protected O options() {
        ExporterOptions opts = exportConfiguration.getOptions();
        if (opts != null) {
            if (defaultOptions.getClass().isAssignableFrom(opts.getClass())) {
                return (O) opts;
            }
            else {
                throw new IllegalArgumentException("Options must be an instance of " + defaultOptions.getClass().getName());
            }
        }

        return defaultOptions;
    }
Gets and caches the list of UIColumns that are exportable="true", visible="true", and rendered="true".
Orders them by displayPriority so they match the UI display of the columns.

@param table the Table with columns to export
@return the List<UIColumn> that are exportable
primefaces/src/main/java/org/primefaces/component/export/TableExporter.java