Java 8 introduced cool new features such as Lambdas and Streams. We'll take a look at what they are how to use them effectively. We'll also walkthrough an example of a lightweight Java 8 service running in AWS cloud, which can read and index tweets into an ElasticSearch cluster

1. Java 8
Level Up with new features!
1
Socal Code Camp 2015
14 Nov, Los Angeles

2. Java 8
Level Up with new features!
2
Image: http://blog.takipi.com/

3. Who am I?
3
@cganoo
@cganoo
Trademarks and pictures belong to respective copyright owners
@caganoo

4. Agenda
 Introduction
 Default Methods
 Lambdas
4
 Streams
 CompletableFuture
 Demo

5. Intro
5
Popularity Rank on GitHub
PopularityRankonStackOverflow
https://redmonk.com/sogrady/2015/07/01/language-rankings-6-15/

6. Intro
6
https://dzone.com/articles/java-version-statistics-2015http://www.oracle.com/technetwork/java/eol-135779.html

7. Default Methods
7
Interview Question:
What is an interface in java?

8. Default Methods
Interfaces can now declare methods with
implementation:
 Static methods
 Default Methods
8

9. Default Methods
List<Integer> numbers = Arrays.asList(3, 5, 1);
9

10. Default Methods
List<Integer> numbers = Arrays.asList(3, 5, 1);
Collections.sort(numbers);
10

11. Default Methods
List<Integer> numbers = Arrays.asList(3, 5, 1);
Collections.sort(numbers);
Collections.sort(numbers, myComparator);
11

12. Default Methods
List<Integer> numbers = Arrays.asList(3, 5, 1);
numbers.sort(Comparator.naturalOrder());
12

13. Default Methods
13

14. Default Methods
14
public class Dog implements Bark {
// No overridden method
}
public interface Bark {
default String bark() {
return "Woof Woof!";
}
}
public static void main(String[] args) {
Dog dog = new Dog();
dog.bark(); // Woof Woof!
}

15. Default Methods
15
Interview Question:
What's the difference between Abstract
classes and Interfaces?

16. Default Methods
16

17. Default Methods
17
3 Resolution Rules:
 Classes always win
 Then, sub-interfaces win
 Then, the inheriting class inheriting has to
explicitly select

18. Lambdas
18
Image: http://blog.takipi.com/

19. Lambdas
19
Concise way to express
Behavior Parametrization

20. Lambdas
20
List<Student> filterByGrade(students, grade) {
List<Student> result = new ArrayList<>();
for (Student student : students) {
if ( student.getGrade().equals(grade) ) {
result.add(student);
}
}
return result;
}

21. Lambdas
21
List<Student> gradeAStudents =
filterByGrade(students, "A");
List<Student> gradeBStudents =
filterByGrade(students, "B");

22. Lambdas
22
List<Student> filterByAge(students, age) {
List<Student> result = new ArrayList<>();
for (Student student : students) {
if ( student.getAge() > age ) {
result.add(student);
}
}
return result;
}

23. Lambdas
23
List<Student> oldStudents =
filterByAge(students, 30);
List<Student> youngStudents =
filterByAge(students, 20);

24. Lambdas
24
public interface Predicate<T> {
boolean test(T t);
}
List<T> filter(List<T> list, Predicate<T> p) {
List<T> result = new ArrayList<>();
for(T e: list) {
if(p.test(e)){ result.add(e); }
}
return result;
}

25. Lambdas
25
filter(
students,
(Student s) -> "A".equals(s.getGrade())
);

26. Lambdas
26
Comparator<Student> c = new Comparator<Student>()
{
public int compare(Student a1, Student a2) {
return a1.getAge().compareTo(a2.getAge());
}
};

27. Lambdas
27
Comparator<Student> c = new Comparator<Student>()
{
public int compare(Student a1, Student a2) {
return a1.getAge().compareTo(a2.getAge());
}
};
Comparator<Student> c =
(Student a1, Student a2) ->
a1.getGrade().compareTo(a2.getGrade());

28. Lambdas
28
So where can you use lambdas?
In the context of a functional interface

29. Lambdas
29
A functional interface is an interface that
specifies exactly one abstract
method

30. Lambdas
30
@FunctionalInterface
public interface Runnable {
public abstract void run();
}
@FunctionalInterface
public interface Callable<V> {
V call() throws Exception;
}

31. Lambdas
31
Thread thread1 = new Thread(new Runnable() {
@Override
public void run(){
doSomething();
}
});
thread1.start();

32. Lambdas
32
Thread thread1 = new Thread(new Runnable() {
@Override
public void run(){
doSomething();
}
});
thread1.start();
new Thread(() -> doSomething()).start();

33. Lambdas
33
@FunctionalInterface
public interface Predicate<T> {
boolean test(T t);
}
@FunctionalInterface
public interface Function<T, R> {
R apply(T t);
}

