Android实现圆形图片

public static Bitmap createCircleImage(Bitmap bitmap) {

        int length = bitmap.getWidth() < bitmap.getHeight() ? bitmap.getWidth() : bitmap.getHeight();
        Paint paint = new Paint();
        paint.setAntiAlias(true);
        Bitmap target = Bitmap.createBitmap(length, length, Bitmap.Config.ARGB_8888);
        Canvas canvas = new Canvas(target);
        canvas.drawCircle(length / 2, length / 2, length / 2, paint);
        paint.setXfermode(new PorterDuffXfermode(PorterDuff.Mode.SRC_IN));
        canvas.drawBitmap(bitmap, 0, 0, paint);
        return target;
    }