public class CSVExportFormatter implements TableExportFormatter {

	private CopyOnWriteArrayList<String> fieldList = new CopyOnWriteArrayList<>();

	public String preFormat(EntityProjection projection, TableExport query) {
		// Retrieve fields in query order
		List<String> fields = parseFieldsFrom(query.getQuery());
		
		if(fields.isEmpty()){
			fieldList.clear();
			// default field order
			return String.join(", ", projection.getRequestedFields()))
		} else {
			fieldList.addAll(fields);
			return String.join(", ", fields))
		}
	}
	
	public String format(PersistentResource resource, Integer recordNumber) {
                // Either uses fieldList or default order
		return generateCsv(resource, fieldList);
	}
}

public String preFormat(EntityProjection projection, TableExport query) {
    log.info("query = " + query.getQuery());
    log.info("requested = " + String.join(", ", projection.getRequestedFields()));
}

Log:
query = /foo?page%5Btotals%5D=true&page%5Bnumber%5D=1&page%5Bsize%5D=500&fields%5Bfoo%5D=startDate,endDate,status,createdAt,createdBy,updatedAt,updatedBy
requested = updatedAt, startDate, updatedBy, endDate, createdBy, createdAt, status