follow this structure:

---

1. Controller Layer

Handles HTTP requests. No business logic here.

@RestController
public class UserController {
    @GetMapping("/users/{id}")
    public UserDto getUser(@PathVariable Long id) {
        return userService.getUser(id);
    }
}

2. Service Layer

Business logic lives here. Talks to repos.

@Service
public class UserService {
    public UserDto getUser(Long id) {
        User user = repo.findById(id).orElseThrow();
        return mapper.toDto(user);
    }
}

3. Repository Layer

Handles database. Nothing else.

@Repository
public interface UserRepository extends JpaRepository<User, Long> {}

Straight-forward:

-Easier to test -Easier to maintain -Grows better with time

Golden Rule: -Don’t mix layers. -Controllers don’t talk to DB. -Services don’t return ResponseEntity.

Keep it clean. Keep it boring. That’s how systems survive.

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