Java Spring CrudRepository .orElseThrow()
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Spring CrudRepository .orElseThrow()
提问by szxnyc
What is the proper way to throw an exception if a database query returns empty? I'm trying to use the .orElseThrow()method but it won't compile :
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，但它无法编译：
Meeting meeting = meetingRepository.findByMeetingId(meetingId).orElseThrow(new MeetingDoesNotExistException(meetingId));
The compiler is saying :
编译器说：
"he method orElseThrow(Supplier) in the type Optional is not applicable for the arguments (MeetingRestController.MeetingDoesNotExistException)
“可选类型中的方法 orElseThrow(Supplier) 不适用于参数 (MeetingRestController.MeetingDoesNotExistException)
Is it possible to do this with lambda expressions?
可以用 lambda 表达式做到这一点吗？
CrudRepository :
CrudRepository ：
import java.util.Optional;
import org.springframework.data.repository.CrudRepository;
public interface MeetingRepository extends CrudRepository<Meeting, Long>{
Optional<Meeting> findByMeetingId(Long id);
}
Exception :
例外 ：
@ResponseStatus(HttpStatus.CONFLICT) // 409
class MeetingDoesNotExistException extends RuntimeException{
public MeetingDoesNotExistException(long meetingId){
super("Meeting " + meetingId + " does not exist.");
}
}
采纳答案by Eran
Try passing a lambda expression of type Supplier<MeetingDoesNotExistException>:
尝试传递类型为 的 lambda 表达式Supplier<MeetingDoesNotExistException>：
Meeting meeting =
meetingRepository.findByMeetingId(meetingId)
.orElseThrow(() -> new MeetingDoesNotExistException(meetingId));
回答by Jason C
The error means what it says.
错误意味着它所说的。
The documentation for orElseThrowstates that it takes a Supplieras a parameter.
的文档orElseThrow说明它将 aSupplier作为参数。
You have stated your exception is a RuntimeException, which is not a Supplier. Therefore, orElseThrow()is not applicable to that argument type. You would have to pass it a Supplier, not a RuntimeException.
您已经声明您的异常是 a RuntimeException，而不是 a Supplier。因此，orElseThrow()不适用于该参数类型。您必须将其传递给 a Supplier，而不是 a RuntimeException。
It would be simpler syntax to use a lambda expression.
使用 lambda 表达式会更简单的语法。
