private static void makeMqttPluginDir() throws IOException {
    File file = SystemFileFactory.INSTANCE.getFile(mqttDir);
    if (file.exists() && file.isDirectory()) {
      return;
    }
    FileUtils.forceMkdir(file);
  }
PayloadFormatManager loads payload formatter from SPI services.
iotdb-core/datanode/src/main/java/org/apache/iotdb/db/protocol/mqtt/PayloadFormatManager.java