C#_.NetCore_WebAPI项目_EXCEL数据导出（ExcelHelper_第二版_优化逻辑）

项目需要引用NPOI的Nuget包：DotNetCore.NPOI-v1.2.2

1-简单的设置下载文件的控制器方法：

//
        // 摘要:
        //     /// Returns a file with the specified fileContents as content (Microsoft.AspNetCore.Http.StatusCodes.Status200OK),
        //     the /// specified contentType as the Content-Type and the specified fileDownloadName
        //     as the suggested file name. /// This supports range requests (Microsoft.AspNetCore.Http.StatusCodes.Status206PartialContent
        //     or /// Microsoft.AspNetCore.Http.StatusCodes.Status416RangeNotSatisfiable if
        //     the range is not satisfiable). ///
        //
        // 参数:
        //   fileContents:
        //     The file contents.
        //
        //   contentType:
        //     The Content-Type of the file.
        //
        //   fileDownloadName:
        //     The suggested file name.
        //
        // 返回结果:
        //     The created Microsoft.AspNetCore.Mvc.FileContentResult for the response.
        [NonAction]
        public FileContentResult File(byte[] fileContents, string contentType, string fileDownloadName)

//这里以下载txt文件为例：

byte[] logByte = System.IO.File.ReadAllBytes(dateLogFilePath);
                MediaTypeHeaderValue mediaTypeHeaderValue = new MediaTypeHeaderValue("text/plain");
                mediaTypeHeaderValue.Encoding = Encoding.UTF8;
                return File(logByte, mediaTypeHeaderValue.ToString(), date.ToString("yyyy-MM-dd") + ".log");

2-本篇文章是对WebAPI项目使用NPOI操作Excel时的帮助类：ExcelHelper的改进优化做下记录：

备注：下面的帮助类代码使用的文件格式为：xlsx文件，xlsx相对xls的优缺点代码里有注释，推荐使用xlsx文件保存数据！

using Microsoft.AspNetCore.Mvc;
using Microsoft.Extensions.Logging;
using Microsoft.Net.Http.Headers;
using NPOI.SS.UserModel;
using NPOI.XSSF.UserModel;
using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Reflection;

namespace PaymentAccountAPI.Helper
{
    /// <summary>
    /// EXCEL帮助类
    /// </summary>
    /// <typeparam name="T">泛型类</typeparam>
    /// <typeparam name="TCollection">泛型类集合</typeparam>
    public class ExcelHelp
    {
        private ILogger Logger = null;

        public ExcelHelp(ILogger<ExcelHelp> logger)
        {
            this.Logger = logger;
        }

        /// <summary>
        /// 将数据导出EXCEL
        /// </summary>
        /// <param name="tList">要导出的数据集</param>
        /// <param name="fieldNameAndShowNameDic">键值对集合（键：字段名，值：显示名称）</param>
        /// <param name="fileDirectoryPath">文件路径</param>
        /// <param name="excelName">文件名（必须是英文或数字）</param>
        /// <returns></returns>
        public IWorkbook CreateOrUpdateWorkbook<T>(List<T> tList, Dictionary<string, string> fieldNameAndShowNameDic, IWorkbook workbook = null, string sheetName = "sheet1") where T : new()
        {
            //xls文件格式属于老版本文件，一个sheet最多保存65536行；而xlsx属于新版文件类型；
            //Excel 07 - 2003一个工作表最多可有65536行，行用数字1—65536表示; 最多可有256列，列用英文字母A—Z，AA—AZ，BA—BZ，……，IA—IV表示；一个工作簿中最多含有255个工作表，默认情况下是三个工作表；
            //Excel 2007及以后版本，一个工作表最多可有1048576行，16384列；
            if (workbook == null)
            {
                workbook = new XSSFWorkbook();
                //workbook = new HSSFWorkbook();
            }
            ISheet worksheet = workbook.CreateSheet(sheetName);

            List<string> columnNameList = fieldNameAndShowNameDic.Values.ToList();
            //设置首列显示
            IRow row1 = worksheet.CreateRow(0);

            ICell cell = null;
            ICellStyle cellHeadStyle = workbook.CreateCellStyle();
            //设置首行字体加粗
            IFont font = workbook.CreateFont();
            font.Boldweight = short.MaxValue;
            cellHeadStyle.SetFont(font);
            int cloumnCount = columnNameList.Count;
            for (var i = 0; i < cloumnCount; i++)
            {
                cell = row1.CreateCell(i);
                cell.SetCellValue(columnNameList[i]);
                cell.CellStyle = cellHeadStyle;
            }

