code: private void doFileRoll(final File from, final File to) {
      final FileHelper fileHelper = FileHelper.getInstance();
      if (!fileHelper.deleteExisting(to)) {
        this.getAppender().getErrorHandler()
            .error("Unable to delete existing " + to + " for rename");
      }
      final String original = from.toString();
      if (fileHelper.rename(from, to)) {
        LogLog.debug("Renamed " + original + " to " + to);
      } else {
        this.getAppender().getErrorHandler()
            .error("Unable to rename " + original + " to " + to);
      }
    }
docs: Renames the current base log file to the roll file name.
  
  @param from
  The current base log file.
  @param to
  The backup file.