public DataFormatData dataFormatData(int dateFormatIndexInteger) {
        return dataFormatDataCache.computeIfAbsent(dateFormatIndexInteger, key -> {
            DataFormatData dataFormatData = new DataFormatData();
            if (stylesTable == null) {
                return null;
            }
            XSSFCellStyle xssfCellStyle = stylesTable.getStyleAt(dateFormatIndexInteger);
            if (xssfCellStyle == null) {
                return null;
            }
            dataFormatData.setIndex(xssfCellStyle.getDataFormat());
            dataFormatData.setFormat(BuiltinFormats.getBuiltinFormat(dataFormatData.getIndex(),
                xssfCellStyle.getDataFormatString(), globalConfiguration().getLocale()));
            return dataFormatData;
        });
    }
excel Relationship, key: sheetNo value: PackageRelationshipCollection
fastexcel-core/src/main/java/cn/idev/excel/read/metadata/holder/xlsx/XlsxReadWorkbookHolder.java