Javaslang Demo @ Javaland 2017

1. #JavalandJavaslang @koenighotze
java
slang
The Monad strikes back

2. #JavalandJavaslang @koenighotze
David Schmitz - koenighotze
Senacor Technologies
Principal Architect
Programmer!
That’s me coding Scala

3. #JavalandJavaslang @koenighotze
What’s in it for you?
Functional programming is hip
How Javaslang helped us
Live Code - OMG!
Because
of
Beamer

4. #JavalandJavaslang @koenighotze
Functors,
applicatives, monads
stay home

5. #JavalandJavaslang @koenighotze
Code that is easier
to reason about

6. #JavalandJavaslang @koenighotze
Side-effects are evil
try {
int i = 1/0;
} catch (Throwable t) {
…
}
Exceptions are goto-statements
:(

7. #JavalandJavaslang @koenighotze
Referential Transparency
Math.random();
Math.max(1, 2);
Math.random();
Math.max(1, 2);
Pure functions are a Good ThingTm
:(

8. #JavalandJavaslang @koenighotze
Thinking in values
Immutability
Performance
Safety

9. #JavalandJavaslang @koenighotze
In a nutshell, think about
“what to code“
not
“how to code”

10. #JavalandJavaslang @koenighotze
Enter java Eight
(a) -> a + 2
list.stream().filter…
Excitement…

11. #JavalandJavaslang @koenighotze
Try filtering all
invalid users from
a list of users

12. #JavalandJavaslang @koenighotze
Excitement?…until
users.stream()
.filter(user -> {
try {
return user.validate();
} catch (Exception ex) {
return false;
}})
.collect(Collectors.toList());

13. #JavalandJavaslang @koenighotze
import static javaslang.API.*;

14. #JavalandJavaslang @koenighotze
What we’ll cover
Immutable collections
Some functional sugar
Pattern matching
Property based testing
Circuit breaker

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

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

17. #JavalandJavaslang @koenighotze
Functional collections
List.ofAll(users)
.filter(user -> {
try {
return user.validate();
} catch (Exception ex) {
return false;
}})
.collect(Collectors.toList());

18. #JavalandJavaslang @koenighotze
No need for Collectors
List.ofAll(users)
.filter(user -> {
try {
return user.validate();
} catch (Exception ex) {
return false;
}})
.collect(Collectors.toList());

19. #JavalandJavaslang @koenighotze
No need for Collectors
List.ofAll(users)
.filter(user -> {
try {
return user.validate();
} catch (Exception ex) {
return false;
}}); .collect(Collectors.toLis
t());

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

21. #JavalandJavaslang @koenighotze
Wrapping Exceptions
List.ofAll(users)
.filter(user ->
Try.of(user::validateAddress)
.getOrElse(false)
); } catch (IllegalStateException
ex) { return
); .collect(Collectors.toList();

22. #JavalandJavaslang @koenighotze
List.ofAll(users)
List.filter(user ->
Try.of(user::validateAddress)
.getOrElse(false));

23. #JavalandJavaslang @koenighotze
immutable Collections

24. #JavalandJavaslang @koenighotze
Mutable Collections are Evil
Returning void == Side-Effect!
interface Collection<E> {
…
void clear();
}
interface Collection<E> {
…
void clear();
}

25. #JavalandJavaslang @koenighotze
java.util.Collections
Collections
.unmodifiableList(list);
.add(“💥”)

26. #JavalandJavaslang @koenighotze
java.util.Collections
Collections
.unmodifiableList(list)
.add(“💥”);

27. #JavalandJavaslang @koenighotzePainting 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)

28. #JavalandJavaslang @koenighotze
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

29. #JavalandJavaslang @koenighotze
Functional data structures
Immutable
Referentially transparent
Persistent

30. #JavalandJavaslang @koenighotze
heroes = List.of("Han", "Luke")
Cons@661 “Han” T
Cons@666 “Luke” ()
heroes
Effectively immutable

31. #JavalandJavaslang @koenighotze
Cons@661 “Han” T
Cons@666 “Luke” ()
heroes
Cons@662 “Ben” Tmore
more = heroes.prepend("Ben")
Effectively immutable

32. #JavalandJavaslang @koenighotze
droids =
TreeSet.of(
"C3PO",
"R2D2",
"K2SO"
)
Node@676
Node@679 Node@681“K2SO”
() ()“C3PO”
() ()“R2D2”
Effectively immutable

33. #JavalandJavaslang @koenighotze
droids.add("Chopper");
Effectively immutable

34. #JavalandJavaslang @koenighotze
Node@689
Node@691
() Node@694
() ()“Chopper”
Node@676
Node@679 Node@681“K2SO”
() ()“C3PO”
() ()“R2D2”
Effectively immutable

35. #JavalandJavaslang @koenighotze
old == new
Checking for updates?

