java 8 dos and don'ts - javabin oslo may 2015

Java 8 and .

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javaBin Oslo – 12.05.2015

Fredrik Vraalsen

fredriv [email protected]

mailto:[email protected]

Java 8 – what’s new?Lambdas

Method handles

Extension methods

Streams

Optional3

Java 8 – what’s new?Lambdas (anonymous functions)

Method handles

Extension methods

Streams

Optional4

Java 7 vs 8Collections.sort(people, new Comparator<Person>() { public int compare(Person x, Person y) { return x.getName().compareTo(y.getName()); } });

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vs

sort(people, (x, y) -> x.getName().compareTo(y.getName()));

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vs

sort(people, comparing(person -> person.getName()));

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vs

sort(people, comparing(Person::getName));

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vs

people.sort(comparing(Person::getName));

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Streams

© Fredrik Vraalsen 2008

Old fashioned imperative

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List<RoadData> filtered = new ArrayList<>();int count = 0; for (Iterator<RoadData> i = roadData.iterator(); i.hasNext() && count < 10; ) { RoadData data = i.next(); if (nameQuery.matches(data.getName())) { filtered.add(data); count++; }}

Streams

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roadData.stream() .filter(data -> nameQuery.matches(data.getName())) .limit(10) .collect(toList());

Streams – pipelines

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cat roadData.txt | grep … | head > output.txt

Learn you a Stream API

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Map<String, List<Article>> articlesByCategory =


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Map<String, List<Article>> articlesByCategory = articleTransports.stream()


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Map<String, List<Article>> articlesByCategory = articleTransports.stream() .map(transport -> convertToArticle(transport))


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Map<String, List<Article>> articlesByCategory = articleTransports.stream() .map(transport -> convertToArticle(transport)) .collect(groupingBy(article -> article.getCategory()));


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Method handles

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Map<String, List<Article>> articlesByCategory = articleTransports.stream() .map(transport -> convertToArticle(transport)) .collect(groupingBy(article -> article.getCategory()));

Map<String, List<Article>> articlesByCategory = articleTransports.stream() .map(this::convertToArticle) .collect(groupingBy(article -> article.getCategory()));

Method handles

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Method handles

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Map<String, List<Article>> articlesByCategory = articleTransports.stream() .map(this::convertToArticle) .collect(groupingBy(Article::getCategory));

Naming, caching, counting

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Map<String, List<Article>> articlesByCategory = articleTransports.stream() .map(this::convertToArticle) .collect(groupingBy(Article::getCategory));

Naming, caching, counting

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Map<String, List<Article>> articlesByCategory = articleTransports.stream() .map(this::transportToArticle) .collect(groupingBy(Article::category));

Extract functions

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Map<String, List<Article>> articlesByCategory = articleTransports.stream() .map(transportToArticle) .collect(groupingBy(Article::category));

Function<ArticleTransport, Article> transportToArticle = transport -> convertToArticle(transport);

Lambdas everywhere!!!1!links.stream() .map(link -> link.build()) .forEach(abderaElement::addLink);

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Old school ifs and forslinks.stream() .map(link -> link.build()) .forEach(abderaElement::addLink);

for (LinkBuilder lb : links) { abderaElement.addLink(lb.build()); }

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Parsing nested JSON "suggest": { "tag_suggest": [ { "length": 5, "offset": 0, "options": [ { "freq": 25, "score": 0.8, "text": "fakta" } ], "text": "fanta" } ] } 28

Lambdas everywhere!!!1!List<String> terms = new ArrayList<>();

suggestions.getAsJsonObject().getAsJsonArray(“tag_suggest”) .forEach(tag -> tag.getAsJsonObject().getAsJsonArray("options") .forEach(option -> terms .add(option.getAsJsonObject().getAsJsonPrimitive("text") .getAsString())));

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Old school ifs and forsList<String> terms = new ArrayList<>();

for (JsonElement tag : suggestions.getAsJsonObject().getAsJsonArray("tag_suggest")) { for (JsonElement option : tag.getAsJsonObject().getAsJsonArray("options")) { terms.add(option.getAsJsonObject().getAsJsonPrimitive("text").getAsString()); } }

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Old school ifs and forsList<String> terms = new ArrayList<>();

for (JsonElement tag : getAll("tag_suggest", suggestions)) { for (JsonElement option : getAll("options", tag)) { terms.add(getString("text", option)); } }

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List<String> terms = getAll("tag_suggest", suggestions).stream() .flatMap(tag -> getAll("options", tag).stream()) .map(option -> getString("text", option)) .collect(Collectors.toList());

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Lambdas everywhere!!!1!

