Java: MQTT MessageProducerSupport to Flux - spring-integration

Question

I have a simple MQTT Client that outputs received messages via IntegrationFlow:
public MqttPahoClientFactory mqttClientFactory() {
DefaultMqttPahoClientFactory factory = new DefaultMqttPahoClientFactory();
MqttConnectOptions options = new MqttConnectOptions();
options.setServerURIs(new String[] { "tcp://test.mosquitto.org:1883" });
factory.setConnectionOptions(options);
return factory;
}
public MessageProducerSupport mqttInbound() {
MqttPahoMessageDrivenChannelAdapter adapter = new MqttPahoMessageDrivenChannelAdapter(
"myConsumer",
mqttClientFactory(),
"/test/#");
adapter.setCompletionTimeout(5000);
adapter.setConverter(new DefaultPahoMessageConverter());
adapter.setQos(1);
return adapter;
}
public IntegrationFlow mqttInFlow() {
return IntegrationFlows.from(mqttInbound())
.transform(p -> p + ", received from MQTT")
.handle(logger())
.get();
}
private LoggingHandler logger() {
LoggingHandler loggingHandler = new LoggingHandler("INFO");
loggingHandler.setLoggerName("siSample");
return loggingHandler;
}
I need to pipe all received messages into a Flux though for further processing.
public Flux<String> mqttChannel() {
...
return mqttFlux;
}
How can I do that? The loggingHandler receives all messages from the IntegrationFlow. Couldn't my Flux get it's input in a similar fashion - by passing it somehow to IntegrationFlows handle function?
MQTT Example code is take from https://github.com/spring-projects/spring-integration-samples/blob/master/basic/mqtt/src/main/java/org/springframework/integration/samples/mqtt/Application.java
Attempt: Following Artem Bilans advise I'm now trying to use toReactivePublisher to convert my inbound IntegrationFlow to Flux.
public Flux<String> mqttChannel() {
Publisher<Message<Object>> flow = IntegrationFlows.from(mqttInbound())
.toReactivePublisher();
Flux<String> mqttFlux = Flux.from(flow)
.log()
.map(i -> "TESTING: Received a MQTT message");
return mqttFlux;
}
Running the example i get following error:
10:14:39.541 [MQTT Call: myConsumer] ERROR o.s.i.m.i.MqttPahoMessageDrivenChannelAdapter - Unhandled exception for GenericMessage [payload=OFF,26.70,65.00,663,-62,192.168.2.100,0.026,25,4,6,7,933,278,27,4,1,0,1580496218,730573600,1800000,1980000,1580496218,730573600,10800000,11880000, headers={mqtt_receivedRetained=true, mqtt_id=0, mqtt_duplicate=false, id=3f7565aa-ff4f-c389-d8a9-712d4f06f1cb, mqtt_receivedTopic=/083B7036697886C41D2DF2FD919143EE/MasterBedroom/Sensor/, mqtt_receivedQos=0, timestamp=1602231279537}]
Conclusion: as soon as the first message arrives, it's handled wrong and an exception is thrown.

Answer 1

Please, read this doc: https://docs.spring.io/spring-integration/docs/5.3.2.RELEASE/reference/html/reactive-streams.html#reactive-streams
It is not clear what you would like to achieve with that "my flux" and how that could look, but for your current configuration there are a couple of solutions.
You can use a FluxMessageChannel which is already a Publisher, so you can simply use Flux.from() and subscriber to that for consuming data produced by the mentioned MqttPahoMessageDrivenChannelAdapter.
Another way is to use a toReactivePublisher() on the IntegrationFlowBuilder to expose the whole flow as a reactive Publsiher source. In this case, of course, you can't use the LoggingHandler because it is a one-way and makes your flow ending exactly here. You may consider to use a log() operator instead though: https://docs.spring.io/spring-integration/docs/5.3.2.RELEASE/reference/html/dsl.html#java-dsl-log
By the way the FluxMessageChannel is publish-subscribe, so you can have it in the flow for those logs and also have it externally for Flux.from() subscription. All the subscribers to this channel are going to get the same message.