Spring cloud function Cosuming rabbitmq queue - Dispatcher has no subscribers for channel

Question

Given:

  cloud:
    stream:
      rabbit:
      bindings:
        inboundApolloLookupVehicleChannel:
          destination: fed.apollo-vehicle-lookup-test
          group: apollo-mngt-group
          consumer:
            missingQueuesFatal: true
            prefetch: 25
            autoBindDlq: true
            maxAttempts: 1
            republishToDlq: true
            requeueRejected: false
            durableSubscription: true
            maxConcurrency: 6              
      function:
        definition: consume  

and:

@SpringBootApplication
@EnableEurekaClient
@EnableBinding(LookupMessageChannel.class)
public class ApolloLookupServiceApplication {

    public static void main(String[] args) {
        SpringApplication.run(ApolloLookupServiceApplication.class, args);
    }
}


public interface LookupMessageChannel {

    String INBOUND_LOOKUP_VEHICLE_CHANNEL = "inboundApolloLookupVehicleChannel";

    @Input(INBOUND_LOOKUP_VEHICLE_CHANNEL)
    SubscribableChannel inboundApolloLookupVehicleChannel();

}

@Service
@MessageEndpoint
@RequiredArgsConstructor
public class ApolloVehicleLookupService {

    private final ApolloVehicleLookUpRepository apolloVehicleLookUpRepository;
    private static final Logger LOGGER = LoggerFactory.getLogger(ApolloVehicleLookupService.class);

    @Bean
    public Consumer<Flux<ApolloVehicleLookUp>> consume() {
        return stream -> stream             
                .flatMap(this.apolloVehicleLookUpRepository::save)
                .subscribe(value -> {
                        LOGGER.info("stored value: " + value.toString());
                });
    }

}

POM:

    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>2.2.6.RELEASE</version>
        <relativePath />
        <!-- lookup parent from repository -->
    </parent>

    <properties>
        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
        <project.reporting.outputEncoding>UTF-8</project.reporting.outputEncoding>
        <java.version>14</java.version>
        <spring-cloud.version>Hoxton.SR3</spring-cloud.version>
        <os-maven-plugin.version>1.5.0.Final</os-maven-plugin.version>
        <spotify-docker-maven.version>1.2.0</spotify-docker-maven.version>      
        <os.detected.classifier>linux-x86_64</os.detected.classifier>
    </properties>

  <dependencies>

        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-data-mongodb-reactive</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-rsocket</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-webflux</artifactId>
        </dependency>
        <dependency>
            <groupId>org.projectlombok</groupId>
            <artifactId>lombok</artifactId>
            <optional>true</optional>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-actuator</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.cloud</groupId>
            <artifactId>spring-cloud-starter-bus-amqp</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.cloud</groupId>
            <artifactId>spring-cloud-starter-stream-rabbit</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.cloud</groupId>
            <artifactId>spring-cloud-starter-config</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.cloud</groupId>
            <artifactId>spring-cloud-starter-netflix-eureka-client</artifactId>
        </dependency>
  </dependencies>

Why am I getting the following exception?

[payload=org.springframework.messaging.MessageDeliveryException: Dispatcher has no subscribers for channel 'apollo-lookup-service-1.inboundApolloLookupVehicleChannel'. ; nested exception is org.springframework.integration.MessageDispatchingException: Dispatcher has no subscribers, failedMessage=GenericMessage [payload=byte[439]

I've just wanted to consume messages from that queue.

Any help would be appreciated, thanks.

Answer 1

The exception simple means that your channel defined in LookupMessageChannel has no subscribers and why should it since, you have not defined any. It also appears to me that you are attempting to use functional approach while the rest of your stream app uses legacy configurations that is all but deprecated.

Don't get me wrong but there are few things that are wrong with your app at the moment so it's hard to determine what exactly you are looking for to do, so. . .

Please consider following this quick start (5 min top) to get you into proper functional approach and then feel free to follow up with additional questions.