比较<文件>对于“目录优先”订购 [英] Comparator<File> for "directories-first" order

问题描述

我很难过...假设我有这个目录树：

I'm stumped... Let's say I have this directory tree:

{someRoot}/
{someRoot}/bar/
{someRoot}/bar/file1.txt
{someRoot}/foo/
{someRoot}/foo/baz/
{someRoot}/foo/baz/file3.txt
{someRoot}/foo/abracadabra.txt
{someRoot}/foo/file2.txt
{someRoot}/aardvark.txt
{someRoot}/food.txt
{someRoot}/zebra.txt

您会注意到订购。将此 order1 称为。在每个阶段，目录首先出现在文件之前。 （注意： bar / file1.txt 在 foo 之前，所以在全球范围内，目录并非都在所有文件之前。）

You'll note the ordering. Call this order1. At each stage, the directories come first before the files. (NOTE: bar/file1.txt comes before foo, so on a global basis, the directories do not all come before all the files.)

如果我枚举这个目录树，然后递归枚举子目录，我将得到以下列表<文件> ，订购 order2 。

If I enumerate this directory tree, and then recursively enumerate the subdirectories, I'll get the following List<File>, with ordering order2.

{someRoot}/
{someRoot}/aardvark.txt
{someRoot}/bar/
{someRoot}/foo/
{someRoot}/food.txt
{someRoot}/zebra.txt
{someRoot}/bar/file1.txt
{someRoot}/foo/abracadabra.txt
{someRoot}/foo/baz/
{someRoot}/foo/file2.txt
{someRoot}/foo/baz/file3.txt

如果我创建直截了当的比较器<文件> ：

If I create the straightforward Comparator<File>:

Comparator<File> fc = new Comparator<File>(){
    @Override public int compare(File o1, File o2) {
        return o1.compareTo(o2);
    }
};

我排序，我从词典排序中得到这个排序（ order3 ） ：

and I sort, I get this ordering (order3) from lexicographic ordering:

{someRoot}
{someRoot}/aardvark.txt
{someRoot}/bar
{someRoot}/bar/file1.txt
{someRoot}/foo
{someRoot}/food.txt
{someRoot}/foo/abracadabra.txt
{someRoot}/foo/baz
{someRoot}/foo/baz/file3.txt
{someRoot}/foo/file2.txt
{someRoot}/zebra.txt

但我不想要这个订单（有问题：注意 food.txt 介于目录 foo 及其子项目之间），我想 order1 。我怎么能写一个比较器来帮我？

But I don't want this ordering (which has problems: note that food.txt comes between directory foo and its sub-items), I want order1. How can I write a Comparator to get me that?

推荐答案

这在我的测试中有效。

new Comparator<File>() {
    @Override
    public int compare(File first, File second) {
        if (first.isDirectory() && second.isDirectory())
            return first.compareTo(second);

        if (first.isDirectory())
            return this.compareToFile(first, second);

        if (second.isDirectory())
            return -(this.compareToFile(second, first));

        return this.compareFiles(first, second);
    }

    private int compareFiles(File first, File second) {
        File firstParentFile = first.getParentFile();
        File secondParentFile = second.getParentFile();

        if (isSubDir(firstParentFile, secondParentFile))
            return -1;

        if (isSubDir(secondParentFile, firstParentFile))
            return 1;

        return first.compareTo(second);
    }

    private int compareToFile(File directory, File file) {
        File fileParent = file.getParentFile();
        if (directory.equals(fileParent))
            return -1;

        if (isSubDir(directory, fileParent))
            return -1;

        return directory.compareTo(file);
    }

    private boolean isSubDir(File directory, File subDir) {
        for (File parentDir = directory.getParentFile(); parentDir != null; parentDir = parentDir.getParentFile()) {
            if (subDir.equals(parentDir)) {
                return true;
            }
        }

        return false;
    }

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