Question

我正在使用Spring框架，在下面的代码中，我希望从数据库中获取纬度和经度并将其存储在ArrayList中，然后计算它们之间的距离。

问题是我无法弄清楚如何在变量中获取两列的值，当我按照以下方式执行此操作[Ljava.lang.Object; cannot be cast to java.lang.Double异常抛出

任何人都可以帮助我吗？我知道我们可以使用2D ArrayList，但如何在以下代码中使用ArrayList

RiderService.java

@Component
public class RiderService {

     @Autowired RiderLocationRepository riderLocationRepository;

    public float Location(Double lattitude,Double longitude)
    {
        Double lat2=24.927437;
        Double lng2=67.094412;

          ArrayList<Double> allRidersLocation  = new ArrayList<Double>();
          allRidersLocation= riderLocationRepository.findAllRidersLocation();
          Iterator<Double> iterator = allRidersLocation.iterator();
            while (iterator.hasNext()) {
                System.out.println(" DB value " +  iterator.next().doubleValue());
            } 
            float distance=distFrom(lattitude, longitude, lat2, lng2);
            System.out.println("Distance : " + (distance/1000));
            return distance;
    }

RiderRepository

public interface RiderLocationRepository extends JpaRepository<RiderLocation, Long>{

    @Query("select r.latitude,r.longitude from RiderLocation r ")
    ArrayList<Double>  findAllRidersLocation();

}

Answer 1

您的查询返回一个Object数组，如下所示：

@Query("select r.latitude, r.longitude from RiderLocation r")
ArrayList<Object[]> array =  //execute_your_query();

要获得结果，您可以使用此功能：

for(Object[] obj : array){//<<---------------list of object with two columns
   double d1 = (Double) obj[0];//<<-------col 1
   double d2 = (Double) obj[1];//<<-------col 2
}

Answer 2

使用JpaRepository默认提供给你的findAll方法，你需要这样的东西：

public float Location(Double lattitude,Double longitude)
    {
        Double lat2=24.927437;
        Double lng2=67.094412;

          List<RiderLocation> allRidersLocation  = riderLocationRepository.findAll();
          for (RiderLocation riderLocation : allRidersLocation) {
            // use the riderLocation as required, it's not clear to me what methods this has!!
            System.out.println("Distance : " + (distance/1000));
            return distance;
    }

Answer 3

试试这个，

public float Location(Double lattitude,Double longitude)
    {
        Double lat2=24.927437;
        Double lng2=67.094412;

          List<RiderLocation> allRidersLocation  = riderLocationRepository.findAll();
          for (RiderLocation riderLocation : allRidersLocation) {
            float distance=distFrom(riderLocation.getLattitude(), riderLocation.getLongitude(), lat2, lng2);
            System.out.println("Distance : " + (distance/1000));
            return distance;
    }
    }

默认情况下，findAll()方法可用于CrudRepository

public interface RiderLocationRepository extends JpaRepository<RiderLocation, Long>{

}

如何获取两列的值并存储在ArrayList中

3 个答案: