使用POI 导出Excel 动态合并单元格

使用POI导出Excel并动态合并单元格需要以下几个步骤：

1. 创建工作簿和工作表对象

Workbook workbook = new XSSFWorkbook();
Sheet sheet = workbook.createSheet("Sheet1");

2. 创建单元格样式对象

CellStyle style = workbook.createCellStyle();
style.setAlignment(HorizontalAlignment.CENTER);
style.setVerticalAlignment(VerticalAlignment.CENTER);

3. 创建行和单元格对象，并设置单元格内容和样式

Row row = sheet.createRow(0);
Cell cell = row.createCell(0);
cell.setCellValue("合并单元格");
cell.setCellStyle(style);

4. 动态合并单元格

CellRangeAddress cellRangeAddress = new CellRangeAddress(0, 2, 0, 2); // 合并第1行到第3行，第1列到第3列的单元格
sheet.addMergedRegion(cellRangeAddress);

完整代码示例：

Workbook workbook = new XSSFWorkbook();
Sheet sheet = workbook.createSheet("Sheet1");

CellStyle style = workbook.createCellStyle();
style.setAlignment(HorizontalAlignment.CENTER);
style.setVerticalAlignment(VerticalAlignment.CENTER);

Row row = sheet.createRow(0);
Cell cell = row.createCell(0);
cell.setCellValue("合并单元格");
cell.setCellStyle(style);

CellRangeAddress cellRangeAddress = new CellRangeAddress(0, 2, 0, 2); // 合并第1行到第3行，第1列到第3列的单元格
sheet.addMergedRegion(cellRangeAddress);

FileOutputStream fos = new FileOutputStream("test.xlsx");
workbook.write(fos);
fos.close();
workbook.close();