引用文章地址：https://www.cnblogs.com/caiba/p/9118259.html

先在pom.xml加上包

<!-- poi -->
        <dependency>
            <groupId>org.apache.poi</groupId>
            <artifactId>poi</artifactId>
            <version>RELEASE</version>
        </dependency>
        <dependency>
            <groupId>org.apache.poi</groupId>
            <artifactId>poi-ooxml</artifactId>
            <version>RELEASE</version>
        </dependency>

service代码

public void exportExcel(HttpServletResponse response) throws Exception {
    HSSFWorkbook workbook = new HSSFWorkbook();
    HSSFSheet sheet = workbook.createSheet("碳排放月报表(纳入交易)");
    createTitle(workbook,sheet);
    HSSFRow row = sheet.createRow(2);
        row.setHeightInPoints(18);
        row.createCell(0).setCellValue("装机容量");
        row.createCell(1).setCellValue("MW");
        row.createCell(2).setCellValue("11");
        row.createCell(3).setCellValue("12");
        row.createCell(4).setCellValue("23");
        String fileName = "导出excel例子.xls";

        //生成excel文件
        buildExcelFile(fileName, workbook);

        //浏览器下载excel
        buildExcelDocument(fileName,workbook,response);
}
//创建表头
private void createTitle(HSSFWorkbook workbook,HSSFSheet sheet){
    //合并单元格
    //参数1：起始行 参数2：终止行 参数3：起始列 参数4：终止列
    CellRangeAddress region1 = new CellRangeAddress(0, 1, 0, 0);
    sheet.addMergedRegion(region1);
    HSSFRow row = sheet.createRow(0);
    //设置行高
    row.setHeightInPoints(18);
    //设置列宽度
    sheet.setColumnWidth(0,30*256);
    //设置为居中加粗
    HSSFCellStyle style = workbook.createCellStyle();
    HSSFFont font = workbook.createFont();
    font.setBold(true);
    style.setFont(font);
    style.setAlignment(HorizontalAlignment.CENTER);
    style.setVerticalAlignment(VerticalAlignment.CENTER);
    HSSFCell cell;
    cell = row.createCell(0);
    cell.setCellValue("指标名称");
    cell.setCellStyle(style);
        
    cell = row.createCell(1);
    cell.setCellValue("单位");
    cell.setCellStyle(style);
        
    cell = row.createCell(2);
    cell.setCellValue("本月实际");
    cell.setCellStyle(style);
        
    cell = row.createCell(5);
    cell.setCellValue("全厂小计");
    cell.setCellStyle(style);
}
//生成excel文件
 public void buildExcelFile(String filename,HSSFWorkbook workbook) throws Exception{
        FileOutputStream fos = new FileOutputStream(filename);
        workbook.write(fos);
        fos.flush();
        fos.close();
  }

  //浏览器下载excel
  public void buildExcelDocument(String filename,HSSFWorkbook workbook,HttpServletResponse response) throws Exception{
        response.setContentType("application/vnd.ms-excel");
        response.setHeader("Content-Disposition", "attachment;filename="+URLEncoder.encode(filename, "utf-8"));
        OutputStream outputStream = response.getOutputStream();
        workbook.write(outputStream);
        outputStream.flush();
        outputStream.close();
    }