This document provides an overview of reactive programming with Spring. It begins by contrasting imperative programming, which uses statements to change program state, with declarative programming, which expresses logic without control flow details. It then defines reactive programming as a subset of asynchronous programming where availability of new information drives logic forward in a non-blocking fashion. The document discusses the reactive manifesto and how reactive streams and Spring support reactive programming through interfaces like Publisher/Subscriber and implementations like Project Reactor's Flux and Mono types as well as Spring WebFlux. It concludes with a promise of a demo comparing traditional Spring MVC to the new reactive Spring WebFlux.

1. Reactive Programming with Spring
Petru Flueras
Software Architect - Visma Software
@pflueras

2. Imperative programming
● Imperative programming is a programming paradigm that uses statements
that change a program's state
○ Statements: conditional statements, loop statements, algorithms, control flow
○ You tell the computer how to do things - low level instructions closer to hardware
○ Higher cyclomatic complexity, less cleaner code, more difficult to test
● Real world example: hey waiter, I want to order a salad, but if the cheese is
too salted then please don’t add olives. Instead you could add more corn!

3. Declarative programming
● Is a programming paradigm that expresses the logic of a computation without
describing its control flow
○ Less direct control, without going into implementation details!
○ Tell the computer what to do, without specifying how!
○ You create expressions instead of statements + evaluate functions
● Real world example: Hey waiter, I want to order a slightly salted salad!

4. Exercise 1: Imperative & Declarative

5. Exercise 1: Imperative

6. Exercise 2: Declarative

7. Reactive programming
● Declarative event-based
● Subset of asynchronous programming where the availability of new
information drives the logic forward rather than having control flow driven by a
thread-of-execution
● It supports decomposing the problem into multiple discrete steps where
each can be executed in an asynchronous and non-blocking fashion, and
then be composed to produce a workflow (~ data streams)
● Contention is the biggest enemy of scalability. Reactive program should
rarely, if ever, have to block

8. Reactive manifesto
Reactive systems are:
● Responsive
● Resilient
● Elastic
● Message Driven
https://www.reactivemanifesto.org/

9. Reactive Streams + Spring
● Reactive Streams Specification
○ Publisher + Subscriber
○ http://www.reactive-streams.org/
○ JDK 9!
● Project Reactor (Reactive Streams implementation)
○ Flux<T>, Mono<T>
● Spring WebFlux
○ ReactiveCrudRepository, ReactiveMongoRepository, ReactiveRedis*, RouterFunction, …

10. DEMO!

11. Spring MVC

12. Spring WebFlux

13. Thank you!