POI를 사용하여 Java에서 Excel 테이블을 가져오고 내보내는 방법

<dependency>
      <groupId>org.apache.poi</groupId>
      <artifactId>poi-ooxml</artifactId>
       <version>4.1.2</version>
</dependency>

/**
     * Excel导入 
     */
    @PostMapping("/import")
    public Result userImport2(@RequestParam("file") MultipartFile file) throws Exception{
        Result result=userService.userImportExcel(file);
        return result;
    }

public Result userImportExcel(MultipartFile file){
    try {
        InputStream inputStream = file.getInputStream();
        XSSFWorkbook sheets = new XSSFWorkbook(inputStream);
        //获取表单sheet 第一个
        XSSFSheet sheetAt = sheets.getSheetAt(0);
        //获取第一行
        int firstRowNum = sheetAt.getFirstRowNum();
        //最后一行
        int lastRowNum = sheetAt.getLastRowNum();
        //存入数据集合
        List<User> users=new ArrayList<>();
        //遍历数据
        for(int i=firstRowNum+1;i<lastRowNum+1;i++){
            XSSFRow row = sheetAt.getRow(i);
            if(row!=null){
               /* //获取第一行的第一列
                int firstCellNum = row.getFirstCellNum();
                //获取第一行的最后列
                short lastCellNum = row.getLastCellNum();
                for (int j=firstCellNum;j<lastCellNum+1;j++){
                    //放入集合中需要可以用这种方法
                    String cellValue = getValue(row.getCell(firstCellNum));
                }*/
                //这里我就直接赋值
                User user = new User();
                user.setUname(row.getCell(0).getStringCellValue());
                user.setUpassword(row.getCell(1).getStringCellValue());
                user.setUsex(row.getCell(2).getStringCellValue());
                user.setRole(row.getCell(3).getStringCellValue());
                user.setUlove((int) row.getCell(4).getNumericCellValue());
                user.setUphoto(row.getCell(5).getStringCellValue());
                user.setUaddress(row.getCell(6).getStringCellValue());
                users.add(user);
            }
        }
        //保存数据
        saveBatch(users);
        return Result.success();
    }catch (Exception e){
        e.printStackTrace();
        log.info("error:{}",e);
    }

    return Result.error("300","导入失败");
}

/**
 * 判断值的类型
 */
public String getValue(HSSFCell cell) {

    if(cell==null){
        return "";
    }
    String cellValue= "";
    try {
        DecimalFormat df=new DecimalFormat("0.00");
        if(cell.getCellType()== CellType.NUMERIC){
            //日期时间转换
            if(HSSFDateUtil.isCellDateFormatted(cell)){
                cellValue=DateFormatUtils.format(cell.getDateCellValue(),"yyyy-MM-dd");
            }else{
                NumberFormat instance = NumberFormat.getInstance();
                cellValue=instance.format(cell.getNumericCellValue()).replace(",","");
            }

        }else if(cell.getCellType() == CellType.STRING){
            //字符串
            cellValue=cell.getStringCellValue();
        }else if(cell.getCellType() == CellType.BOOLEAN){
            //Boolean
            cellValue= String.valueOf(cell.getBooleanCellValue());
        }else if(cell.getCellType() == CellType.ERROR){
            //错误
        }else if(cell.getCellType() == CellType.FORMULA){
            //转换公式 保留两位
            cellValue=df.format(cell.getNumericCellValue());
        }else{
            cellValue=null;
        }