36. #JavalandJavaslang @koenighotze
Streams are glorified iterators
Stream<String> jdk
= Stream.of("a", “B");
jdk.map(String::toUpperCase);
jdk.map(String::toLowerCase);

37. #JavalandJavaslang @koenighotzePainting 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)

38. #JavalandJavaslang @koenighotze
Stream<String> slang =
Stream.of("a", "B");
slang.map(String::toUpperCase);
// “A”,“B”
slang.map(String::toLowerCase);
// “a”,“b”
Javaslang streams

39. #JavalandJavaslang @koenighotze
Javaslang Streams
Stream<String> slang =
Stream.of("a", "B");
slang.map(String::toUpperCase)
.take(2);
slang.map(String::toLowerCase)
.take(2);

40. #JavalandJavaslang @koenighotze
Javaslang Streams
Stream<String> slang =
Stream.of("a", "B");
slang.map(String::toUpperCase)
.take(2);// “A”,“B”
slang.map(String::toLowerCase)
.take(2);// “a”,“b”

41. #JavalandJavaslang @koenighotze
Better performance
Less unexpected behaviour

42. #Devoxx #Javaslang @koenighotze
functional Sugar

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

44. #JavalandJavaslang @koenighotze
Cascading Pile of Shame
User user = repo.findOne("id");
if (user != null) {
Address address = user.getAddress();
if (null != address) {
return address.getStreet();
}
}

45. #JavalandJavaslang @koenighotze
optional?
Optional<User> opt =
Optional.ofNullable(user);
if (optional.isPresent()) {
User user = optional.get();
}

46. #JavalandJavaslang @koenighotze
And now, young
coder...
you will die.

47. #JavalandJavaslang @koenighotze

48. #JavalandJavaslang @koenighotze
map or flatmap
There is no
isPresent()

49. #JavalandJavaslang @koenighotze
optional or option?
Optional

50. #JavalandJavaslang @koenighotze
optional or option?
Option
Some None

51. #JavalandJavaslang @koenighotze
optional or option?
Option
Some None
Value
Iterable

52. #JavalandJavaslang @koenighotze
optional or option?
Option
Some None
Value
Iterable

53. #JavalandJavaslang @koenighotze
optional or option?
Option
Some None
Value
Iterable
Serializable

54. #JavalandJavaslang @koenighotze
An option is like a Gift Box
NoneSome

55. #JavalandJavaslang @koenighotze
Map opens the Gift Box
Map
Some Some
( )->

56. #JavalandJavaslang @koenighotze
nothing from nothing
( )->
Map
None None

57. #JavalandJavaslang @koenighotze
Fixing the Pile of Shame
User user = repo.findOne("id");
if (user != null) {
Address address = user.getAddress();
if (null != address) {
return address.getStreet();
}
}

58. #JavalandJavaslang @koenighotze
option all the Things
User user = repo.findOne("id");
if (user != null) {
Address address = user.getAddress();
if (null != address) {
return address.getStreet();
}
}

59. #JavalandJavaslang @koenighotze
option all the Things
Option<User> user = repo.findOne("id");
if (user != null) {
Address address = user.getAddress();
if (null != address) {
return address.getStreet();
}
}

60. #JavalandJavaslang @koenighotze
option all the Things
Option<User> user = repo.findOne("id");
if (user != null) {
Address address = user.getAddress();
if (null != address) {
return address.getStreet();
}
}

61. #JavalandJavaslang @koenighotze
option all the Things
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()

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

63. #JavalandJavaslang @koenighotze
option all the Things
Option<User> user = repo.findOne("id");
user.flatMap(User::getAddress)
Address address = user.getAddress();
.map(Address::getStreet)
return address.getStreet();
}
}

64. #JavalandJavaslang @koenighotze
repo.findOne("id")
.flatMap(User::getAddress)
.map(Address::getStreet)
.getOrElse("");

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

66. #JavalandJavaslang @koenighotze
working with legacy code

67. #JavalandJavaslang @koenighotze
Nice validation Code
public static String check(String iban){
if (validationMagic(iban)) {
return iban;
}
throw new IllegalArgumentException(“Peng”);
}

68. #JavalandJavaslang @koenighotze
Awesome WTF Code
String iban;
try {
iban = check(“AL47…”);
}
catch (IllegalArgumentException ex) {
iban = "";
}