            //根据反射创建其他行数据
            var raws = tList.Count;
            Dictionary<string, PropertyInfo> titlePropertyDic = this.GetIndexPropertyDic<T>(fieldNameAndShowNameDic);

            PropertyInfo propertyInfo = null;
            T t = default(T);
            for (int i = 0; i < raws; i++)
            {
                if (i % 10000 == 0)
                {
                    this.Logger.LogInformation($"Excel已创建{i + 1}条数据");
                }
                row1 = worksheet.CreateRow(i + 1);
                t = tList[i];

                int cellIndex = 0;
                foreach (var titlePropertyItem in titlePropertyDic)
                {
                    propertyInfo = titlePropertyItem.Value;
                    cell = row1.CreateCell(cellIndex);

                    if (propertyInfo.PropertyType == typeof(int)
                        || propertyInfo.PropertyType == typeof(decimal)
                        || propertyInfo.PropertyType == typeof(double))
                    {
                        cell.SetCellValue(Convert.ToDouble(propertyInfo.GetValue(t) ?? 0));
                    }
                    else if (propertyInfo.PropertyType == typeof(DateTime))
                    {
                        cell.SetCellValue(Convert.ToDateTime(propertyInfo.GetValue(t)?.ToString()).ToString("yyyy-MM-dd HH:mm:ss"));
                    }
                    else if (propertyInfo.PropertyType == typeof(bool))
                    {
                        cell.SetCellValue(Convert.ToBoolean(propertyInfo.GetValue(t).ToString()));
                    }
                    else
                    {
                        cell.SetCellValue(propertyInfo.GetValue(t)?.ToString() ?? "");
                    }
                    cellIndex++;
                }

                //重要：设置行宽度自适应(大批量添加数据时，该行代码需要注释，否则会极大减缓Excel添加行的速度！)
                //worksheet.AutoSizeColumn(i, true);
            }

            return workbook;
        }

        /// <summary>
        /// 保存Workbook数据为文件
        /// </summary>
        /// <param name="workbook"></param>
        /// <param name="fileDirectoryPath"></param>
        /// <param name="fileName"></param>
        public void SaveWorkbookToFile(IWorkbook workbook, string fileDirectoryPath, string fileName)
        {
            //xls文件格式属于老版本文件，一个sheet最多保存65536行；而xlsx属于新版文件类型；
            //Excel 07 - 2003一个工作表最多可有65536行，行用数字1—65536表示; 最多可有256列，列用英文字母A—Z，AA—AZ，BA—BZ，……，IA—IV表示；一个工作簿中最多含有255个工作表，默认情况下是三个工作表；
            //Excel 2007及以后版本，一个工作表最多可有1048576行，16384列；

            MemoryStream ms = new MemoryStream();
            //这句代码非常重要，如果不加，会报：打开的EXCEL格式与扩展名指定的格式不一致
            ms.Seek(0, SeekOrigin.Begin);
            workbook.Write(ms);
            byte[] myByteArray = ms.GetBuffer();

            fileDirectoryPath = fileDirectoryPath.TrimEnd('\') + "\";
            if (!Directory.Exists(fileDirectoryPath))
            {
                Directory.CreateDirectory(fileDirectoryPath);
            }

            string filePath = fileDirectoryPath + fileName;
            if (File.Exists(filePath))
            {
                File.Delete(filePath);
            }
            File.WriteAllBytes(filePath, myByteArray);
        }

        /// <summary>
        /// 保存Workbook数据为下载文件
        /// </summary>
        public FileContentResult SaveWorkbookToDownloadFile(IWorkbook workbook)
        {
            MemoryStream ms = new MemoryStream();
            //这句代码非常重要，如果不加，会报：打开的EXCEL格式与扩展名指定的格式不一致
            ms.Seek(0, SeekOrigin.Begin);
            workbook.Write(ms);
            byte[] myByteArray = ms.GetBuffer();

