Understanding Reactive Programming
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This document provides an overview of reactive programming concepts like state, time, sync vs async operations, futures and promises. It discusses different approaches to reactive programming in Java like using CompletableFuture, JDeferred and RxJava. It also covers functional programming concepts, data streams, reactive Spring and the future of reactive programming in Java 9 and beyond.
Understanding Reactive Programming
- 2. @aalmiray
- 3. @aalmiray JCP Executive Committee Associate Seat Committer Committer JSR377 Specification Lead
- 5. @aalmiray STATE Imperative Programming (Procedural) var a := b + c println a Declarative Programming (Functional) (println (sum(b, c))
- 6. @aalmiray TIME Imperative Programming var a := b + c println a Reactive Programming var a := b + c a.done( v -> println v)
- 7. @aalmiray SYNC VS ASYNC Synchronous operations block the flow until they yield a result (success or error). Asynchronous operations DO NOT block the flow, rather they allow the program to continue. Results (or errors) will be handled at a later point in time, typically using functions (callbacks).
- 8. @aalmiray FUTURES AND PROMISES They describe an object that acts as mediator for a value that may be unknown at init time. The terms Future and Promise are normally used interchangeably but there’s a difference: • A Future is a read-only reference of the expected value. • A Promise is a write-once container that sets the value of the Future. https://en.wikipedia.org/wiki/Futures_and_promises
- 9. @aalmiray FUTURES AND PROMISES Futures in Java are synchronous, this can be demonstrated by the following method signatures found in java.util.concurrent.Future V get() V get(long timeout, TimeUnit unit)
- 10. @aalmiray FUTURES AND PROMISES Java 8 added a new type, CompletableFuture, that implements CompletableStage, which in turns defines the contract of a Promise, such as thenAccept(Consumer<? Super T> action) whenComplete(BiConsumer<? super T,? super Throwable> action) exceptionally(Function<Throwable,? extends T> fn) … and many others
- 11. @aalmiray FUTURES AND PROMISES JDeferred offers a different API that allows better function composition Promise<D, F, P> then(DoneCallback<D> doneCallback) Promise<D, F, P> done(DoneCallback<D> callback) Promise<D, F, P> fail(FailCallback<F> callback) Promise<D, F, P> always(AlwaysCallback<D, F> callback)
- 13. @aalmiray GET /orgs/${organization}/repos data as JSON https://developer.github.com/v3/
- 16. @aalmiray (1) PRODUCER public List<Repository> repositories(final String organization) { try { Response<List<Repository>> response = api.repositories(organization).execute(); if (response.isSuccessful()) { return response.body(); } throw new IllegalStateException(response.message()); } catch (IOException e) { throw new IllegalStateException(e); } }
- 17. @aalmiray (2) CONSUMER public class AppController { @Inject private AppModel model; @Inject private GithubAPI api; public void loadRepositories() { model.setState(RUNNING); String organization = model.getOrganization(); try { List<Repository> repositories = repositories(organization); model.getRepositories().addAll(repositories); } catch (Throwable throwable) { handleError(throwable); } finally { model.setState(READY); } } }
- 19. @aalmiray (1) PRODUCER public CompletableFuture<List<Repository>> repositories(final String organization) { Supplier<List<Repository>> supplier = () -> { try { Response<List<Repository>> response = api.repositories(organization).execute(); if (response.isSuccessful()) { return response.body(); } throw new IllegalStateException(response.message()); } catch (IOException e) { throw new IllegalStateException(e); } }; return CompletableFuture.supplyAsync(supplier, executorService); }
- 20. @aalmiray (2) CONSUMER public class AppController { @Inject private AppModel model; @Inject private Github github; public void loadRepositories() { model.setState(RUNNING); github.repositories(model.getOrganization()) .thenAccept(model.getRepositories()::addAll) .exceptionally(throwable -> { handleError(throwable); return null; }) .thenAccept(result -> model.setState(READY)); } }
- 22. @aalmiray (1) PRODUCER public Promise<Collection<Repository>, Throwable, Void> repositories(final String organization) { return deferredManager.when(() -> { Response<List<Repository>> response = api.repositories(organization).execute(); if (response.isSuccessful()) { return response.body(); } throw new IllegalStateException(response.message()); }); }
- 23. @aalmiray (2) CONSUMER public class AppController { @Inject private AppModel model; @Inject private Github github; public void loadRepositories() { model.setState(RUNNING); github.repositories(model.getOrganization()) .done(model.getRepositories()::addAll) .fail(this::handleError) .always((state, resolved, rejected) -> model.setState(READY)); } }
