code: public ReadableGridFileChannel getReadableChannel(String pathname) throws FileNotFoundException {
        GridFile file = (GridFile) getFile(pathname);
        checkFileIsReadable(file);
        return new ReadableGridFileChannel(file, data);
     }
docs: Opens a ReadableGridFileChannel for reading from the file denoted by the given file path. One of the benefits
  of using a channel over an InputStream is the possibility to randomly seek to any position in the file (see
  #ReadableGridChannel.position()).
  @param pathname path of the file to open for reading
  @return a ReadableGridFileChannel for reading from the file
  @throws FileNotFoundException if the file does not exist or is a directory