Since both Tomcat 9 and Spring 5 support asynchronous thread execution, request handlers can now return Mono<T> and Flux<T> data streams and receive automatic subscription with the client through the DispatcherServlet of Spring 5 platform. Conventionally, the @Controller can still programmatically execute the Flux<T> or Mono<T> cold stream through supplying the appropriate Supplier<T> to the stream's subscribe() method and wrapping the task and result in a Callable<T> for publishing. However, since Spring 5 understands full-blown reactive programming using Reactor Core, cold stream as well as hot stream can be published directly to the client. Thus, it can be concluded that the Spring 5 context fully understands reactive and functional programming.