geodeticLineBuf.java

public static Geometry getGeodeticLineBuf(Geometry inline, int dist) {
  GeometryFactory geometryFactory = JTSFactoryFinder.getGeometryFactory(null );
  GeodeticCalculator calc = new GeodeticCalculator(DefaultGeographicCRS.WGS84);
  Coordinate[] subsat_points = inline.getCoordinates();

  ArrayList<Coordinate> hull_right = new ArrayList<Coordinate>();
  ArrayList<Coordinate> hull_left = new ArrayList<Coordinate>();
  for (int i = 0; i < subsat_points.length-1; i++) {

   calc.setStartingGeographicPoint(subsat_points[i].x,subsat_points[i].y);
   calc.setDestinationGeographicPoint(subsat_points[i+1].x,subsat_points[i+1].y);
   double angle = calc.getAzimuth();

   if (angle<=-90 ){angle = angle+180;}
   if (angle>=90 ){angle = angle-180;}
   calc.setStartingGeographicPoint(subsat_points[i].x,subsat_points[i].y);
   calc.setDirection(angle+90,dist);
   Point2D dest1 = calc.getDestinationGeographicPoint();
   hull_right.add(new Coordinate(dest1.getX(),dest1.getY(),0));
   calc.setDirection(angle-90, dist);
   Point2D dest2 = calc.getDestinationGeographicPoint();
   hull_left.add(new Coordinate(dest2.getX(),dest2.getY(),0));

  }
 Collections.reverse(hull_left);

  ArrayList<Coordinate> hull = new ArrayList<Coordinate>();
  hull.addAll(hull_right);
  hull.addAll(hull_left);
  hull.add(hull_right.get(0)); //close ring
  Coordinate[] hull1 = new Coordinate[hull.size()];
  hull1 = hull.toArray(hull1);

  LinearRing ring = geometryFactory.createLinearRing( hull1 );

  LinearRing holes[] = null; // use LinearRing[] to represent holes
  Polygon polygon = geometryFactory.createPolygon(ring, holes );

  return polygon;

}

Source: https://geoaware.wordpress.com/2013/10/16/geodetic-buffers-with-geotools/