code: public static long getDirectorySize(Path path, FileSystem fs) throws IOException {
      ContentSummary cs = fs.getContentSummary(path);
      return cs.getLength();
    }
docs: Calculates the total size of all the contents of a directory,
  including the contents of all of its subdirectories.
  Does not include the size of directories themselves
  (which are 0 in HDFS but may not be 0 on local file systems)
  
  @param path path to recursively walk
  @param fs FileSystem for this path
  @return size of the directory's contents in bytes
  @throws IOException