69. #JavalandJavaslang @koenighotze
From Exceptions to options
String iban = lift(Iban::check)
.apply("AL47...")
.getOrElse("");

70. #JavalandJavaslang @koenighotze
From Exceptions to options
String iban = lift(Iban::check)
.apply("AL47...")
.getOrElse("");

71. #JavalandJavaslang @koenighotze
Wrapping Exceptions with Try
Try.of(() -> stuffToDo())

72. #JavalandJavaslang @koenighotze
Wrapping Exceptions with Try
Failure
Exception
Success
Result
Try.of(() -> stuffToDo())

73. #JavalandJavaslang @koenighotze
Exceptions to options with Try
Try.of(() -> check("AL.."))
.getOrElse("")

74. #JavalandJavaslang @koenighotze
Exceptions to options with Try
Try.of(() -> check("AL.."))
.getOrElse("")

75. #JavalandJavaslang @koenighotze
Lifting and Try-ing reduce
exception handling
clutter and side-effects

76. #JavalandJavaslang @koenighotze
Structural Decomposition

77. #JavalandJavaslang @koenighotze
(?:[a-z0-9!#$%&'*+/=?^_`{|}~-]+(?:.[a-z0-9!#$%&'*+/=?
^_`{|}~-]+)*|"(?:[x01-x08x0bx0cx0e-x1fx21x23-
x5bx5d-x7f]|[x01-x09x0bx0cx0e-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-x08x0bx0cx0e-x1fx21-
x5ax53-x7f]|[x01-x09x0bx0cx0e-x7f])+)])
Pattern Matching Basics

78. #JavalandJavaslang @koenighotze
Pattern Matching Basics
Match(expression)
.of(cases)

79. #JavalandJavaslang @koenighotze
Cases map patterns to function
Case(pattern, function)

80. #JavalandJavaslang @koenighotze
Example Patterns
$() wildcard pattern
$(“foo”) equals pattern
isIn(“a”, “b”) conditional pattern

81. #JavalandJavaslang @koenighotze
Classic HTTP Handling
if (OK.equals(res.getStatusCode()))
{
return res.getBody();
}
return emptyList();

82. #JavalandJavaslang @koenighotze
HTTP Handling Fixed
*Note: some type details missing
Match(res.getStatusCode())
.of(
Case($(OK), res.getBody()),
Case($(), emptyList())
);

83. #JavalandJavaslang @koenighotze
Match(res.getStatusCode())
.of(
Case($(OK), res.getBody()),
Case($(), emptyList())
);
HTTP Handling Fixed
*Note: some type details missing
OK or anything else

84. #JavalandJavaslang @koenighotze
HTTP Handling Fixed
*Note: some type details missing
Match(res.getStatusCode())
.of(
Case($(OK), res.getBody()),
Case($(), emptyList())
);

85. #JavalandJavaslang @koenighotze
HTTP Handling Fixed
*Note: some type details missing
Match(res.getStatusCode())
.of(
Case($(OK), res.getBody()),
Case($(), emptyList())
);

86. #JavalandJavaslang @koenighotze
HTTP Handling Fixed
Match(res.getStatusCode())
.of(
Case($(OK), res.getBody()),
Case($(), emptyList())
);
*Note: some type details missing

87. #JavalandJavaslang @koenighotze
Matching a Try
public Try<…> fetchFromUrl(…) {
…
}

88. #JavalandJavaslang @koenighotze
Matching a Try
Match(fetchFromUrl(“…”))
.of(
Case(Success($()), identity()),
Case(Failure($()), emptyList())
);

89. #JavalandJavaslang @koenighotze
Matching a Try
Match(fetchFromUrl(“…”))
.of(
Case(Success($()), identity()),
Case(Failure($()), emptyList())
);

90. #JavalandJavaslang @koenighotze
Matching a Try
Match(fetchFromUrl(“…”))
.of(
Case(Success($()), identity()),
Case(Failure($()), emptyList())
);

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

92. #JavalandJavaslang @koenighotze
Pattern matching
replaces complex if-
then-else sequences
with clear expressions

93. #JavalandJavaslang @koenighotze
property tEST

94. #JavalandJavaslang @koenighotze
property Based - The idea
Describe the arguments
Describe the results
Let the olde computer prove you
wrong

95. #JavalandJavaslang @koenighotze
Javaslang property test
Property.def(“Add works")
.forAll(Generated Data)
.suchThat(Checked Function)
.check()
.assertIsSatisfied();

96. #JavalandJavaslang @koenighotze
Javaslang property test
Property.def(“Add works")
.forAll(integer(), integer())
.suchThat(
(a,b)-> calc.add(a, b) == a + b)
.check()
.assertIsSatisfied();

97. #JavalandJavaslang @koenighotze
Running tests
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`a@0c..-.--db-.T5-.2-g,
Storing User@4e6280de[username=vptafghfwuwwrwall,email=sByP@6jLA4.J.1c..5h269O3-1M6-c6...-.-,,,
Storing User@2fca282c[username=qmhkjdtvbtjzfciwcceqgzfznzkhhcokiyoipdefbr,email=Q96!@6.n8.
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.

