Intro to Retrofit 2 and RxJava2
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This document provides an introduction to Retrofit 2 and RxJava 2. It discusses how Retrofit allows turning a REST API into a Java interface and how RxJava implements reactive programming with observable sequences. It demonstrates making synchronous and asynchronous HTTP requests with Retrofit and handling the "callback hell" problem with RxJava. Operators like map, flatMap, zip and concatMap are shown to transform and combine observables. The document emphasizes that RxJava contains over 400 methods and discusses additional RxJava concepts like error handling and threading.
![27
Multi value map
Observable<Observable<Integer>> observable =
Observable.just(1, 2, 3).map(
i -> Observable.just(i * 10, i * 10 + 1)
);
[1, 2, 3]
[[10, 11], [20, 21], [30, 31]]](https://image.slidesharecdn.com/introtoretrofit2rxjava2export-170518165805/85/Intro-to-Retrofit-2-and-RxJava2-27-320.jpg)
![29
map
Observable<Integer> observable =
Observable.just(1, 2, 3).flatMap(
i -> Observable.just(i * 10, i * 10 + 1)
);
[1, 2, 3]
[10, 11, 20, 21, 30, 31]
[1, 2, 3]
[[10, 11], [20, 21], [30, 31]]
Observable<Observable<Integer>> observable =
Observable.just(1, 2, 3).map(
i -> Observable.just(i * 10, i * 10 + 1)
);
flatMap](https://image.slidesharecdn.com/introtoretrofit2rxjava2export-170518165805/85/Intro-to-Retrofit-2-and-RxJava2-29-320.jpg)
Intro to Retrofit 2 and RxJava2
- 1. Introduction to Retrofit 2 and RxJava 2 Fabio Collini Google I/O extended Florence May 2017
- 3. 3 Retrofit Turns your REST API into a Java interface Simple to use JSON conversion using Gson Custom converters …
- 4. 4 RxJava A Java VM implementation of ReactiveX (Reactive Extensions): a library for composing asynchronous and event-based programs by using observable sequences.
- 5. 5 RxJava is not simple…
- 7. 7 HTTP request definition public interface StackOverflowService { @GET("/users") Call<List<User>> getTopUsers(); @GET("/users/{userId}/top-tags") Call<List<Tag>> getTags(@Path("userId") int userId); @GET("/users/{userId}/badges") Call<List<Badge>> getBadges(@Path("userId") int userId); }
- 8. 8 Other annotations @GET, @POST, @PUT, @DELETE, @HEAD @Path @Query @QueryMap @Body @FormUrlEncoded @Field @Headers
- 9. OkHttpClient okHttpClient = new OkHttpClient.Builder() .addInterceptor(chain -> { Request request = chain.request(); HttpUrl url = request.url().newBuilder() .addQueryParameter("site", "stackoverflow") .addQueryParameter("key", “...”) .build(); request = request.newBuilder().url(url).build(); return chain.proceed(request); }) .build(); Gson gson = new GsonBuilder() .registerTypeAdapterFactory(MyAdapterFactory.create()) .create(); StackOverflowService service = new Retrofit.Builder() .baseUrl("http://api.stackexchange.com/2.2/") .addCallAdapterFactory(RxJava2CallAdapterFactory.create()) .client(okHttpClient) .addConverterFactory(new DenvelopingConverter(gson)) .addConverterFactory(GsonConverterFactory.create(gson)) .build() .create(StackOverflowService.class); 9 Service creation
- 10. 10 Synchronous request try { Response<List<User>> response = service.getTopUsers().execute(); if (response.isSuccessful()) { List<User> users = response.body(); //... } else { //server error } } catch (IOException e) { //connection error }
- 11. 11 Asynchronous request service.getTopUsers().enqueue(new Callback<List<User>>() { @Override public void onResponse(Call<List<User>> call, Response<List<User>> r) { if (r.isSuccessful()) { List<User> users = response.body(); //... } else { //server error } } @Override public void onFailure(Call<List<User>> call, Throwable t) { //connection error } });
- 12. 12 Callback hell enqueue(service.getTopUsers(), new MyCallback<List<User>>() { @Override public void onResponse(List<User> users) { User user = users.get(0); enqueue(service.getTags(user.id()), new MyCallback<List<Tag>>() { @Override public void onResponse(List<Tag> tags) { enqueue(service.getBadges(user.id()), new MyCallback<List<Badge>>() { @Override public void onResponse(List<Badge> badges) { callback.onResponse(UserStats.create(user, tags, badges)); } @Override public void onFailure(Throwable throwable) { callback.onFailure(throwable); } }); } @Override public void onFailure(Throwable throwable) { callback.onFailure(throwable); } }); } @Override public void onFailure(Throwable throwable) { callback.onFailure(throwable); } });
- 13. + RxJavaRetrofit 13 public interface StackOverflowService { @GET("/users") Call<List<User>> getTopUsers(); }_
- 14. 14 Retrofit + RxJava public interface StackOverflowService { @GET("/users") Single<List<User>> getTopUsers(); }_
- 15. 15 RxJava in action service.getTopUsers() .subscribe( users -> { if (users.size() > 5) users = users.subList(0, 5); System.out.println(users); }, Throwable::printStackTrace );
- 16. 16 Threading service.getTopUsers() .subscribeOn(Schedulers.io()) .observeOn(AndroidSchedulers.mainThread) .subscribe( users -> { if (users.size() > 5) users = users.subList(0, 5); System.out.println(users); }, Throwable::printStackTrace );
- 18. 18 Observable onNext* (onComplete | onError)?
