Integrating Spring Boot and Reactor-Kafka's KafkaReceiver

riccardo.cardin :

I am trying to develop a Spring Boot application using the library reactor-kafka to react to some messages read from a Kafka topic.

I have a configuration class that builds a KafkaReceiver.

@Configuration
public class MyConfiguration {

    @Bean
    public KafkaReceiver<String, String> kafkaReceiver() {
        Map<String, Object> props = new HashMap<>();
        // Options initialisation...
        final ReceiverOptions<String, String> receiverOptions =
                ReceiverOptions.<String, string>create(props)
                               .subscription(Collections.singleton(consumer.getTopic()));
        return KafkaReceiver.create(receiverOptions);
    } 
}

Well...and now? Using not-so-reactive spring-kafka library, I can annotate a method with @KafkaListener and Spring Boot will create for me a thread listening from a Kafka topic.

Where should I place the KafkaReceiver, instead? In all the examples I found the use directly the main method, but this is not the Boot way.

I am using Spring Boot 2.1.3 and Reactor-Kafka 1.1.0

Thanks in advance.

Artem Bilan :

Since you have that KafkaReceiver bean, now you can do like this:

@Bean
public ApplicationRunner runner(KafkaReceiver<String, String> kafkaReceiver) {
        return args -> {
                kafkaReceiver.receive()
                          ...
                          .sunbscribe();
        };
}

This ApplicationRunner bean is going to be kicked when the ApplicationContext is ready. See its JavaDocs for more info.