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Reactive Android: RxJava and beyond
The document discusses the concept of 'reactive' programming, focusing on its application in Android through the use of RxJava. It explains the core traits of reactive systems—including responsiveness, resilience, elasticity, and message-driven architecture—as well as various reactive patterns. Additionally, it highlights the benefits of asynchronous programming and observable streams in mobile engineering.
Reactive Android: RxJava and beyond
- 1. Reactive Android: RxJava& beyond Fabio Tiriticco / @ticofab AMSTERDAM 11-12 MAY 2016
- 2. A little infoabout myself Android Engineer Scala Engineer
- 3. The Reactive Amsterdammeetup Reactive Amsterdam Because nobody knows what Reactive means To explore the concept in all of its forms.
- 4. “Reactive” in thevocabulary Reactive (adjective): Tending to act in response to an agent or influence
- 5.
- 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 handin 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 witha stream of items class Cat { ... public Collar getCollar() {…} public Picture fetchPicture() {…} ... }
- 12. RxJava: dealing witha stream of items Observable.from(myCats); (cat -> Log.d(TAG, “got cat”)); List<Cat> myCats; Observable obs = obs.subscribe
- 13. RxJava: dealing witha stream of items Observable.from(myCats) .subscribe(cat -> Log.d(TAG, “got cat”)); List<Cat> myCats;
- 14. RxJava: work onthe 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 tomanipulate 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 waysof 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 withRetrofit & Meetup Streams http://stream.meetup.com/2/rsvp Meetup Streaming API
- 21. RxJava: demo withMeetup Streams
- 22. RxJava: demo withRetrofit & Meetup Streams interface MeetupAPI { @GET("http://stream.meetup.com/2/rsvp") @Streaming Observable<ResponseBody> meetupStream(); }
- 23. RxJava: demo withRSVP 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 withMeetup Streams
- 25. RxJava: demo withMeetup 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 serverapplications & 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)
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- 29. The Reactive traits A reactive computer system mustTrait 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
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- 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
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- 34. Reactive traits: MessageDriven 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
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- 38. Reactive Pattern: SimpleComponent 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: SimpleComponent 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: Letit 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: Letit 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: Letit crash! Actor supervision example Actor 1 Actor 2 Supervisor WhateverException! X Fix or Restart
- 44. Reactive Patterns: Letit crash! • the machine only accepts exact change
- 45. Reactive Patterns: Letit crash! Scenario 1: The user inserts wrong amount of coins X Error!
- 46. Reactive Patterns: Letit crash! Scenario 2: The machine is out of coffee beans Failure! ( != error)
- 47. Reactive Patterns: Letit crash!
- 48. Reactive Patterns: Letit 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 inAndroid? Can we apply some of the Reactive Manifesto principles to our Android development?
- 51. Reactive traits inAndroid? 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 inAndroid? …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.orgThe 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 totheir respective authors AMSTERDAM 11-12 MAY 2016