Method Level @SendTo

Selection Criteria

If @SendTo is present on valid method with @KafkaListener or @KafkaListeners, and non-void return type

@Component
public class MultiMessagesListener {

    @KafkaListener(topics = {"messages.blue"})
    @KafkaListener(topics = {"messages.green"})
    @SendTo({"messages.*.replies", "messages.*.replies-2"})
    public String listen(Object message) {}

}

Registration process

When listener is registered with @SendTo annotation, one-to-many operation will be created for each @KafkaListener annotation.

@Component
public class MultiMessagesListener {

    @KafkaListener(topics = {"messages.blue"})
    @KafkaListener(topics = {"messages.green", "messages.yellow"}, groupId = "group-id")
    @SendTo({"messages.replies.1", "messages.replies.2"})
    public String listen(Object message) {}

}

The next operations will be created:

1. receive Object from messages.blue and reply to messages.replies.1 with String
2. receive Object from messages.blue and reply to messages.replies.2 with String
3. receive Object from messages.green with groupId group-id and reply to messages.replies.1 with String
4. receive Object from messages.green with groupId group-id and reply to messages.replies.2 with String
5. receive Object from messages.yellow with groupId group-id and reply to messages.replies.1 with String
6. receive Object from messages.yellow with groupId group-id and reply to messages.replies.2 with String

When @SendTo will be ignored?

Empty @SendTo

When @SendTo annotation is empty

@Component
public class MultiMessagesListener {

    @KafkaListener(topics = {"messages.blue"})
    @KafkaListener(topics = {"messages.green"})
    @SendTo
    public String listen(Object message) {}

}

Void method

When method is void

@Component
public class MultiMessagesListener {

    @KafkaListener(topics = {"messages.blue"})
    @KafkaListener(topics = {"messages.green"})
    @SendTo({"messages.*.replies", "messages.*.replies-2"})
    public void listen(Object message) {}

}