Introduction to Retrofit 2 and RxJava2

1. Introduction to Retrofit 2
and RxJava 2
Fabio Collini
Google I/O extended
Florence
May 2017

2. 2
Ego slide
@fabioCollini
linkedin.com/in/fabiocollini
github.com/fabioCollini
medium.com/@fabioCollini
codingjam.it
Android programmazione avanzata

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…

6. 6
github.com/fabioCollini/
IntroToRetrofit2RxJava2
Demo project

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
);

17. 17
Single
(onSuccess | onError)?

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

46. github.com/fabioCollini/IntroToRetrofit2RxJava2
@fabioCollini
linkedin.com/in/fabiocollini
github.com/fabioCollini
medium.com/@fabioCollini
Thanks for your attention!
Questions?