Java 8 Streams Deep Dive

Streams are the new Java API that let's us manipulate collections of data in a declarative way. But this API is much more than just fancy iterators over collections of data.
Streams are the API that will completely change how we code in Java. In this talk we will make a deep dive in the Streams power, covering:
- Review Streams API covering filtering techniques, map-reduce, finding and matching and collectors;
- Learn how to build my own streams and collectors;
- Deep dive in parallels streams, spliterators and parallels best practices;
- Explore lazy evaluation and infinite streams;
The talk will consist of a balance between theoretical concepts and practical applications. Attendees will leave with deep knowledge of the theory and practical use of the power of the Streams API.

Transcript

1. Java Streams Deep Dive Eder Ignatowicz Sr. Software Engineer JBoss by Red Hat
3. FP <3
4. Linguagens de Programação <3
5. Java <3
6. Pugs <3
7. Dora
8. Bento
9. public Pug( String name, String color, Integer weight ) { this.name = nome; this.color = color; this.weight = weight; } Pug dora = new Pug( "Dora", "abricot", 10 ); Pug bento = new Pug( "Bento", "abricot", 13 ); Pug jesse = new Pug( "Jesse", "black", 9 );
10. Streams API
11. Streams: Manipula coleções de forma declarativa Quais são os nomes dos Pugs com peso maior do que 9 quilos?
12. Streams: Manipula coleções de forma declarativa SELECT nome FROM pugs WHERE weight < 9 order by peso.
13. Em Java List<Pug> gordinhos = new ArrayList<>(); for ( Pug pug : pugs ) { if ( pug.getWeight() > 9 ) { gordinhos.add( pug ); } } Collections.sort( gordinhos, new Comparator<Pug>() { @Override public int compare( Pug p1, Pug p2 ) { return Integer.compare( p1.getWeight(), p2.getWeight() ); } }); List<String> nomeGordinhos = new ArrayList<>(); for ( Pug pug : gordinhos ) { nomeGordinhos.add( pug.getNome() ); }
15. Java 8 Streams API
16. List<String> fatName = pugs.stream() .filter( p -> p.getWeight() > 9 ) .sorted( comparing( Pug::getWeight ) ) .map( Pug::getNome ) .collect( toList() ); Em Java Seleciona > 9 kg Ordena por peso Extrai o nome Coleta em uma lista
17. List<String> fatName = pugs.parallelStream() .filter( p -> dora.getWeight() > 9 ) .sorted( comparing( Pug::getWeight ) ) .map( Pug::getNome ) .collect( toList() ); Em Java Seleciona > 9 kg Ordena por peso Extrai o nome Coleta em uma lista
19. (
20. Parallel streams não são mágica!
21. )
22. Stream Pipelines filter pugs -> —> sorted —> map —> collect lambda lambda lambda
23. Código: Declarativo Componentizável Paralelizável Streams API
24. Sequência de elementos de uma fonte que suporta operações de processamento em seus dados Streams
25. Sequência de elementos de uma fonte que suporta operações de processamento em seus dados Streams
26. Sequência de elementos de uma fonte que suporta operações de processamento em seus dados Streams
27. Streams Uma fonte de dados para a query Uma cadeia de operações intermediárias (pipeline) Uma operação terminal que gera o resultado
28. Vamos a prática
29. public Venda( Vendedor vendedor, int ano, int valor ) { this.vendedor = vendedor; this.ano = ano; this.valor = valor; } public Vendedor( String nome, String cidade ) { this.nome = nome; this.cidade = cidade; }
30. Vendedor eder = new Vendedor("Eder", "Campinas"); Vendedor pedro = new Vendedor("Pedro", "Apucarana"); Vendedor luciano = new Vendedor("Luciano", "Piracicaba"); Vendedor junior = new Vendedor("Junior", "Londrina"); List<Venda> transactions = Arrays.asList( new Venda( eder, 2015, 100 ), new Venda( eder, 2016, 200 ), new Venda( pedro, 2015, 300 ), new Venda( luciano, 2015, 500 ), new Venda( luciano, 2015, 400 ), new Venda( junior, 2016, 500 ));
