poi导出合并单元格工具类

以下是使用POI导出合并单元格的工具类示例代码：

public class ExcelUtil {
    /**
     * 导出Excel
     * @param response HttpServletResponse
     * @param fileName 文件名
     * @param title 标题
     * @param headers 表头
     * @param dataset 数据集合
     * @throws IOException
     */
    public static void exportExcel(HttpServletResponse response, String fileName, String title, String[] headers, Collection<?> dataset) throws IOException {
        OutputStream out = null;
        try {
            // 创建工作簿
            HSSFWorkbook workbook = new HSSFWorkbook();
            // 创建工作表
            HSSFSheet sheet = workbook.createSheet(title);
            // 设置表格默认列宽度为15个字符
            sheet.setDefaultColumnWidth(15);
            // 创建标题行
            HSSFRow row = sheet.createRow(0);
            HSSFCell cellTitle = row.createCell(0);
            // 合并单元格
            sheet.addMergedRegion(new CellRangeAddress(0, 0, 0, headers.length - 1));
            // 设置标题样式
            HSSFCellStyle titleStyle = getTitleStyle(workbook);
            cellTitle.setCellStyle(titleStyle);
            cellTitle.setCellValue(title);
            // 创建表头行
            row = sheet.createRow(1);
            // 设置表头样式
            HSSFCellStyle headerStyle = getHeaderStyle(workbook);
            for (int i = 0; i < headers.length; i++) {
                HSSFCell cell = row.createCell(i);
                cell.setCellStyle(headerStyle);
                cell.setCellValue(headers[i]);
            }
            // 创建数据行
            Iterator<?> it = dataset.iterator();
            int index = 2;
            while (it.hasNext()) {
                row = sheet.createRow(index);
                Object t = it.next();
                Field[] fields = t.getClass().getDeclaredFields();
                for (int i = 0; i < fields.length; i++) {
                    HSSFCell cell = row.createCell(i);
                    cell.setCellValue(getFieldValueByName(fields[i].getName(), t));
                }
                index++;
            }
            // 输出Excel文件
            response.setContentType("application/vnd.ms-excel");
            response.setHeader("Content-disposition", "attachment;filename=" + URLEncoder.encode(fileName, "UTF-8"));
            out = response.getOutputStream();
            workbook.write(out);
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            if (out != null) {
                out.close();
            }
        }
    }

    /**
     * 根据属性名获取属性值
     * @param fieldName 属性名
     * @param o 对象
     * @return 属性值
     */
    private static Object getFieldValueByName(String fieldName, Object o) {
        try {
            String firstLetter = fieldName.substring(0, 1).toUpperCase();
            String getter = "get" + firstLetter + fieldName.substring(1);
            Method method = o.getClass().getMethod(getter, new Class[] {});
            Object value = method.invoke(o, new Object[] {});
            return value;
        } catch (Exception e) {
            return null;
        }
    }

    /**
     * 获取标题样式
     * @param workbook 工作簿
     * @return 标题样式
     */
    private static HSSFCellStyle getTitleStyle(HSSFWorkbook workbook) {
        HSSFCellStyle style = workbook.createCellStyle();
        style.setAlignment(HorizontalAlignment.CENTER);
        style.setVerticalAlignment(VerticalAlignment.CENTER);
        HSSFFont font = workbook.createFont();
        font.setFontName("宋体");
        font.setFontHeightInPoints((short) 16);
        font.setBold(true);
        style.setFont(font);
        return style;
    }

    /**
     * 获取表头样式
     * @param workbook 工作簿
     * @return 表头样式
     */
    private static HSSFCellStyle getHeaderStyle(HSSFWorkbook workbook) {
        HSSFCellStyle style = workbook.createCellStyle();
        style.setAlignment(HorizontalAlignment.CENTER);
        style.setVerticalAlignment(VerticalAlignment.CENTER);
        style.setFillForegroundColor(IndexedColors.GREY_25_PERCENT.getIndex());
        style.setFillPattern(FillPatternType.SOLID_FOREGROUND);
        HSSFFont font = workbook.createFont();
        font.setFontName("宋体");
        font.setFontHeightInPoints((short) 12);
        font.setBold(true);
        style.setFont(font);
        return style;
    }
}