Practical RxJava workshop v1

Practical RxJava workshop v1

A workshop to discover RxJava by migrating an application from classical blocking code to nonblocking reactive code. Skeleton for the workshop is on http://github.com/simonbasle/PracticalRx (just use it to practice the workshop).

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Simon Baslé

April 16, 2015
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Transcript

  1. Practical RxJava

  2. @Couchbase @InfoQFR @bbl_fr @SimonBasle

  3. the Plan & Goals

  4. RxJava 101

  5. migrate a Legacy application RxJava 101

  6. migrate a Legacy application learn Operators of interest RxJava 101

  7. migrate a Legacy application learn Operators of interest 9 steps

    + Q& A RxJava 101
  8. Why?

  9. Blocking it’s Evil, m’kay?

  10. Blocking it’s Evil, m’kay?

  11. we need asynchronous code

  12. we need reactive asynchronous code

  13. we need parallelisable asynchronous code

  14. we need composable asynchronous code

  15. we need readable asynchronous code

  16. but how ?

  17. Futures<T>? Callbacks?

  18. Futures<T>? Callbacks? too easy to block (get) complex beyond 1

    level of composition no composition have you heared of Callback Hell?
  19. DocumentService.find("userId", new Callback<List<Document>>() { public void onSuccess(List<Document> result) { final

    List<String> jsonList = new ArrayList<String>(10); int taken = 0; for (Document doc : result) { if (taken >= 10) break; if (!doc.isStarred()) continue; taken++; final CountDownLatch rendezVous = new CountDownLatch(3); final JsonObject jsonBuffer = new JsonObject(); jsonBuffer.appendInt("id", doc.getId()); jsonBuffer.append("text", doc.getText()); CommentService.findForDoc(doc, new Callback<List<Comment>>() { public void onSuccess(List<Comment> comments) { final JsonObject commentArray = JsonObject.createArray(); CountDownLatch userLatch = new CountDownLatch(comments.size()); for (Comment c : comments) { JsonObject cj = new JsonObject(); cj.append("content", c.getText()); cj.append("date", c.getDate()); UserService.find(c.getUserId(), new Callback<User>() { public void onSuccess(User user) { cj.append("author", user.getName()); cj.append("nickname", user.getLogin()); Futures<T>? Callbacks? too easy to block (get) complex beyond 1 level of composition no composition have you heared of Callback Hell?
  20. RxJava 101

  21. RxJava 101

  22. Netflix OpenSource

  23. dual of Iterable - Iterator

  24. Iterable - Iterator becomes Observable - Observer

  25. Iterable - Iterator becomes Observable - Observer “Pull” “Push”

  26. compose

  27. compose asynchronous programs based on events

  28. compose asynchronous programs based on events using observable sequences

  29. the Reactive Manifesto reactivemanifesto.org

  30. reactive-streams.org standardize on the jvm

  31. reactive-streams.org standardize on the jvm akka - reactor - rxjava

  32. Show Me how it works !

  33. interface Observer<T>

  34. interface Observer<T> onNext(T data)

  35. interface Observer<T> onNext(T data) onCompleted()

  36. interface Observer<T> onNext(T data) onCompleted() onError(Throwable t)

  37. interface Observer<T> onNext(T data) onCompleted() onError(Throwable t)

  38. Observable<T>

  39. Observable<T> compose & chain a stream

  40. Observable<T> subscribe an Observer<T>

  41. so much Choice, you’ll see!

  42. still lost… time to practice

  43. The Legacy app

  44. Wow pool API? Much Legacy!

  45. Doge Mining Pool Client (UI?) Rest Controller Rest Controller Rest

    Controller Rest Controller Service Service Service External API External API External API DB L E G A C Y
  46. Doge Mining Pool Client (UI?) Rest Controller Rest Controller Rest

    Controller Rest Controller Service Service Service External API External API External API DB
  47. Doge Mining Pool Client (UI?) Rest Controller Rest Controller Rest

    Controller Rest Controller Service Service Service External API External API External API DB
  48. simple Creation 1

  49. Migrate Services • AdminService • CoinService • HashrateService • PoolService

    *
  50. Useful Operators • Observable.just • Observable.from • Observable.create • map

  51. Useful Operators • Observable.just • Observable.from • Observable.create • map

  52. But now it doesn’t compile how to adapt the Controllers?

  53. Naively Block on an Observable take(n) vs single() vs first()

    xxxOrDefault(t), toList()
  54. Take

  55. Single

  56. SingleOrDefault

  57. Transform 2

  58. Migrate Services • PoolService ◦ poolGigaHashrate method

  59. Useful Operators • flatMap • reduce

  60. flatMap

  61. reduce

  62. Filter 3

  63. Migrate Services • UserService ◦ findAll for now naively adapted

    (Observable.from) ◦ compose on findAll for getUser / getUserByLogin • SearchService
  64. Useful Operators • filter • take • flatMap to asynchronously

    retrieve additional data needed for filter
  65. filter

  66. Count 4

  67. Migrate Services RankingService ◦ use from for rankByHashrate / rankByCoins

    ◦ complete migration for other methods
  68. Useful Operators • takeUntil • count • take

