// not only this cell but other cells.
HSSFCellStyle cellStyle = wb.createCellStyle();
DataFormat df = wb.createDataFormat();
// cellStyle.setDataFormat(HSSFDataFormat.getBuiltinFormat("m/d/yy"));
cellStyle.setDataFormat(df.getFormat("YYYY-MM-DD HH:MM:SS"));
cell = row.createCell(1);
cell.setCellValue(new Date());
cell.setCellStyle(cellStyle);
// Write the output to a file
FileOutputStream fileOut = new FileOutputStream("src/test/resources/workbook.xls");
wb.write(fileOut);