For date format try this if condition on your date formatted cell.
if(HSSFDateUtil.isCellDateFormatted(cell))
{
// data.append(cell.getDateCellValue() + "|");
SimpleDateFormat DtFormat = new SimpleDateFormat("yyyy-mm-dd");
Date date=Test.getRow(RowNum).getCell(CellNum).getDateCellValue();
data.append(date);
}