code: public Geometry lngLatToMeters(Geometry geometry) {
          GeometryTransformer transformer = new GeometryTransformer() {
              @Override
              protected CoordinateSequence transformCoordinates(CoordinateSequence coords, Geometry parent) {
                  Coordinate[] newCoords = new Coordinate[coords.size()];
                  for (int i = 0; i < coords.size(); ++i) {
                      Coordinate coord = coords.getCoordinate(i);
                      newCoords[i] = lngLatToMeters(coord);
                  }
                  return new CoordinateArraySequence(newCoords);
              }
          };
          Geometry result = transformer.transform(geometry);
          return result;
      }
docs: Converts geometry from lat/lon (EPSG:4326)) to Spherical Mercator
  (EPSG:3857)
  
  @param geometry the geometry to convert
  @return the geometry transformed to EPSG:3857