Hjelp, vi skal kode funksjonelt i Java!

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JavaZone 2016

Fredrik Vraalsen

fredriv fredrik.vraalsen@schibsted.com

KompleksitetIboende

Utilsiktet / tilfeldig

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

Funksjonell programmering?

© Fredrik Vraalsen 2012

Java 8Anonyme funksjoner (lambda)

Stream

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Java 8Anonyme funksjoner (lambda)

Stream

Optional ?

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Hva mangler?Immutability

Value-objekter

Datastrukturer (lister, maps, etc.)

Parallellitet

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Unngå endringVerdier kan ikke endres – beregne nye

Dele data fritt

Lettere å resonnere

Ytelsesforbedringer

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Value-objekter

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

Value-objekterimmutables.io

Lombok

Ren Java

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immutables.iopublic interface Person { String name(); int age();}

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

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

Person person = ImmutablePerson.builder() .name("Fredrik") .age(40) .build();

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

Person person = ...

Person older = ImmutablePerson.copyOf(person) .withAge(41);

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Lombokpublic class Person { String name; int age;}

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Lombok@Valuepublic class Person { String name; int age;}

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Lombok@Valuepublic class Person { String name; int age;}

Person person = new Person("Fredrik", 40);

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Lombok@Valuepublic class Person { String name; @Wither int age;}

Person person = new Person("Fredrik", 40);

Person older = person.withAge(41);

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UtfordringerAnnotation processing

IDE plugins

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Ren Javapublic 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, ...}

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Collections

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© Fredrik Vraalsen 2012

Funksjonelle datastrukturerUnmodifiable

Immutable

Persistent

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Immutable

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123original

Immutable

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123

123

original

Immutable

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123

1234new

original

Persistent

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123original

Persistent

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123

4new

original

Funksjonelle datastrukturerpCollections

Javaslang

FunctionalJava

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

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

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pCollectionsPStack<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());

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Functional JavaList<String> names = list("Luke Skywalker", "Han Solo");

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

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

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

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Velge riktig datastruktur

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Velge riktig datastruktur

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

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Performance

© Fredrik Vraalsen 2012

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

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

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StarvationCommon F/J thread pool

Workarounds?

Execute within explicit F/J pool

Use CompletableFuture

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CompletableFutureChaining of async futures and actions

Waiting for all or any future(s)

Explicitly complete (like Promise)

Control of executor service

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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

To parallelStream or not to …Batch?

parallelStream FTW!

Interactive? Concurrency?

CompletableFuture FTW!45

AlternativerJavaslang Future

FunctionalJava parMap etc.

cyclops-react

Actors

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For comprehensionsimport static javaslang.API.For;

For( someAsyncTask(), otherAsyncTask() )

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For comprehensionsimport static javaslang.API.For;

For( someAsyncTask(), otherAsyncTask() ).yield((foo, bar) -> foo + bar)

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For comprehensionsimport static javaslang.API.For;

String result = For( someAsyncTask(), otherAsyncTask() ).yield((foo, bar) -> foo + bar).get();

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ActorsMeldingsbasert

Lokalt = Sekvensiell kø

Flere actors = Parallellitet

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ActorsAkka

FunctionalJava

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Andre hjelpemidler

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

JavaslangStreams = lazy linked lists

Tupler, funksjoner

Option, Either, Future

Feilhåndtering (Try)

Pattern matching53

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

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

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

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

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EitherKan returnere en av to verdier

Typisk suksess eller feilmelding

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

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

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EitherDocument result = doComputation() .flatMap(r -> toXml(r)) .getOrElseGet(errorMsg -> toErrorXml(errorMsg));

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jOOλTupler, funksjoner

Seq

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cyclops-reactAsynkron programmering

Utvidelser av JDK, pCollections, m.m.

Interoperabilitet (AnyM)

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Functional programmingEnklere kode

Mer robust

Bedre ytelse

Spørsmål?

© Fredrik Vraalsen 2012

fredriv

fredrik.vraalsen@schibsted.com