code: public static double length(@NonNull MultiPolygon multiPolygon,
                                @NonNull @TurfConstants.TurfUnitCriteria String units) {
      double len = 0;
      List<List<List<Point>>> coordinates = multiPolygon.coordinates();
      for (List<List<Point>> coordinate : coordinates) {
        for (List<Point> theCoordinate : coordinate) {
          len += length(theCoordinate, units);
        }
      }
      return len;
    }
docs: Takes a {@link MultiPolygon} and measures each polygons perimeter in the specified units. if
  one of the polygons contains holes, the perimeter will also be included.
  
  @param multiPolygon geometry to measure
  @param units        one of the units found inside {@link TurfConstants.TurfUnitCriteria}
  @return total perimeter of the input polygons combined, in the units specified
  @see <a href="http://turfjs.org/docs/#linedistance">Turf Line Distance documentation</a>
  @since 1.2.0