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
   

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2. REACTIVE FUNCTIONAL
   

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3. FUNCTIONAL
   • Functions are first-class citizens
   • Immutability
   • No side-effects
   • Referential transparency
   • Declarative
   • Favours concurrency
   

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4. private boolean isDivisibleBy2(int number) {
   return number % 2 == 0;
   }
   Example 1
   

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5. private boolean isDivisibleBy2(int number) {
   return number % 2 == 0;
   }
   Example 1
   

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6. integers
   .stream()
   .map(number -> isDivisibleBy2(number) ? "Even" : "Odd");
   Example 2
   

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7. integers
   .stream()
   .map(number -> isDivisibleBy2(number) ? "Even" : "Odd");
   Example 2
   

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8. integers
   .stream()
   .map(number -> isDivisibleBy2(number) ? "Even" : "Odd");
   Example 2
   

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9. integers
   .stream()
   .map(number -> isDivisibleBy2(number) ? "Even" : "Odd");
   Example 2
   

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10. REACTIVE
    

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15. REACTIVE
    • Responsive
    • Resilient
    • Elastic
    • Message Driven
    

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16. REACTIVE
    • Speed Traps
    • Fire Alarms
    • Airbags
    • Autonomous Vehicles
    • Excel
    • GUI Systems
    • Hystrix
    Real World Examples
    

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17. ~ Callbacks ~
    An imperative way to build reactive systems.
    

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18. login(“username", “password", new Callback() {
    public void onSuccess(String authToken) {
    // Do something...
    }
    });
    

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19. login(“username", “password", new Callback() {
    public void onSuccess(String authToken) {
    // Do something...
    }
    });
    

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20. login(“username", “password", new Callback() {
    public void onSuccess(String authToken) {
    // Do something...
    }
    public void onFailure(Exception e) {
    // Show error message...
    }
    });
    

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21. RxJava
    

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22. A library for composing asynchronous and event-
    based programs using observable sequences for
    the Java VM.
    

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23. Where is it used?
    • Back-end to build highly scalable systems.
    • Front-end to create maintainable code.
    

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24. RxJava
    • Primitives
    • Operators
    

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25. Primitive - Observable
    • Produces events
    • Usually lazy
    • Can produce one, many or zero events
    •Serialized access
    

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26. button
    .setOnClickListener(click -> doSomething());
    buttonClicksObservable
    .subscribe(click -> doSomething());
    Callback
    RxJava
    

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27. button
    .setOnClickListener(click -> doSomething());
    buttonClicksObservable
    .subscribe(click -> doSomething());
    Callback
    RxJava
    

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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
    

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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
    

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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
    

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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
    

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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
    

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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
    

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34. buttonClicksObservable
    .flatMap(click -> api.authenticate(username, password))
    .onErrorReturn(null)
    .subscribe(authToken ->
    if (authToken != null) saveToken(authToken) else showError();
    );
    RxJava
    

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35. buttonClicksObservable
    .flatMap(click -> api.authenticate(username, password))
    .onErrorReturn(null)
    .subscribe(authToken ->
    if (authToken != null) saveToken(authToken) else showError();
    );
    RxJava
    

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36. buttonClicksObservable
    .flatMap(click -> api.authenticate(username, password))
    .onErrorReturn(null)
    .subscribe(authToken ->
    if (authToken != null) saveToken(authToken) else showError();
    );
    RxJava
    

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37. buttonClicksObservable
    .flatMap(click -> api.authenticate(username, password))
    .onErrorReturn(null)
    .subscribe(authToken ->
    if (authToken != null) saveToken(authToken) else showError();
    );
    RxJava
    

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38. buttonClicksObservable
    .flatMap(click -> api.authenticate(username, password))
    .onErrorReturn(null)
    .subscribe(authToken ->
    if (authToken != null) saveToken(authToken) else showError();
    );
    RxJava
    

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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
    

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40. Observable - Anatomy
    Data
    Error
    Completion
    

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41. Observable - Anatomy
    Data
    Error
    Completion
    

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42. Observable - Anatomy
    Data
    Error
    Completion
    

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43. Observable - Anatomy
    Data
    Error
    Completion
    

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44. Primitive - Subscriber
    • onNext(T)
    • onError(Throwable)
    • onComplete()
    

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45. RxJava - Operators
    • Single Observable
    • Multiple Observable
    • Higher-Order Observables
    •Finite and infinite Observables (any of the
    above)
    

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46. Marble Diagrams
    

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47. filter
    

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48. map
    

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49. debounce
    

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50. delay
    

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51. interval
    

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52. amb
    

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53. merge
    

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54. combineLatest
    

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55. zip
    

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56. flatMap
    

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57. onError*
    

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58. retry*
    

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59. Error Handling
    • Exceptions are normal
    • Error handling operators
    • Retry operators
    

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60. Declarative Threading
    • Using Schedulers
    • subscribeOn(Scheduler)
    • observeOn(Scheduler)
    

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61. Debugging
    • Could be a pain 
    • Use doOn* operators to inspect the
    pipeline
    • Traceur (RxJava 2)
    

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62. Testing
    • Mockito
    • Subjects / Relays
    

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63. Further Reading
    André Staltz
    

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64. Questions?
    

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