@Override
  public void validate(final PipeParameterValidator validator) throws Exception {
    if (!validator
        .getParameters()
        .getBooleanOrDefault(
            Arrays.asList(
                PipeExtractorConstant.EXTERNAL_EXTRACTOR_SINGLE_INSTANCE_PER_NODE_KEY,
                PipeExtractorConstant.EXTERNAL_SOURCE_SINGLE_INSTANCE_PER_NODE_KEY),
            PipeExtractorConstant.EXTERNAL_EXTRACTOR_SINGLE_INSTANCE_PER_NODE_DEFAULT_VALUE)) {
      throw new PipeParameterNotValidException("single mode should be true in MQTT extractor");
    }
  }
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