How to sort List to list directories first and grouping files by directory?

问题

In order to get all files contained in a specified directory and according to some extensions, I'm using the method listFiles of class FileUtils from Apache Commons IO library, as in the following code sample.

ArrayList<String> wildcards = new ArrayList<>();
wildcards.add("*.cpp");
wildcards.add("*.h");
wildcards.add("*.txt");

File dir = new File("/path/to/dir");
Collection<File> found = FileUtils.listFiles(
        dir,
        new WildcardFileFilter(wildcards, IOCase.SENSITIVE),
        DirectoryFileFilter.DIRECTORY);

List<File> files = new ArrayList<>(found);

The order of items in the resulting Collection<File> varies in the different operating systems, so I would sort them (ie. the wrapping list files) in according to the following rules.

The directories should be listed before the files.
The sorting routine should group files by directory.

Example:

/path/to/dir/first/subpath/main.cpp
/path/to/dir/first/subpath/utils.cpp
/path/to/dir/first/subpath/utils.h
/path/to/dir/first/main.cpp
/path/to/dir/first/utils.cpp
/path/to/dir/first/utils.h
/path/to/dir/second/main.cpp
/path/to/dir/second/utils.cpp
/path/to/dir/second/utils.h
/path/to/dir/README.txt

回答1:

You can use Java 8's streams to solve your problem. Something like this should work:

//untested
Map<Path, List<Path>> dirToFileMap = files.stream()
            .map(f -> Paths.get(f.getAbsolutePath()))
            .collect(Collectors.groupingBy(Path::getParent));

With that map you can achieve what you need. Iterate over keySet first, for example.

回答2:

Just a matter of typing; below I do not take canonical paths (Windows is case-insensitive), but the gist is clear.

So a Comparator for sorting:

public class FileComparator extends Comparator<File> {

    @Override
    public int compareTo(File lhs, File rhs) {
        if (lhs == null && rhs == null) {
            return 0;
        } else if (lhs == null || rhs == null) {
            return lhs == null ? -1 : 1;
        }
        int cmp = compareTo(lhs.getParentFile(), rhs.getParentFile());
        if (cmp == 0) {
            if (lhs.isDirectory() != rhs.isDirectory()) {
                return lhs.isDirectory() ? -1 : 1;
            }
            cmp = lhs.getName().compareTo(rhs.getName());
        }
        return cmp;
    }

    @Override
    public boolean equals(Object comparator) {
        return comparator != null && comparator.getClass().equals(getClass());
    }
}

As always the equals just compares comparators, not Files.

来源：https://stackoverflow.com/questions/32312738/how-to-sort-listfile-to-list-directories-first-and-grouping-files-by-directory

标签

java