@Override
    public String convertToJavaData(ReadCellData<?> cellData, ExcelContentProperty contentProperty,
                                    GlobalConfiguration globalConfiguration) {
        // If there are "DateTimeFormat", read as date
        if (contentProperty != null && contentProperty.getDateTimeFormatProperty() != null) {
            return DateUtils.format(cellData.getNumberValue(),
                contentProperty.getDateTimeFormatProperty().getUse1904windowing(),
                contentProperty.getDateTimeFormatProperty().getFormat());
        }
        // If there are "NumberFormat", read as number
        if (contentProperty != null && contentProperty.getNumberFormatProperty() != null) {
            return NumberUtils.format(cellData.getNumberValue(), contentProperty);
        }
        // Excel defines formatting
        boolean hasDataFormatData = cellData.getDataFormatData() != null
            && cellData.getDataFormatData().getIndex() != null && !StringUtils.isEmpty(
            cellData.getDataFormatData().getFormat());
        if (hasDataFormatData) {
            return NumberDataFormatterUtils.format(cellData.getNumberValue(),
                cellData.getDataFormatData().getIndex(), cellData.getDataFormatData().getFormat(), globalConfiguration);
        }
        // Default conversion number
        return NumberUtils.format(cellData.getNumberValue(), contentProperty);
    }
String and number converter

@author Jiaju Zhuang
fastexcel-core/src/main/java/cn/idev/excel/converters/string/StringNumberConverter.java