Vavr - functional Java the easy way

@koenighotze Revenge of the JavaSlang

@koenighotze David Schmitz - @koenighotze

@koenighotze Sticker construction kit

@koenighotze

@koenighotze What’s in it for you?

@koenighotze Functional programming is hip How VAVR helped us Lot’s
of code - OMG!

@koenighotze Functors, applicatives, monads stay home

@koenighotze Code that is easier to reason about

@koenighotze Side-effects are evil

@koenighotze try { int i = 1/0; } catch (Throwable
t) { … } Exceptions are goto-statements :(

@koenighotze Referential Transparency

@koenighotze Math.random(); Math.max(1, 2); Math.random(); Math.max(1, 2); Pure functions are
a Good ThingTm :(

@koenighotze Thinking in values

@koenighotze Immutability Performance Safety

@koenighotze In a nutshell, think about “what to code“ not
“how to code”

@koenighotze Enter Java eight

@koenighotze (a) -> a + 2 list.stream().filter… Excitement…

@koenighotze until…

@koenighotze Try filtering all invalid users from a list of
users

@koenighotze users.stream() .filter(user -> { try { return user.validate(); }
catch (Exception ex) { return false; }}) .collect(Collectors.toList());

@koenighotze import static io.vavr.API.*;

@koenighotze Immutable collections Some functional sugar Functional exception handling Pattern
matching Property based testing Circuit breaker

@koenighotze Before we get to the details… Let’s fix that
ugly code

@koenighotze users.stream() .filter(user -> { try { return user.validate(); }

@koenighotze List.ofAll(users) .filter(user -> { try { return user.validate(); }

@koenighotze List.ofAll(users) .filter(user -> { try { return user.validate(); }
catch (Exception ex) { return false; }}); .collect(Collectors.toLis t());

@koenighotze List.ofAll(users) .filter(user -> Try.of(user::validate) .getOrElse(false) ); } catch (IllegalStateException
ex) { return ); .collect(Collectors.toList();

@koenighotze List.ofAll(users) List.filter(user -> Try.of(user::validate) .getOrElse(false));

@koenighotze immutable Collections

@koenighotze Mutable Collections are Evil

@koenighotze Returning void == side-effect! interface Collection<E> { … void
clear(); } interface Collection<E> { … void clear(); }

@koenighotze Collections .unmodifiableList(list); .add(“”)

@koenighotze Collections .unmodifiableList(list) .add(“”);

@koenighotze Painting by Gustav Courbet java.lang.UnsupportedOperationException at java.util.Collections$UnmodifiableCollection .add(Collections.java:1055) at
java.util.stream.AbstractPipeline.<init> (AbstractPipeline.java:203) at java.util.stream.ReferencePipeline.<init> (ReferencePipeline.java:94)

@koenighotze https://cdn.infoq.com/statics_s2_20170314-0434/resource/news/2016/11/the-road-to-javaslang-3/en/resources/1infoq-version2.0-library.png

@koenighotze Functional data structures

@koenighotze Immutable Referentially transparent Persistent

@koenighotze Effectively immutable

heroes = List.of("Han", "Luke") Cons@661 “Han” T Cons@666 “Luke” ()
heroes

Cons@661 “Han” T Cons@666 “Luke” () heroes Cons@662 “Ben” T
more more = heroes.prepend("Ben")

droids = TreeSet.of( "C3PO", "R2D2", "K2SO" ) Node@676 Node@679 Node@681
“K2SO” () () “C3PO” () () “R2D2”

droids.add("Chopper");

Node@689 Node@691 () Node@694 () () “Chopper” Node@676 Node@679 Node@681
“K2SO” () () “C3PO” () () “R2D2”

Checking for updates?

old == new

@koenighotze Streams are glorified iterators

@koenighotze Stream<String> jdk = Stream.of("a", “B"); jdk.map(String::toUpperCase); jdk.map(String::toLowerCase);

@koenighotze Painting by Gustav Courbet java.lang.IllegalStateException: stream has already been
operated upon or closed at java.util.stream.AbstractPipeline.<init> (AbstractPipeline.java:203) at java.util.stream.ReferencePipeline.<init> (ReferencePipeline.java:94)

@koenighotze vavr streams

Stream<String> vavr = Stream.of("a", "B"); slang.map(String::toUpperCase); // “A”,“B” slang.map(String::toLowerCase); //
“a”,“b”

@koenighotze Stream<String> vavr = Stream.of("a", "B"); vavr.map(String::toUpperCase) .take(2); vavr.map(String::toLowerCase) .take(2);

@koenighotze Stream<String> vavr = Stream.of("a", "B"); vavr.map(String::toUpperCase) .take(2);// “A”,“B” vavr.map(String::toLowerCase)
.take(2);// “a”,“b”

@koenighotze Better performance Less unexpected behaviour

@koenighotze functional Sugar

@koenighotze find a user and, if an address is available,
fetch the user’s street

@koenighotze User user = repo.findOne("id"); if (user != null) {
Address address = user.getAddress(); if (null != address) { return address.getStreet(); } }

@koenighotze Cascading Pile of Shame

@koenighotze optional

@koenighotze Optional<User> opt = Optional.ofNullable(user); if (opt.isPresent()) { User user
= opt.get(); }

And now, young coder... you will die.

