Reactive Thinking in Java
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The document discusses reactive programming concepts in Java using RxJava. It defines key RxJava terms like Observable, Observer, and Operator. It explains how RxJava uses asynchronous message passing with Observables that push data to Observer subscribers, unlike traditional Java APIs that use synchronous pulling of data. It provides examples of creating Observables and applying operators like map, filter, and flatMap. It also covers multi-threading in RxJava using schedulers, backpressure, and other advanced topics.
Reactive Thinking in Java
- 1. Reactive Thinking in Java Yakov Fain, Farata Systems @yfain
- 2. Reactive thinking is not new
- 3. Бди! Козьма Прутков Reactive thinking is not new
- 4. Reactive thinking is not new
- 5. The reactive style app • Message-driven - components communicates via notifications • Non-imperative - the app logic is coded in async, non-blocking, composable functions • The data moves through your app’s algorithm www.reactivemanifesto.org
- 6. Java concurrency • Blocking I/O is the problem • Future.get() - blocks till all threads are complete • CompletableFuture.supplyAsync(task).thenAccept(action) - what if the tasks need to fetch millions of records?
- 7. Some open-source Rx libraries • RxJava • RxAndroid, RxJavaFX, RxSwing • Rx.NET, RxCpp, RxJS, Rx.rb, Rx.py, RxSwift, RxScala, RxPHP http://reactivex.io JDK 9 will include reactive streams in java.util.concurrent.Flow
- 8. Main RxJava players • Observable - producer of data • Observer - consumer of observable sequences • Subscriber - connects observer with observable • Operator - en-route data transformation • Scheduler - multi-threading support
- 9. beers.forEach(brr -> { if ("USA".equals(brr.country)){ americanBeers.add(brr); } }); Java Iterable: a pull
- 10. beers.stream() .skip(1) .limit(3) .filter(b -> "USA".equals(b.country)) .map(b -> b.name + ": $" + b.price) .forEach(beer -> System.out.println(beer)); Java 8 Stream: a pull
- 11. A fool with a tool is still a fool Американская народная мудрость
- 12. A pull with a tool is still a pull A fool with a tool is still a fool Американская народная мудрость Yakov Fain
- 13. Observable is an Iterable inside out
- 14. Word Antonym Iterable Observable Iterator Observer Pull Push
- 16. Observable Data Source Data Flow
- 17. Observable Data Source Data Flow
- 20. Event-driven push Subscribe to messages from Observable and handle them by Observer Observable Observer Subscriber Observer Subscriber push push push Observer Subscriber
- 21. Observable.subscribe(Subscriber) class Subscriber implements Observer {}
- 22. observableBeer .skip(1) .take(3) .filter(b -> "USA".equals(b.country)) .map(b -> b.name + ": $" + b.price) .subscribe( beer -> System.out.println(beer), err -> System.out.println(err), () -> System.out.println("Streaming is complete") ); Rx Observable: a push
- 23. Demo HelloObservable Get rxjava.jar on http://search.maven.org
- 24. An Operator Observable Observable A transforming function
- 25. An Operator Observable Observable A transforming function observableBeer .filter(b -> "USA".equals(b.country))
- 26. An Operator Observable Observable A transforming function An operator is a higher-order function observableBeer .filter(b -> "USA".equals(b.country)) pure function
- 30. Operator chaining: map and filter
- 31. RX: the data moves across your algorithm
- 33. Creating an Observable • Observable.create() - returns Observable that can invoke methods on Observer • Observable.from() - converts an Iterable or Future into Observable • Observable.fromCallable() - converts a Callable into Observable • Observable.empty() - returns empty Observable that invokes onCompleted() • Observable.range() - returns a sequence of integers in the specified range • Observable.just() - converts up to 10 items into Observable
- 34. Demo BeerClient
- 35. Functions with side effects • doOnNext() • doOnError() • doOnCompleted() • doOnEach() • doOnSubscribe() Affect environment outside the function.
- 37. Error-handling operators • Errors sent using onError() kill the subscription • retryWhen() - intercept, anylize the error, resubscribe • onErrorResumeNext() - used for failover to another Observable • onResumeReturn() - returns an app-specific value
- 42. Schedulers
- 43. Concurrency with Schedulers • An observable stream is single-threaded by default • subscribeOn(strategy) - run Observable in a separate thread • observeOn(strategy) - run Observer in a separate thread
- 44. Multi-threading strategies • Schedulers.computation() - for computations: # of threads <= # of cores • Schedulers.io() - for long running communications; backed by a thread pool • Schedulers.newThread() - new thread fo each unit of work • Schedulers.from(Executor) - a wrapper for Java Executor • Scedulers.trampoline() - queues the work on the current thread • AndroidSchedulers.mainThread() - handle data on the main thread (RxAndroid)
- 45. Switching threads Operator1() Operator2() ObserveOn() Observable Subscriber Thread 1 Thread 2
- 46. Parallel processing Operator1() Operator2() flatMap() Observable Subscriber Thread 1 Observable/Thr2 Observable/Thr3 Observable/ThrN
- 48. Hot and cold observables • Cold: emits items only when someone subscribes to it • Hot: emits items when it’s created regardless if there is a subscriber or not
- 49. Backpressure • Throttling: sample(), throttleFirst(), debounce() • Buffers: buffer() • Window: window(n) • Reactive pull: Subscriber.request(n) https://github.com/ReactiveX/RxJava/wiki/Backpressure
- 50. Links • Code samples and slides: https://github.com/yfain/rxjava • Our company: faratasystems.com • Blog: yakovfain.com • Twitter:@yfain discount code: faindz