Java8 Stream操作

参考:

http://ifeve.com/stream/

http://docs.oracle.com/javase/8/docs/api/java/util/stream/package-summary.html

学习java8中Stream的操作，自己做了一些测试代码如下：

package test;import java.util.ArrayList;import java.util.Arrays;import java.util.List;import java.util.stream.Collectors;import java.util.stream.Stream;public class NewFeature {//java8的新特性public static void main(String [] args){class Gen{private int i;public Gen(int value){i=value;}public Integer get(){return i--;}}Integer [] iArray={0,1,1,1,2,3,4,5,6,7,8,9};List<Integer> list = Arrays.asList(iArray);/** * Stream 的转换 * *///distinctSystem.out.println("========== test distinct ====================");list.stream().distinct().forEach(System.out::println);//filterSystem.out.println("========== test filter ====================");list.stream().filter(x->x<5).forEach(System.out::println);//mapSystem.out.println("========== test map ====================");list.stream().map(x->x*10).forEach(System.out::println);//flatMapSystem.out.println("========== test flatMap ====================");//<R> Stream<R> flatMap(Function<? super T,? extends Stream<? extends R>> mapper)//flatMap与map的区别是 map将每个元素做一些简单的转化（如上面*10）  flatMap则会对每一个元素生成一个新的stream，合并到旧的stream中list.stream().flatMap(x->{Gen gen = new Gen(x);return Stream.generate(gen::get).limit(x+1);//如 Gen(9) 则会产生一个 [9,8,7,6,5,4,3,2,1,0] 的stream}).forEach(System.out::println);//peekSystem.out.println("========== test peek ====================");list.stream().peek(x->{System.out.println("hi~ I'm in peek["+x+"}");}).forEach(x->{});list.stream().peek(x->{System.out.println("hi~ I'm in peek["+x+"}");}).forEach(System.out::println);//limitSystem.out.println("========== test limit ====================");list.stream().limit(5).forEach(System.out::println);//skipSystem.out.println("========== test skip ====================");list.stream().skip(5).forEach(System.out::println);//sortedSystem.out.println("========== test sorted ====================");list.stream().sorted().forEach(System.out::println);System.out.println("========== test sorted2 ====================");list.stream().sorted((a,b)->b.compareTo(a)).forEach(System.out::println);/** * 汇聚 * *///collectSystem.out.println("========== test collect ====================");//<R> R collect(Supplier<R> supplier,    //          BiConsumer<R,? super T> accumulator,    //          BiConsumer<R,R> combiner)//supplier = ()->new ArrayList<Integer>()  工厂类，生成容器//accumulator = (l,item)->l.add(item)  l是之前工厂类生成的，item是每个元素  将元素添加到新生成的容器//combiner 并行stream中使用 parallelStream()中生效，最终做合并操作System.out.println(list.stream().collect(()->new ArrayList<Integer>(),(l,item)->l.add(item*5),(l1,l2)->l1.addAll(l2)));//list.stream().collect(ArrayList::new,(l,item)->l.add(item*10),(l1,l2)->l1.addAll(l2));System.out.println("========== test collect 2 ====================");System.out.println(list.stream().collect(Collectors.toList()));//reduceSystem.out.println("========== test reduce ====================");Integer res1 = list.stream().reduce((x,y)->x+y).get();System.out.println("reduce res1 is:"+res1); //0+1+1+1+2+3+4+5+6+7+8+9Integer res2 = list.stream().reduce(100, (x,y)->x+y);System.out.println("reduce res2 is:"+res2); //100 + 0+1+1+1+2+3+4+5+6+7+8+9String res3 = list.stream().reduce("result is:",(a,b)->a+"--"+b,(x,y)->x+","+y);System.out.println("reduce res3 is:"+res3); //result is:--0--1--1--1--2--3--4--5--6--7--8--9//<U> U reduce(U identity,    //       BiFunction<U,? super T,U> accumulator,    //       BinaryOperator<U> combiner)//combiner 参数是在并行stream中生效，如下parallelStream//每个并行的stream初始值是"result is" 并且确定为String类型//每个并行的Stream会使用accumulator = (a,b)=>a+"--"+b  将两两元素变成Stream类型//combiner = (x,y)->x+","+y  在所有并行stream操作完后最终合并String res4 = list.parallelStream().reduce("result is:",(a,b)->a+"--"+b,(x,y)->x+","+y);System.out.println("reduce res4 is:"+res4); //reduce res4 is:result is:--0--1--1,result is:--1--2--3,result is:--4--5--6,result is:--7--8--9//all MatchSystem.out.println("========== test allMatch ====================");boolean isAllMatch = list.stream().allMatch((x)->x>0);//boolean isAllMatch = list.parallelStream().allMatch((x)->x>=0);System.out.println("isAllMatch:"+isAllMatch); //false  0>0//anyMatchSystem.out.println("========== test anyMatch ====================");boolean isAnyMatch = list.stream().anyMatch((x)->x>0);System.out.println("isAnyMatch:"+isAnyMatch); //true//noneMatchSystem.out.println("========== test noneMatch ====================");boolean isNoneMatch  = list.stream().noneMatch((x)->x>0);System.out.println("isNoneMatch:"+isNoneMatch); //false  是否所有元素都不满足要求//findFirstSystem.out.println("========== test findFirst ====================");Integer first = list.stream().findFirst().get();System.out.println("first is:"+first);//findAnySystem.out.println("========== test findAny ====================");Integer any=list.stream().findAny().get();System.out.println("any is:"+any);//Integer any2 = Arrays.asList(new Integer[]{}).stream().findAny().get();//System.out.println("any2 is:"+any2);//max minSystem.out.println("========== test max min====================");Integer max = list.stream().max((a,b)->a.compareTo(b)).get();System.out.println("max is:"+max);Integer min = list.stream().min((a,b)->a.compareTo(b)).get();System.out.println("min is:"+min);//countSystem.out.println("========== test count====================");long count = list.stream().count();System.out.println("count is:"+count);//forEachSystem.out.println("========== test forEach====================");list.stream().forEach(System.out::print);System.out.println();Arrays.asList(new Integer[]{3,2,1,4}).stream().forEachOrdered(System.out::print);}}

