Functional Web Route in Spring 5

Routes.java

import org.springframework.boot.web.servlet.ServletRegistrationBean;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.http.server.reactive.HttpHandler;
import org.springframework.http.server.reactive.ServletHttpHandlerAdapter;
import org.springframework.web.reactive.config.EnableWebFlux;
import org.springframework.web.reactive.function.server.RouterFunction;
import org.springframework.web.server.adapter.WebHttpHandlerBuilder;
import reactor.core.publisher.Mono;

import static org.springframework.web.reactive.function.server.RequestPredicates.GET;
import static org.springframework.web.reactive.function.server.RouterFunctions.route;
import static org.springframework.web.reactive.function.server.RouterFunctions.toHttpHandler;
import static org.springframework.web.reactive.function.server.ServerResponse.ok;

@Configuration
@EnableWebFlux
public class Routes {

    private static String ROUTE_PREFIX = "/flux";

    public RouterFunction<?> routesBean() {
        return
                route(
                        GET(ROUTE_PREFIX + "/hi"),
                        request -> ok().body(Mono.just("hi"), String.class))
                ;
    }

    @Bean
    public ServletRegistrationBean routeServlet() throws Exception {
        HttpHandler httpHandler = WebHttpHandlerBuilder
                .webHandler(toHttpHandler(routesBean()))
                .build();
        ServletRegistrationBean registrationBean = new ServletRegistrationBean<>(new ServletHttpHandlerAdapter(httpHandler), ROUTE_PREFIX + "/*");
        registrationBean.setLoadOnStartup(1);
        registrationBean.setAsyncSupported(true);
        return registrationBean;
    }
}