98. #JavalandJavaslang @koenighotze
Failures
Should not go boom: Falsified after 23 passed tests in 3005 ms.
java.lang.AssertionError: Expected satisfied check result but was Falsified(…,
sample = ( 풧 ꜏, 燤䠽뾌密ᵓ뫶খﾡ ꌎ ⬆鹮 라鄽뾮魨 붐맧놌 엍첮
䏨➰ìឧ寅罟 溌椡‫ﲡ‬셋欙밶ῴ‫ﯯ‬缲ꢶꇞ⌽ꪂ惗 쎂蘄펮뎷粻뵞?푠쏽쥎,
fzqlbkljxhfrghllzcthvgqiglaabihkzgsqwgfcichamyonmayiewwsfwmw
ntzvozqqydkqillhpyi, +g4@F.8yOkj.-....C6GUP..3.4.-..h-
V74.E.-----2T.z97..3f1ZM6))

99. #JavalandJavaslang @koenighotze
Why property Based tests?
Declarative, infinit test cases
Have you tested for all characters…
…even for 💩?
Have you tested usernames like…
౧ప唆⏑쀋䯰㨼ᮁ娤즶?搃蘸阁뺬ᡧ㫈葷㖒‫ܪ‬匘ᤫ䳴㻅
댇껓痯믶㙃銐璚풔랾ᄰ 䩰삀싲闆䩟嗀嗀侀

100. #JavalandJavaslang @koenighotze
functional resilience

101. #JavalandJavaslang @koenighotze
Circuit breaker one-o-one
Consumer Backend

102. #JavalandJavaslang @koenighotze
Fallback
Resilience decorator
Circuit breaker one-o-one
Closed
Open
Half-Open
Consumer

103. #JavalandJavaslang @koenighotze
Resilience decorator
Circuit breaker one-o-one
Closed
Open
Half-Open
Consumer
Fallback

104. #JavalandJavaslang @koenighotze
Fallback
Resilience decorator
Circuit breaker one-o-one
Closed
Open
Half-Open
Consumer

105. #JavalandJavaslang @koenighotze
Fallback
Resilience decorator
Circuit breaker one-o-one
Closed
Open
Half-Open
Consumer

106. #JavalandJavaslang @koenighotze
Resilience For J
BackendConsumer
Backend
Service
Resilience decorator
Circuit Breaker
Retry
Cache

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

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

109. #JavalandJavaslang @koenighotze
Decorators.ofCheckedFunction(db::fetchBoard)
.withCircuitBreaker(circuitBreaker)
.decorate();
Decorating a function

110. #JavalandJavaslang @koenighotze
Try.of(() -> decorated.apply(stationId))
.getOrElse(Option.of(empty()))
Functional resilience

111. #JavalandJavaslang @koenighotze
final celebration

112. #JavalandJavaslang @koenighotze
HashMap.of("Foo", "Bar",
"Qux", "Baz")
Tuple.of("Foo", 1)
String help = TODO("Implement me")
Javaslang offers much more

113. #JavalandJavaslang @koenighotze
Javaslang offers much more

114. #JavalandJavaslang @koenighotze
So, is this is the
mother of all free
lunches?

115. #JavalandJavaslang @koenighotze
What are the drawbacks?

116. #JavalandJavaslang @koenighotze
What are the drawbacks?
count(Collection-libs)
>
count(Logging-libs)

117. #JavalandJavaslang @koenighotze
What are the drawbacks?
Option.of(foo)
.map
.filter
.flatMap
.map
.flatMap
.getOrElse(null)
N
O
T
a
drawback!

118. #JavalandJavaslang @koenighotze
Wrapping up
Slick, stable, consistent API
Object-functional advantages now
Complex(?)
Version 3 coming soon!

119. #JavalandJavaslang @koenighotze
RESISTTHE TYRANNY OF THE
COLLECTIONS FRAMEWORK
JOIN THE RESISTANCE!

120. #JavalandJavaslang @koenighotze
thank
you
david.schmitz at senacor.com