ASP.NET Core 导出数据到 Excel 文件

在ASP.Net Core开发中，使用NPOI将数据导出到Excel文件中，并返回给前端。

service 层代码：

　　　　 /// <summary>
        /// 将数据导出到excel
        /// </summary>
        /// <param name="projectId"></param>
        /// <param name="ids"></param>
        /// <returns></returns>
        public async Task<IWorkbook> ExportToExcel(Guid projectId, List<Guid> ids = null)
        {
            var entities = await attendanceRecordRepository.Find(x =>
                                                x.ProjectId == projectId)
                                                .ToListAsync();

            if (entities == null || entities.Count == 0) return null;

            //创建工作簿
            IWorkbook workbook = new XSSFWorkbook();
            ISheet sheet = workbook.CreateSheet("xxxx");

            //添加表头
            IRow tableHeader = sheet.CreateRow(0);
            var colNames = new List<string>()
            {
                "xxx", "xxx", "xxx", "xxx"
            };
            for (int i = 0; i < colNames.Count; i++)
            {
                tableHeader.CreateCell(i).SetCellValue(colNames[i]);
                // 自适应宽高
                sheet.AutoSizeColumn(i);
            }

            // 将数据写入表格中
            if (ids == null || ids.Count == 0)
            {
                // 导出全部
                for (int i = 0; i < entities.Count; i++)
                {
                    // 跳过表头
                    var row = sheet.CreateRow(i + 1);

                    row.CreateCell(0).SetCellValue(entities[i].xxx);
                    row.CreateCell(1).SetCellValue(entities[i].xxx);
                    row.CreateCell(2).SetCellValue(entities[i].xxxx);
                }
            }
            else
            {
                // 导出部分
                int rowIndex = 1;
                foreach (var entity in entities)
                {
                    foreach (var id in ids)
                    {
                        if (entity.Id == id)
                        {
                            var row = sheet.CreateRow(rowIndex);

                            row.CreateCell(0).SetCellValue(entity.xxx);
                            row.CreateCell(1).SetCellValue(entity.xxx);
                            row.CreateCell(2).SetCellValue(entity.xxx);

                            rowIndex++;
                        }
                    }
                }
            }

            return workbook;
        }

controller 层代码： 

　　　　 /// <summary>
        /// 将数据导出为Excel文件
        /// </summary>
        /// <param name="projectId"></param>
        /// <param name="ids"></param>
        /// <returns></returns>
        [HttpPost("export-to-excel")]
        public async Task<IActionResult> ExportToExcel(Guid projectId, List<Guid> ids = null)
        {
            var workbook = await _attendanceRecordService.ExportToExcel(projectId, ids);

            if(workbook != null)
            {
                var path = Path.Combine(webHostEnvironment.ContentRootPath, "FileName");
                if (!Directory.Exists(path)) //没有此路径就新建
                {
                    Directory.CreateDirectory(path);
                }
                var fileFullName = Path.Combine(path, $"{DateTime.Now.ToString("yyyy_MM_dd_HH_mm_ss")}.xlsx");

                // 将表格写入文件流
                FileStream creatStream = new FileStream(fileFullName, FileMode.Create, FileAccess.Write);
                workbook.Write(creatStream);
                creatStream.Close();

                // 将表格文件转换成可读的文件流
                FileStream fileStream = new FileStream(fileFullName, FileMode.Open, FileAccess.Read, FileShare.Read); //读

                // 将可读文件流写入 byte[]
                byte[] bytes = new byte[fileStream.Length];
                fileStream.Read(bytes, 0, bytes.Length);
                fileStream.Close();

                // 把 byte[] 转换成 Stream （创建其支持存储区为内存的流。）
                MemoryStream stream = new(bytes);

                try
                {
                    return File(stream, "application/vnd.openxmlformats-officedocument.spreadsheetml.sheet",
                            $"{DateTime.Now.ToString("yyyyMMddHHmmss")}");
                }
                finally
                {
                    System.IO.File.Delete(fileFullName);
                }
                
            }
            return BadRequest();
        }