Check if file is in (sub)directory

Question

I would like to check whether an existing file is in a specific directory or a subdirectory of that.

I have two File objects.

File dir;
File file;
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Answer 1

I would create a small utility method:

public static boolean isInSubDirectory(File dir, File file) {

    if (file == null)
        return false;

    if (file.equals(dir))
        return true;

    return isInSubDirectory(dir, file.getParentFile());
}