    } catch (Exception e) {
        e.printStackTrace();
        cellValue="-1";
    }

    return cellValue;
}

/**
 * 导出 
 * @param response
 * @return
 * @throws Exception
 */
@GetMapping("/export")
public Result userExport2(HttpServletResponse response) throws Exception{
    Result result=userService.userExportExcel(response);
    return result;
}

public Result userExportExcel(HttpServletResponse response) {
    try {
        //创建excel
        XSSFWorkbook sheets = new XSSFWorkbook();
        //创建行
        XSSFSheet sheet = sheets.createSheet("用户信息");
        //格式设置
        XSSFCellStyle cellStyle = sheets.createCellStyle();
        //横向居中
        cellStyle.setAlignment(HorizontalAlignment.CENTER);
        //创建单元格第一列
        XSSFRow row = sheet.createRow(0);
        //表头
        this.titleExcel(row,cellStyle);
        //查询全部的用户数据  mybatis-plus
        List<User> list = list();
        //遍历设置值
        for(int i=0;i<list.size();i++){
            XSSFRow rows = sheet.createRow(i+1);
            User user=list.get(i);
            //表格里赋值
            this.titleExcelValue(user,rows,cellStyle);
        }
        //设置浏览器响应格式
        response.setContentType("application/vnd.openxmlformats-officedocument.spreadsheetml.sheet;charset=utf-8");
        String filName= URLEncoder.encode("用户信息","UTF-8");
        response.setHeader("Content-Disposition","attachment;filename="+filName+".xls");

        ServletOutputStream outputStream=response.getOutputStream();
        sheets.write(outputStream);
        outputStream.close();
        sheets.close();
        return Result.success();

    }catch (Exception e){
        e.printStackTrace();
        log.info("error:{}",e);
    }

    return Result.error("300","导出失败");
}

/**
*表格里赋值
**/
public void titleExcelValue(User user, XSSFRow row,XSSFCellStyle cellStyle) {
    XSSFCell cellId = row.createCell(0);
    cellId.setCellValue(user.getUid());
    cellId.setCellStyle(cellStyle);

    XSSFCell cellUserName = row.createCell(1);
    cellUserName.setCellValue(user.getUname());
    cellUserName.setCellStyle(cellStyle);

    XSSFCell cellPassword = row.createCell(2);
    cellPassword.setCellValue(user.getUpassword());
    cellPassword.setCellStyle(cellStyle);

    XSSFCell cellSex = row.createCell(3);
    cellSex.setCellValue(user.getUsex());
    cellSex.setCellStyle(cellStyle);

    XSSFCell cellRole = row.createCell(4);
    cellRole.setCellValue(user.getRole());
    cellRole.setCellStyle(cellStyle);

    XSSFCell cellLoveValue = row.createCell(5);
    cellLoveValue.setCellValue(user.getRole());
    cellLoveValue.setCellStyle(cellStyle);

    XSSFCell cellPhone = row.createCell(6);
    cellPhone.setCellValue(user.getUphoto());
    cellPhone.setCellStyle(cellStyle);

    XSSFCell cellAddress = row.createCell(7);
    cellAddress.setCellValue(user.getUaddress());
    cellAddress.setCellStyle(cellStyle);


}
/**
    表头
**/
public void titleExcel(XSSFRow row,XSSFCellStyle cellStyle){

    XSSFCell cellId = row.createCell(0);
    cellId.setCellValue("用户ID");
    cellId.setCellStyle(cellStyle);

    XSSFCell cellUserName = row.createCell(1);
    cellUserName.setCellValue("用户名");
    cellUserName.setCellStyle(cellStyle);

    XSSFCell cellPassword = row.createCell(2);
    cellPassword.setCellValue("密码");
    cellPassword.setCellStyle(cellStyle);

    XSSFCell cellSex = row.createCell(3);
    cellSex.setCellValue("性别");
    cellSex.setCellStyle(cellStyle);

    XSSFCell cellRole = row.createCell(4);
    cellRole.setCellValue("角色");
    cellRole.setCellStyle(cellStyle);

    XSSFCell cellLoveValue = row.createCell(5);
    cellLoveValue.setCellValue("爱心值");
    cellLoveValue.setCellStyle(cellStyle);

    XSSFCell cellPhone = row.createCell(6);
    cellPhone.setCellValue("电话号码");
    cellPhone.setCellStyle(cellStyle);

    XSSFCell cellAddress = row.createCell(7);
    cellAddress.setCellValue("地址");
    cellAddress.setCellStyle(cellStyle);

}