Kafka Spring: How to create Listeners dynamically or in a loop?

Question

I have 4 ConsumerFactory listeners that are reading from 4 different topics like this:

@KafkaListener(
      id = "test1",
      topicPattern  = "test.topic1",
      groupId = "pp-test1")
  public void listenTopic1(ConsumerRecord<String, String> record) {
    System.out.println("Topic is: " + record.topic());   
  }

But we'll have 50 topics and I want to set up atleast 25 listeners for betetr performance. How can I do this dynamically instead of manually writing 25 listeners?

Answer 1

You cannot create @KafkaListeners programmatically, only discrete listener containers (with a custom listener).

You can do it by programmatically creating a child application context for each listener.

EDIT

@SpringBootApplication
public class So53715268Application {

    public static void main(String[] args) {
        ConfigurableApplicationContext context = SpringApplication.run(So53715268Application.class, args);
        for (int i = 0; i < 2; i++) {
            AnnotationConfigApplicationContext child = new AnnotationConfigApplicationContext();
            child.setParent(context);
            child.register(ChildConfig.class);
            Properties props = new Properties();
            props.setProperty("group", "group." + i);
            props.setProperty("topic", "topic" + i);
            PropertiesPropertySource pps = new PropertiesPropertySource("listenerProps", props);
            child.getEnvironment().getPropertySources().addLast(pps);
            child.refresh();
        }
    }

}

and

@Configuration
@EnableKafka
public class ChildConfig {

    @Bean
    public Listener listener() {
        return new Listener();
    }

}

and

public class Listener {

    @KafkaListener(id = "${group}", topics = "${topic}")
    public void listen(String in) {
        System.out.println(in);
    }

}

and

: partitions assigned: [topic0-0]
: partitions assigned: [topic1-0]

Note that, if you are using Spring Boot, the child config class and listener must be in a different package to the main app (and not a sub-package either).