@koenighotze map or flatmap There is no isPresent()

@koenighotze optional or option

@koenighotze Optional

@koenighotze Option Some None

@koenighotze Option Some None Value Iterable

@koenighotze Option Some None Value Iterable Serializable

@koenighotze option is A Gift Box

@koenighotze None Some

@koenighotze Map opens the Gift Box

@koenighotze Map Some Some ( )->

@koenighotze nothing from nothing

@koenighotze ( )-> Map None None

@koenighotze Fixing the Pile of Shame

@koenighotze User user = repo.findOne("id"); if (user != null) {

@koenighotze Option<User> user = repo.findOne("id"); if (user != null) {

@koenighotze Option<User> user = repo.findOne("id"); user.flatMap(User::getAddress) Address address = user.getAddress();
if (null != address) { return address.getStreet(); } } Option<User> user = repo.findOne("id"); user.flatMap(User::getAddress) Address address = user.getAddress(); if (null != address) { return address.getStreet(); } } Option<Address> getAddress()

if (null != address) { return address.getStreet(); } }

.map(Address::getStreet) return address.getStreet(); } }

repo.findOne("id") .flatMap(User::getAddress) .map(Address::getStreet) .getOrElse("");

@koenighotze option.of(value) .map(nested code) == understandable story

@koenighotze functional exception Handling

@koenighotze validation like back in the days

@koenighotze public static String check(String iban){ if (validationMagic(iban)) { return
iban; } throw new IllegalArgumentException(“Peng”); }

@koenighotze Partial function

@koenighotze Awesome WTF Code

@koenighotze String iban; try { iban = check(“AL47…”); } catch
(IllegalArgumentException ex) { iban = ""; }

@koenighotze Lifting Exceptions to options

@koenighotze total function

@koenighotze String iban = lift(Iban::check) .apply("AL47...") .getOrElse("");

@koenighotze Wrapping Exceptions with Try

@koenighotze Try.of(() -> stuffToDo())

@koenighotze Failure Exception Success Result Try.of(() -> stuffToDo())

@koenighotze Try.of(() -> check("AL..")) .getOrElse("")

@koenighotze Lifting and Try-ing reduce exception handling clutter and side-effects

@koenighotze Structural decomposition

@koenighotze Structural decomposition discouraged! http://cr.openjdk.java.net/ ~briangoetz/amber/pattern- match.html

@koenighotze (?:[a-z0-9!#$%&'*+/=?^_`{|}~-]+(?:\.[a-z0-9!#$%&'*+/=? ^_`{|}~-]+)*|"(?:[\x01-\x08\x0b\x0c\x0e-\x1f\x21\x23- \x5b\x5d-\x7f]|\\[\x01-\x09\x0b\x0c\x0e-\x7f])*")@(?:(?: [a-z0-9](?:[a-z0-9-]*[a-z0-9])?\.)+[a-z0-9](?:[a- z0-9-]*[a-z0-9])?|\[(?:(?:25[0-5]|2[0-4][0-9]|[01]?[0-9] [0-9]?)\.){3}(?:25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?|[a- z0-9-]*[a-z0-9]:(?:[\x01-\x08\x0b\x0c\x0e-\x1f\x21- \x5a\x53-\x7f]|\\[\x01-\x09\x0b\x0c\x0e-\x7f])+)\]) Pattern
Matching Basics

@koenighotze Match(expression) .of(cases)

@koenighotze Case(pattern, function)

@koenighotze $() wildcard pattern $(“foo”) equals pattern isIn(“a”, “b”) conditional
pattern

@koenighotze Classic HTTP Handling

@koenighotze if (OK.equals(res.getStatusCode())) { return res.getBody(); } return emptyList();

@koenighotze Functional version

@koenighotze Note: some type details missing Match(res.getStatusCode()) .of(  Case($(OK), res.getBody()), 
Case($(), emptyList())  );

@koenighotze Match(res.getStatusCode()) .of(  Case($(OK), res.getBody()),  Case($(), emptyList())  ); Note: some
type details missing OK or anything else

@koenighotze Note: some type details missing Match(res.getStatusCode()) .of(  Case($(OK), res.getBody()), 
Case($(), emptyList())  );

@koenighotze Match(res.getStatusCode()) .of(  Case($(OK), res.getBody()),  Case($(), emptyList())  ); Note: some
type details missing

@koenighotze Matching a Try

@koenighotze public Try<…> fetchFromUrl(…) { … }

@koenighotze Match(fetchFromUrl(“…”)) .of( Case(Success($()), identity()), Case(Failure($()), emptyList()) );

@koenighotze Match(fetchFromUrl(“…”)) .of( Case($Success($()), identity()), Case($Failure($()), emptyList()) );

@koenighotze Pattern matching replaces complex if- then-else sequences with clear
expressions

