Reactive Android: RxJava and beyond
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For most of us, Reactive Android means using RxJava. In this presentation, I try to borrow a few ideas from the backend world and enrich the concept of Reactive in Android.
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Reactive Android: RxJava and beyond
- 1. Reactive Android: RxJava & beyond Fabio Tiriticco / @ticofab AMSTERDAM 11-12 MAY 2016
- 2. A little info about myself Android Engineer Scala Engineer
- 3. The Reactive Amsterdam meetup Reactive Amsterdam Because nobody knows what Reactive means To explore the concept in all of its forms.
- 4. “Reactive” in the vocabulary Reactive (adjective): Tending to act in response to an agent or influence
- 6. Reactive Confusion • The concept of “Reactive” has common basis but slightly different meanings in each domain • Most of us think that Reactive == React.js Two main observations:
- 7. Reactive in (Android) frontend VS backend ANDROID Using RxJava WHAT DO PEOPLE THINK THAT “BEING REACTIVE” MEANS? BACKEND ?
- 8. Hello, RxJava! • Asynchronous programming • Observable streams Open source libraries for
- 9. Hello, RxJava! Mobile engineering is hard and there are high expectations. RxJava is cool because • it makes it super easy to switch between threads • lets us deal with data as a stream • brings us some degree of functional programming.
- 10. RxJava goes hand in hand with Java8’s Lambdas new Func1<String, Integer>() { @Override public Integer call(String s) { return s.length(); } } (String s) -> { return s.length(); } s -> s.length(); Retrolamba plugin for Android < N
- 11. RxJava: dealing with a stream of items class Cat { ... public Collar getCollar() {…} public Picture fetchPicture() {…} ... }
- 12. RxJava: dealing with a stream of items Observable.from(myCats); (cat -> Log.d(TAG, “got cat”)); List<Cat> myCats; Observable obs = obs.subscribe
- 13. RxJava: dealing with a stream of items Observable.from(myCats) .subscribe(cat -> Log.d(TAG, “got cat”)); List<Cat> myCats;
- 14. RxJava: work on the stream Observable.from(myCats) .map(cat -> cat.getCollar()) .subscribe(collar -> Log.d(TAG, “got collar”)); map: T -> R (this map: Cat -> Collar)
- 15. RxJava: operators to manipulate the stream Observable.from(myCats) .distinct() .delay(2, TimeUnit.SECONDS) .filter(cat -> cat.isWhite()) .subscribe(cat -> Log.d(TAG, “got white cat”));
- 16. Observable.from(myCats) .subscribe( cat -> Log.d(TAG, “cat”), error -> error.printStackTrace(), () -> Log.d(TAG, “done”) ); RxJava: subscriber interface Observable<T>.from(myCats) .subscribe( onNext<T>, // next item T onError, // throwable onComplete // void );
- 17. Observable.from(myCats) .subscribe(cat -> Log.d(TAG, “cat”)); RxJava: unsubscribe Subscription subs = subs.unsubscribe();
- 18. RxJava: threading Observable.from(myCats) .map(cat -> cat.fetchPicture()) .map(picture -> Filter.applyFilter(picture)) .subscribe( filteredPicture -> display(filteredPicture) ); .subscribeOn(Schedulers.newThread()) .observeOn(AndroidSchedulers.mainThread())
- 19. RxJava: other ways of creating Observables // emits on single item and completes Observable.just // emits one item after a certain delay Observable.timer .. plus many others, and you can create your own!
- 20. RxJava: demo with Retrofit & Meetup Streams http://stream.meetup.com/2/rsvp Meetup Streaming API
- 21. RxJava: demo with Meetup Streams
- 22. RxJava: demo with Retrofit & Meetup Streams interface MeetupAPI { @GET("http://stream.meetup.com/2/rsvp") @Streaming Observable<ResponseBody> meetupStream(); }
- 23. RxJava: demo with RSVP Meetup Streams meetupAPI.meetupStream() ... .flatMap(responseBody -> events(responseBody.source())) .map(string -> gson.fromJson(string, RSVP.class)) ... .subscribe(rsvp -> ...); map: T -> R flatMap: T -> Observable<R>
- 24. RxJava: demo with Meetup Streams
- 25. RxJava: demo with Meetup Streams https://github.com/ticofab/android-meetup-streams
- 26. Reactive in (Android) frontend VS backend ANDROID Using RxJava WHAT DO PEOPLE THINK THAT “BEING REACTIVE” MEANS? BACKEND ?
