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Class Level @KafkaListener ​

Selection Criteria ​

Found class will be selected for further processing only if:

It has @KafkaHandler annotation on one of its methods

When you use @KafkaListener at the class-level, you must specify @KafkaHandler at the method level. If no @KafkaHandler on any methods of this class or its sub-classes, the framework will reject such a configuration.

Spring Documentation: Class level KafkaListener

Registration process ​

Each @KafkaListener annotation is considered as a separate channel

Operations registration process depends on @SendTo annotation usage.

Without @SendTo ​

java
@KafkaListener(topics = "messages.1", groupId = "group_1")
@KafkaListener(topics = {"messages.2", "messages.3"}, groupId = "group_2")
public class MultiMessagesListener {}

The next channels will be registered:

  • messages.1
  • messages.2
  • messages.3

With @SendTo ​

java
@KafkaListener(topics = "messages.1", groupId = "group_1")
@KafkaListener(topics = {"messages.2", "messages.3"}, groupId = "group_2")
@SendTo("messages.replies")
public class MultiMessagesListener {}

The next channels will be registered:

  • messages.1
  • messages.2
  • messages.3
  • messages.replies

Messages registration ​

Without @SendTo ​

When class contains only void methods annotated with @KafkaHandler, than each incoming message will be associated with chanel from @KafkaListener annotation

When class contains void and non-void methods annotated with @KafkaHandler, than only incoming messages will be associated with chanel from @KafkaListener annotation

With @SendTo ​

When class contains only void methods annotated with @KafkaHandler, than each incoming message will be associated with chanel from @KafkaListener annotation

When class contains void and non-void methods annotated with @KafkaHandler, than:

  • incoming messages will be associated with chanel from @KafkaListener annotation
  • outgoing messages will be associated with chanel from @SendTo annotation