public static String makeSafeName(final FeedKey feedKey) {
        // Make a dir name.
        final StringBuilder sb = new StringBuilder();
        if (feedKey.feed() != null) {
            sb.append(DirUtil.makeSafeName(feedKey.feed()));
        }
        sb.append("__");
        if (feedKey.type() != null) {
            sb.append(DirUtil.makeSafeName(feedKey.type()));
        }
        return sb.toString();
    }
@param feedKey
@return A dir name like '{@code <feed>__<type>}',
where {@link DirUtil#makeSafeName(String)} has been called for each part.
stroom-proxy/stroom-proxy-app/src/main/java/stroom/proxy/app/handler/DirUtil.java