如何在api < 20 (Android)上获取圆形图像视图

public class CircleImageView extends ImageView {

    public CircleImageView(Context context) {
        super(context);
    }

    public CircleImageView(Context context, AttributeSet attrs) {
        super(context, attrs);
    }

    public CircleImageView(Context context, AttributeSet attrs, int defStyle) {
        super(context, attrs, defStyle);
    }

    @Override
    protected void onDraw(Canvas canvas) {
        Drawable drawable = getDrawable();

        if (drawable == null) {
            return;
        }

        if (getWidth() == 0 || getHeight() == 0) {
            return;
        }

        Bitmap bitmap = ((BitmapDrawable) drawable).getBitmap();
        Bitmap circularBitmap = getCircularBitmap(bitmap);
        canvas.drawBitmap(circularBitmap, 0, 0, null);
    }

    private Bitmap getCircularBitmap(Bitmap bitmap) {
        Bitmap output = Bitmap.createBitmap(bitmap.getWidth(), bitmap.getHeight(), Bitmap.Config.ARGB_8888);
        Canvas canvas = new Canvas(output);

        final Paint paint = new Paint();
        final Rect rect = new Rect(0, 0, bitmap.getWidth(), bitmap.getHeight());

        paint.setAntiAlias(true);
        canvas.drawARGB(0, 0, 0, 0);
        canvas.drawCircle(bitmap.getWidth() / 2, bitmap.getHeight() / 2, bitmap.getWidth() / 2, paint);
        paint.setXfermode(new PorterDuffXfermode(PorterDuff.Mode.SRC_IN));
        canvas.drawBitmap(bitmap, rect, rect, paint);

        return output;
    }
}

CircleImageView circleImageView = findViewById(R.id.circle_image_view);
String imageUrl = "https://example.com/image.jpg";

Picasso.get().load(imageUrl).into(circleImageView);