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 list = Arrays.asList(iArray);
/**
* Stream 的转换
* */
//distinct
System.out.println("========== test distinct ====================");
list.stream().distinct().forEach(System.out::println);
//filter
System.out.println("========== test filter ====================");
list.stream().filter(x->x<5).forEach(System.out::println);
//map
System.out.println("========== test map ====================");
list.stream().map(x->x*10).forEach(System.out::println);
//flatMap
System.out.println("========== test flatMap ====================");
// Stream flatMap(Function> 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);
//peek
System.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);
//limit
System.out.println("========== test limit ====================");
list.stream().limit(5).forEach(System.out::println);
//skip
System.out.println("========== test skip ====================");
list.stream().skip(5).forEach(System.out::println);
//sorted
System.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
* */
//collect
System.out.println("========== test collect ====================");
// R collect(Supplier supplier,
// BiConsumer accumulator,
// BiConsumer combiner)
//supplier = ()->new ArrayList() 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(),(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()));
//reduce
System.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+9
Integer 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+9
String 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
//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 Match
System.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
//anyMatch
System.out.println("========== test anyMatch ====================");
boolean isAnyMatch = list.stream().anyMatch((x)->x>0);
System.out.println("isAnyMatch:"+isAnyMatch); //true
//noneMatch
System.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
//findFirst
System.out.println("========== test findFirst ====================");
Integer first = list.stream().findFirst().get();
System.out.println("first is:"+first);
//findAny
System.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 min
System.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);
//count
System.out.println("========== test count====================");
long count = list.stream().count();
System.out.println("count is:"+count);
//forEach
System.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{
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 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 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);
}
}