* comment: Field name for content length in the index.
     * @return The value of found property. (NotNull: if not found, exception but basically no way)
     */
    String getIndexFieldContentLength();

    /**
     * Get the value for the key 'index.field.filetype'. <br>
     * The value is, e.g. filetype <br>
     * comment: Field name for file type in the index.

            // filetype
            putResultDataBody(dataMap, fessConfig.getIndexFieldFiletype(), fileTypeHelper.get(mimeType));
        }
        // content_length
        putResultDataBody(dataMap, fessConfig.getIndexFieldContentLength(), Long.toString(responseData.getContentLength()));
        // last_modified
        final Date lastModified = responseData.getLastModified();
        if (lastModified != null) {

            // filetype
            putResultDataBody(dataMap, fessConfig.getIndexFieldFiletype(), fileTypeHelper.get(mimeType));
        }
        // content_length
        putResultDataBody(dataMap, fessConfig.getIndexFieldContentLength(), Long.toString(responseData.getContentLength()));
        // last_modified
        final Date lastModified = getLastModified(dataMap, responseData);
        if (lastModified != null) {