This presentation should give you an insight on how to work with Java 8's and 9's CompletableFuture class.

1. Back to the
[Completable] Future

2. Intro
{
"name":"Sophia",
"job":"Java developer",
"employer":"N-iX",
"experience":"2+ years"
}
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3. Agenda

4. Why now?1

5. Why now?
Era of…
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Mash-up
apps

6. What for?2

7. What for?
Speed up the application...
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8. What for?
... in a simpler way than working directly
with threads
Image URL: http://static.codeceo.com/images/2015/01/33095007e134e8630fe35771795f3ac8.jpg

9. So, we need to do
asynchronous
programming …

10. Right

11. Speeding up3

12. Speeding up
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Concurrency Parallelismvs.

13. Concurrency
Multiple tasks
make progress at
the same time
Time
CPU

14. Concurrency
Time
In concurrency,
tasks do
compete for
processor time

15. Parallelism
Each task is
broken into sub
tasks which can
be processed in
parallel
CPU 1 CPU 2
Time

16. Parallelism
Time
In parallelism,
tasks do not
compete for
processor time

17. Variations
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18. Concurrency is an
illusion of parallelism,
don‘t you agree?

19. Sync vs. Async4

20. Sync vs. Async
Asynchronous
Synchronous

21. Well, it can be
Is asynchronous
any faster?

22. Sync vs. Async
The advantage is obvious, isn't it?
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23. Sync vs. Async
Make your calls non-blocking!
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24. So, what about Java?

25. Java retirement party5

26. Java retirement party
How it used to be…
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• Threads
• Future<T>
• ForkJoinPool
• Streams (parallel)

27. Threads
Thread 1 Thread 2
Object 1 Object 2
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28. Threads

29. Threads
Image URL: https://avaldes.com/wp-content/uploads/2013/03/multithreading_starvation.png?2d262d, http://blog.takipi.com/wp-content/uploads/2014/05/Blog_key_.png.
http://blog.takipi.com/wp-content/uploads/2013/08/blog_trampoline.png

30. Callables & Future<T>
Image URL: http://www.deadcoderising.com/content/images/2015/Jan/timeout2.png

31. ForkJoinPool

32. Parallel streams
Splitting Parallel processing Combining

33. 6
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34. More…
◦ Chain callbacks
◦ Wait for completion
◦ Retrieve the value
◦ Complete a Future
◦ React & Recover

35. CF: let's get acquainted!7

36. CompletableFuture
◦ java.util.concurrent
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◦ implements Future<T>
◦ implements CompletionStage<T>

37. CompletableFuture
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38. Concept
Brings the concept of promises to Java.
Image URL: https://pbs.twimg.com/media/CzTp1YBW8AEFAMI.jpg

39. API8
Image URL: https://www.amisw.com/en/wp-content/uploads/2015/08/image-demo-b.png

40. API: Simplest asynchronous computation
◦ Pitfall #1:
Specify custom executor to
avoid using default common
pool.
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41. API
Image URL: http://www.sqlhammer.com/wp-content/uploads/2016/10/demo-god-meme.jpg

42. API: Chaining callbacks
◦ Pitfall #2:
Use thenCompose instead of
thenApply to avoid the
nestings.
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43. API
Image URL: http://bladerunnerjs.org/blog/img/demo-time.jpg

44. API: Parallel computations
◦ Pitfall #3:
Keep in mind that the order of
execution is not guaranteed.
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45. API
Image URL: http://i.memecaptain.com/gend_images/PssWXg.jpg

46. API: Dealing with many CompletableFuture instances
◦ Pitfall #4:
We get CompletableFuture<Void>
as the result of execution of all
futures.
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47. API
Image URL: https://cdn.meme.am/instances/500x/61002060/grumpy-cat-demo-time.jpg

48. API: Dealing with many CompletableFuture instances
◦ Pitfall #5:
We get
CompletableFuture<Object>
as the result of execution of the
fastest future.
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49. API
Image URL: http://www.memegen.com/m/kwfxrc.jpg

50. API: Exceptions
◦ Pitfall #6:
Exceptions can not be handled
with usual CompletableFuture
methods.
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51. Java 9 concurrency
improvements
9

52. Java 9 concurrency improvements
JEP 266: More Concurrency Updates
8 new methods;
5 new static methods.
Image URL: https://ilaborie.github.io/devfest-toulouse-16-slides/pictures/Java9.png

53. Java 9 concurrency improvements: API Additions
orTimeout(long timeout,
TimeUnit unit)
Image URL: https://ilaborie.github.io/devfest-toulouse-16-slides/pictures/Java9.png

54. Java 9 concurrency improvements: API Additions
completeOnTimeout(T value,
long timeout, TimeUnit
unit)
Image URL: https://ilaborie.github.io/devfest-toulouse-16-slides/pictures/Java9.png

55. Java 9 concurrency improvements: API Additions
completeAsync(Supplier<?
extends T> supplier,
Executor executor)
Image URL: https://ilaborie.github.io/devfest-toulouse-16-slides/pictures/Java9.png

56. Java 9 concurrency improvements: API Additions
completeAsync(Supplier<?
extends T> supplier)
Image URL: https://ilaborie.github.io/devfest-toulouse-16-slides/pictures/Java9.png

57. Java 9 concurrency improvements: API Additions
defaultExecutor()
Image URL: https://ilaborie.github.io/devfest-toulouse-16-slides/pictures/Java9.png

58. Java 9 concurrency improvements: API Additions
newIncompleteFuture()
Image URL: https://ilaborie.github.io/devfest-toulouse-16-slides/pictures/Java9.png

59. Java 9 concurrency improvements: API Additions
copy()
Image URL: https://ilaborie.github.io/devfest-toulouse-16-slides/pictures/Java9.png

60. Java 9 concurrency improvements: API Additions
minimalCompletionStage()
Image URL: https://ilaborie.github.io/devfest-toulouse-16-slides/pictures/Java9.png

61. Static API additions10

62. Java 9 concurrency improvements: Static API Additions
◦ Executor delayedExecutor(long delay, TimeUnit
unit, Executor executor)
◦ Executor delayedExecutor(long delay, TimeUnit
unit)
Image URL: https://ilaborie.github.io/devfest-toulouse-16-slides/pictures/Java9.png

63. Java 9 concurrency improvements: Static API Additions
◦ <U> CompletionStage<U> completedStage(U value)
◦ <U> CompletionStage<U> failedStage(Throwable ex)
◦ <U> CompletableFuture<U> failedFuture(Throwable
ex)
Image URL: https://ilaborie.github.io/devfest-toulouse-16-slides/pictures/Java9.png

64. Takeaways11

65. Takeaways
understand the input;
avoid the pitfalls;
use Java 9 before the release!

66. Q&A12

67. Thanks!
Find me at
sophia.khomyn@gmail.com
https://github.com/KhomynSophia/completable-future
COMPLETABLEFUTURE OVERVIEW
http://javaday.org.ua/completablefuture-overview/

68. CREDITS
Special thanks to all the people who made and
released these awesome resources for free:
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