Javaslang Talk @ Javaland 2017

#JavalandJavaslang @koenighotze

java slang

The Monad strikes back


David Schmitz - koenighotze

Senacor Technologies Principal Architect

Programmer! Thats me coding Scala


Whats in it for you?

Functional programming is hip

How Javaslang helped us

Live Code - OMG!

Becaus

e of B

eamer


Functors, applicatives, monads

stay home


Code that is easier to reason about


Side-effects are eviltry { int i = 1/0; } catch (Throwable t) { }Exceptions are goto-statements

:(


Referential Transparency

Math.random();

Math.max(1, 2);

Math.random();

Math.max(1, 2);

Pure functions are a Good ThingTm

:(


Thinking in values

Immutability

Performance

Safety


In a nutshell, think about what to code

not how to code


Enter java Eight

(a) -> a + 2

list.stream().filter

Excitement


Try filtering all invalid users from

a list of users


Excitement?untilusers.stream() .filter(user -> { try { return user.validate(); } catch (Exception ex) { return false; }}) .collect(Collectors.toList());


import static javaslang.API.*;


What well coverImmutable collections

Some functional sugar

Pattern matching

Property based testing

Circuit breaker


Before we get to the details

Lets fix that ugly code


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


Functional collectionsList.ofAll(users) .filter(user -> { try { return user.validate(); } catch (Exception ex) { return false; }}) .collect(Collectors.toList());


No need for CollectorsList.ofAll(users) .filter(user -> { try { return user.validate(); } catch (Exception ex) { return false; }}) .collect(Collectors.toList());


No need for CollectorsList.ofAll(users) .filter(user -> { try { return user.validate(); } catch (Exception ex) { return false; }}); .collect(Collectors.toList());


Wrapping ExceptionsList.ofAll(users) .filter(user -> { try { return user.validate(); } catch (Exception ex) { return false; }}); .collect(Collectors.toList());


Wrapping ExceptionsList.ofAll(users) .filter(user ->

Try.of(user::validateAddress) .getOrElse(false) ); } catch (IllegalStateException ex) { return ); .collect(Collectors.toList();


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


immutable Collections


Mutable Collections are Evil

Returning void == Side-Effect!

interface Collection { void clear(); }

interface Collection { void clear(); }


java.util.Collections

Collections .unmodifiableList(list); .add()


java.util.Collections

Collections .unmodifiableList(list) .add();

#JavalandJavaslang @koenighotzePainting by Gustav Courbet

java.lang.UnsupportedOperationException at java.util.Collections$UnmodifiableCollection.add(Collections.java:1055) at java.util.stream.AbstractPipeline. (AbstractPipeline.java:203) at java.util.stream.ReferencePipeline. (ReferencePipeline.java:94)


Javaslang Collections

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


Functional data structures

Immutable

Referentially transparent

Persistent


heroes = List.of("Han", "Luke")

Cons@661 Han T

Cons@666 Luke ()

heroes

Effectively immutable


Cons@661 Han T

Cons@666 Luke ()

heroes

Cons@662 Ben Tmore

more = heroes.prepend("Ben")



droids = TreeSet.of( "C3PO", "R2D2", "K2SO" )

Node@676

Node@679 Node@681K2SO

() ()C3PO

() ()R2D2



droids.add("Chopper");



Node@689

Node@691

() Node@694

() ()Chopper

Node@676

Node@679 Node@681K2SO

() ()C3PO

() ()R2D2



old == new

Checking for updates?


Streams are glorified iterators

Stream jdk = Stream.of("a", B");

jdk.map(String::toUpperCase); jdk.map(String::toLowerCase);

#JavalandJavaslang @koenighotzePainting by Gustav Courbet

java.lang.IllegalStateException: stream has already been operated upon or closed at java.util.stream.AbstractPipeline. (AbstractPipeline.java:203) at java.util.stream.ReferencePipeline. (ReferencePipeline.java:94)


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

Javaslang streams


Javaslang StreamsStream slang = Stream.of("a", "B"); slang.map(String::toUpperCase) .take(2); slang.map(String::toLowerCase) .take(2);


Javaslang StreamsStream slang = Stream.of("a", "B"); slang.map(String::toUpperCase) .take(2);// A,B slang.map(String::toLowerCase) .take(2);// a,b


Better performance Less unexpected behaviour

#Devoxx #Javaslang @koenighotze

functional Sugar


find a user and, if an address is

available, fetch the users street


Cascading Pile of ShameUser user = repo.findOne("id"); if (user != null) { Address address = user.getAddress(); if (null != address) {

return address.getStreet(); } }


optional?

Optional opt = Optional.ofNullable(user);

if (optional.isPresent()) { User user = optional.get(); }


And now, young coder...

you will die.


map or flatmap There is no isPresent()


optional or option?

Optional


optional or option?

Option

Some None


optional or option?

Option

Some None

Value

Iterable


optional or option?

