Recursively list files in Java

Question

How do I recursively list all files under a directory in Java? Does the framework provide any utility?

I saw a lot of hacky implementations. But none from the fra

Answer 1

My version (of course I could have used the built in walk in Java 8 ;-) ):

public static List findFilesIn(File rootDir, Predicate predicate) {
        ArrayList collected = new ArrayList<>();
        walk(rootDir, predicate, collected);
        return collected;
    }

    private static void walk(File dir, Predicate filterFunction, List collected) {
        Stream.of(listOnlyWhenDirectory(dir))
                .forEach(file -> walk(file, filterFunction, addAndReturn(collected, file, filterFunction)));
    }

    private static File[] listOnlyWhenDirectory(File dir) {
        return dir.isDirectory() ? dir.listFiles() : new File[]{};
    }

    private static List addAndReturn(List files, File toAdd, Predicate filterFunction) {
        if (filterFunction.test(toAdd)) {
            files.add(toAdd);
        }
        return files;
    }