How to sort 3D vertices of a polygon in order?

we are given multiple random coplanar 3D points. Compute normal by any 3 Point. we need to rotate all these point in X-Y plane. So compute rotation matrix normal to (0,0,1). rotate all these in X-Y plane.

      double[] normal = PlaneUtils.getNormal(tverts);

      Vector3 srcNormal = new Vector3(normal[0], normal[1], normal[2]).normalize();

      Vector3 destNormal = new Vector3(0, 0, 1);

      // Rotation Matrix of Arbitrary Polygon From Current Plane to XY Plane

      Matrix4 rotationMatrix = Matrix4.rotate(destNormal, srcNormal);

      for (int i = 0; i < PointArrVal.length; i++) {

        PointArrVal[i].timesEquals(rotationMatrix);

      }

Now Compute Mean of All X-coordinate and mean of All Y-coordinate.

Mean of X= Sum of All X-coordinate/number of Point and in same way compute mean of Y.

Compute Atan2 angle between Mean Point and given coordinate.

Math.atan2(clipCornerPoint[i].y - cY, clipCornerPoint[i].x - cX), clipCornerPoint[i]

Store computed angle with vertices in Ordered Multi Map like

TreeMap <Double, List<Point3>> multimap = new TreeMap<Double, List<Point3>>();
      for (int i = 0; i < clipCornerPoint.length; i++) {
        putObjects(multimap, Math.atan2(clipCornerPoint[i].y - cY, clipCornerPoint[i].x - cX), clipCornerPoint[i]);
      }

Sort map angle as key and it will give you vertices in order.

now reverse your point in same previous Arbitrary Axis by inverse Rotation Matrix.