Iterator it = dataStore.iterator();
int rownum = beginRowData;
short formatIndexInt = HSSFDataFormat.getBuiltinFormat("#,##0");
CellStyle cellStyleInt = wb.createCellStyle(); // cellStyleInt is the default cell style for integers
cellStyleInt.cloneStyleFrom(dCellStyle);
cellStyleInt.setDataFormat(formatIndexInt);
short formatIndexDoub = HSSFDataFormat.getBuiltinFormat("#,##0.00");
CellStyle cellStyleDoub = wb.createCellStyle(); // cellStyleDoub is the default cell style for doubles
cellStyleDoub.cloneStyleFrom(dCellStyle);