code: public static boolean unsafeRenameIfNotExists(FileSystem fs, Path from, Path to) throws IOException {
      if (!fs.exists(to)) {
        if (!fs.exists(to.getParent())) {
          fs.mkdirs(to.getParent());
        }
  
        if (!renamePathHandleLocalFSRace(fs, from, to)) {
          if (!fs.exists(to)) {
            throw new IOException(String.format("Failed to rename %s to %s.", from, to));
          }
  
          return false;
        }
        return true;
      }
      return false;
    }
docs: Renames from to to if to doesn't exist in a non-thread-safe way.
  
  @param fs filesystem where rename will be executed.
  @param from origin {@link Path}.
  @param to target {@link Path}.
  @return true if rename succeeded, false if the target already exists.
  @throws IOException if rename failed for reasons other than target exists.