code: private static Map<String, Map<String, String>> getStatsMap(String json)
        throws IOException {
      if (json == null || json.isEmpty()) {
        return new HashMap<String, Map<String, String>>();
      }
      TypeReference<Map<String, Map<String, String>>> type = new TypeReference<Map<String, Map<String, String>>>() {
      };
      return mapper.readValue(json, type);
    }
docs: Get the map corresponding to the JSON string