Reactive Programming with NetBeans and Java 8
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The document provides an overview of reactive programming with NetBeans and Java 8. It discusses key concepts like Observables, Subscribers, and asynchronous data streams. It also covers topics such as creating Observables, subscribing, integrating existing code, handling concurrency, and composable functions like map and buffer. The document is intended to introduce developers to reactive programming principles and how they can be applied using libraries like RxJava.
![72016-05-31
REACTIVE MANIFESTO
Responsive
Resilient
Message Driven
Elastic
“[…] 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](https://image.slidesharecdn.com/reactive-programming-160601103647/85/Reactive-Programming-with-NetBeans-and-Java-8-7-320.jpg)
![142016-05-31
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-programming-160601103647/85/Reactive-Programming-with-NetBeans-and-Java-8-14-320.jpg)
Reactive Programming with NetBeans and Java 8
- 1. REACTIVE PROGRAMMING WITH NETBEANS AND JAVA 8 Stefan Reuter
- 2. 22016-05-31 STEFAN REUTER @StefanReuter ● IT Architect ● Trainer and Consultant for trion development GmbH – www.trion.de
- 3. 32016-05-31 trion www.trion.de ● Professional services ● Architecture ● Consulting ● Development ● Training
- 4. 42016-05-31 reactive programming is programming with asynchronous data streams
- 5. 52016-05-31 AGENDA Subscribing Integrating Existing Code Hot vs. Cold Concurrency Item Creating Introduction Composable Functions
- 6. 62016-05-31 AGENDA Subscribing Integrating Existing Code Hot vs. Cold Concurrency Item Creating IntroductionIntroductionIntroduction Composable Functions
- 7. 72016-05-31 REACTIVE MANIFESTO Responsive Resilient Message Driven Elastic “[…] 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
- 8. 82016-05-31 REACTIVE SCENARIOS I/O Push Events User Events Mouse movement and clicks Keyboard typing Changing GPS signals as a user moves with a device Touch events Latency-bound I/O events from disk Data sent or received via network Distributed and cloud-based systems System events received from a server Signals received from hardware Events triggered by sensors Data received from IoT
- 10. 102016-05-31 OBSERVABLE AND SUBSCRIBER Subscriber Observable subscribe onNext* onCompleted or: onError OnNext* (OnCompleted|OnError)?
- 11. 112016-05-31 ITERATOR vs. OBSERVABLE T next() onNext(T t) boolean hasNext() onCompleted() throws RuntimeException onError(Throwable e) Iterator Observable blocking synchronous pull non-blocking asynchronous push
- 12. 122016-05-31Source: Reactive Programming with RxJava, O'Reilly 2016
- 14. 142016-05-31 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(); }
- 16. 162016-05-31 SUBSCRIBE (1/2) Observables do 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);
- 17. 172016-05-31 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));
- 18. 182016-05-31 SHARING A SUBSCRIPTION ConnectableObservable<> co = o.publish(); co.subscribe(…); co.subscribe(…); co.subscribe(…); co.connect(); // or: co.refCount(); ConnectableObservable created via publish() starts emitting items when connect() is called instead of when it is subscribed to
- 19. 192016-05-31 SUBSCRIPTION subscribing to an Observable returns a Subscription allows client code to cancel subscription and query status Subscription subscription = tweets.subscribe(System.out::println); //... subscription.unsubscribe(); //subscription.isUnsubscribed() == true
- 20. 202016-05-31 SUBSCRIBER Subscriber is an abstract implementation of Observer and Subscription can unsubscribe itself o.subscribe(new Subscriber<Tweet>() { @Override public void onNext(Tweet tweet) { if (tweet.getText().contains("Java")) { unsubscribe(); } } ...