31. Quais são as vendas que fizemos em 2015? Ordenadas?
32. List<Venda> vendas2015 = transactions .stream()
33. List<Venda> vendas2015 = transactions .stream() .filter( venda -> venda.getAno() == 2015 )
34. List<Venda> vendas2015 = transactions .stream() .filter( venda -> venda.getAno() == 2015 ) .sorted( comparing( Venda::getValor ) )
35. List<Venda> vendas2015 = transactions .stream() .filter( venda -> venda.getAno() == 2015 ) .sorted( comparing( Venda::getValor ) ) .collect( toList() );
36. List<Venda> vendas2015 = transactions .stream() .filter( venda -> venda.getAno() == 2015 ) .sorted( comparing( Venda::getValor ) ) .collect( toList() ); vendas2015.forEach(System.out::println); Venda{vendedor=Vendedor{nome='Eder', cidade='Campinas'}, ano=2015, valor=100} Venda{vendedor=Vendedor{nome='Pedro', cidade='Apucarana'}, ano=2015, valor=300} Venda{vendedor=Vendedor{nome='Luciano', cidade='Piracicaba'}, ano=2015, valor=400} Venda{vendedor=Vendedor{nome='Luciano', cidade='Piracicaba'}, ano=2015, valor=500}
37. Em que cidades temos vendedores?
38. Campinas Apucarana Piracicaba Londrina List<String> cidadesAtendidas = vendas.stream() .map( venda ->venda.getVendedor().getCidade() ) .distinct() .collect( toList() );
39. Qual foi a maior venda?
40. 500 OptionalInt maiorVenda = vendas.stream() .mapToInt(Venda::getValor) .reduce( Integer::max ); maiorVenda.ifPresent( i -> System.out.println(i));
41. Total de vendas?
42. 2000 OptionalInt total = vendas.stream() .mapToInt(Venda::getValor) .reduce( Integer::sum ); total.ifPresent( i -> System.out.println(i));
43. Quais são as vendas de cada vendedor? Ordenadas?
44. Map<Vendedor, List<Venda>> vendedorPorVendas = vendas.stream() .sorted( comparing( Venda::getValor ) ) .collect( groupingBy( Venda::getVendedor ) );
45. {Vendedor{nome='Junior', cidade='Londrina'}=[Venda{vendedor=Vendedor{nome='Junior', cidade='Londrina'}, ano=2016, valor=500}], Vendedor{nome='Eder', cidade='Campinas'}=[Venda{vendedor=Vendedor{nome='Eder', cidade='Campinas'}, ano=2015, valor=100}, Venda{vendedor=Vendedor{nome='Eder', cidade='Campinas'}, ano=2016, valor=200}], Vendedor{nome='Pedro', cidade='Apucarana'}=[Venda{vendedor=Vendedor{nome='Pedro', cidade='Apucarana'}, ano=2015, valor=300}], Vendedor{nome='Luciano', cidade='Piracicaba'} =[Venda{vendedor=Vendedor{nome='Luciano', cidade='Piracicaba'}, ano=2015, valor=400}, Venda{vendedor=Vendedor{nome='Luciano', cidade='Piracicaba'}, ano=2015, valor=500}]} Map<Vendedor, List<Venda>> vendedorPorVendas = vendas.stream() .sorted( comparing( Venda::getValor ) ) .collect( groupingBy( Venda::getVendedor ) );
46. Refactoring Loops to Collection Pipelines
47. public class Client { private String name; private String email; private Company company; public Client( String name, String email, Company company ) { this.name = name; this.email = email; this.company = company; } public Client( String name ) { this.name = name; } public Client( String name, String email ) { this.name = name; this.email = email; } … }
48. public class ClientRepositoryTest { private ClientRepository repo; @Before public void setup() { Company empresa = new Company( "RedHat" ); Client completo1 = new Client( "Completo1", "completo1@redhat.com", empresa ); Client completo2 = new Client( "Completo2", "completo2@redhat.com", empresa ); Client semEmpresa = new Client( "SemEmpresa", "semEmpresa@ederign.me" ); Client somenteNome = new Client( "SomenteNome" ); repo = new ClientRepository( Arrays.asList( completo1, semEmpresa, completo2, somenteNome ) ); } @Test public void getClientEmailsWithCompanyTest() { List<String> clientMails = repo.getClientMails(); assertEquals( 2, clientMails.size() ); assertTrue( clientMails.contains( "completo1@redhat.com" ) ); assertTrue( clientMails.contains( "completo2@redhat.com" ) ); assertTrue( !clientMails.contains( "semEmpresa@ederign.me" ) ); } }
49. public List<String> getClientMails() { ArrayList<String> emails = new ArrayList<>(); for ( Client client : clients ) { if ( client.getCompany() != null ) { String email = client.getEmail(); if ( email != null ){ emails.add( email ); } } } return emails; }
