Spring Kafka Listener on Http Request

Question

I am using Spring and Kafka, I make an HTTP POST request as shown below and send some info to another service via a Kafka topic.

@RequestMapping(method = RequestMethod.POST, value = "/portfolio")
public void getPortfolio(
       Authentication auth,
    @RequestBody User user
) {
    //Data Transfer Object
    UserDTO dto = user.toDTO();
    dto.setId(((AuthenticatedUser) auth.getPrincipal()).getId());

    //Sending message to Kafka topic
    sender.sendPortfolioRequest(dto);
}

I then want to listen for the response on a different topic and return data in the HTTP response but am stuck here. I am able to listen to for the response using the below listener method but don't know how to put the two together.

@KafkaListener(
    topics = Topics.PORTFOLIO_RESULT,
    containerFactory = "portfolioKafkaListenerContainerFactory"
)
public void portfolioListener(UserPortfolioDTO portfolio) {
    System.out.println("Recieved Portfolio: " + portfolio.toString());
}

P.S. I am new to using HTTP requests and don't know if this is the correct way to do what I'm trying to achieve or if I should be creating a new resource with the POST and redirecting to that or something else.

Answer 1

This can't be done with the @KafkaListener since it is started separately and fully works in its own thread(s). Meanwhile you expect a reply in the HTTP request thread.

Only the solution possible for you here is a ConsumerFactory and manual usage of the Apache Kafka Consumer. So, you send, you obtain a Consumer instance from the factory, call its poll() being blocked until a result, build a response for HTTP and close Consumer.