34. Lambdas
34
Method References:
items.forEach((x) -> System.out.print(x));
items.forEach(System.out::print);

35. Lambdas
35
Image taken from the book ‘Java 8 in Action’ by Urma, Fusco and Mycroft

36. Streams
36
Image: http://www.123rf.com/photo_5391089_blue-tsunami-wave-two.html

37. Streams
37
Stream is a sequence of elements from a
source that supports data processing
operations

38. Streams
Motivation:
38
 Collections is the most heavily used API in
Java

39. Streams
Motivation:
39
 Collections is the most heavily used API in
Java
 Lacks declarative syntax

40. Streams
Motivation:
40
 Collections is the most heavily used API in
Java
 Lacks declarative syntax
 Lacks easy parallelization API

41. Streams
41
Stream is a sequence of elements from a
source that supports data processing
operations:
Fancy iterators that let you manipulate
collections of data in a declarative,
composable and transparently parallel way

42. Streams
42
Streams are Collections on steroids!

43. Streams
43
List<String> someStudentNames =
students.stream()
.filter(s -> s.getAge() > 20)
.sorted(comparing(Student::getGrade))
.map(Student::getName)
.collect(toList());

44. Streams
44
List<Student> someStudents =
students.stream()
.filter(s -> s.getAge() > 20)
.sorted(comparing(Student::getGrade))
.map(Student::getName)
.collect(toList());
Get a list of the names of all students, sorted by their
grades and who are above 20 years of age

45. Streams
45
List<Student> someStudents =
students.parallelStream()
.filter(s -> s.getAge() > 20)
.sorted(comparing(Student::getGrade))
.map(Student::getName)
.collect(toList());
Get a list of the names of all students, sorted by their
grades and who are above 20 years of age

46. Streams
46
Intermediate Operations: Return Stream<X>
filter Predicate<T> T -> boolean
map Function<T, R> T -> R
sorted Comparator<T> (T, T) -> int
distinct

47. Streams
47
Terminal Operations:
forEach Consumer<T> T -> void
count Returns a long
collect Collector<T, A, R>
reduce T identity, BinaryOperator<T>

48. Streams
48
Generating Streams:
 Stream.of("Code", "Camp")
 Arrays.stream(new int[] {1, 2})
 Files.lines() (Java NIO)

49. Streams
49
Generating Infinite Streams:
 Stream.iterate(0, n -> n + 2)
 Stream.generate(Math::random)

50. CF
50
Interview Question:
What's the difference between
Concurrency and Parallelism?

51. CF
51
http://joearms.github.io/2013/04/05/concurrent-and-parallel-programming.html

52. CF
52
Interview Question:
What's a Future in Java?

53. CF
53
Future models an asynchronous computation and
provides a reference to its result that will be available
when the computation itself is completed

54. CF
54
Future<Double> future = executor.submit(
() -> doSomething());
doSomethingElse();
try {
Double result =
future.get(1, TimeUnit.SECONDS);
} catch (TimeoutException e) {...}

55. CF
55
public Future<Double> getPrice(String product) {
CF<Double> f = new CF<>();
new Thread(() -> {
try {
double price = price(product);
f.complete(price);
} catch (Exception ex) {
f.completeExceptionally(ex);
}
}).start();
return f;
}

56. CF
56
public Future<Double> getPrice (String product) {
return CF.supplyAsync(() -> price(product))
.exceptionally(() -> 0.0);
}

57. Question
57
Parallel Streams vs CompletableFutures

58. CF
58
Which one to prefer?

59. CF
59
Pattern 1: Async Sequencing
thenAccept*
Run a function when complete
thenApply*
Convert the result using a function when complete

60. CF
60
Pattern 2: Async Join
thenAcceptBoth*
Run a function when both futures are done
thenCombine*
Convert the result of 2 futures into a new thing
when both are done

61. CF
61
CF<String> user =
CF.supplyAsync(() -> "John");
CF<String> id =
CF.supplyAsync( () -> "1");
user
.thenCombineAsync(id, (u, i) -> u + i)
.thenAccept(System.out::println);

62. References
 Java 8 in Action: https://www.manning.com/books/java-8-in-action
 @Winterberg: http://winterbe.com/posts/2014/03/16/java-8-tutorial/
 IntelliJ for Java Projects
62

63. Demo
63

64. Demo
64
Demo 1:
• Run code to periodically fetch tweets from Twitter
• Store the fetched tweets somewhere
Tech Stack used:
• AWS Lambda to create scheduled function
• AWS S3 to store fetched tweets
• Twitter Streaming Endpoint to fetch tweets

65. Demo
65
Demo 2:
• Index the stored tweets into an ElasticSearch cluster
• Explore and visualize patterns using Kibana Dashboards
Tech Stack used:
• AWS Lambda to create a function reacting to S3 events
• AWS ElasticSearch Service
• Kibana 4

66. Demo
66
C03E
 https://github.com/cganoo/codecamptweetfetcher
 https://github.com/cganoo/codecamptweetsearcher
The next few slides show screenshots from the demo

67. Text Search in ES
67

68. Summary metrics in ES
68

69. Custom Dashboard in ES
69

70. AWS Cloudwatch Metrics
70

71. AWS Lambda Cloudwatch Logs
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72. 72
Questions?