Java 8 åpnet slusene for funksjonell programmering (FP) i Java, men verktøykassen som følger med JDKen er ganske mangelfull. Man har ingen støtte for immutable objekter og datastrukturer, som er helt essensielt innen FP og hjelper deg å fjerne en rekke typer kodefeil. I tillegg mangler for eksempel mer høynivå mekanismer for parallellisering av oppgaver. I dette foredraget vil vi gå igjennom et utvalg av tredjepartsbiblioteker som du kan ta i bruk for å bøte på disse problemene og gjøre Java-koden din ennå mer sikker og funksjonell!

1. Hjelp, vi skal kode
funksjonelt i Java!
1
JavaZone 2016
Fredrik Vraalsen
fredriv
fredrik.vraalsen@schibsted.com

4. Kompleksitet
Iboende
Utilsiktet / tilfeldig
4http://i533.photobucket.com/albums/ee339/Sushigirl-94/Funny%20Signs/crazy-sign-0508141.jpg

5. Funksjonell
programmering?© Fredrik Vraalsen 2012

6. Java 8
Anonyme funksjoner (lambda)
Stream
6

7. Java 8
Anonyme funksjoner (lambda)
Stream
Optional ?
7

8. Hva mangler?
Immutability
Value-objekter
Datastrukturer (lister, maps, etc.)
Parallellitet
8

9. Unngå endring
Verdier kan ikke endres – beregne nye
Dele data fritt
Lettere å resonnere
Ytelsesforbedringer
9

10. Value-objekter
10https://blog.perbrage.com/2012/04/07/is-it-an-entity-or-a-value-object/

11. Value-objekter
immutables.io
Lombok
Ren Java
11

12. immutables.io
public interface Person {
String name();
int age();
}
12

13. immutables.io
@Value.Immutable
public interface Person {
String name();
int age();
}
13

14. immutables.io
@Value.Immutable
public interface Person {
String name();
int age();
}
Person person = ImmutablePerson.builder()
.name("Fredrik")
.age(40)
.build();
14

15. immutables.io
@Value.Immutable
public interface Person {
String name();
int age();
}
Person person = ...
Person older = ImmutablePerson.copyOf(person)
.withAge(41);
15

16. Lombok
public class Person {
String name;
int age;
}
16

17. Lombok
@Value
public class Person {
String name;
int age;
}
17

18. Lombok
@Value
public class Person {
String name;
int age;
}
Person person = new Person("Fredrik", 40);
18

19. Lombok
@Value
public class Person {
String name;
@Wither int age;
}
Person person = new Person("Fredrik", 40);
Person older = person.withAge(41);
19

20. Utfordringer
Annotation processing
IDE plugins
20

21. Ren Java
public class Person {
public final String name;
public final int age;
public Person(String name, int age) {
this.name = name;
this.age = age;
}
// equals, hashCode, withAge, ...
}
21

22. Collections
22
© Fredrik Vraalsen 2012

23. Funksjonelle datastrukturer
Unmodifiable
Immutable
Persistent
23

24. Immutable
24
123original

25. Immutable
25
123
123
original

26. Immutable
26
123
1234new
original

27. Persistent
27
123original

28. Persistent
28
123
4new
original

29. Funksjonelle datastrukturer
pCollections
Javaslang
FunctionalJava
29

30. pCollections
PStack<String> names = ConsPStack.from(
Arrays.asList("Luke Skywalker”, "Han Solo"));
30

31. pCollections
PStack<String> names = ConsPStack.from(
Arrays.asList("Luke Skywalker”, "Han Solo”));
PStack<String> moreNames = names.plus("Darth Vader");
31

32. pCollections
PStack<String> names = ConsPStack.from(
Arrays.asList("Luke Skywalker”, "Han Solo"));
PStack<String> moreNames = names.plus("Darth Vader");
List<String> skywalkers = moreNames
.stream()
.filter(name -> name.contains("Skywalker"))
.collect(Collectors.toList());
32

