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![82016-09-20
REACTIVE MANIFESTO
“[…] Systems built as Reactive Systems are more flexible, loosely-coupled and scalable. This
makes them easier to develop and amenable to change. They are significantly more tolerant
of failure and when failure does occur they meet it with elegance rather than disaster.
Reactive Systems are highly responsive, giving users effective interactive feedback. […]”
From: Reactive Manifesto, Version 2, September 2014
Elastic
Responsive
Resilient
Message Driven](https://image.slidesharecdn.com/reactive-everywhere-160920215307/85/Reactive-Everywhere-8-320.jpg)
![162016-09-20
CREATING OBSERVABLES
Edge cases
Custom
Pre defined values
Observable.just(T value)
Observable.from(T[] values) / from(Iterable<T> values)
Observable.range(int start, int count)
Observable.interval()
Observable.empty()
Observable.never()
Observable.error(Throwable exception)
Observable.create(OnSubscribe<T> f)
Observable.create(subscriber -> {
subscriber.onNext(“Hello World”);
subscriber.onCompleted();
}](https://image.slidesharecdn.com/reactive-everywhere-160920215307/85/Reactive-Everywhere-16-320.jpg)
![532016-09-20
Angular 2 WebSockets
3. Create Observer (Client can notify update of data)
• Event-Handler Functions to be defined in
● [onNext] – what to do if new value emitted,
● [onError] – what to do if error emitted,
● [onCompleted] – what to do if observable completes
Observer.create(
[onNext], [onError], [onCompleted]
);](https://image.slidesharecdn.com/reactive-everywhere-160920215307/85/Reactive-Everywhere-53-320.jpg)
Uploaded bytrion development GmbH
Reactive Everywhere
This document discusses reactive programming and its applications. It introduces reactive programming concepts like Observables and Subscribers. It then covers implementing reactive backends with frameworks like RxJava and Spring, including reactive databases, services, and third party APIs. It also discusses reactive web frontends using Angular, covering reactive HTTP requests, Server-Sent Events through Observables, and wrapping WebSockets in Observables. The document advocates that reactive programming allows building flexible, scalable systems and is available to use with frameworks like Spring and Angular today.
Reactive Everywhere
- 1. REACTIVE EVERYWHERE JAVAONE 2016 Stefan Reuter,Karsten Sitterberg
- 2. 22016-09-20 STEFAN REUTER @StefanReuter ● IT Architect ●Trainer and Consultant for trion development GmbH – www.trion.de
- 3. 32016-09-20 KARSTEN SITTERBERG @kakulty ● Java, JavaScript/TypeScript,Web ● Trainer and Consultant for trion development GmbH – www.trion.de
- 4. 42016-09-20 trion www.trion.de ● Professional services ●Architecture ● Consulting ● Development ● Training slideshare.net/triondevelopment
- 5. 52016-09-20 AGENDA Reactive Backends Summary Reactive WebFrontends Item Introduction to Reactive Programming Situation
- 6. 62016-09-20 SITUATION Environment Expectations Changes Massive changesto both environment and expectations in recent years Mobile applications (native and web-based) Cloud environment and infrastructure Multicore Order of magnitude increase in number of connections Interactive Real-time Responsive Collaborative
- 7. 72016-09-20 TODAY'S APPLICATIONS MUST... Reactto Events Event-Driven React to Load Elastic React to Failure Resilient React to Users Responsive
- 8. 82016-09-20 REACTIVE MANIFESTO “[…] Systemsbuilt as Reactive Systems are more flexible, loosely-coupled and scalable. This makes them easier to develop and amenable to change. They are significantly more tolerant of failure and when failure does occur they meet it with elegance rather than disaster. Reactive Systems are highly responsive, giving users effective interactive feedback. […]” From: Reactive Manifesto, Version 2, September 2014 Elastic Responsive Resilient Message Driven
- 9. 92016-09-20 INTRO TO REACTIVEPROGRAMMING INTRODUCTION TO REACTIVE PROGRAMMING
- 10. 102016-09-20 reactive programming is programmingwith asynchronous data streams
- 11.
- 12. 122016-09-20 OBSERVABLE AND SUBSCRIBER SubscriberObservable subscribe onNext* onCompleted or: onError OnNext* (OnCompleted|OnError)?
- 13. 132016-09-20 ITERATOR vs. OBSERVABLE Tnext() onNext(T t) boolean hasNext() onCompleted() throws RuntimeException onError(Throwable e) Iterator Observable blocking synchronous pull non-blocking asynchronous push
- 14. 142016-09-20Source: Reactive Programmingwith RxJava, O'Reilly 2016
- 15.
- 16. 162016-09-20 CREATING OBSERVABLES Edge cases Custom Predefined values Observable.just(T value) Observable.from(T[] values) / from(Iterable<T> values) Observable.range(int start, int count) Observable.interval() Observable.empty() Observable.never() Observable.error(Throwable exception) Observable.create(OnSubscribe<T> f) Observable.create(subscriber -> { subscriber.onNext(“Hello World”); subscriber.onCompleted(); }
- 17.
