docs: public static void copyDir(File from, File to) throws FileNotFoundException, IOException {
          File[] files = from.listFiles();
  
          if (files != null) {
              for (File ff : files) {
                  File tf = new File(to, ff.getName());
                  if (ff.isDirectory()) {
                      if (tf.mkdir()) {
                          copyDir(ff, tf);
                      }
                  } else if (ff.isFile()) {
                      copyFile(tf, ff);
                  }
              }
          }
      }