java导出Excel

加入pom依赖：
<dependency>
<groupId>org.apache.poi</groupId>
<artifactId>poi</artifactId>
<version>3.17</version>
</dependency>
<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>

下载Excel：
public void download(HttpServletRequest request, HttpServletResponse response) throws IOException {

    // HSSFWorkbook workbook = new HSSFWorkbook();
    XSSFWorkbook workbook = new XSSFWorkbook();
    // 创建一个Excel表单,参数为sheet的名字
    XSSFSheet sheet = workbook.createSheet();
    // 创建表头
    setTitle(workbook, sheet);

    // 新增数据行，并且设置单元格数据
    int rowNum = 1;
    for (Map<String, Object> answer : answerList) {
        XSSFRow row = sheet.createRow(rowNum);
        row.createCell(0).setCellValue(answer.get("totalAmount").toString());
        row.createCell(1).setCellValue(answer.get("generationTime").toString());
        row.createCell(2).setCellValue(answer.get("username").toString());
        rowNum++;
    }

    String fileName = "orders.xlsx";
    // 清空response
    response.reset();
    // 设置response的Header
    response.addHeader("Content-Disposition", "attachment;filename=" + fileName);
    OutputStream os = new BufferedOutputStream(response.getOutputStream());
    response.setContentType("application/vnd.ms-excel;charset=gb2312");
    // 将excel写入到输出流中
    workbook.write(os);
    System.out.println(os);
    os.flush();
    os.close();
}

设置表头：
private void setTitle(XSSFWorkbook workbook, XSSFSheet sheet) {
XSSFRow row = sheet.createRow(0);
// 设置列宽，setColumnWidth的第二个参数要乘以256，这个参数的单位是1/256个字符宽度
sheet.setColumnWidth(0, 20 * 256);
sheet.setColumnWidth(1, 20 * 256);
sheet.setColumnWidth(2, 20 * 256);

    // 设置为居中加粗
    XSSFCellStyle style = workbook.createCellStyle();
    XSSFFont font = workbook.createFont();
    font.setBold(true);
    style.setFont(font);

    XSSFCell cell;
    cell = row.createCell(0);
    cell.setCellValue("订单金额");
    cell.setCellStyle(style);

    cell = row.createCell(1);
    cell.setCellValue("订单时间");
    cell.setCellStyle(style);

    cell = row.createCell(2);
    cell.setCellValue("购买人");
    cell.setCellStyle(style);
}