- 18. 182016-09-20 SUBSCRIBE (1/2) Observablesdo not emit items until someone subscribes Observables can have numerous subscribers (unlike a Java 8 stream that can only be consumed once) Observable<Integer> o = Observable.range(1,3); o.subscribe(System.out::println); o.subscribe(System.out::println);
- 19. 192016-09-20 SUBSCRIBE (2/2) o.subscribe(new Observer<Integer>(){ public void onNext(Integer t) { } public void onError(Throwable e) { } public void onCompleted() { } }); o.subscribe(System.out::println, Throwable::printStackTrace, this::completed); o.subscribe(i -> logger.info("{}", i));
- 20.
- 21. 212016-09-20 WRAPPING AN EXISTINGASYNC API
- 22.
- 23. 232016-09-20 COMPOSABLE FUNCTIONS (1/2) Filter Combine Transform map, flatMap groupBy, buffer window ... take, skip, last distinct filter ... concat, merge, zip, combineLatest multicast, publish switchOnNext ...
- 24. 242016-09-20 COMPOSABLE FUNCTIONS (2/2) ErrorHandling Custom Concurrency observeOn subscribeOn onErrorReturn onErrorResumeNext retry ... any public class that implements the Operator interface or a subclass like Transformer most likely you will never need this!
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- 27. 272016-09-20 TWEETS PER SECOND Observable<Integer>o = tweets() .buffer(1, TimeUnit.SECONDS) .map(items -> items.size()) Observable<Integer> itemsPerSecond (Observable<?> o) { return o.buffer(1, TimeUnit.SECONDS) .map(items -> items.size()); }
- 28.
- 29. 292016-09-20 REACTIVE ECOSYSTEM Service Database Consumed 3rd Party API MessageQueue Web Frontend Provided API
- 30.
- 31. 312016-09-20 IMPLEMENTATIONS ON THEJVM Project Reactor Java 9 j.u.c.Flow RxJava Reactive Extensions (ReactiveX.io) for the JVM Zero Dependencies Polyglot (Scala, Groovy, Clojure and Kotlin) RxJava 2: Java 8+ and Reactive Streams compatible Spring Ecosystem Reactive Streams compatible Will become part of Spring Framework 5.0 Flow.Processor, Publisher, Subscriber and Subscription Interfaces correspond to Reactive Streams specification Will be used in Java EE 9, estimated 2018
- 32. 322016-09-20 REACTIVE WEB IMPLEMENTATION @Controller,@RequestMapping Spring Web Reactive Reactive HTTP Spring MVC Servlet API Any Servlet Container Servlet 3.1, Netty, Undertow
- 33. 332016-09-20 CONTROLLER With RxJava: @GetMapping("/persons") Observable<Person>list() { return this.repository.findAll(); } @GetMapping("/persons") Flux<Person> list() { return this.repository.findAll(); } With Project Reactor:
- 34. 342016-09-20 PLAIN JSON ORSERVER SENT EVENTS JSON Array of persons: GET /persons HTTP/1.1 Host: localhost Accept: application/json GET /persons HTTP/1.1 Host: localhost Accept: text/event-stream Event stream of JSON person objects: Backend implementation is agnostic of the exact transport
- 35.
