Java POI导出Excel时合并单元格没有边框的问题解决

// 使用这种方式合并单元格时，要给单元格逐一设置带边框的样式
sheet.addMergedRegion(new CellRangeAddress(1, 1, 1, 3));
// 例如：
HSSFCellStyle defaultStyle = ExportToExcelUtil.setDefaultStyle(workbook);
// 为单元格设置带边框的样式
setCellStyles(row, 2, 3, defaultStyle );

/**
* 设置单元格样式
*/
private void setCellStyles(HSSFRow row, int start, int end, HSSFCellStyle cellStyle) {
    for (int i = start; i <= end; i++) {
       cell = row.createCell(i);
       cell.setCellStyle(cellStyle);
    }
} 

/**
* 带边框的样式+
*/
public static HSSFCellStyle setDefaultStyle(HSSFWorkbook workbook) {
	HSSFCellStyle cellStyle = workbook.createCellStyle();
	// 边框
	cellStyle.setBorderBottom(BorderStyle.THIN);
	cellStyle.setBorderLeft(BorderStyle.THIN);
	cellStyle.setBorderRight(BorderStyle.THIN);
	cellStyle.setBorderTop(BorderStyle.THIN);
	return cellStyle;
}

// 合并单元格
CellRangeAddress region = new CellRangeAddress(1, 1, 2, 2);
sheet.addMergedRegion(region);
                        
// 合并之后为合并的单元格设置样式
setRegionStyle(sheet, region, defaultStyle);

/**
* 为合并的单元格设置样式（可根据需要自行调整）
*/
@SuppressWarnings("deprecation")
public static void setRegionStyle(HSSFSheet sheet, CellRangeAddress region, HSSFCellStyle cs) {
    for (int i = region.getFirstRow(); i <= region.getLastRow(); i++) {
         HSSFRow row = sheet.getRow(i);
         if (null == row) row = sheet.createRow(i);
         for (int j = region.getFirstColumn(); j <= region.getLastColumn(); j++) {
              HSSFCell cell = row.getCell(j);
              if (null == cell) cell = row.createCell(j);
              cell.setCellStyle(cs);
         }
     }
}