@koenighotze property tEST

@koenighotze property Based - The idea

@koenighotze Declarative, infinite test cases Have you tested for all
characters… …even for ? Have you tested usernames like… ౧ప唆⏑㐿䯰㨼ᮁ娤㮘?搃蘸阁㌃ᡧ㫈葷㖒ܪ匘ᤫ䳴㻅 ⦷♻痯ヲ㙃銐璚ೃⶕᄰ 䩰㒭㙵闆䩟嗀嗀侀

@koenighotze vavr property test

@koenighotze Property.def(“Something works”) .forAll(Generated Data) .suchThat(Checked Function) .check() .assertIsSatisfied();

@koenighotze Arbitrary<String> arbitraryUnicodeId() { Gen<Character> id = r -> (char)
r.nextInt(); return Arbitrary.string(id); }

@koenighotze Property .def("Should not go boom”) .forAll(arbitraryUnicodeString()) .suchThat(id -> isOkOrNotFound(id))
.check() .assertIsSatisfied();

@koenighotze 2017-03-21 10:45:59.913 INFO 45701 --- FrameworkServlet '': initialization started
2017-03-21 10:45:59.925 INFO 45701 --- FrameworkServlet '': initialization completed in 12 ms Storing User@217b0952[username=rwxbeoigyesbeqqz,email=W`[email protected], Storing User@4e6280de[username=vptafghfwuwwrwall,[email protected],,, Storing User@2fca282c[username=qmhkjdtvbtjzfciwcceqgzfznzkhhcokiyoipdefbr,[email protected]. Storing User@64d53f0d[publicId=e9d7a121-9f23-483a-828a-f9e3045fc297,username=unflrpvztxtmi... ... Storing User@1b10f60e[publicId=6f084c18-415c-42c4-b1a8-00c5c1fc9e67,username=xwhpdpjowirsmjym... Storing User@4b916cc2[publicId=a2b9db2c-0189-4fe8-843d-e709ef3886fa,username=yxdidpexnayyjpzo... Should not go boom: OK, passed 1000 tests in 3719 ms.

@koenighotze Should not go boom: Falsified after 23 passed tests
in 3005 ms. java.lang.AssertionError: Expected satisfied check result but was Falsified(…, sample = ( 䒖 ꜏, 燤䠽㏊密ᵓ〞খﾡ ꌎ ⬆鹮 ۄ鄽㏫魨 ࠞ⽆⢕ 㣁㸎Ԩ 䏨➰ìឧ寅罟溌椡ﲡࣇ欙ㄓῴﯯ缲ꢶꇞ⌽ꪂ惗㛨蘄䏄⩂粻ㇼ?ವ㝓㭃, fzqlbkljxhfrghllzcthvgqiglaabihkzgsqwgfcichamyonmayiewwsfwmw ntzvozqqydkqillhpyi, [email protected] V74.E.-----2T.z97..3f1ZM6))

@koenighotze functional resilience

@koenighotze Circuit breaker one-o-one

@koenighotze Consumer Backend

@koenighotze Fallback Resilience decorator Closed Open Half-Open Consumer Backend

@koenighotze Resilience decorator Closed Open Half-Open Consumer Fallback

@koenighotze Fallback Resilience decorator Closed Open Half-Open Consumer

@koenighotze Resilience For J

@koenighotze Backend Consumer Backend Service Resilience decorator Circuit Breaker Retry
Cache

@koenighotze Option<…> fetchBoard(String id) { result = restTemplate.getForEntity(…); return Match(result.getStatusCode())
.option(…); }

@koenighotze CircuitBreaker .decorateCheckedFunction( circuitBreaker, db::fetchBoard);

@koenighotze Try.of(() -> decorated.apply(stationId)) .getOrElse(empty())

@koenighotze The last monad?

@koenighotze http://www.vavr.io/

@koenighotze Spring data integration

@koenighotze interface UserRepository extends MongoRepository<User, String> { Option<User> findByPublicId(String publicId);
Seq<User> findByLastname(String lastname); }

@koenighotze Resilience for J

@koenighotze CircuitBreaker .decorateCheckedFunction( circuitBreaker, db::fetchBoard);

@koenighotze Property based tests

@koenighotze Property .def("Should not go boom”) .forAll(arbitraryUnicodeString()) .suchThat(id -> isFoundOrNotFound(id))
.check() .assertIsSatisfied();

@koenighotze So, is this is the mother of all free
lunches?

@koenighotze What are the drawbacks?

@koenighotze

@koenighotze count(Collection-libs) > count(Logging-libs)

@koenighotze Option.of(foo) .map .filter .flatMap .map .flatMap .getOrElse(null) N O
T a drawback!

@koenighotze version one

@koenighotze Modularization Alignment with Java 9 Obsolete pattern match (maybe)
http://blog.vavr.io/fast-forward-to-vavr-1-0/

@koenighotze Wrapping up

@koenighotze Slick, stable, non-invasive, consistent API Object-functional advantages now Complex(?)
Property test(?) Pattern match(?)

@koenighotze RESIST THE TYRANNY OF THE COLLECTIONS FRAMEWORK JOIN THE
RESISTANCE!

@koenighotze thank you @Koenighotze

Vavr - functional Java the easy way

Vavr - functional Java the easy way

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