Readability ≫ Style / LOC

Always code as if the person who ends up maintaining your code is a violent psychopath who knows where you live.

http://c2.com/cgi/wiki?CodeForTheMaintainer

OH NOES

NullPointerException!!?!© Fredrik Vraalsen 201

Optional<T>Wrapper object

Make explicit if a value is present or absent (empty)

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Optional examplepublic Optional<Image> getImage(Article article)

---

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Optional examplepublic Optional<Image> getImage(Article article)

---

Optional<Image> image = getImage(article);

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Check presencepublic Optional<Image> getImage(Article article)

---

Optional<Image> image = getImage(article);if (image.isPresent()) { doSomething(image.get());}

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---

Optional<Image> image = getImage(article);image.ifPresent(img -> doSomething(img));

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---

getImage(article).ifPresent(image -> doSomething(image));

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Default / fallback valuepublic Optional<Image> getImage(Article article)

---

Image image = getImage(article).orElse(defaultImage);

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Optional in / Optional outpublic Optional<String> getCaption(Optional<Image> image)

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Optional<Image> image = getImage(article);Optional<String> caption = getCaption(image);

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Optional in / Optional outpublic String getCaption(Image image)

---

Optional<Image> image = getImage(article);Optional<String> caption = ???

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Reaching into the void …public String getCaption(Image image)

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Optional<Image> image = getImage(article);Optional<String> caption = image.map(img -> getCaption(img));

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Reaching into the void …public String getCaption(Image image)

---

Optional<String> caption = getImage(article) .map(img -> getCaption(image));

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Bye bye NullPointerException?Marker – this may not return/contain value

Public APIs

Not a general solution to NPEs

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Optional + Streams = true?

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myStream.map(v -> functionReturningOptional(v))


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Stream<Optional<T>>


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Stream<Optional<T>> ⇒ Stream<T> ???

Guava Optional

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Iterable<T> presentInstances(Iterable<Optional<T>> optionals)


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public Optional<Image> getImage(Article article)

---

List<Image> images = articles.stream() // Stream<Article>


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---

List<Image> images = articles.stream() // Stream<Article> .map(article -> getImage(article)) // Stream<Optional<Image>>


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---

List<Image> images = articles.stream() // Stream<Article> .map(article -> getImage(article)) // Stream<Optional<Image>> .filter(Optional::ifPresent) .map(Optional::get) // Stream<Image>


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---

List<Image> images = articles.stream() // Stream<Article> .map(article -> getImage(article)) // Stream<Optional<Image>> .filter(Optional::ifPresent) .map(Optional::get) // Stream<Image> .collect(toList());

flatMap to the rescue!flatMap = map + flatten

Stream<Stream<T>> ⇒ Stream<T>

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flatMap to the rescue!flatMap = map + flatten

Stream<Optional<T>> ⇒ Stream<T> ???

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flatMap to the rescue!Easy to create helper functions

Stream<T> toStream(Optional<T> optValue)

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http://stackoverflow.com/questions/22725537/using-java-8s-optional-with-streamflatmap


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---

List<Image> images = articles.stream() // Stream<Article> .map(article -> getImage(article)) // Stream<Optional<Image>> .filter(Optional::ifPresent) .map(Optional::get) // Stream<Image> .collect(toList());

Optional + Streams = true

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---

List<Image> images = articles.stream() // Stream<Article> .flatMap(article -> toStream(getImage(article))) // Stream<Image> .collect(toList());

Optional + Streams = true

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---

List<Image> images = articles.stream() // Stream<Article> .flatMap(article -> getImage(article).stream()) // Stream<Image> .collect(toList());

Java 9

https://bugs.openjdk.java.net/browse/JDK-8050820

Take one stream and pass it around…

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public Stream<Image> getImage(Article article)

---

List<Image> images = articles.stream() // Stream<Article> .flatMap(article -> getImage(article)) // Stream<Image> .collect(toList());

No method handle for you!

