@Override
  public void requestReadPage(long pageNumber, ReadingPageResultHandler readingPageResultHandler) {
    readingPageExecutor.execute(() -> {
      try {
        Page page = getPage_wait(pageNumber);
        readingPageResultHandler.run(page);
      }
      catch (IOException e) {
        logger.warn(e);
        readingPageResultHandler.run(null);
      }
    });
  }
@Override
  public void requestReadPage(long pageNumber, ReadingPageResultHandler readingPageResultHandler)