public static void downloadFile(final Long fileId) throws IOException {
        response.setHeader("Accept-Ranges", "bytes");
        notFoundIfNull(fileId);
        
        File underlyingFile = ... //load file
        String fileName = ...//name of the file

        Header rangeHeader = request.headers.get("range");
        if (rangeHeader != null) {
            throw new PartialContent(underlyingFile, fileName);
        } else {
            renderBinary(new FileInputStream(underlyingFile),
                         fileName, underlyingFile.length(),
                         MimeTypes.getContentType(fileName), false);
        }
}