数据是这样

模板是这样

导出后是这样

DataSet set = new DataSet();

DataRow row = new DataRow();
row.put("Y","2020");
row.put("M","1");
row.put("D","1");
set.add(row);

DataRow row2 = new DataRow();
row2.put("Y","2020");
row2.put("M","1");
row2.put("D","2");
set.add(row2);

DataRow row3 = new DataRow();
row3.put("Y","1999");
row3.put("M","1");
row3.put("D", null);
set.add(row3);

set.replaceEmpty("/");//替换空值的数据

TableBuilder builder = TableBuilder.init()
.setDatas(set)//设置数据源
.setFields("Y","M","D")//设置需要导出的属性(列)
.addUnion("Y","M(Y)");//设置需要合并行的列,如果年相同的合并,月相同的合并(前提是年相同)
File file = new File("模板地址");
ExcelUtil.export(file, "sheet名称", 2, builder.build()); //从第2行插入(根据表头行数)

System.out.println(builder.build().build()); //看一下输入对应的html

参考【示例源码】