Spring Cloud Stream RabbitMQ

Question

I am trying to understand why I would want to use Spring cloud stream with RabbitMQ. I've had a look at the RabbitMQ Spring tutorial 4 (https://www.rabbitmq.com/tutorials/tutorial-four-spring-amqp.html) which is basically what I want to do. It creates a direct exchange with 2 queues attached and depending on the routing key a message is either routed to Q1 or to Q2.

The whole process is pretty straight forward if you look at the tutorial, you create all the parts, bind them together and youre ready to go.

I was wondering what benefit I would gain in using Sing Cloud Stream and if that is even the use case for it. It was easy to create a simple exchange and even defining destination and group was straight forward with stream. So I thought why not go further and try to handle the tutorial case with stream.

I have seen that Stream has a BinderAwareChannelResolver which seems to do the same thing. But I am struggling to put it all together to achieve the same as in the RabbitMQ Spring tutorial. I am not sure if it is a dependency issue, but I seem to misunderstand something fundamentally here, I thought something like:

spring.cloud.stream.bindings.output.destination=myDestination
spring.cloud.stream.bindings.output.group=consumerGroup
spring.cloud.stream.rabbit.bindings.output.producer.routing-key-expression='key'

should to the trick.

Is there anyone with a minimal example for a source and sink which basically creates a direct exchange, binds 2 queues to it and depending on routing key routes to either one of those 2 queues like in https://www.rabbitmq.com/tutorials/tutorial-four-spring-amqp.html?

EDIT:

Below is a minimal set of code which demonstrates how to do what I asked. I did not attach the build.gradle as it is straight forward (but if anyone is interested, let me know)

application.properties: setup the producer

spring.cloud.stream.bindings.output.destination=tut.direct
spring.cloud.stream.rabbit.bindings.output.producer.exchangeType=direct
spring.cloud.stream.rabbit.bindings.output.producer.routing-key-expression=headers.type

Sources.class: setup the producers channel

public interface Sources {

    String OUTPUT = "output";

    @Output(Sources.OUTPUT)
    MessageChannel output();
}

StatusController.class: Respond to rest calls and send message with specific routing keys

/**
 * Status endpoint for the health-check service.
 */
@RestController
@EnableBinding(Sources.class)
public class StatusController {

    private int index;

    private int count;

    private final String[] keys = {"orange", "black", "green"};

    private Sources sources;

    private StatusService status;

    @Autowired
    public StatusController(Sources sources, StatusService status) {
        this.sources = sources;
        this.status = status;
    }

    /**
     * Service available, service returns "OK"'.
     * @return The Status of the service.
     */
    @RequestMapping("/status")
    public String status() {
        String status = this.status.getStatus();

        StringBuilder builder = new StringBuilder("Hello to ");
        if (++this.index == 3) {
            this.index = 0;
        }
        String key = keys[this.index];
        builder.append(key).append(' ');
        builder.append(Integer.toString(++this.count));
        String payload = builder.toString();
        log.info(payload);

        // add kv pair - routingkeyexpression (which matches 'type') will then evaluate
        // and add the value as routing key
        Message<String> msg = new GenericMessage<>(payload, Collections.singletonMap("type", key));
        sources.output().send(msg);

        // return rest call
        return status;
    }
}

consumer side of things, properties:

spring.cloud.stream.bindings.input.destination=tut.direct
spring.cloud.stream.rabbit.bindings.input.consumer.exchangeType=direct
spring.cloud.stream.rabbit.bindings.input.consumer.bindingRoutingKey=orange
spring.cloud.stream.bindings.inputer.destination=tut.direct
spring.cloud.stream.rabbit.bindings.inputer.consumer.exchangeType=direct
spring.cloud.stream.rabbit.bindings.inputer.consumer.bindingRoutingKey=black

Sinks.class:

public interface Sinks {

    String INPUT = "input";

    @Input(Sinks.INPUT)
    SubscribableChannel input();

    String INPUTER = "inputer";

    @Input(Sinks.INPUTER)
    SubscribableChannel inputer();
}

ReceiveStatus.class: Receive the status:

@EnableBinding(Sinks.class)
public class ReceiveStatus {
    @StreamListener(Sinks.INPUT)
    public void receiveStatusOrange(String msg) {
       log.info("I received a message. It was orange number: {}", msg);
    }

    @StreamListener(Sinks.INPUTER)
    public void receiveStatusBlack(String msg) {
        log.info("I received a message. It was black number: {}", msg);
    }
}

Answer 1

Spring Cloud Stream lets you develop event driven micro service applications by enabling the applications to connect (via @EnableBinding) to the external messaging systems using the Spring Cloud Stream Binder implementations (Kafka, RabbitMQ, JMS binders etc.,). Apparently, Spring Cloud Stream uses Spring AMQP for the RabbitMQ binder implementation.

The BinderAwareChannelResolver is applicable for dynamically binding support for the producers and I think in your case it is about configuring the exchanges and binding of consumers to that exchange.

For instance, you need to have 2 consumers with the appropriate bindingRoutingKey set based on your criteria and a single producer with the properties(routing-key-expression, destination) you mentioned above (except the group). I noticed that you have configured group for the outbound channel. The group property is applicable only for the consumers (hence inbound).

You might also want to check this one: https://github.com/spring-cloud/spring-cloud-stream-binder-rabbit/issues/57 as I see some discussion around using routing-key-expression. Specifically, check this one on using the expression value.