Option

Some None

Value

Iterable

Serializable


An option is like a Gift Box

NoneSome


Map opens the Gift Box

MapSome Some

( )->


nothing from nothing

( )->

MapNone None


Fixing the Pile of ShameUser user = repo.findOne("id"); if (user != null) { Address address = user.getAddress(); if (null != address) {



option all the ThingsUser user = repo.findOne("id"); if (user != null) { Address address = user.getAddress(); if (null != address) {



option all the ThingsOption user = repo.findOne("id"); if (user != null) { Address address = user.getAddress(); if (null != address) {



option all the ThingsOption user = repo.findOne("id"); user.flatMap(User::getAddress) Address address = user.getAddress(); if (null != address) {


Option user = repo.findOne("id"); user.flatMap(User::getAddress) Address address = user.getAddress(); if (null != address) {

return address.getStreet(); } } Option getAddress()


option all the ThingsOption user = repo.findOne("id"); user.flatMap(User::getAddress) Address address = user.getAddress(); if (null != address) {



option all the ThingsOption user = repo.findOne("id"); user.flatMap(User::getAddress) Address address = user.getAddress(); .map(Address::getStreet)



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


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


working with legacy code


Nice validation Codepublic static String check(String iban){ if (validationMagic(iban)) { return iban; }

throw new IllegalArgumentException(Peng); }


Awesome WTF Code String iban; try { iban = check(AL47); } catch (IllegalArgumentException ex) { iban = ""; }


From Exceptions to options

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


Wrapping Exceptions with Try

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


Wrapping Exceptions with Try

FailureException

SuccessResult

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


Exceptions to options with Try

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


Lifting and Try-ing reduce exception handling

clutter and side-effects


Structural Decomposition


(?:[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


Pattern Matching Basics

Match(expression) .of(cases)


Cases map patterns to function

Case(pattern, function)


Example Patterns

$() wildcard pattern $(foo) equals pattern isIn(a, b) conditional pattern


Classic HTTP Handlingif (OK.equals(res.getStatusCode())) { return res.getBody(); }

return emptyList();


HTTP Handling Fixed

*Note: some type details missing

Match(res.getStatusCode()) .of( Case($(OK), res.getBody()), Case($(), emptyList()) );



HTTP Handling Fixed


OK or anything else


HTTP Handling Fixed




Matching a Try

public Try fetchFromUrl() { }


Matching a Try

Match(fetchFromUrl()) .of( Case(Success($()), identity()), Case(Failure($()), emptyList()) );


Presto

Match(fetchFromUrl()) .of( Case(Success($()), identity()), Case(Failure($()), emptyList()) );


Pattern matching replaces complex if-then-else sequences

with clear expressions


property tEST


property Based - The idea

Describe the arguments

Describe the results

Let the olde computer prove you wrong


Javaslang property test

Property.def(Add works") .forAll(Generated Data) .suchThat(Checked Function) .check() .assertIsSatisfied();


Javaslang property test

Property.def(Add works") .forAll(integer(), integer()) .suchThat( (a,b)-> calc.add(a, b) == a + b) .check() .assertIsSatisfied();


Running tests2017-03-21 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.


FailuresShould not go boom: Falsified after 23 passed tests in 3005 ms.

java.lang.AssertionError: Expected satisfied check result but was Falsified(,

sample = (, ?,

fzqlbkljxhfrghllzcthvgqiglaabihkzgsqwgfcichamyonmayiewwsfwmwntzvozqqydkqillhpyi, [email protected]))


Why property Based tests?Declarative, infinit test cases

Have you tested for all characters even for ?

Have you tested usernames like ?


functional resilience


Circuit breaker one-o-one

Consumer Backend


Fallback

Resilience decorator

Circuit breaker one-o-oneClosed

Open

Half-Open

Consumer




Open

Half-Open

Consumer

Fallback


Fallback



Open

Half-Open

Consumer


Resilience For J

BackendConsumerBackend Service


Circuit Breaker

Retry

Cache


Option fetchBoard(String id) { result = restTemplate.getForEntity();

return Match(result.getStatusCode()) .option(); }

flakey functions


Decorators.ofCheckedFunction(db::fetchBoard) .withCircuitBreaker(circuitBreaker) .decorate();

Decorating a function


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

Functional resilience


final celebration


HashMap.of("Foo", "Bar", "Qux", "Baz")

Tuple.of("Foo", 1)

String help = TODO("Implement me")

Javaslang offers much more


Javaslang offers much more


So, is this is the mother of all free

lunches?


What are the drawbacks?


What are the drawbacks?

count(Collection-libs)

>

count(Logging-libs)


What are the drawbacks?Option.of(foo) .map .filter .flatMap .map .flatMap .getOrElse(null)

NOT a drawback!


Wrapping up

Slick, stable, consistent API

Object-functional advantages now

Complex(?)

Version 3 coming soon!


RESISTTHE TYRANNY OF THE

COLLECTIONS FRAMEWORKJOIN THE RESISTANCE!


thank you

david.schmitz at senacor.com

Technology

Javaslang Talk @ Javaland 2017