class FileGroupReader {

  static Map<String, String> loadContents(Path rootDir) throws IOException {
    try (Stream<Path> walk = Files.walk(rootDir, 1)) {
      return walk.filter(path -> !Files.isDirectory(path))
          .collect(Collectors.toMap(FileGroupReader::asString, FileGroupReader::readContents));
    }
  }

    FileGroupReader(String pathToGroup);

}