Java: how to get all subdirs recursively?

You can get all subdirs with the following snippet:

File file = new File("path");
File[] subdirs = file.listFiles(new FileFilter() {
    public boolean accept(File f) {
        return f.isDirectory();
    }
});

This gets only immediate subdirs, to retrieve all of them recursively you could write:

List<File> getSubdirs(File file) {
    List<File> subdirs = Arrays.asList(file.listFiles(new FileFilter() {
        public boolean accept(File f) {
            return f.isDirectory();
        }
    }));
    subdirs = new ArrayList<File>(subdirs);

    List<File> deepSubdirs = new ArrayList<File>();
    for(File subdir : subdirs) {
        deepSubdirs.addAll(getSubdirs(subdir)); 
    }
    subdirs.addAll(deepSubdirs);
    return subdirs;
}

No, there is no such functionality in the Java standard API. But there is in Apache commons-io; if you don't want to include it as a library, you could also look at the source code.

Another version with no recursion, and alphabetical order. Also uses a Set to avoid loops (a problem in Unix systems with links).

   public static Set<File> subdirs(File d) throws IOException {
        TreeSet<File> closed = new TreeSet<File>(new Comparator<File>() {
            @Override
            public int compare(File f1, File f2) {
                return f1.toString().compareTo(f2.toString());
            }
        });
        Deque<File> open = new ArrayDeque<File>();
        open.push(d);
        closed.add(d);
        while ( ! open.isEmpty()) {
            d = open.pop();
            for (File f : d.listFiles()) {
                if (f.isDirectory() && ! closed.contains(f)) {
                    open.push(f);
                    closed.add(f);
                }
            }
        }
        return closed;
    }