引言
在 java8 中，Stream 不能被重用，一旦它被使用或使用，流将被关闭。
1. 流关闭
查看下面的示例，它将抛出一个 IllegalStateException，表示“ stream is closed”。
public static void main(String[] args) {
String[] array = {"a", "b", "c", "d", "e"};
Stream<String> stream = Arrays.stream(array);
// loop a stream
stream.forEach(x-> System.out.println(x));
// 拒绝过滤，抛出 throws IllegalStateException
long count = stream.filter(x -> "b".equals(x)).count();
System.out.println(count);
}
输出：
a
b
c
d
e
Exception in thread "main" java.lang.IllegalStateException: stream has already been operated upon or closed
at java.util.stream.AbstractPipeline.<init>(AbstractPipeline.java:203)
at java.util.stream.ReferencePipeline.<init>(ReferencePipeline.java:94)
at java.util.stream.ReferencePipeline$StatelessOp.<init>(ReferencePipeline.java:618)
at java.util.stream.ReferencePipeline$2.<init>(ReferencePipeline.java:163)
at java.util.stream.ReferencePipeline.filter(ReferencePipeline.java:162)
at com.jimzhang.stream.ClosedTest.main(ClosedTest.java:22)
2. 重用流
不管出于什么原因，你真的想重用一个数据流，试试下面的 Supplier 解决方案:
public static void main(String[] args) {
String[] array = {"a", "b", "c", "d", "e"};
Supplier<Stream<String>> streamSupplier = () -> Stream.of(array);
//get new stream
streamSupplier.get().forEach(x-> System.out.println(x));
//get another new stream
long count = streamSupplier.get().filter(x -> "b".equals(x)).count();
System.out.println(count);
}
输出：
a
b
c
d
e
1
每个 get ()将返回一个新的流。
源码见：java-8-demo
系列文章详见：Java 8 教程