A request-response API lets a client send one request and receive one corresponding response. HTTP and REST commonly use this pattern. RSocket supports it too, but handles the exchange with nonblocking, reactive types: the client still awaits a reply without tying up a thread while it waits. section 14.0 section 14.1
Choose request-response when one reply is what the client needs. If a request should produce many values, RSocket offers request-stream; if it needs no reply, fire-and-forget; if both sides need to keep sending data, a channel. section 14.1
To make a request-response exchange in Spring:
- Add the Spring Boot RSocket starter and configure a server port, such as 7000. section 14.2 section 14.2.1
- Handle a route with a controller method annotated @MessageMapping. A Mono<String> can carry the incoming value and the single reply. section 14.2.1
- Build an RSocketRequester, select the route, supply the payload, and call retrieveMono(String.class). Subscribe to handle the returned value. section 14.2.1
A greeting exchange
A client sends “Hello RSocket!” to the greeting route. The controller returns “Hello back to you!” as a Mono<String>; the client subscribes to that Mono and logs the reply. A route such as greeting/{name} can also take a value supplied by the client. section 14.2.1
Listing 14.2 A simple RSocket request-response server
package rsocket;
import org.springframework.messaging.handler.annotation.MessageMapping;
import org.springframework.stereotype.Controller;
import lombok.extern.slf4j.Slf4j;
import reactor.core.publisher.Mono;
@Controller
@Slf4j
public class GreetingController {
@MessageMapping("greeting")
public Mono<String> handleGreeting(Mono<String> greetingMono) {
return greetingMono
.doOnNext(greeting ->
log.info("Received a greeting: {}", greeting))
.map(greeting -> "Hello back to you!");
}
}
The server listing shows how @MessageMapping connects the greeting route to a handler that turns one incoming greeting into one reply. section 14.2.1
Listing 14.3 Sending a request from a client
RSocketRequester tcp = requesterBuilder.tcp("localhost", 7000);
// ... send messages with RSocketRequester ...
tcp
.route("greeting")
.data("Hello RSocket!")
.retrieveMono(String.class)
.subscribe(response -> log.info("Got a response: {}", response));
The client listing shows the matching route, payload, retrieveMono call, and subscription in one exchange. section 14.2.1
