Hi Durim,
The only 'Hello World !' example that you'll see in this book is in the first chapter. The rest of the chapters aim to help you build real-world applications.
With this edition of book, we've introduced fresh content on functional programming, reactive programming using RxJava 2 and Spring Reactor, developing reactive RESTful web services using Spring Data MongoDB and Spring Security, developing reactive web applications using Spring WebFlux, accessing RESTful web services using WebClient, and so on.
regards
Ashish