public static String getStringFromJsonObject(JsonObject jsonObject, String key, String defaultValue) {
    if (System.getProperty(key) == null) {
      return jsonObject.getString(key, defaultValue);
    } else {
      return System.getProperty(key);
    }
  }
Gets the String value from a given json object,
overwrite it with System env or a default value if applicable

@param jsonObject   the json object
@param key          name of the attribute
@param defaultValue default value

@return an String value
KITE-Framework/src/main/java/org/webrtc/kite/Utils.java