Java 8 Streams Deep Dive

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Java Streams Deep Dive Eder Ignatowicz Sr. Software Engineer JBoss by Red Hat

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FP <3

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Linguagens de Programação <3

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Java <3

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Pugs <3

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Dora

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Bento

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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 );

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Streams API

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Streams: Manipula coleções de forma declarativa Quais são os nomes dos Pugs com peso maior do que 9 quilos?

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Streams: Manipula coleções de forma declarativa SELECT nome FROM pugs WHERE weight < 9 order by peso.

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Em Java List gordinhos = new ArrayList<>(); for ( Pug pug : pugs ) { if ( pug.getWeight() > 9 ) { gordinhos.add( pug ); } } Collections.sort( gordinhos, new Comparator() { @Override public int compare( Pug p1, Pug p2 ) { return Integer.compare( p1.getWeight(), p2.getWeight() ); } }); List nomeGordinhos = new ArrayList<>(); for ( Pug pug : gordinhos ) { nomeGordinhos.add( pug.getNome() ); }

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Java 8 Streams API

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List 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

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List 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

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(

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Parallel streams não são mágica!

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)

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Stream Pipelines ﬁlter pugs -> —> sorted —> map —> collect lambda lambda lambda

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Código: Declarativo Componentizável Paralelizável Streams API

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Sequência de elementos de uma fonte que suporta operações de processamento em seus dados Streams

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Sequência de elementos de uma fonte que suporta operações de processamento em seus dados Streams

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Sequência de elementos de uma fonte que suporta operações de processamento em seus dados Streams

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Streams Uma fonte de dados para a query Uma cadeia de operações intermediárias (pipeline) Uma operação terminal que gera o resultado

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Vamos a prática

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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; }

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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 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 ));

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Quais são as vendas que ﬁzemos em 2015? Ordenadas?

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List vendas2015 = transactions .stream()

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List vendas2015 = transactions .stream() .filter( venda -> venda.getAno() == 2015 )

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List vendas2015 = transactions .stream() .filter( venda -> venda.getAno() == 2015 ) .sorted( comparing( Venda::getValor ) )

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List vendas2015 = transactions .stream() .filter( venda -> venda.getAno() == 2015 ) .sorted( comparing( Venda::getValor ) ) .collect( toList() );

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List 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}

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Em que cidades temos vendedores?

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Campinas Apucarana Piracicaba Londrina List cidadesAtendidas = vendas.stream() .map( venda ->venda.getVendedor().getCidade() ) .distinct() .collect( toList() );

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Qual foi a maior venda?

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500 OptionalInt maiorVenda = vendas.stream() .mapToInt(Venda::getValor) .reduce( Integer::max ); maiorVenda.ifPresent( i -> System.out.println(i));

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Total de vendas?

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2000 OptionalInt total = vendas.stream() .mapToInt(Venda::getValor) .reduce( Integer::sum ); total.ifPresent( i -> System.out.println(i));

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Quais são as vendas de cada vendedor? Ordenadas?

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Map> vendedorPorVendas = vendas.stream() .sorted( comparing( Venda::getValor ) ) .collect( groupingBy( Venda::getVendedor ) );

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{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> vendedorPorVendas = vendas.stream() .sorted( comparing( Venda::getValor ) ) .collect( groupingBy( Venda::getVendedor ) );

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Refactoring Loops to Collection Pipelines

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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; } … }

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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 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" ) ); } }

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public List getClientMails() { ArrayList emails = new ArrayList<>(); for ( Client client : clients ) { if ( client.getCompany() != null ) { String email = client.getEmail(); if ( email != null ){ emails.add( email ); } } } return emails; }

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public List getClientMails() { ArrayList emails = new ArrayList<>(); List pipeline = clients; for ( Client client : pipeline ) { if ( client.getCompany() != null ) { String email = client.getEmail(); if ( email != null ){ emails.add( email ); } } } return emails; } } Extract Variable

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public List getClientMails() { ArrayList emails = new ArrayList<>(); List 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

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public List getClientMails() { ArrayList emails = new ArrayList<>(); List 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

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Filter Operation public List getClientMails() { ArrayList emails = new ArrayList<>(); List 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; }

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Pipeline public List getClientMails() { ArrayList 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; }

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public List getClientMails() { return clients .stream() .filter( c -> c.getCompany() != null ) .map( c -> c.getEmail() ) .filter( m -> m != null ) .collect( Collectors.toList() ); }

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Streams são lazy

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Stream Pipelines ﬁlter pugs -> —> map —> collect lambda lambda

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Stream Pipelines intermediate pugs -> —> —> ﬁndFirst lambda lambda intermediate

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Lazy Streams List 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 ) );

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Qual o nome do primeiro SRD que pesa mais do que 5kg?

