protected <T> T processVirtualHost(final Function<String, T> func, final T defaultValue) {
        final Tuple3<String, String, String>[] vHosts = ComponentUtil.getFessConfig().getVirtualHosts();
        return LaRequestUtil.getOptionalRequest().map(req -> {
            for (final Tuple3<String, String, String> host : vHosts) {
                final String headerValue = req.getHeader(host.getValue1());