Annotation that marks a method to be the target of a Kafka message listener on the specified topics. The containerFactory() identifies the KafkaListenerContainerFactory to use to build the Kafka listener container. If not set, a default container factory is assumed to be available with a bean name of kafkaListenerContainerFactory unless an explicit default has been provided through configuration.

Processing of @KafkaListener annotations is performed by registering a KafkaListenerAnnotationBeanPostProcessor. This can be done manually or, more conveniently, through EnableKafka annotation.

Annotated methods are allowed to have flexible signatures similar to what MessageMapping provides, that is

ConsumerRecord to access to the raw Kafka message

Acknowledgment to manually ack

@Payload-annotated method arguments including the support of validation

@Header-annotated method arguments to extract a specific header value, defined by KafkaHeaders

@Headers-annotated argument that must also be assignable to Map for getting access to all headers.

MessageHeaders arguments for getting access to all headers.

MessageHeaderAccessor for convenient access to all method arguments.

When defined at the method level, a listener container is created for each method. The MessageListener is a MessagingMessageListenerAdapter, configured with a MethodKafkaListenerEndpoint.

When defined at the class level, a single message listener container is used to service all methods annotated with @KafkaHandler. Method signatures of such annotated methods must not cause any ambiguity such that a single method can be resolved for a particular inbound message. The MessagingMessageListenerAdapter is configured with a MultiMethodKafkaListenerEndpoint.

https://www.baeldung.com/spring-kafka