50. public List<String> getClientMails() { ArrayList<String> emails = new ArrayList<>(); List<Client> pipeline = clients; for ( Client client : pipeline ) { if ( client.getCompany() != null ) { String email = client.getEmail(); if ( email != null ){ emails.add( email ); } } } return emails; } } Extract Variable
51. public List<String> getClientMails() { ArrayList<String> emails = new ArrayList<>(); List<Client> pipeline = clients .stream() .filter( c -> c.getCompany() != null ) .collect( Collectors.toList() ); for ( Client client : pipeline ) { if ( client.getCompany() != null ) { String email = client.getEmail(); if ( email != null ) { emails.add( email ); } } } return emails; } } Filter Operation
52. public List<String> getClientMails() { ArrayList<String> emails = new ArrayList<>(); List<String> pipeline = clients .stream() .filter( c -> c.getCompany() != null ) .map( c -> c.getEmail() ) .collect( Collectors.toList() ); for ( String mail : pipeline ) { String email = client.getEmail(); if ( mail != null ) { emails.add( mail ); } } return emails; } Map Operation
53. Filter Operation public List<String> getClientMails() { ArrayList<String> emails = new ArrayList<>(); List<String> pipeline = clients .stream() .filter( c -> c.getCompany() != null ) .map( c -> c.getEmail() ) .filter( m -> m != null ) .collect( Collectors.toList() ); for ( String mail : pipeline ) { if ( mail != null ) { emails.add( mail ); } } return emails; }
54. Pipeline public List<String> getClientMails() { ArrayList<String> emails = new ArrayList<>(); return clients .stream() .filter( c -> c.getCompany() != null ) .map( c -> c.getEmail() ) .filter( m -> m != null ) .collect( Collectors.toList() ); for ( String mail : pipeline ) { if ( mail != null ) { emails.add( mail ); } } return emails; }
55. public List<String> getClientMails() { return clients .stream() .filter( c -> c.getCompany() != null ) .map( c -> c.getEmail() ) .filter( m -> m != null ) .collect( Collectors.toList() ); }
58. Streams são lazy
59. Stream Pipelines filter pugs -> —> map —> collect lambda lambda
60. Stream Pipelines intermediate pugs -> —> —> findFirst lambda lambda intermediate
61. Lazy Streams List<Dog> dogs = Arrays.asList( new Dog( "Dora", 10, Dog.BREED.PUG ), new Dog( "Bento", 13, Dog.BREED.PUG ), new Dog( "Rex", 8, Dog.BREED.SRD ), new Dog( "Tetezinha", 6, Dog.BREED.SRD ), new Dog( "Banze", 7, Dog.BREED.SRD ), new Dog( "Rufus", 15, Dog.BREED.BULLDOG ) );
62. Qual o nome do primeiro SRD que pesa mais do que 5kg?
63. String nomePrimeiroSRDMaiorDoQue5Kg = dogs.stream() .filter( dog -> { return dog.getBreed().equals( Dog.BREED.SRD ) && dog.getWeight() > 5; } ) .map( dog -> { return dog.getName(); } ) .findFirst() .get();
64. Eager Streams Dora Bento Rex Teté Banzé Rin Tin tin —> SRD e peso> 5 filter map Rex Teté Banzé —> Nome "Rex" “Teté" “Banzé" —> —> Nome findFirst “Rex" —> —>
65. Lazy Stream Dora Bento Rex Teté Banzé Rin Tin tin —> SRD e peso> 5 filter map Rex —> Nome “Rex" —> —> first() findFirst “Rex" —> —>
66. String nomePrimeiroSRDMaiorDoQue5Kg = dogs.stream() .filter( dog -> { return dog.getBreed().equals( Dog.BREED.SRD ) && dog.getWeight() > 5; } ) .map( dog -> { return dog.getName(); } ) .findFirst() .get(); List<Dog> dogs = Arrays.asList( new Dog( "Dora", 10, Dog.BREED.PUG ), new Dog( "Bento", 13, Dog.BREED.PUG ), new Dog( "Rex", 8, Dog.BREED.SRD ), new Dog( "Tetezinha", 6, Dog.BREED.SRD ), new Dog( "Banze", 7, Dog.BREED.SRD ), new Dog( "Rufus", 15, Dog.BREED.BULLDOG ) ); filter - Dora filter - Bento filter - Rex map - Rex Rex
67. Streams "infinitos"
68. Criar uma lista de números primos infinita
69. public static boolean isPrime( final int number ) { return number > 1 && IntStream.rangeClosed( 2, ( int ) Math.sqrt( number ) ) .noneMatch( divisor -> number % divisor == 0 ); } public static int primeAfter( final int number ) { if ( isPrime( number + 1 ) ) { return number + 1; } else { return primeAfter( number + 1 ); } }
70. public static IntStream primesInfinityStream( int fromNumber) { return IntStream.iterate( primeAfter( fromNumber - 1 ), Primes::primeAfter ); } primesInfinityStream( 1 ) .limit( 10 ) .forEach( i -> System.out.print( i+ ", " ) ); primesInfinityStream( 1000 ) .limit( 5 ) .forEach( i -> System.out.print( i+ ", " ) ); 2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 1009, 1013, 1019, 1021, 1031
