private URL _getPictureURL(String objectId, int width, int height) throws FacebookException {
        String url = buildEndpoint(objectId, "picture");
        HttpResponse res;
        if (width > 0 && height > 0) {
            res = get(url, new HttpParameter[] { new HttpParameter("width", Integer.toString(width)), new HttpParameter("height", Integer.toString(height)) });
        } else {
            res = get(url);
        }
        try {
            return new URL(res.getResponseHeader("Location"));
        } catch (MalformedURLException urle) {
            throw new FacebookException(urle.getMessage(), urle);
        }
    }