递归流 [英] Recursive stream

问题描述

我想使用Java 8递归列出计算机上的所有文件。

I want to list all the files on my computer recursively using Java 8.

Java 8提供 listFiles 返回所有文件和目录但没有递归的方法。如何使用它来获取完整的递归文件列表（不使用变异集合）？

Java 8 provides a listFiles method that returns all the files and directories but without recursion. How can I use it to get a full recursive list of files (without using a mutating collection)?

我已经尝试了下面的代码，但它只有一个深度：

I've tried the code below but it only goes one level deep:

static Function<Path, Stream<Path>> listFiles = p -> {
    if (p.toFile().isDirectory()) {
        try { return Files.list(p); }
        catch (Exception e) { return Stream.empty(); }
    } else {
        return Stream.of(p);
    }
};

public static void main(String[] args) throws IOException {
    Path root = Paths.get("C:/temp/");
    Files.list(root).flatMap(listFiles).forEach(System.out::println);
}

并使用返回Files.list（p）。 flatMap（listFiles）; 无法编译（不确定原因）......

And using return Files.list(p).flatMap(listFiles); does not compile (not sure why)...

注意：我对涉及FileVisitors或外部的解决方案不感兴趣库。

Note: I am not interested in solutions involving FileVisitors or external libraries.

推荐答案

通过递归遍历文件系统生成路径流的新API是 Files。步行。

A new API to generate a stream of Paths by walking the filesystem recursively is Files.walk.

如果你真的想递归生成一个流（不一定要走文件树，但我会继续使用它作为一个例如，使用方法引用完成递归可能会更直接：

If you really want to generate a stream recursively (not necessarily walking the file tree, but I'll continue using that as an example), it might be a bit more straightforward to accomplish the recursion using method references:

class RecursiveStream {
    static Stream<Path> listFiles(Path path) {
        if (Files.isDirectory(path)) {
            try { return Files.list(path).flatMap(RecursiveStream::listFiles); }
            catch (Exception e) { return Stream.empty(); }
        } else {
            return Stream.of(path);
        }
    }

    public static void main(String[] args) {
        listFiles(Paths.get(".")).forEach(System.out::println);
    }
}

方法参考对于调整a非常有用具有相同形状（参数和返回类型）的命名方法，作为该功能接口的功能接口。这也避免了在实例或静态变量中存储lambda并以递归方式调用自身的潜在初始化循环。

Method references turn out to be quite useful for adapting a named method that has the same "shape" (arguments and return type) as a functional interface to that functional interface. This also avoids the potential initialization circularity with storing a lambda in an instance or static variable and calling itself recursively.

这篇关于递归流的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！