- 25. @aalmiray (1) PRODUCER public Observable<Repository> repositories(String organization) { Observable<Response<List<Repository>>> observable = api.repositories(organization); return observable.flatMap(response -> { if (response.isSuccessful()) { return Observable.fromIterable(response.body()); } return Observable.error(new HttpResponseException( response.code(), response.message())); }); }
- 26. @aalmiray (2) CONSUMER public class AppController { @Inject private AppModel model; @Inject private Github github; public void load() { Observable<Repository> observable = github.repositories(model.getOrganization()); observable .timeout(10, TimeUnit.SECONDS) .doOnSubscribe(disposable -> model.setState(RUNNING)) .doOnTerminate(() -> model.setState(READY)) .doOnError(this::handleError) .subscribeOn(Schedulers.io()) .subscribe(model.getRepositories()::add)); } }
- 27. @aalmiray GET /orgs/${organization}/repos data as JSON data as JSON https://developer.github.com/v3/ GET /organizations/1/repos?page=2
- 28. @aalmiray MULTPLE PAGES public Observable<Repository> repositories(String organization) { return paginatedObservable( () -> { return api.repositories(organization); }, (Links links) -> { return api.repositoriesPaginate(links.next()); }); }
- 29. @aalmiray MULTIPLE PAGES <T> Observable<T> paginatedObservable(FirstPageSupplier<T> firstPage, NextPageSupplier<T> nextPage) { return processPage(nextPage, firstPage.get()); } <T> Observable<T> processPage(NextPageSupplier<T> supplier, Observable<Response<List<T>>> items) { return items.flatMap(response -> { Links links = Links.of(response.headers().get("Link")); Observable<T> currentPage = Observable.from(response.body()); if (links.hasNext()) { return currentPage.concatWith( processPage(supplier, supplier.get(links))); } return currentPage; }); }
- 30. @aalmiray HTTP://REACTIVEX.IO/ Reactive Programming API, provides observable data flows. Multiple implementations in more than 20 programming languages Java adn Javascript implement the http://www.reactive- streams.org/ specification
- 31. @aalmiray HTTP://REACTIVEX.IO/ Java implementations: https://github.com/ReactiveX/RxJava Created by Netflix https://projectreactor.io Sponsored by Pivotal (Spring framework)
- 33. @aalmiray DATA STREAMS A sequence of values calculated over time. Values are emitted when ready; they are computed without blocking consumers. Consumers listen to changes in the data stream and react to said changes (hence the name Reactive Programming). Push vs pull model.
- 34. @aalmiray OBSERVABLE/OBSERVER Data streams are of type Observable while consumer are of type Observer. The Observable type exposes multiple operations that allow value composition, combinations, filtering, and other value transformations. NOTE: many operations from RxJava/Reactor generate a new Observable (decorator pattern)
- 42. @aalmiray FUNCTIONS Functions should follow two concepts: • Do not produce side effects during invocation. • Given the same input they must produce the same output.
- 43. @aalmiray IMMUTABILITY Immutable data structures and/or data containers (POJOs) complement Functional Programming in a natural way. They allow data sharing with multiple consumers and/or functions without fear of changes affecting the original data. They help reduce synchronization points.
- 44. @aalmiray OTHER OPTIONS http://vertx.io/ Toolkit for reactive applications Based on Netty. https://grpc.io/ RPC framework. Supports data streaming both ways
- 45. @aalmiray RXGRPC https://github.com/salesforce/reactive-grpc Combines gRPC with Reactive Streams Encapsulates gRPC’s API Producers/Consumers only see Rx API
- 47. @aalmiray JAVA 9+ FLOW Java 9 implements the Reactive Streams in its own way with java.util.concurrent.Flow This API allows combining streams from different providers (RxJava, Reactor, etc). Additions to the CompletableStage/CompletableFuture API.
- 48. @aalmiray REACTIVE SPRING (WEB) @GetMapping("/accounts/{id}/alerts") public Flux<Alert> getAccountAlerts(@PathVariable Long id) { return this.repository.getAccount(id) .flatMap(account -> this.webClient .perform(get("/alerts/{key}", account.getKey())) .extract(bodyStream(Alert.class))); } https://spring.io/blog/2016/07/28/reactive-programming-with-spring-5-0-m1
- 49. @aalmiray REACTIVE SPRING (DATA+WEB) @RestController class PersonController { private final PersonRepository people; public PersonController(PersonRepository people) { this.people = people; } @GetMapping("/people") Flux<String> namesByLastname(@RequestParam Mono<String> lastname) { Flux<Person> result = repository.findByLastname(lastname); return result.map(it -> it.getFullName()); } } https://spring.io/blog/2016/11/28/going-reactive-with-spring-data
- 53. @aalmiray