code: private File getJournalDir(String jid) {
      String dir = conf.get(JournalConfigKeys.DFS_JOURNALNODE_DIR_KEY,
          JournalConfigKeys.DFS_JOURNALNODE_DIR_DEFAULT);
      Preconditions.checkArgument(jid != null &&
          !jid.isEmpty(),
          "bad journal identifier: %s", jid);
      return new File(new File(new File(dir), "edits"), jid);
    }
docs: Return the directory inside our configured storage
  dir which corresponds to a given journal.
  @param jid the journal identifier
  @return the file, which may or may not exist yet