Spring CrudRepository .orElseThrow()

Question

如果数据库查询返回空,抛出异常的正确方法是什么？我正在尝试使用该.orElseThrow()方法,但它不会编译:

Meeting meeting = meetingRepository.findByMeetingId(meetingId).orElseThrow(new MeetingDoesNotExistException(meetingId));

编译器说:

"他的方法orElseThrow(Supplier)中的Optional类型不适用于参数(MeetingRestController.MeetingDoesNotExistException)

是否可以使用lambda表达式执行此操作？

CrudRepository:

import java.util.Optional;

import org.springframework.data.repository.CrudRepository;

public interface MeetingRepository extends CrudRepository<Meeting, Long>{
    Optional<Meeting> findByMeetingId(Long id);
}

例外:

@ResponseStatus(HttpStatus.CONFLICT) // 409
class MeetingDoesNotExistException extends RuntimeException{
  public MeetingDoesNotExistException(long meetingId){
    super("Meeting " + meetingId + " does not exist.");
  }
}

Answer 1

尝试传递类型的lambda表达式Supplier<MeetingDoesNotExistException>:

Meeting meeting = 
    meetingRepository.findByMeetingId(meetingId)
                     .orElseThrow(() -> new MeetingDoesNotExistException(meetingId));