我目前正在使用Spring创建一个网站，但偶然发现了这种基本情况，我对如何解决此特定代码一无所知：Entity = Optional;

RoomEntity roomEntity =  roomRepository.findById(roomId);

ReservationResource（API请求类）：

    public class ReservationResource {
    @Autowired
    RoomRepository roomRepository;

    @RequestMapping(path = "/{roomId}", method = RequestMethod.GET, produces = MediaType.APPLICATION_JSON_UTF8_VALUE)
    public ResponseEntity<RoomEntity> getRoomById(
    @PathVariable
    Long roomId){
        RoomEntity roomEntity =  roomRepository.findById(roomId);
        return new ResponseEntity<>(roomEntity, HttpStatus.OK);}
    }}

RoomRepository类：

public interface RoomRepository extends CrudRepository<RoomEntity, Long> {
    List<RoomEntity> findAllById(Long id);
}

房间实体

@Entity
@Table(name = "Room")
public class RoomEntity {
    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    private Long id;

    @NotNull
    private Integer roomNumber;

    @NotNull
    private String price;

    public RoomEntity() {
        super();
    }
}