What is DefaultKafkaConsumerFactory?

DefaultKafkaConsumerFactory is the implementation for ConsumerFactory. This dictates how consumer instances will be created.

This is a typical Java based configuration for Spring Kafka...

@Configuration
public class KafkaConsumerConfig {
    @Bean
    public ConsumerFactory<String, String> consumerFactory() {
        Map<String, Object> props = new HashMap<>();
        props.put(
                ConsumerConfig.BOOTSTRAP_SERVERS_CONFIG,
                "http://localhost:9092");
        props.put(
                ConsumerConfig.KEY_DESERIALIZER_CLASS_CONFIG,
                StringDeserializer.class);
        props.put(
                ConsumerConfig.VALUE_DESERIALIZER_CLASS_CONFIG,
                StringDeserializer.class);
        return new DefaultKafkaConsumerFactory<>(props);
    }
    @Bean
    public ConcurrentKafkaListenerContainerFactory<String, String>
    kafkaListenerContainerFactory() {
        ConcurrentKafkaListenerContainerFactory<String, String> factory =
                new ConcurrentKafkaListenerContainerFactory<>();
        factory.setConsumerFactory(consumerFactory());
        return factory;
    }
}

Notice how the first bean returns a new DefaultKafkaConsumerFactory

Notice how the ConcurrentKafkaListenerContainerFactory sets it's consumer factory (for configuring it's instances)

A container factory creates container instances.

These container instances are ConcurrentMessageListenerContainer instances.

These are really collections of KafkaMessageListenerContainers

These KafkaMessageListenerContainers are consumers that can read from Kafka :)

DefaultKafkaConsumerFactory is THE implementation of the ContainerFactory interface.

The default factory for creating consumer instances.