修復Java使用POI合並Excel單元格后，邊框不顯示的問題

使用Apache POI生成Excel文檔時，當進行單元格合並操作后，被合並的單元格邊框會消失，使用如下方式可以解決。

• 創建方法：

      public void setBorderStyle(int border, CellRangeAddress region, HSSFSheet sheet, HSSFWorkbook wb){
          RegionUtil.setBorderBottom(border, region, sheet, wb);　　//下邊框
          RegionUtil.setBorderLeft(border, region, sheet, wb);     //左邊框
          RegionUtil.setBorderRight(border, region, sheet, wb);    //右邊框
          RegionUtil.setBorderTop(border, region, sheet, wb);      //上邊框
      }

• 調用方式：

      //創建wb,sheet的過程略過
      CellRangeAddress region = new CellRangeAddress(0, 0, i, i+1);    //給定要合並的單元格范圍
      sheet.addMergedRegion(region);      //這是合並單元格過程
      setBorderStyle(HSSFCellStyle.BORDER_THIN, region, sheet, wb);   //給合並過的單元格加邊框