*
     * @param doc the document data map
     * @return the stream response containing document content
     * @throws FessSystemException if content cannot be retrieved
     */
    public StreamResponse asContentResponse(final Map<String, Object> doc) {
        if (logger.isDebugEnabled()) {
            logger.debug("writing the content of: {}", doc);
        }
        final FessConfig fessConfig = ComponentUtil.getFessConfig();