Spring

@Service
class UserService(private val userRepository: UserRepository) {
    fun getUser(id: Long): User {
        return userRepository.findById(id).orElseThrow()
    }
}

@Service
class UserService {
  private final UserRepository repo;

  UserService(UserRepository repo) {
    this.repo = repo;
  }
}

@Service
class PaymentService {
  @Transactional
  public void pay() {
    // DB writes here
  }
}

@ControllerAdvice
class ApiErrors {
  @ExceptionHandler(IllegalArgumentException.class)
  ResponseEntity<String> badRequest(IllegalArgumentException e) {
    return ResponseEntity.badRequest().body(e.getMessage());
  }
}

@Configuration
class AppConfig {
  @Bean
  Clock clock() {
    return Clock.systemUTC();
  }
}

@GetMapping("/users/{id}")
UserDto getUser(@PathVariable String id, @RequestParam(defaultValue = "false") boolean verbose) {
  return service.get(id, verbose);
}

@ConfigurationProperties(prefix = "app")
public class AppProps {
  private String name;
  public String getName() { return name; }
  public void setName(String name) { this.name = name; }
}