Getting your feet wet with RxJava

Presented in Feb '18 at JUG NCR Meetup, New Delhi.
https://www.meetup.com/Delhi-NCR-JUG/events/245487927/

Transcript

1. Getting your feet wet with RxJava Ragunath Jawahar • @ragunathjawahar
2. REACTIVE FUNCTIONAL
3. FUNCTIONAL • Functions are first-class citizens • Immutability • No side-effects • Referential transparency • Declarative • Favours concurrency
4. private boolean isDivisibleBy2(int number) { return number % 2 == 0; } Example 1
5. private boolean isDivisibleBy2(int number) { return number % 2 == 0; } Example 1
6. integers .stream() .map(number -> isDivisibleBy2(number) ? "Even" : "Odd"); Example 2
7. integers .stream() .map(number -> isDivisibleBy2(number) ? "Even" : "Odd"); Example 2
8. integers .stream() .map(number -> isDivisibleBy2(number) ? "Even" : "Odd"); Example 2
9. integers .stream() .map(number -> isDivisibleBy2(number) ? "Even" : "Odd"); Example 2
10. REACTIVE
15. REACTIVE • Responsive • Resilient • Elastic • Message Driven
16. REACTIVE • Speed Traps • Fire Alarms • Airbags • Autonomous Vehicles • Excel • GUI Systems • Hystrix Real World Examples
17. ~ Callbacks ~ An imperative way to build reactive systems.
18. login(“username", “password", new Callback() { public void onSuccess(String authToken) { // Do something... } });
19. login(“username", “password", new Callback() { public void onSuccess(String authToken) { // Do something... } });
20. login(“username", “password", new Callback() { public void onSuccess(String authToken) { // Do something... } public void onFailure(Exception e) { // Show error message... } });
21. RxJava
22. A library for composing asynchronous and event- based programs using observable sequences for the Java VM.
23. Where is it used? • Back-end to build highly scalable systems. • Front-end to create maintainable code.
24. RxJava • Primitives • Operators
25. Primitive - Observable • Produces events • Usually lazy • Can produce one, many or zero events •Serialized access
26. button .setOnClickListener(click -> doSomething()); buttonClicksObservable .subscribe(click -> doSomething()); Callback RxJava
27. button .setOnClickListener(click -> doSomething()); buttonClicksObservable .subscribe(click -> doSomething()); Callback RxJava
28. button .setOnClickListener(click -> api.authenticate(username, password, new Callback() { public void onSuccess(String authToken) { // Save Token } public void onLoginFailed(LoginException e) { // Show Error } }) ); Callback
29. button .setOnClickListener(click -> api.authenticate(username, password, new Callback() { public void onSuccess(String authToken) { // Save Token } public void onLoginFailed(LoginException e) { // Show Error } }) ); Callback
30. button .setOnClickListener(click -> api.authenticate(username, password, new Callback() { public void onSuccess(String authToken) { // Save Token } public void onLoginFailed(LoginException e) { // Show Error } }) ); Callback
31. button .setOnClickListener(click -> api.authenticate(username, password, new Callback() { public void onSuccess(String authToken) { // Save Token } public void onLoginFailed(LoginException e) { // Show Error } }) ); Callback
32. button .setOnClickListener(click -> api.authenticate(username, password, new Callback() { public void onSuccess(String authToken) { // Save Token } public void onLoginFailed(LoginException e) { // Show Error } }) ); Callback
33. button .setOnClickListener(click -> api.authenticate(username, password, new Callback() { public void onSuccess(String authToken) { // Save Token } public void onLoginFailed(LoginException e) { // Show Error } }) ); Callback
34. buttonClicksObservable .flatMap(click -> api.authenticate(username, password)) .onErrorReturn(null) .subscribe(authToken -> if (authToken != null) saveToken(authToken) else showError(); ); RxJava
35. buttonClicksObservable .flatMap(click -> api.authenticate(username, password)) .onErrorReturn(null) .subscribe(authToken -> if (authToken != null) saveToken(authToken) else showError(); ); RxJava
36. buttonClicksObservable .flatMap(click -> api.authenticate(username, password)) .onErrorReturn(null) .subscribe(authToken -> if (authToken != null) saveToken(authToken) else showError(); ); RxJava
37. buttonClicksObservable .flatMap(click -> api.authenticate(username, password)) .onErrorReturn(null) .subscribe(authToken -> if (authToken != null) saveToken(authToken) else showError(); ); RxJava
38. buttonClicksObservable .flatMap(click -> api.authenticate(username, password)) .onErrorReturn(null) .subscribe(authToken -> if (authToken != null) saveToken(authToken) else showError(); ); RxJava
39. buttonClicksObservable .flatMap(click -> api.authenticate(username, password)) .onErrorReturn(null) .subscribeOn(Schedulers.io()) .observeOn(AndroidSchedulers.mainThread()) .subscribe(authToken -> if (authToken != null) saveToken(authToken) else showError(); ); RxJava
40. Observable - Anatomy Data Error Completion
41. Observable - Anatomy Data Error Completion
42. Observable - Anatomy Data Error Completion
43. Observable - Anatomy Data Error Completion
44. Primitive - Subscriber • onNext(T) • onError(Throwable) • onComplete()
45. RxJava - Operators • Single Observable • Multiple Observable • Higher-Order Observables •Finite and infinite Observables (any of the above)
46. Marble Diagrams
47. filter
48. map
49. debounce
50. delay
51. interval
52. amb
53. merge
54. combineLatest
55. zip
56. flatMap
57. onError*
58. retry*
59. Error Handling • Exceptions are normal • Error handling operators • Retry operators
60. Declarative Threading • Using Schedulers • subscribeOn(Scheduler) • observeOn(Scheduler)
61. Debugging • Could be a pain  • Use doOn* operators to inspect the pipeline • Traceur (RxJava 2)
62. Testing • Mockito • Subjects / Relays
63. Further Reading André Staltz
64. Questions?