java 导出多级表头

Java中导出多级表头可以使用POI库和自定义实现，下面分别介绍两种方法：

1. 使用POI库

使用POI库的方法比较简单，只需要创建Workbook对象，然后在其中创建Sheet对象和Row对象，并在Row对象中创建Cell对象，最后将数据写入Cell中即可。其中，多级表头可以通过合并单元格实现，代码示例：

Workbook workbook = new XSSFWorkbook();
Sheet sheet = workbook.createSheet("Sheet1");
Row row = sheet.createRow(0);

// 创建第一级表头
Cell cell11 = row.createCell(0);
cell11.setCellValue("表头1");
CellRangeAddress region1 = new CellRangeAddress(0, 0, 0, 1); // 合并单元格
sheet.addMergedRegion(region1);

Cell cell12 = row.createCell(2);
cell12.setCellValue("表头2");
CellRangeAddress region2 = new CellRangeAddress(0, 0, 2, 4);
sheet.addMergedRegion(region2);

// 创建第二级表头
Row row2 = sheet.createRow(1);
Cell cell21 = row2.createCell(0);
cell21.setCellValue("子表头1");

Cell cell22 = row2.createCell(1);
cell22.setCellValue("子表头2");

Cell cell23 = row2.createCell(2);
cell23.setCellValue("子表头3");

Cell cell24 = row2.createCell(3);
cell24.setCellValue("子表头4");

Cell cell25 = row2.createCell(4);
cell25.setCellValue("子表头5");

// 创建数据
Row row3 = sheet.createRow(2);
Cell cell31 = row3.createCell(0);
cell31.setCellValue("数据1");

Cell cell32 = row3.createCell(1);
cell32.setCellValue("数据2");

Cell cell33 = row3.createCell(2);
cell33.setCellValue("数据3");

Cell cell34 = row3.createCell(3);
cell34.setCellValue("数据4");

Cell cell35 = row3.createCell(4);
cell35.setCellValue("数据5");

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

2. 自定义实现

如果不想使用POI库，也可以自己实现导出多级表头的功能。具体实现方法是，通过递归实现多级表头的创建和数据的写入，代码示例：

public class ExportExcelUtil {

    public static void exportExcel(HttpServletResponse response, List<List<Object>> dataList, String fileName) {
        response.setContentType("application/vnd.ms-excel");
        response.setHeader("Content-Disposition", "attachment;filename=" + fileName);

        try (OutputStream out = response.getOutputStream()) {
            // 创建工作簿
            HSSFWorkbook workbook = new HSSFWorkbook();

            // 创建工作表
            HSSFSheet sheet = workbook.createSheet("Sheet1");

            // 创建表头
            createHeader(sheet, dataList);

            // 填充数据
            fillData(sheet, dataList);

            workbook.write(out);
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

    private static void createHeader(HSSFSheet sheet, List<List<Object>> dataList) {
        List<Object> headerList = dataList.get(0);
        int rowCnt = getRowCnt(headerList);

        // 创建多级表头
        createMultiLevelHeader(sheet, headerList, rowCnt, 0);
    }

    private static int getRowCnt(List<Object> headerList) {
        int rowCnt = 1;
        for (Object obj : headerList) {
            if (obj instanceof List) {
                int cnt = getRowCnt((List<Object>) obj);
                if (cnt > rowCnt) {
                    rowCnt = cnt;
                }
            }
        }
        return rowCnt;
    }

    private static void createMultiLevelHeader(HSSFSheet sheet, List<Object> headerList, int rowCnt, int rowIndex) {
        HSSFRow row = sheet.getRow(rowIndex);
        if (row == null) {
            row = sheet.createRow(rowIndex);
        }

        int colIndex = 0;
        for (Object obj : headerList) {
            if (obj instanceof List) {
                List<Object> subHeaderList = (List<Object>) obj;
                int subRowCnt = getRowCnt(subHeaderList);
                int subRowIndex = rowIndex + rowCnt - subRowCnt;
                createMultiLevelHeader(sheet, subHeaderList, subRowCnt, subRowIndex);

                int colSpan = getColSpan(subHeaderList);
                HSSFCell cell = row.createCell(colIndex);
                cell.setCellValue((String) subHeaderList.get(0));
                CellRangeAddress region = new CellRangeAddress(rowIndex, rowIndex + rowCnt - 1, colIndex, colIndex + colSpan - 1);
                sheet.addMergedRegion(region);

                colIndex += colSpan;
            } else {
                HSSFCell cell = row.createCell(colIndex);
                cell.setCellValue((String) obj);

                colIndex++;
            }
        }
    }

    private static int getColSpan(List<Object> headerList) {
        int colSpan = 0;
        for (Object obj : headerList) {
            if (obj instanceof List) {
                colSpan += getColSpan((List<Object>) obj);
            } else {
                colSpan += 1;
            }
        }
        return colSpan;
    }

    private static void fillData(HSSFSheet sheet, List<List<Object>> dataList) {
        int rowIndex = getRowCnt(dataList.get(0));
        int colIndex = 0;
        for (List<Object> rowList : dataList) {
            HSSFRow row = sheet.createRow(rowIndex++);
            colIndex = 0;
            for (Object obj : rowList) {
                HSSFCell cell = row.createCell(colIndex++);
                cell.setCellValue((String) obj);
            }
        }
    }
}

以上两种方法都可以实现多级表头的导出，选择哪种方法取决于具体情况。