            //对于.xls文件
            //application/vnd.ms-excel
            //用于.xlsx文件。
            //application/vnd.openxmlformats-officedocument.spreadsheetml.sheet
            MediaTypeHeaderValue mediaType = new MediaTypeHeaderValue("application/vnd.openxmlformats-officedocument.spreadsheetml.sheet");
            mediaType.Encoding = System.Text.Encoding.UTF8;
　　　　　　　//设置下载文件名
            FileContentResult fileResult= new FileContentResult(myByteArray, mediaType.ToString());
　　　　　　　fileResult.FileDownloadName="xxx.xlsx";

            return new FileContentResult(myByteArray, mediaType.ToString());
        }


        /// <summary>
        /// 读取Excel数据
        /// </summary>
        /// <param name="filePath"></param>
        /// <param name="fieldNameAndShowNameDic"></param>
        /// <returns></returns>
        public List<T> ReadDataList<T>(string filePath, Dictionary<string, string> fieldNameAndShowNameDic) where T : new()
        {
            List<T> tList = null;
            T t = default(T);

            //标题属性字典列表
            Dictionary<string, PropertyInfo> titlePropertyDic = this.GetIndexPropertyDic<T>(fieldNameAndShowNameDic);
            //标题下标列表
            Dictionary<string, int> titleIndexDic = new Dictionary<string, int>(0);

            PropertyInfo propertyInfo = null;

            using (FileStream fileStream = new FileStream(filePath, FileMode.Open, FileAccess.Read))
            {
                IWorkbook xssfWorkbook = new XSSFWorkbook(fileStream);
                var sheet = xssfWorkbook.GetSheetAt(0);

                var rows = sheet.GetRowEnumerator();
                tList = new List<T>(sheet.LastRowNum + 1);
                //第一行数据为标题，
                if (rows.MoveNext())
                {
                    IRow row = (XSSFRow)rows.Current;
                    ICell cell = null;
                    string cellValue = null;
                    for (int i = 0; i < row.Cells.Count; i++)
                    {
                        cell = row.Cells[i];
                        cellValue = cell.StringCellValue;
                        if (titlePropertyDic.ContainsKey(cellValue))
                        {
                            titleIndexDic.Add(cellValue, i);
                        }
                    }
                }
                //从第2行数据开始获取
                while (rows.MoveNext())
                {
                    IRow row = (XSSFRow)rows.Current;
                    t = new T();

                    foreach (var titleIndexItem in titleIndexDic)
                    {
                        var cell = row.GetCell(titleIndexItem.Value);
                        if (cell != null)
                        {
                            propertyInfo = titlePropertyDic[titleIndexItem.Key];
                            if (propertyInfo.PropertyType == typeof(int))
                            {
                                propertyInfo.SetValue(t, Convert.ToInt32(cell.NumericCellValue));
                            }
                            else if (propertyInfo.PropertyType == typeof(decimal))
                            {
                                propertyInfo.SetValue(t, Convert.ToDecimal(cell.NumericCellValue));
                            }
                            else if (propertyInfo.PropertyType == typeof(double))
                            {
                                propertyInfo.SetValue(t, Convert.ToDouble(cell.NumericCellValue));
                            }
                            else if (propertyInfo.PropertyType == typeof(bool))
                            {
                                propertyInfo.SetValue(t, Convert.ToBoolean(cell.StringCellValue));
                            }
                            else if (propertyInfo.PropertyType == typeof(DateTime))
                            {
                                propertyInfo.SetValue(t, Convert.ToDateTime(cell.StringCellValue));
                            }
                            else
                            {
                                propertyInfo.SetValue(t, cell.StringCellValue);
                            }

                        }
                    }
                    tList.Add(t);
                }
            }
            return tList ?? new List<T>(0);
        }

        /// <summary>
        /// 根据属性名顺序获取对应的属性对象
        /// </summary>
        /// <param name="fieldNameList"></param>
        /// <returns></returns>
        private Dictionary<string, PropertyInfo> GetIndexPropertyDic<T>(Dictionary<string, string> fieldNameAndShowNameDic)
        {
            Dictionary<string, PropertyInfo> titlePropertyDic = new Dictionary<string, PropertyInfo>(fieldNameAndShowNameDic.Count);

            List<PropertyInfo> tPropertyInfoList = typeof(T).GetProperties().ToList();
            PropertyInfo propertyInfo = null;

            foreach (var item in fieldNameAndShowNameDic)
            {
                propertyInfo = tPropertyInfoList.Find(m => m.Name.Equals(item.Key, StringComparison.OrdinalIgnoreCase));
                titlePropertyDic.Add(item.Value, propertyInfo);
            }
            return titlePropertyDic;
        }

    }
}