- 19. 19 Observable creation Observable.just(1, 2, 3); Observable.interval(5, TimeUnit.SECONDS); Observable.fromCallable(() -> { //... return createFirstValue(); }); Observable.create(emitter -> { try { emitter.onNext(createFirstValue()); emitter.onNext(createSecondValue()); emitter.onComplete(); } catch (Throwable t) { emitter.onError(t); } });
- 20. 20 Observable in action public Disposable subscribe( Consumer<? super T> onNext, Consumer<? super Throwable> onError, Action onComplete); Observable.just(1, 2, 3).subscribe( System.out::println, Throwable::printStackTrace, () -> System.out.println("Completed") );
- 22. 22 service.getTopUsers() .subscribe( users -> { if (users.size() > 5) users = users.subList(0, 5); System.out.println(users); }, Throwable::printStackTrace );
- 23. 23 service.getTopUsers() .map(users -> users.size() > 5 ? users.subList(0, 5) : users) .subscribe( System.out::println, Throwable::printStackTrace );
- 25. 25 zip private Single<UserStats> loadUserStats(User user) { return Single.zip( service.getBadges(user.id()),__ service.getTags(user.id()),___ (badges, tags) -> UserStats.create(user, tags, badges) ); }_
- 26. 26 zip private Single<UserStats> loadUserStats(User user) { return Single.zip( service.getBadges(user.id()).subscribeOn(Schedulers.io()),__ service.getTags(user.id()).subscribeOn(Schedulers.io()),___ (badges, tags) -> UserStats.create(user, tags, badges) ); }_
- 27. 27 Multi value map Observable<Observable<Integer>> observable = Observable.just(1, 2, 3).map( i -> Observable.just(i * 10, i * 10 + 1) ); [1, 2, 3] [[10, 11], [20, 21], [30, 31]]
- 29. 29 map Observable<Integer> observable = Observable.just(1, 2, 3).flatMap( i -> Observable.just(i * 10, i * 10 + 1) ); [1, 2, 3] [10, 11, 20, 21, 30, 31] [1, 2, 3] [[10, 11], [20, 21], [30, 31]] Observable<Observable<Integer>> observable = Observable.just(1, 2, 3).map( i -> Observable.just(i * 10, i * 10 + 1) ); flatMap
- 30. 30 flatMap Single<Profile> single = service.login(userName, password) .flatMap(service::getProfile);
- 31. 31 service.getTopUsers() //1 List<20 User> .map(users -> users.size() > 5 ? users.subList(0, 5) : users) //1 List<5 User>
- 32. 32 service.getTopUsers() //1 List<20 User> .map(users -> users.size() > 5 ? users.subList(0, 5) : users) //1 List<5 User> .flatMapObservable(users -> Observable.fromIterable(users)) //5 User
- 33. 33 service.getTopUsers() //1 List<20 User> .map(users -> users.size() > 5 ? users.subList(0, 5) : users) //1 List<5 User> .flattenAsObservable(users -> users) // 5 User
- 34. 34 service.getTopUsers() //1 List<20 User> .flattenAsObservable(users -> users) // 20 User .take(5) // 5 User
- 35. 35 service.getTopUsers() //1 List<20 User> .flattenAsObservable(users -> users) // 20 User .take(5) // 5 User .flatMapSingle(user -> loadUserStats(service, user)) // 5 UserStats
- 36. 36 Single<List<UserStats>> single = service.getTopUsers() //1 List<20 User> .flattenAsObservable(users -> users) // 20 User .take(5) // 5 User .flatMapSingle(user -> loadUserStats(service, user)) // 5 UserStats .toList(); // 1 List<5 UserStats>
- 37. 37 Single<List<UserStats>> single = service.getTopUsers() //1 List<20 User> .flattenAsObservable(users -> users) // 20 User .take(5) // 5 User .flatMapSingle(user -> loadUserStats(service, user)) // 5 UserStats .toList(); // 1 List<5 UserStats> single.subscribe( UserStats::printList, Throwable::printStackTrace );
