Java 8：处理文件的供应商抛出“流已经被操作或关闭”。 [英] Java 8: Supplier working with files throws "stream has already been operated upon or closed"

问题描述

使用 JUnit 和 Stream 我有以下错误消息：

Working with JUnit and Stream I have the following error message:

java.lang.IllegalStateException: stream has already been operated upon or closed

我做了一项研究，很明显不可能重复使用流

I did a research, and is clear is not possible reuse a stream

但是根据这篇文章：

• Java - Stream已经被操作或关闭

• Java – Stream has already been operated upon or closed

使用供应商可以解决这个问题。

working with Supplier is possible work around with this problem.

所以我当前代码如下：

    try (Stream<String> stream =  Files.lines(Paths.get(fileName)) ) {

        Supplier<Stream<String>> supplier = () -> stream;

        logger.info("A");
        logger.info("ABC {}", supplier.get().findFirst().get());
        logger.info("B");
        logger.info("XYZ {}", supplier.get().skip(1050).findFirst().get());
        logger.info("C");

        assertThat(supplier.get().count(), is(1051));

    }
    catch (IOException e) {
        logger.error("{}", e.getMessage());
    }

如何看待我使用 supplier.get （）使用 Stream （根据教程），但 @Test 打印直到 B ，因此 @Test 在 supplier.get（）中失败.skip（1050）.findFirst（）。get（）并且它仍然生成相同的错误消息。

How you can see I use the supplier.get() to work with the Stream (it according with the tutorial), but the @Test prints until B, therefore the @Test fails in supplier.get().skip(1050).findFirst().get() and it is still generating the same error message.

我的代码和教程之间的独特区别，mime通过文件工作，教程可以在数组中运行。

The unique difference between my code and the tutorial, the mime works through a File and the tutorial works around an array.

编辑工作没有任何问题？

Something special to edit to work without any problem?

Alpha

我做了以下版本（根据Eugene的代码段）

I did the following edition (according with the snippet code of Eugene)

   try (Stream<String> stream =  Files.lines(Paths.get(fileName)) ) {

        Supplier<Stream<String>> supplier = () -> stream.collect(Collectors.toList()).stream();

        logger.info("A");
        logger.info("ABC {}", supplier.get().findFirst().get());
        logger.info("B");
        logger.info("XYZ {}", supplier.get().skip(1050).findFirst().get());
        logger.info("C");

        assertThat(supplier.get().count(), is(1051));

    }

相同的错误信息。

推荐答案

供应商并不神奇，您仍然需要提供新流来自该供应商的所有时间。

Supplier is no magic, you still need to provide a new Stream all the time from that Supplier.

所以你可以这样做：

Supplier<Stream<String>> supplier = () -> Files.lines(Paths.get(fileName));

但这意味着要一直读取文件。您可以将所有行读入一个 List ，将其存储在内存中，并将 stream 存储在其中。

But that would mean to read the file, all the time. You could read all the lines into a single List, store that in memory and stream out of that.

List<String> allLines = Files.readAllLines(Paths.get(fileName));

Supplier<Stream<String>> supplier = () -> allLines.stream();

请注意，即使您链接的教程也会返回一个新的Stream，通过 Stream.of 如下：

Notice that even the tutorial that you have linked returns a new Stream, created via Stream.of like so:

 Supplier<Stream<String>> streamSupplier = () -> Stream.of(array);

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