Spring Kafka Requirements for Supporting Multiple Consumers

Question

As one would expect its common to want to have different Consumers deserializing in different ways off topics in Kafka. There is a known problem with spring boot autoconfig. It seems that as soon as other factories are defined Spring Kafka or the autoconfig complains about not being able to find a suitable consumer factory anymore. Some have pointed out that one solution is to include a ConsumerFactory of type (Object, Object) in the config. But no one has shown the source code for this or clarified if it needs to be named in any particular way. Or if simply adding this Consumer to the config removes the need to turn off autoconfig. All that remains very unclear.

If you are not familiar with this issue please read https://github.com/spring-projects/spring-boot/issues/19221

Where it was just stated ok, define the ConsumerFactory and add it somewhere in your config. Can someone be a bit more precise about this please.

1. Show exactly how to define the ConsumerFactory so that Spring boot autoconfig will not complain.
2. Explain if turning off autoconfig is or is not needed?
3. Explain if Consumer Factory needs to be named in any special way or not.

Answer 1

The simplest solution is to stick with Boot's auto-configuration and override the deserializer on the @KafkaListener itself...

@SpringBootApplication
public class So63108344Application {

    public static void main(String[] args) {
        SpringApplication.run(So63108344Application.class, args);
    }

    @KafkaListener(id = "so63108344-1", topics = "so63108344-1")
    public void listen1(String in) {
        System.out.println(in);
    }

    @KafkaListener(id = "so63108344-2", topics = "so63108344-2", properties =
            ConsumerConfig.VALUE_DESERIALIZER_CLASS_CONFIG +
                "=org.apache.kafka.common.serialization.ByteArrayDeserializer")
    public void listen2(byte[] in) {
        System.out.println(in);
    }

    @Bean
    public NewTopic topic1() {
        return TopicBuilder.name("so63108344-1").partitions(1).replicas(1).build();
    }

    @Bean
    public NewTopic topic2() {
        return TopicBuilder.name("so63108344-2").partitions(1).replicas(1).build();
    }

}

For more advanced container customization (or if you don't want to pollute the @KafkaListener, you can use a ContainerCustomizer...

@Component
class Customizer {
    
    public Customizer(ConcurrentKafkaListenerContainerFactory<?, ?> factory) {
        factory.setContainerCustomizer(container -> {
            if (container.getGroupId().equals("so63108344-2")) {
                container.getContainerProperties().setAckMode(AckMode.MANUAL_IMMEDIATE);
                container.getContainerProperties().getKafkaConsumerProperties()
                    .setProperty(ConsumerConfig.VALUE_DESERIALIZER_CLASS_CONFIG, "org.apache.kafka.common.serialization.ByteArrayDeserializer");
            }
        });
    }
    
}