- 38. 38 730.876 Darin Dimitrov (Sofia, Bulgaria) c# (7.260), asp.net-mvc (6.780), asp.net-mvc-3 (4.629), jquery (3.043), asp.net (3.455) Teacher, Student, Editor, Cleanup, Organizer 724.614 BalusC (Amsterdam, Netherlands) java (6.468), jsf (6.957), jsf-2 (3.809), servlets (2.234), jsp (2.860) php, regex, servlets, java, security 677.074 VonC (France) git (8.555), eclipse (1.715), github (2.417), java (951), version-control (1.075) c, python, php, regex, c# 692.535 Hans Passant (Madison, WI) c# (8.199), .net (4.254), winforms (2.485), c++ (2.084), vb.net (1.457) Tag Editor, Announcer, reference, c, excel 944.295 Jon Skeet (Reading, United Kingdom) c# (18.363), java (10.213), .net (5.338), linq (2.879), string (954) cryptography, reference, c, python, php Single<List<UserStats>> single = service.getTopUsers() //1 List<20 User> .flattenAsObservable(users -> users) // 20 User .take(5) // 5 User .flatMapSingle(user -> loadUserStats(service, user)) // 5 UserStats .toList(); // 1 List<5 UserStats> single.subscribe( UserStats::printList, Throwable::printStackTrace );
- 39. 39 flatMap source code (RxJava1) public final <R> Observable<R> flatMap( Func1< ? super T, ? extends Observable<? extends R> > func) { return merge(map(func)); }
- 42. 42 Single<List<UserStats>> single = service.getTopUsers() //1 List<20 User> .flattenAsObservable(users -> users) // 20 User .take(5) // 5 User .concatMapEager(user -> loadUserStats(service, user).toObservable()) // 5 User .toList(); // 1 List<5 UserStats> single.subscribe( UserStats::printList, Throwable::printStackTrace );
- 43. 43 944.295 Jon Skeet (Reading, United Kingdom) c# (18.363), java (10.213), .net (5.338), linq (2.879), string (954) cryptography, reference, c, python, php 730.876 Darin Dimitrov (Sofia, Bulgaria) c# (7.260), asp.net-mvc (6.780), asp.net-mvc-3 (4.629), jquery (3.043), asp.net (3.455) Teacher, Student, Editor, Cleanup, Organizer 724.614 BalusC (Amsterdam, Netherlands) java (6.468), jsf (6.957), jsf-2 (3.809), servlets (2.234), jsp (2.860) php, regex, servlets, java, security 692.535 Hans Passant (Madison, WI) c# (8.199), .net (4.254), winforms (2.485), c++ (2.084), vb.net (1.457) Tag Editor, Announcer, reference, c, excel 677.074 VonC (France) git (8.555), eclipse (1.715), github (2.417), java (951), version-control (1.075) c, python, php, regex, c# Single<List<UserStats>> single = service.getTopUsers() //1 List<20 User> .flattenAsObservable(users -> users) // 20 User .take(5) // 5 User .concatMapEager(user -> loadUserStats(service, user).toObservable()) // 5 User .toList(); // 1 List<5 UserStats> single.subscribe( UserStats::printList, Throwable::printStackTrace );
- 44. 44 service.getTopUsers() .flattenAsObservable(users -> users) .take(5) .concatMapEager(user -> Single.zip( service.getBadges(user.id()).subscribeOn(Schedulers.io()), service.getTags(user.id()).subscribeOn(Schedulers.io()), (badges, tags) -> UserStats.create(user, tags, badges) ).toObservable()) .toList() .subscribeOn(Schedulers.io()) .observeOn(AndroidSchedulers.mainThread()) .subscribe( UserStats::printList, Throwable::printStackTrace ); Wrapping up
- 45. 45 This is just the beginning… Observable class contains more than 400 methods: distinct, debounce, retry, repeat, timeout, … disposable error management Single, Observable, Flowable, Completable, Maybe hot and cold observable subjects TestScheduler