Event connection listeners using mqttClient automatically generated using by micronaut

[tomgeek27]

Feature description

I'm defining a subscriber using @MqttSubscriber and therefore I can only configure it by the application.yml file. The problem is that some configurations are limited, for example event connection listeners.

It would be interesting to have a way to define a custom listener related to connection events using the MqttClient injectable by micronaut. For instance, I would like to log something when the client connects to or disconnects from the broker.

This could be a way to implement but due to immutable list it's not possible to add elements to the connected/disconnected listeners list:

@Slf4j
@Singleton
public class StartupListener implements ApplicationEventListener<ApplicationStartupEvent> {

  @Inject
  MqttClient mqttClient;

  @Override
  public void onApplicationEvent(ApplicationStartupEvent event) {
    mqttClient.getConfig().getConnectedListeners().add(
            mqttClientConnectedContext -> log.debug("LOGGING SOMETHING USEFUL...")
    );

    log.debug("Starting up service");
  }
}