- 27. Evolution of server applications & user expectations 2006 2016 Servers ~10 The sky is the limit. Response time seconds milliseconds Offline maintenance hours what? Data amount Gigabytes Petabytes Machines Single core, little distribution Must work across async boundaries (location, threads) Kind of data Request - response Streams (endless)
- 28. Evolution of internet usage
- 29. The Reactive traits A reactive computer system must Trait React to its users Responsive React to failure and stay available Resilient React to varying load conditions Elastic Its components must react to inputs Message-driven
- 31. Reactive traits: Responsive • A human who visits a website • A client which makes a request to a server • A consumer which contacts a provider • . . . A Reactive system responds to inputs and usage from its user.
- 32. Reactive traits: Elastic • Scale OUT and IN: use just the right amount • Elasticity relies on distribution • Ensure replication in case of failure Scale on demand to react to varying load
- 33. Reactive traits: Resilient It doesn't matter how great your application is if it doesn't work. FAULT TOLERANCE RESILIENCEVS
- 34. Reactive traits: Message Driven Reactive systems design concentrates on Messages. Asynchronous messaging enables: • Separation between components • Error containment - avoid chain failures • Domain mapping closer to reality
- 35. The Reactive Manifesto, take 2 Responsive ResilientElastic Message Driven
- 36. Why Functional Programming? More supportive of reasoning about problems in concurrent and parallelised applications. • encourages use of pure functions - minimise side effects • encourages immutability - state doesn’t get passed around • higher-order functions - reusability and composability
- 38. Reactive Pattern: Simple Component Pattern “One component should do only one thing but do it in full. The aim is to maximise cohesion and minimise coupling between components.”
- 39. Reactive Pattern: Simple Component Pattern Actor 1 Actor 3 Actor 2 • contains state • has a mailbox to receive and send messages • contains behaviour logic • has a supervisor Actor model Supervisor
- 40. Reactive Patterns: Let it crash! "Prefer a full component restart to complex internal failure handling". • failure conditions WILL occur • they might be rare and hard to reproduce • it is much better to start clean than to try to recover • …which might be expensive and difficult!
- 42. Reactive Patterns: Let it crash! • Components should be isolated - state is not shared • Components should have a supervisor and delegate to it some or all error handling • The supervisor can transparently restart the component • Message-passing architectures enforce state confinement, error containment and transparency In practice…
- 43. Reactive Patterns: Let it crash! Actor supervision example Actor 1 Actor 2 Supervisor WhateverException! X Fix or Restart
- 44. Reactive Patterns: Let it crash! • the machine only accepts exact change
- 45. Reactive Patterns: Let it crash! Scenario 1: The user inserts wrong amount of coins X Error!
- 46. Reactive Patterns: Let it crash! Scenario 2: The machine is out of coffee beans Failure! ( != error)
- 47. Reactive Patterns: Let it crash!
- 48. Reactive Patterns: Let it crash! Randomly kills instances of their AWS system to ensure that no failure is propagated.
- 49. BACKEND ? BACKEND Elasticity Asyncrhonicity Resilience Supervision Message passing State encapsulation Streams Backpressure … Reactive in (Android) frontend VS backend ANDROID Using RxJava WHAT DO PEOPLE THINK THAT “BEING REACTIVE” MEANS?
- 50. Reactive traits in Android? Can we apply some of the Reactive Manifesto principles to our Android development?
- 51. Reactive traits in Android? Reactive trait In Android? Responsive Execute as much as possible asynchronously Elastic — Resilient Delegate risky stuff to (Intent)Services or isolated components Message passing Communication via ResultReceiver Use some event Bus
- 52. Reactive traits in Android? …but I am sure that we can take this further.
- 53. Resources https://github.com/ReactiveX/RxJava/wiki RxJava documentation & wiki http://rxmarbles.com RxJava operators explained visually http://www.reactivemanifesto.org The reactive manifesto https://www.youtube.com/watch?v=fNEZtx1VVAk https://www.youtube.com/watch?v=ryIAibBibQI https://www.youtube.com/watch?v=JvbUF33sKf8 The Reactive Revealed series: awesome webinars by the creators of the Reactive Manifesto. https://www.manning.com/books/reactive-design-patterns https://www.youtube.com/watch?v=nSfXcSWq0ug Reactive design patterns, book and webinar.
- 54. Thanks! @ticofab All pictures belong to their respective authors AMSTERDAM 11-12 MAY 2016