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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" —> —>

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Lazy Stream Dora Bento Rex Teté Banzé Rin Tin tin —> SRD e peso> 5 filter map Rex —> Nome “Rex" —> —> first() findFirst “Rex" —> —>

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String nomePrimeiroSRDMaiorDoQue5Kg = dogs.stream() .filter( dog -> { return dog.getBreed().equals( Dog.BREED.SRD ) && dog.getWeight() > 5; } ) .map( dog -> { return dog.getName(); } ) .findFirst() .get(); List 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

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Streams "inﬁnitos"

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Criar uma lista de números primos inﬁnita

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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 ); } }

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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

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FlatMap

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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 devs = Arrays.asList( eder, dora ); List booksNames = devs .stream() .map( dev -> dev.getBooks() ) //Stream> .flatMap( books -> books.stream() )//Stream .distinct() .collect( Collectors.toList() ); booksNames.forEach( System.out::println );

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IntStream DoubleStream, LongStream…

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IntStream.of( 1, 2, 3 ); // > 1, 2, 3 IntStream.range( 1, 3 ); // > 1, 2

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dogs.stream() .filter( dog -> dog.getBreed().equals( Dog.BREED.PUG ) ) .map( Dog::getWeight ) .filter( weight -> weight > 10 ) .mapToInt( weight -> weight ) .sum(); 0.185s

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dogs.stream() .filter( dog -> dog.getBreed().equals( Dog.BREED.PUG ) ) .mapToInt( Dog::getWeight ) .filter( weight -> weight > 10 ) .sum(); 0.004s

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dogs.stream() //Stream .filter( dog -> dog.getBreed().equals( Dog.BREED.PUG ) )//Stream .map( Dog::getWeight )//Stream boxing :( .filter( weight -> weight > 10 )//Stream boxing reboxing .mapToInt( weight -> weight ) //IntStream .sum(); 0.185s

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dogs.stream()//Stream .filter( dog -> dog.getBreed().equals( Dog.BREED.PUG ) )//Stream .mapToInt( Dog::getWeight ) //IntStream .filter( weight -> weight > 10 ) //IntStream .sum(); 0.004s

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dogs.stream()//Stream .filter( dog -> dog.getBreed().equals( Dog.BREED.PUG ) )//Stream .mapToInt( Dog::getWeight ) //IntStream .filter( weight -> weight > 10 ) //IntStream .max(); 0.004s

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dogs.stream()//Stream .filter( dog -> dog.getBreed().equals( Dog.BREED.PUG ) )//Stream .mapToInt( Dog::getWeight ) //IntStream .filter( weight -> weight > 10 ) //IntStream .summaryStatistics(); IntSummaryStatistics{count=224, sum=4490, min=11, average=20.044643, max=30}

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ParallelStreams

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dogs.stream()//Stream .mapToInt( Dog::getWeight ) //IntStream .filter( weight -> weight > 10 ) //IntStream .sum(); 0.129s

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dogs.parallelStream()//Stream .mapToInt( Dog::getWeight ) //IntStream .filter( weight -> weight > 10 ) //IntStream .sum(); 0.017s

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dogs.parallelStream() .mapToInt( Dog::getWeight ) .reduce( Math::max ) .ifPresent( p -> System.out.println( "Maior peso: " + p ) );

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java.util.Spliterator java.util.concurrent.ForkJoinPool.commonPool()

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java.util.Spliterator

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Spliterator = splitter + iterator

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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

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java.util.concurrent.ForkJoinPool.commonPool()

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Fork Join Framework

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Task Child Task fork() fork() join() join() … … … … Child Task

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CommonPool Singleton fork-join pool instance

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public static String query( String question ) { List 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 result = engines.stream() .parallel().map( ( base ) -> { String url = base + question; // open connection and fetch the result return Util.read( url ); } ).findAny(); return result.get(); }

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dogs.parallelStream() .mapToInt( Dog::getWeight ) .reduce( Math::max ) .ifPresent( p -> System.out.println( "Maior peso: " + p ) );

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public List getClientMails() { return clients .stream() .filter( c -> c.getCompany() != null ) .map( c -> c.getEmail() ) .filter( m -> m != null ) .collect( Collectors.toList() ); }