从文件中获取Stream

需要自己实现Spliterator接口，然后使用StreamSupport.stream(Spliterator spliterator, boolean pallel)方法

package test;import java.util.Spliterator;import java.util.function.Consumer;import java.util.stream.StreamSupport;import java.io.BufferedReader;import java.io.FileNotFoundException;import java.io.FileReader;import java.io.IOException;public class StreamTest {public static class FileSpliterator implements Spliterator<String>{private BufferedReader reader = null;public FileSpliterator(String filename){try {                this.reader = new BufferedReader(new FileReader(filename));                } catch (FileNotFoundException e) {                e.printStackTrace();                }}@Override        public boolean tryAdvance(Consumer<? super String> action) {if(this.reader==null){return false;}        String line;            try {            line = reader.readLine();            if(line!=null){        action.accept(line);        return true;        } else {        if(this.reader!=null){        this.reader.close();        }        return false;        }            } catch (IOException e) {            e.printStackTrace();            if(this.reader!=null){            try {                    this.reader.close();                    } catch (IOException e1) {                    e1.printStackTrace();                    }            }            return false;            }        }@Override        public Spliterator<String> trySplit() {return null;        }@Override        public long estimateSize() {return 0;        }@Override        public int characteristics() {//表明是一个不可变的Spliterator        return IMMUTABLE;        }}public static void main(String [] args) throws Exception{StreamSupport.stream(new FileSpliterator("D:\\test.txt"), false).filter(x->!x.isEmpty()).forEach(System.out::println);}}