Workbook workbook = cell.getSheet().getWorkbook();
CellStyle cellStyle = workbook.createCellStyle();
cellStyle.setDataFormat(HSSFDataFormat.getBuiltinFormat("#,##0.00"));
cell.setCellStyle(cellStyle);

Workbook workbook = cell.getSheet().getWorkbook();
CellStyle cellStyle = workbook.createCellStyle();
cellStyle.setDataFormat(HSSFDataFormat.getBuiltinFormat("#,##0.00"));
cell.setCellStyle(cellStyle);