- 36. 362016-09-20 DATABASE CHALLENGES Transactions Locking API Currentstandard APIs like JDBC, JPA, etc. are not build with reactive programming in mind Usually synchronous and blocking Traditional databases couple heavy-weight “connection” and “transaction” Transactions cause blocking Locks at the database level prevent parallel execution Global coordinator Traditional database patterns do not work well in a reactive world
- 37. 372016-09-20 DATABASE TRENDS Abstract API NoSQL NativeAPI Couchbase offers a reactive API since SDK v2 PostgreSQL, MongoDB, Cassandra and others provide at least async APIs Spring Data 2.0 comes with reactive repositories aligned with Spring Framework 5.0 BASE instead of ACID enables scalability Distributed databases without global coordination are a good fit
- 38. 382016-09-20 REACTIVE REPOSITORIES public interfacePersonRepository extends ReactiveCrudRepository<Person, String> { Flux<Person> findByLastName(String ln); Flux<Person> findByFirstName(String fn); }
- 39. 392016-09-20 CONSUMED THIRD PARTYAPI Web Frontend Provided API Service Database Message Queue Consumed 3rd Party API
- 40. 402016-09-20 THIRD PARTY SYSTEMS PlainHTTP API Internals Reactive API Few third party systems offer a native reactive API Examples include Couchbase Non reactive HTTP APIs can be made reactive: Reactive Web Client is part of Spring Framework 5 Reactive Jersey Client RxNetty Client Third party systems that are blocking or synchronous internally prevent a pure reactive everywhere scenario even if the API can be made reactive
- 41. 412016-09-20 REACTIVE WEB CLIENT With RxJava: Observable<Person> response = webClient .perform(get("http://example.com/persons") .accept(APPLICATION_JSON)) .extract(body(Account.class)); Flux<Person> response = webClient .perform(get("http://example.com/persons") .accept(APPLICATION_JSON)) .extract(body(Account.class)); With Project Reactor:
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- 44. 442016-09-20 Web Frontends ● Browser •JavaScript • Single Threaded ● Remote Communication: • HTTP • WebSockets • WebRTC ● Many modern Frameworks • Our Example: Angular 2
- 45. 452016-09-20 Reactive Frontends: Angular2 ● Built on top of RxJS • Implementation of ReactiveX for JavaScript ● Reactive HTTP • All HTTP calls are handled reactive! this.http .get('http://example.com/persons') .map(response => response.json()) .subscribe( person => this.person = person, error => this.errorMessage = <any>error, () => console.log('Completed') ); Returns an Observable<Response>
- 46. 462016-09-20 Angular 2 Server-SentEvents ● Angular 2 reactive SSE ● Use JavaScript event source • No reactive API ● onmessage vs. onnext ● no oncompleted → Need adapter • Wrap JS event source into Rx Observable let source = new EventSource('http://example.com/persons');
- 47. 472016-09-20 Angular 2 SSE ●Create Observable from Event Source public getEventsource(): Observable<MessageEvent> { return Observable.create( (observer: Observer<MessageEvent>) => { let source = new EventSource('http://example.com/persons'); source.onmessage = observer.next; source.onerror = observer.error; return () => { eventSource.close(); }); } Close event source If observable unsubscribed
- 48. 482016-09-20 Angular 2 WebSockets ●Angular 2 reactive WebSockets ● Use javascript WebSockets • No reactive API ● onmessage vs. onnext ● onclose vs oncompleted → Need adapter ● Data flow in both directions with WebSockets • Wrap JS WebSocket into Rx Subject let socket = new WebSocket('http://example.com/persons');
- 49. 492016-09-20 Reactive Subjects ● Observerand Observable combined ● Observable Part: • Client can listen to changes/new data from Subject • Subject obtains this data externally, e.g. from a WebSocket ● Observer Part: • Subject can listen to changed/new data from client • Subject can send this data e.g. via WebSocket Subject.create(observer, observable) Subject subscribe() onNext()
- 50. 502016-09-20 Angular 2 WebSockets 1.Create WebSocket public createWebsocket(): Subject<MessageEvent> { let socket = new WebSocket('http://example.com/persons'); //... return Subject.create(observer, observable); }
- 51. 512016-09-20 Angular 2 WebSockets 2.Create Observable (Make Data from WebSocket available to Client) • Function inside create() defines behavior of observable • Via calls to observer.next(), .error(), .completed() Observable.create(function (observer) { //... });
- 52. 522016-09-20 Angular 2 WebSockets 2.Create Observable (Make Data from WebSocket available to Client) public createWebsocket(): Subject<MessageEvent> { let socket = new WebSocket('http://example.com/persons'); let observable = Observable.create( (observer: Observer<MessageEvent>) => { socket.onmessage = observer.next.bind(observer); socket.onerror = observer.error.bind(observer); socket.onclose = observer.complete.bind(observer); return socket.close.bind(socket); } ); //... } Map WebSocket Events to Observable Handlers
- 53. 532016-09-20 Angular 2 WebSockets 3.Create Observer (Client can notify update of data) • Event-Handler Functions to be defined in ● [onNext] – what to do if new value emitted, ● [onError] – what to do if error emitted, ● [onCompleted] – what to do if observable completes Observer.create( [onNext], [onError], [onCompleted] );
- 54. 542016-09-20 Angular 2 Websockets 3.Create Observer (Client can notify update of data) public createWebsocket(): Subject<MessageEvent> { //... let observer = { next: (data: Object) => { if (socket.readyState === WebSocket.OPEN) { socket.send(JSON.stringify(data)); } }, // implement error, completed handlers }; return Subject.create(observer, observable); } onnext handler for updates from Client
- 55. 552016-09-20 Reactive Angular 2 WebSockets SSE HTTP Reactive built-in with Angular 2 Wrap into Rx subject Wrap into Rx observable
- 56. 562016-09-20 You canstart using reactive program- ming on all tiers right away Begin on the layers where you get most out of reactive If you want to start right now Spring 5 and Angular 2 are good options. Keep an eye on JavaEE for the future. SUMMARY reactive programming is a powerful option that is available today
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- 58. 582016-09-20 Thank you for yourattention We are looking forward to answer your questions @StefanReuter stefan.reuter@trion.de @kakulty karsten.sitterberg@trion.de