我有一个简单的存储库

@Repository
public interface UserRepository extends JpaRepository<User, Long> {
    Optional<User> findUserByUsername(String username);
}

1个基本实体用户，包含2个字段、getter和setter
1服务

@Service
public class UserPrincipalDetailsService implements UserDetailsService {
    @Autowired
    private UserRepository userRepository;
    @Override
    public UserDetails loadUserByUsername(String username) throws UsernameNotFoundException {
        Optional<User> optionalUser = userRepository.findUserByUsername(username);
        User user = optionalUser.orElseThrow(() -> new UsernameNotFoundException("Not found username"));
        return new UserPrincipal(user);
    }
}

我的问题是：当我使用@autowired时，这个loaduserbyusername（）函数按预期工作，但是当我为userrepository执行构造函数注入时，它抛出一个nullpointerexception？

@Service
public class UserPrincipalDetailsService implements UserDetailsService {
    private UserRepository userRepository;
    public UserPrincipalDetailsService(UserRepository userRepository) {
        this.userRepository = userRepository;
    }
    @Override
    public UserDetails loadUserByUsername(String username) throws UsernameNotFoundException {
        Optional<User> optionalUser = userRepository.findUserByUsername(username);
        User user = optionalUser.orElseThrow(() -> new UsernameNotFoundException("Not found username"));
        return new UserPrincipal(user);
    }
}

有人遇到过同样的情况吗？
更新：不知道为什么当我一天后再次尝试时，它会正常运行。nullpointerexception没有显示在控制台中，但在我进行调试时会显示出来。