Instantiating server in Spring Framework 5 and Spring Boot 2 - spring

Question

I am using Spring Boot 2 just to try some reactive programming with Spring 5. I created some standard MVC controller.
#RestController
#RequestMapping("/judge/rest")
public class BasicController {
private static final Logger LOGGER = LoggerFactory.getLogger(BasicController.class);
#GetMapping("/hello")
public Mono<String> handle() {
LOGGER.debug("Invoking hello controller");
return Mono.just("Hello WebFlux");
}
}
And standard router function.
#Configuration
public class WebConfig {
#Bean
public RouterFunction<?> helloRoute() {
return route(GET("/judge/router/hello"),
request -> ServerResponse.ok().body(fromPublisher(Mono.just("Hello Router WebFlux"), String.class)));
}
}
My main spring boot application looks like this
#SpringBootApplication
public class JudgeRuleEngineApplication {
public static void main(String[] args) {
SpringApplication.run(JudgeRuleEngineApplication.class, args);
}
}
But in documentation for spring 5 I ran into
HttpHandler httpHandler = RouterFunctions.toHttpHandler(route);
ReactorHttpHandlerAdapter adapter =
new ReactorHttpHandlerAdapter(httpHandler);
HttpServer server = HttpServer.create("localhost", 8080);
server.startAndAwait(adapter);
It seems that server is intantiated manually.
My question is when should I instantiate the server like this? Because so far it seems with #SpringBootApplication and main it handles requests just fine.

Answer 1

As the document says
Now there is just one piece of the puzzle missing: running a router
function in an HTTP server. You can convert a router function into a
HttpHandler by using RouterFunctions.toHttpHandler(RouterFunction).
The HttpHandler allows you to run on a wide variety of reactive
runtimes: Reactor Netty, RxNetty, Servlet 3.1+, and Undertow.
Which means the above code which you have shown, uses Reactor Netty as the reactive runtime. If you wish to use any other runtimes which has reactive native adapter, you can do so. In such cases you would instantiate the server like this.
By default Spring boot default to Reactor Netty.