  69. takeUntil

  70. count

  71. Time for a Break :)

  72. Side Effects 5

  73. doOnXXX • doOnNext • doOnError • doOnCompleted • doOnEach

  74. Migrate Services PoolService ◦ add a line of log each

    time a user connects
  75. Combine 6

  76. Level: Simple Concat

  77. Level: Intermediate Merge

  78. Level: Advanced Zip

  79. Migrate Services StatService.getAllStats • for each User ◦ retrieve his

    hashrate ◦ retrieve how many coins he mined ◦ combine both and make a UserStat
  80. Live & Let Die and Retry oo 7

  81. The Problem StatService.lastBlockFoundBy ◦ fireproof implementation (choose a random User)

    ◦ but what if… we wanted to do it without knowing the number of users in advance?
  82. The Plan Generate an index randomly (within a broadly guessed

    limit) Retry up to 4 times if out of bounds Last resort: use a default User (eg. “Banned User”)
  83. Useful Operators • flatMap • skip • retry • onErrorReturn

  84. Retry

  85. OnErrorReturn

  86. Trap #1

  87. skip doesn’t error if overflow Trap #1

  88. skip doesn’t error if overflow combine with first/last Trap #1

  89. Trap #2

  90. just caches the value Trap #2

  91. just caches the value use create to regenerate at each

    retry Trap #2
  92. Chain 8

  93. Migrate Services ExchangeRateService ◦ calls two external APIs: doge-to-dollar rate

    and currency-to-currency exchange rate ◦ two chained REST calls ◦ combination of the two gives doge-to-anyCurrency
  94. Useful Operators • Observable.create ◦ wrap the REST call on

    each subscription ◦ catch RestClientException and make them into DogePoolException (especially for timeouts)
  95. Useful Operators • zipWith ◦ similar to zip but called

    from stream A instead of statically ◦ combine both rates to get the final one
  96. Oh Hey! ! WARNING - Incoming Product Owner !

  97. "this free exchange rate API crashes too often, make it

    so we switch to an alternative non-free API when it’s the case" - the Product Owner
  98. "this free exchange rate API crashes too often, make it

    so we switch to an alternative non-free API when it’s the case" - the Product Owner
  99. "oh yeah and if you could go on and track

    costs of these calls it would be great" - the Product Owner, pouring himself a coffee Much Surprise Such Requirements wow
  100. The Plan • AdminService ◦ add method+variable to track cost

    for this month • ExchangeRateService ◦ rate retrieval method similar to current one ◦ use endpoint from exchange.nonfree.api.baseUrl • switch thanks to OnErrorResumeNext • use side effects ◦ log when we switch & track the cost
  101. OnErrorResumeNext

  102. Clean-up Controllers 9

  103. Asynchronous Response • prepare a DeferredResult<T> ◦ that will be

    returned without blocking • subscribe on stream ◦ onNext: inject T via setResult ◦ onError: create a DogePoolException and inject it via setErrorResult
  104. This could be Generalized • using ReturnValueHandler and a simple

    adapter of Observable to DeferredResult • each time an Observable is returned, it’ll be converted into this adapter ◦ WebAsyncUtils.getAsyncManager(...). startDeferredResultProcessing(...)
  105. Migrate Services • AdminController (simple) • IndexController (trickier) ◦ use

    zip, flatMap, single… to detect bad users • UserProfileController (idem)
  106. Q& A

  107. TakeAway

  108. Nonblocking code

  109. without Callbacks

  110. with a minimum of visual cluter

  111. readable and understandable

  112. Hope you loved it!

  113. None
  114. Merci!

  115. ➔ RxJava Logo and Marble Diagrams - ReactiveX Documentation http://reactivex.io

    ➔ Cat Attack - Static416 on Flickr ➔ Stormtroopers Series - J.D. Hancock http://photos.jdhancock.com/series/stormtroopers.html ➔ Blackhole with Corona - NASA on Wikimedia ➔ Broken Keyboard - Santeri Viinamäki on Wikimedia ➔ Gobot Toys- Tom Prankerd on Wikimedia ➔ Coffee Filter - Unsplash on Pixabay ➔ Abacus - Succo on Pixabay ➔ Still from Office Space - Copyright, 20th Century Fox By By-Nc By Cc0 By By Cc0 Cc0 © Credits (1/2)
  116. ➔ Hand Reaching - Kinseykick on Pixabay ➔ Sidecar Motocross

    - Jean-Daniel Echenard on Flickr ➔ Twin Falls - Blese on Flickr ➔ Tumbeast Gnawing on Servers - Matthew Inman on Wikimedia ➔ Trap - Anticiv on Flickr ➔ Kane Cleaning Supplies - Collinanderson on Flickr ➔ Chain - Stomchak on Wikimedia ➔ Takeaway - Edimburgh Blog on Flickr ➔ The End Sands - Elektro-Plan on Pixabay Cc0 By-Nd By-Nc By By-Sa By By By Cc0 Credits (2/2)