Spring Boot procedural, lambda and reactive

SpringBootDemo.java

/* Procedural endpoint */
@GetMapping("/users/{id}")
ResponseEntity<User> get(@PathVariable long id) {
  User user = repository.findById(id);
  if(user != null) {
    return ok(user);
  } else {
    return notFound();
  }
}

/* Lambda endpoint */
@GetMapping("/users/{id}")
ResponseEntity<User> get(@PathVariable long id) {
  return repository
            .findById(id)
            .map(user -> ok(user))
            .orElse(notFound());
}

/* Reactive endpoint - SpringBoot2 webflux */
@Bean
RouterFunction<ServerResponse> route() {
  return route(
    GET("/users/{id}"), request -> Mono
      .justOrEmpty(request.PathVariable("id"))
      .map(Long::parseLong)
      .flatMap(id -> repository.findById(id)
      .flatMap(p -> ok().body(fromObject(p))
      .switchIfEmpty(notFound().build())))
  );
}