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private Article elementToArticle(Map contentById, Element el)

---

List<Article> articles = elements.stream() .map(el -> elementToArticle(contentById, el)) .collect(toList())

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http://en.wikipedia.org/wiki/Malabar_matthi_curry#/media/File:Meen_curry_2_(cropped).JPG

Yummy currying!!

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Mapper mapper = new Mapper(contentById);

---

List<Article> articles = elements.stream() .map(el -> mapper.elementToArticle(el)) .collect(toList())

Yummy currying!!

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Mapper mapper = new Mapper(contentById);

---

List<Article> articles = elements.stream() .map(mapper::elementToArticle) .collect(toList())

Performance


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

http://www.nurkiewicz.com/2013/05/java-8-completablefuture-in-action.html

To parallelStream or not to …Batch?

parallelStream FTW!

Interactive? Concurrency?

CompletableFuture FTW!72

Taking the happy path!Try<RestResponse<ResolvedUri>> resolveURI(URI uri)

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public ResolvedSectionUri resolveSectionUri(String uri) { return client.resolveURI(uri))

??? Try<RestResponse<ResolvedUri>>

}

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---

public ResolvedSectionUri resolveSectionUri(String uri) { return client.resolveURI(uri)) .map(response -> response.getEntity())

??? Try<Optional<ResolvedUri>>

}

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---

public ResolvedSectionUri resolveSectionUri(String uri) { return client.resolveURI(uri)) .map(response -> response.getEntity().get())

??? Try<ResolvedUri>

}

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public ResolvedSectionUri resolveSectionUri(String uri) { return client.resolveURI(uri)) .map(response -> (ResolvedSectionUri) response.getEntity().get())

??? Try<ResolvedSectionUri>

}

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---

public ResolvedSectionUri resolveSectionUri(String uri) { return client.resolveURI(uri)) .map(response -> (ResolvedSectionUri) response.getEntity().get()) .orElse(null);

}

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---

public ResolvedSectionUri resolveSectionUri(String uri) { return client.resolveURI(uri)) .map(response -> (ResolvedSectionUri) response.getEntity().get()) .orElseGet(() -> { log.warn("Cannot resolve section from URI: {}", uri); return null; });}

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https://github.com/lambdista/try

More cool stuff in Java 8String join

Collection removeIf (≈ filter)

Map getOrDefault, putIfAbsent, replace, forEach, etc.

java.util.Optional

java.util.stream.Collectors

count, sum, average, min, max, groupingBy, etc.

java.nio.file.Files lines79

Functional programmingSimpler code

More robust

Better performance

Higher levelDeclarative

Less verbose

Less bugs?

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List<RoadData> filtered = new ArrayList<>();int count = 0; for (Iterator<RoadData> i = roadData.iterator(); i.hasNext() && count < 10; ) { RoadData data = i.next(); if (nameQuery.matches(data.getName())) { filtered.add(data); count++; } }


vs.

Pure functions

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Data In Data Out

Transformation

No external interactions

Functional core

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————- —— ——— —- — —- —-—————————— —- — —- ——————— — — — ——-——- —- — —————- ——— ——————- —— ———— - —-———- — —- — -

Pure functionsI/O I/O

Building blocks


What’s missing?Immutability

Value types

Data structures (lists, maps, etc.)

Concurrency

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What’s the big deal?Functional programming is all about values!

And transformations (functions) computing new values

Parallellism vs. Concurrency

Robustness

Testability

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Some help to be foundImmutable collections

Google Guava, FunctionalJava, clj-ds

Concurrency mechanisms

Akka (Actors, STM)

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github.com/krukow/clj-dsPersistentVector<Person> people = Persistents.vector( new Person("Fredrik", 39), new Person("Hedda", 3));

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PersistentVector<Person> morePeople = people.plus(new Person("Johannes", 5));

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PersistentVector<Person> morePeople = people.plus(new Person("Johannes", 5));

morePeople.stream() .forEach(p -> System.out.println(p.getName()));

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Why use X instead?Java 8 ready for enterprise dev?

JBoss AS, WebSphere – Nope

WildFly, GlassFish, WebLogic, Jetty, Tomcat – OK?

Important things are still missing from Java 8

Clojure and Scala available on JDK 6+!

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Questions?


fredriv

[email protected]

mailto:[email protected]

java 8 dos and don'ts - javabin oslo may 2015

Software

stream api

map articlesbycategory

return x

vs sortpeople

public int compareperson

new comparator

person y

whats new