33. Functional Java
List<String> names = list("Luke Skywalker", "Han Solo");
33

34. Functional Java
List<String> names = list("Luke Skywalker", "Han Solo");
List<String> moreNames = names.cons("Darth Vader");
34

35. Functional Java
List<String> names = list("Luke Skywalker", "Han Solo");
List<String> moreNames = names.cons("Darth Vader");
List<String> skywalkers = names
.filter(name -> name.contains("Skywalker"));
35

36. Javaslang
List<String> names = List.of("Luke Skywalker", "Han Solo");
List<String> moreNames = names.prepend("Darth Vader");
List<String> skywalkers = names
.filter(name -> name.contains("Skywalker"));
36

37. Velge riktig datastruktur
37

38. Velge riktig datastruktur
38

39. Velge riktig datastruktur
(Linked)List/Stack vs Vector vs Array
39

40. Performance
© Fredrik Vraalsen 2012

41. Streams – performance
List<Article> frontpageArticles =
frontpage.getArticleIds().stream()
.map(id -> fetchArticle(id))
.collect(toList());
41

42. This one goes to 11!
List<Article> frontpageArticles =
frontpage.getArticleIds().parallelStream()
.map(id -> fetchArticle(id))
.collect(toList());
42

43. Starvation
Common F/J thread pool
Workarounds?
Execute within explicit F/J pool
Use CompletableFuture
43

44. CompletableFuture
Chaining of async futures and actions
Waiting for all or any future(s)
Explicitly complete (like Promise)
Control of executor service
44
http://blog.krecan.net/2014/03/18/how-to-specify-thread-pool-for-java-8-parallel-streams/
http://www.nurkiewicz.com/2013/05/java-8-completablefuture-in-action.html

45. To parallelStream or not to …
Batch?
parallelStream FTW!
Interactive? Concurrency?
CompletableFuture FTW!
45

46. Alternativer
Javaslang Future
FunctionalJava parMap etc.
cyclops-react
Actors
46

47. For comprehensions
import static javaslang.API.For;
For(
someAsyncTask(),
otherAsyncTask()
)
47

48. For comprehensions
import static javaslang.API.For;
For(
someAsyncTask(),
otherAsyncTask()
).yield((foo, bar) -> foo + bar)
48

49. For comprehensions
import static javaslang.API.For;
String result = For(
someAsyncTask(),
otherAsyncTask()
).yield((foo, bar) -> foo + bar).get();
49

50. Actors
Meldingsbasert
Lokalt = Sekvensiell kø
Flere actors = Parallellitet
50

51. Actors
Akka
FunctionalJava
51

52. Andre hjelpemidler
52Enklere Liv / http://painkillerblogg.blogspot.no/2010/10/hjelpemidler.html

53. Javaslang
Streams = lazy linked lists
Tupler, funksjoner
Option, Either, Future
Feilhåndtering (Try)
Pattern matching
53

54. Try
Try.of(() -> doSomeWork())
54

55. Try
Try.of(() -> doSomeWork())
.map(r -> transform(r))
55

56. Try
Try.of(() -> doSomeWork())
.map(r -> transform(r))
.getOrElse(defaultValue);
56

57. Try
A result =
Try.of(() -> doSomeWork())
.map(r -> transform(r))
.getOrElse(defaultValue);
57

58. Either
Kan returnere en av to verdier
Typisk suksess eller feilmelding
58

59. Either
doComputation() // Either<String, R>
59

60. Either
doComputation()
.flatMap(r -> toXml(r)) // Either<String, Document>
60

61. Either
Document result =
doComputation()
.flatMap(r -> toXml(r))
.getOrElseGet(errorMsg -> toErrorXml(errorMsg));
61

62. jOOλ
Tupler, funksjoner
Seq
62

63. cyclops-react
Asynkron programmering
Utvidelser av JDK, pCollections, m.m.
Interoperabilitet (AnyM)
63

64. Functional programming
Enklere kode
Mer robust
Bedre ytelse

65. Spørsmål?
© Fredrik Vraalsen 2012
fredriv
fredrik.vraalsen@schibsted.com