WritableCellFormat headerFormat = new WritableCellFormat(
                    HEADER_FONT_STYLE);
            //水平居中对齐
            headerFormat.setAlignment(Alignment.CENTRE);
            //竖直方向居中对齐
            headerFormat.setVerticalAlignment

(VerticalAlignment.CENTRE);
           
            //建立标签，参数依次为：列索引、行索引、内容、格式
            Label seqLabel = new Label(0, 0, "序号", headerFormat);
            //增加单元格
            sheet.addCell(seqLabel);
            //合并单元格，参数依次为：列索引、行索引、列索引+需要合并

的列的个数、行索引+需要合并的行的个数
            sheet.mergeCells(0, 0, 0, 1);
            //设置单元格宽度，以字符为单位
            sheet.setColumnView(0, "序号".length() + 10);

            Label basicInfoLabel = new Label(1, 0, "基本信息",

headerFormat);
            sheet.addCell(basicInfoLabel);
            sheet.mergeCells(1, 0, 3, 0);//合并垮了3行。

         sheet.mergeCells(1, 1, 1, 3);//合并垮了3列。

         label = new Label(0, 1, "苹果”);
         sheet.mergeCells(0,1, 0, 3- 1);//合并垮了3列。
         WritableCellFormat cellFormat = new WritableCellFormat();
         cellFormat.setVerticalAlignment(VerticalAlignment.CENTRE);

// 垂直居中
         label.setCellFormat(cellFormat);
         sheet.addCell(label);

         注：再次使cellFormat时，需要重新NEW WritableCellFormat 。