71. FlatMap
72. Developer eder = new Developer(); eder.bestBooks( "Java 8 in Action", "SICP", "The Little Schemer" ); Developer dora = new Developer(); dora.bestBooks( "Effective Java", "Pragmatic Programmer", "SICP" ); List<Developer> devs = Arrays.asList( eder, dora ); List<String> booksNames = devs .stream() .map( dev -> dev.getBooks() ) //Stream<Set<String>> .flatMap( books -> books.stream() )//Stream<String> .distinct() .collect( Collectors.toList() ); booksNames.forEach( System.out::println );
73. IntStream DoubleStream, LongStream…
74. IntStream.of( 1, 2, 3 ); // > 1, 2, 3 IntStream.range( 1, 3 ); // > 1, 2
75. dogs.stream() .filter( dog -> dog.getBreed().equals( Dog.BREED.PUG ) ) .map( Dog::getWeight ) .filter( weight -> weight > 10 ) .mapToInt( weight -> weight ) .sum(); 0.185s
76. dogs.stream() .filter( dog -> dog.getBreed().equals( Dog.BREED.PUG ) ) .mapToInt( Dog::getWeight ) .filter( weight -> weight > 10 ) .sum(); 0.004s
77. dogs.stream() //Stream<Dog> .filter( dog -> dog.getBreed().equals( Dog.BREED.PUG ) )//Stream<Dog> .map( Dog::getWeight )//Stream<Integer> boxing :( .filter( weight -> weight > 10 )//Stream<Integer> boxing reboxing .mapToInt( weight -> weight ) //IntStream .sum(); 0.185s
78. dogs.stream()//Stream<Dog> .filter( dog -> dog.getBreed().equals( Dog.BREED.PUG ) )//Stream<Dog> .mapToInt( Dog::getWeight ) //IntStream .filter( weight -> weight > 10 ) //IntStream .sum(); 0.004s
79. dogs.stream()//Stream<Dog> .filter( dog -> dog.getBreed().equals( Dog.BREED.PUG ) )//Stream<Dog> .mapToInt( Dog::getWeight ) //IntStream .filter( weight -> weight > 10 ) //IntStream .max(); 0.004s
80. dogs.stream()//Stream<Dog> .filter( dog -> dog.getBreed().equals( Dog.BREED.PUG ) )//Stream<Dog> .mapToInt( Dog::getWeight ) //IntStream .filter( weight -> weight > 10 ) //IntStream .summaryStatistics(); IntSummaryStatistics{count=224, sum=4490, min=11, average=20.044643, max=30}
81. ParallelStreams
82. dogs.stream()//Stream<Dog> .mapToInt( Dog::getWeight ) //IntStream .filter( weight -> weight > 10 ) //IntStream .sum(); 0.129s
83. dogs.parallelStream()//Stream<Dog> .mapToInt( Dog::getWeight ) //IntStream .filter( weight -> weight > 10 ) //IntStream .sum(); 0.017s
86. dogs.parallelStream() .mapToInt( Dog::getWeight ) .reduce( Math::max ) .ifPresent( p -> System.out.println( "Maior peso: " + p ) );
87. java.util.Spliterator java.util.concurrent.ForkJoinPool.commonPool()
88. java.util.Spliterator
89. Spliterator = splitter + iterator
90. seq paralel ArrayList 8.33 ms 6.33 ms LinkedList 12.74 ms 19.57 ms HashSet 20.76 ms 16.01 ms TreeSet 19.79 ms 15.49 ms
91. java.util.concurrent.ForkJoinPool.commonPool()
92. Fork Join Framework
93. Task Child Task fork() fork() join() join() … … … … Child Task
94. CommonPool Singleton fork-join pool instance
95. public static String query( String question ) { List<String> engines = new ArrayList<>(); engines.add( "https://www.google.com/?q=" ); engines.add( "https://duckduckgo.com/?q=" ); engines.add( "https://www.bing.com/search?q=" ); // get element as soon as it is available Optional<String> result = engines.stream() .parallel().map( ( base ) -> { String url = base + question; // open connection and fetch the result return Util.read( url ); } ).findAny(); return result.get(); }
96. public static String query( String question ) { List<String> engines = new ArrayList<>(); engines.add( "https://www.google.com/?q=" ); engines.add( "https://duckduckgo.com/?q=" ); engines.add( "https://www.bing.com/search?q=" ); // get element as soon as it is available Optional<String> result = engines.stream() .parallel().map( ( base ) -> { String url = base + question; // open connection and fetch the result return Util.read( url ); } ).findAny(); return result.get(); }
97. dogs.parallelStream() .mapToInt( Dog::getWeight ) .reduce( Math::max ) .ifPresent( p -> System.out.println( "Maior peso: " + p ) );
100. public List<String> getClientMails() { return clients .stream() .filter( c -> c.getCompany() != null ) .map( c -> c.getEmail() ) .filter( m -> m != null ) .collect( Collectors.toList() ); }
102. Obrigado!!! @ederign