Speaker: Wyko Rijnsburger Genre & level: Backend, Medior Reactive programming: everybody seems to be talking about it, but there has been little real-world utilization. This is a shame, since a reactive approach can significantly improve both the quality of your codebase and the performance of your application. At Team 52, we started building a back end for our mobile apps using a reactive architecture about 1.5 years ago. Along the way, we discovered how beautiful Reactive applications can be, but also how small mistakes can lead to huge issues in a way that is not the case with traditional applications. In this talk, I will guide you through the often-messy but ultimately successful process of developing these applications. I will discuss how the Reactive approach changed the way we write code, how we used it to optimize concurrency and performance, but also how it leads to some embarrassing bugs. Finally, I will show you how you can start building a stable, high performing reactive application right now.

1. The Reactive Rollercoaster
Wyko Rijnsburger

2. 1. What, Why?
2. Elements of a Reactive JVM App
3. Real World Example
4. Tips

3. "Programming paradigm concerned
with data stream and the propagation
to change"
https://en.wikipedia.org/wiki/Reactive_programming

4. Writing asynchronous, non-blocking
code using Reactive APIs

5. val product: Product = getProductSync()
val offer: Offer = getOfferSync()
return combine(product, offer)

6. Thread
getProductSync()getOfferSync()combine()

7. Thread Thread Thread
getProductSync() getProductSync() getProductSync()

8. val product: Future<Product> = getProductAsync()
val offer: Future<Offer> = getOfferAsync()
return combine(product, offer)

9. Thread
getProductAsync()getOfferAsync()combine()

10. getProductSync() getOfferSync() combine()
combine()
getProductAsync() getOfferAsync()

11. "Handle concurrency with a small
number of threads and scale with less
hardware resources"
https://docs.spring.io/spring/docs/current/spring-framework-reference/web-reactive.html

12. Reactive API
● Reactive Streams specification
● "Reactive Streams is an initiative to provide a standard for asynchronous
stream processing with non-blocking back pressure."
● JDK9: java.util.concurrent.Flow

13. Project Reactor
Observable<T>
Single<T>
Flux<T>
Mono<T>
RxJava
0..N
0..1

14. ● .map()
● .flatMap()
● .zip()

15. Elements of a Reactive
JVM App

16. HTTP Client
Business logic
Controller/API
Product
ProcessedProduct
Backspin Driver/RestTemplate=
Spring MVC=

17. HTTP Client
Business logic
Controller/API
Mono<Product>
Mono<Processed
Product>
Non-blocking HTTP client
AsyncHttpClient/WebClient=
DeferredResult
Spring 5 -> Return Reactive Types=

19. HTTP Client
Business logic
Controller/API
Observable<Product>
Mono<Processed
Product>
Non-blocking HTTP client
AsyncHttpClient/WebClient=
Spring MVC + DeferredResult
WebFlux=
Mono<Product>

21. val p: Mono<Optional<Product>> = getProduct()

22. HTTP Client
Business logic
Controller/API
Observable<Product>
Mono<Optional<ProcessedProduct>
Non-blocking HTTP client
AsyncHttpClient/WebClient=
Spring MVC + DeferredResult
WebFlux=
Mono<Optional<Product>>

23. App API

26. val bundles = bundleService.getBundles(id, countryCode)
.onErrorReturn(emptyList())
val specifications = productService.getSpecifications(id)
.onErrorReturn(Optional.empty())
val offers = offerService.getOffers(id)
.onErrorReturn(Optional.empty())
Mono.zip(bundles, specifications, offers)
.map { doSomething() }

29. .flatMap()
"Ordering of the flattened values: this operator
does not necessarily preserve original ordering,
as inner elements are flattened as they arrive."

30. .flatMapSequential()
"Ordering of the flattened values: this operator
queues elements from late inners until all
elements from earlier inners have been emitted,
thus emitting inner sequences as a whole, in an
order that matches their source's order."

35. ● Performance: to
● Readability:
● Debugging:
● Number of unexpected issues:
● Future readiness:

36. Tips

37. Start from the top
(HTTP clients/DB drivers)

38. Use Tomcat 8

39. Use Optional within
Reactive Types

40. Convert Reactive Types to
RxJava1 when using
Hystrix
Set Isolation Strategy to
Semaphore

41. Performance test

44. Thanks!