在Java8中,我们可以使用StreamSupport.stream
方法把Iterator
转为Stream
。
// Iterator -> Spliterators -> Stream
Stream<String> stream = StreamSupport.stream(
Spliterators.spliteratorUnknownSize(
iterator,
Spliterator.ORDERED)
, false);
下面是StreamSupport.stream
方法的签名,它接受一个Spliterator
参数。
StreamSupport.java
public static <T> Stream<T> stream(Spliterator<T> spliterator, boolean parallel) {
Objects.requireNonNull(spliterator);
return new ReferencePipeline.Head<>(spliterator,
StreamOpFlag.fromCharacteristics(spliterator),
parallel);
}
1. Iterator转Stream
Iterator
接口没有spliterator()
方法,所有我们需要使用Spliterators.spliteratorUnknownSize
方法把Iterator
转为Spliterator
,再使用Iterator -> Spliterators -> Stream
方法把Spliterator
转为Stream
。
Iterator -> Spliterators -> Stream
下面的代码演示了如何把Iterator
转为Stream
。
JavaStreamExample1.java
package com.mkyong;
import java.util.*;
import java.util.stream.Collectors;
import java.util.stream.StreamSupport;
public class JavaStreamExample1 {
public static void main(String[] args) {
List<String> list = new ArrayList<>();
list.add("mkyong");
list.add("java");
list.add("kotlin");
list.add("spring boot");
list.add("android");
Iterator<String> iterator = list.iterator();
// Iterator -> Spliterators -> Stream -> List
List<Integer> result = StreamSupport.stream(
Spliterators.spliteratorUnknownSize(iterator, Spliterator.ORDERED), false)
.map(x -> x.length())
.collect(Collectors.toList());
result.forEach(x -> System.out.println(x));
System.out.println(result.getClass());
}
}
输出
6
4
6
11
7
class java.util.ArrayList
2. Iterable转Stream
因为Iterable
接口有spliterator()
方法,所有它可以很容易的转为Stream
。
JavaStreamExample2.java
package com.mkyong;
import java.util.*;
import java.util.stream.Collectors;
import java.util.stream.StreamSupport;
public class JavaStreamExample2 {
public static void main(String[] args) {
Iterable<Integer> iterable = Arrays.asList(1, 2, 3, 4, 5);
// Iterable -> Spliterators -> Stream -> List
List<Integer> result = StreamSupport.stream(
iterable.spliterator(), false)
.map(x -> x * 10)
.collect(Collectors.toList());
result.forEach(x -> System.out.println(x));
System.out.println(result.getClass());
}
}
输出
10
20
30
40
50