如何计算两个坐标之间的距离？

private static double degreeToRadian(double degree) {
  return degree * (Math.PI / 180.0d);
}

public static double getDistanceInMeterFromTwoGPSLocations(double firstLat, double firstLong, double secondLat, double secondLong) {
  // Radius of the Earth in m
  final double R = 6371000.0d; 

  final double dlon = degreeToRadian(secondLong - firstLong);
  final double dlat = degreeToRadian(secondLat - firstLat);
  final double a = Math.sin(dlat / 2d) * Math.sin(dlat / 2d) + Math.cos(degreeToRadian(firstLat)) * Math.cos(degreeToRadian(secondLat)) * Math.sin(dlon / 2d) * Math.sin(dlon / 2d);
  final double c = 2d * Math.atan2(Math.sqrt(a), Math.sqrt(1d - a));
  return R * c;
}