- 21. 212016-05-31
- 22. 222016-05-31 HOT vs. COLD Hot Cold Entirely lazy Never starts emiting before someone subscribes Every subscriber receives its own copy of the stream thus events are produced independently for each subscriber Examples: Observable.just(), from(), range() Subscribing often involves a side effect (e.g. db query) Emits events whether subscribers are present or not Emits same events to all subscribers Examples: mouse movements, keyboard input, button clicks Same API for hot and cold Observables
- 24. 242016-05-31 WRAPPING AN EXISTING ASYNC API
- 25. 252016-05-31 WRAPPING AN EXISTING SYNC API (1/3) public Observable<Hotel> listHotels() { return Observable.from( query("SELECT * FROM HOTELS") ); } blocks until all data has been loaded is not lazy, i.e. loads data before there is any subscription
- 26. 262016-05-31 WRAPPING AN EXISTING SYNC API (2/3) public Observable<Hotel> listHotels() { return Observable.defer(() -> Observable.from( query("SELECT * FROM HOTELS") )); } Pass a lambda to Observable.defer() Database is no longer queried until someone subscribes
- 27. 272016-05-31 WRAPPING AN EXISTING SYNC API (3/3) Observable<Booking> getBooking(String id) { return Observable.defer(() -> Observable.just( restTemplate.getForObject( "http://example.com/bookings/{id}", Booking.class, id) )); }
- 28. 282016-05-31 CONVERT TO BLOCKING public Observable<Hotel> listHotels() { // ... } Observable<Hotel> o = listHotels(); Observable<List<Hotel>> hotelList = o.toList(); BlockingObservable<List<Hotel>> block = hotelList.toBlocking(); List<Hotel> people = block.single(); // short: List<Hotel> o = listHotels() .toList() .toBlocking() .single();
- 29. 292016-05-31 SWITCH BETWEEN SYNC AND ASYNC Sync Blocking Pull Async Non Blocking Push Observable.defer() BlockingObservable .toList() .toBlocking() .single();
- 31. 312016-05-31 USING SCHEDULERS observeOn() create() subscribeOn() can be called any time before subscribing the function passed to Observable.create() is executed in the thread provided by the given scheduler controls which scheduler is used to invoke downstream subscribers occurring after observeOn() scheduler can be passed as an additional argument to Observable.create() Scheduler sched = Schedulers.newThread(); observable.subscribeOn(sched);
- 32. 322016-05-31 SCHEDULERS (1/2) io() computation() newThread() starts a new thread each time subscribeOn() or observeOn() is called increased latency due to thread start usually not a good choice as threads are not reused threads are reused unbounded pool of threads useful for I/O bound tasks which require very little CPU resources limits number of threads running in parallel default pool size == Runtime.availableProcessors() useful for tasks thar are entirely CPU-bound, i.e. they require computational power and have no blocking code
- 33. 332016-05-31 SCHEDULERS (2/2) immediate() test() from(Executor exc) wrapper around java.util.concurrent.Executor invokes tasks in the client thread blocking usually not needed because this is the default behavior only used for testing allows arbitrary changes to the clock for simulation ExecutorService executor = Executors.newFixedThreadPool(10); Scheduler s = Schedulers.from(executor);
- 34. 342016-05-31 NOTES ON CONCURRENCY Callbacks will be invoked from only one thread at a time, but events can be emitted from many threads Concurrency often comes already from the source of events so explicit use of schedulers should be a last resort
- 36. 362016-05-31 COMPOSABLE FUNCTIONS (1/2) Filter Combine Transform map, flatMap groupBy, buffer window ... take, skip, last distinct filter ... concat, merge, zip, combineLatest multicast, publish switchOnNext ...
- 37. 372016-05-31 COMPOSABLE FUNCTIONS (2/2) Error Handling 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!
- 38. 382016-05-31 MAP
- 40. 402016-05-31 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()); }
- 41. 412016-05-31 IMPLEMENTATIONS ON THE JVM Project Reactor 2.5 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
- 42. 422016-05-31 Mobile Devices Android Sensors Desktop JavaScript Angular2 JavaFX BigData Cloud IoT Microservices SMALL TO LARGE SCALE Concept applies to all scales
- 43. 432016-05-31 You can start using reactive program- ming right away as you can always convert back using BlockingObservable Have a look at http://reactivex.io/ Check supporting libraries like RxNetty and RxJs SUMMARY reactive programming is a powerful option that is available today
- 45. 452016-05-31 Thank you for your attention I am looking forward to answer your questions at [email protected] @StefanReuter
- 46. BACKUP
- 47. 472016-05-31 RxNetty HTTP CLIENT SocketAddress serverAddress = ... Charset charset = Charset.defaultCharset(); HttpClient.newClient(serverAddress) .enableWireLogging(LogLevel.DEBUG) .createGet("/api/talks") .doOnNext(resp -> logger.info(resp.toString())) .flatMap( resp -> resp.getContent() .map(bb -> bb.toString(charset)) ) .toBlocking() .forEach(logger::info);