@Override
  public void close() throws Exception {
    if (!isClosed.get()) {
      server.stopServer();
      isClosed.set(true);
    }
  }
MQTTExtractor is an external Extractor that uses the MQTT protocol to receive data. It starts an
MQTT broker and listens for incoming messages, which are then processed and passed to the pending
queue.
iotdb-core/datanode/src/main/java/org/apache/iotdb/db/pipe/extractor/mqtt/MQTTExtractor.java