Detailed explanation of HttpPostedFileBase file upload examples

/// <summary>
  /// 文件生成方式
  /// </summary>
  public class UpFileMessage
  {
    /// <summary>
    /// 文件名
    /// </summary>
    public string OriginalFileName { get; set; }

    /// <summary>
    /// 是否保存略缩图
    /// </summary>
    public bool IsImage { get; set; }

    /// <summary>
    /// 文件流
    /// </summary>
    public Stream FileStream { get; set; }

    /// <summary>
    /// 生成缩略图的方式
    /// [WH]-指定宽高
    /// [H]-指定高，按比例缩放宽
    /// [W]-指定宽，按比例缩放高
    /// </summary>
    public string Mode { get; set; }

    /// <summary>
    /// 略缩图高度
    /// </summary>
    public int? ThumbHeight { get; set; }

    /// <summary>
    /// 略缩图宽度
    /// </summary>
    public int? ThumbWidth { get; set; }

  }

/// <summary>
  /// 文件上传返回结果
  /// </summary>
  public class UpFileResultMessage
  {
    /// <summary>
    /// 文件保存是否成功
    /// </summary>
    public bool IsSuccess { get; set; }

    /// <summary>
    /// 错误消息
    /// </summary>
    public string Message { get; set; }

    /// <summary>
    /// 原始文件名-（无扩展名）
    /// </summary>
    public string FileName { get; set; }

    /// <summary>
    /// 文件名扩展名
    /// </summary>
    public string FileSuffix { get; set; }

    /// <summary>
    /// 文件名保存路径
    /// </summary>
    public string FilePath { get; set; }

    /// <summary>
    /// 文件类型为图片时
    /// 缩略图保存路径
    /// </summary>
    public string ThumbPath { get; set; }

    /// <summary>
    /// 保存文件名（无扩展名）
    /// </summary>
    public string SaveFileName { get; set; }

    /// <summary>
    /// 文件自增ID
    /// </summary>
    public int[] FileIdArray { get; set; }
  }

public class FileUtil : System.Web.UI.Page
  {
    /// <summary>
    /// 图片上传
    /// </summary>
    /// <param name="fileMessage">文件生成方式</param>
    /// <returns></returns>
    public UpFileResultMessage UpLoadFile(UpFileMessage fileMessage)
    {
      try
      {
        string now = DateTime.Today.ToString("yyyyMMdd");
        string guid = Guid.NewGuid().ToString();

        //获取文件扩展名
        var fileSuffix = Path.GetExtension(fileMessage.OriginalFileName);

        var uploadFolder = Path.Combine(System.Web.HttpContext.Current.Server.MapPath(ParmsConfig.UpFilePathUrl), now);

        if (!Directory.Exists(uploadFolder))
        {
          Directory.CreateDirectory(uploadFolder);
        }

        //保存文件名
        string saveFileName = guid + fileSuffix;
        string filePath = Path.Combine(uploadFolder, saveFileName);


        UpFileResultMessage upFileResult = new UpFileResultMessage()
        {
          IsSuccess = true,
          FileName = Path.GetFileNameWithoutExtension(fileMessage.OriginalFileName),
          FileSuffix = fileSuffix,
          FilePath = string.Format(@"{0}/{1}", ParmsConfig.UpFileIPAddressUrl, now),
          SaveFileName = guid
        };

        using (Stream sourceStream = fileMessage.FileStream)
        {
          using (FileStream targetStream = new FileStream(filePath, FileMode.Create, FileAccess.Write, FileShare.None))
          {
            const int bufferLen = 1024 * 4;//4KB
            byte[] buffer = new byte[bufferLen];
            int count = 0;
            while ((count = sourceStream.Read(buffer, 0, bufferLen)) > 0)
            {
              targetStream.Write(buffer, 0, count);
            }
          }
          //上传文件为图片时,需创建缩略图
          if (fileMessage.IsImage)
          {
            var uploadThumbFolder = Path.Combine(uploadFolder, "Thumb");

            if (!Directory.Exists(uploadThumbFolder))
            {
              Directory.CreateDirectory(uploadThumbFolder);
            }
            using (FileStream targetStream = new FileStream(filePath, FileMode.Open, FileAccess.Read, FileShare.None))
            {
              System.Drawing.Image image = System.Drawing.Image.FromStream(targetStream);
              int width = image.Width;
              int height = image.Height;
              int thumbWidth = 0;
              int thumbHeight = 0;
              switch (fileMessage.Mode)
              {
                case "WH": //指定高宽缩放（可能变形） 
                  thumbWidth = fileMessage.ThumbWidth.HasValue ? fileMessage.ThumbWidth.Value : 200;
                  thumbHeight = fileMessage.ThumbHeight.HasValue ? fileMessage.ThumbHeight.Value : 200;
                  break;
                case "W":  //指定宽，高按比例   
                  thumbWidth = fileMessage.ThumbWidth.HasValue ? fileMessage.ThumbWidth.Value : 200;
                  thumbHeight = height * thumbWidth / width;
                  break;
                case "H":  //指定高，宽按比例
                  thumbHeight = fileMessage.ThumbHeight.HasValue ? fileMessage.ThumbHeight.Value : 200;
                  thumbWidth = width * thumbHeight / height;
                  break;
                default:
                  thumbWidth = fileMessage.ThumbWidth.HasValue ? fileMessage.ThumbWidth.Value : 200;
                  thumbHeight = height * thumbWidth / width;
                  break;
              }
              string thumbFilePath = Path.Combine(uploadThumbFolder, saveFileName);
              CreateThumbnail(thumbFilePath, targetStream, thumbWidth, thumbHeight);
              upFileResult.ThumbPath = string.Format(@"{0}/{1}/Thumb", ParmsConfig.UpFileIPAddressUrl, now);
            }
          }
        }

        return upFileResult;
      }
      catch (Exception ex)
      {
        return new UpFileResultMessage() { IsSuccess = false, Message = ex.Message };
      }

    }

    /// <summary>
    /// 创建指定图片文件流的缩略图
    /// </summary>
    /// <param name="thumbFilePath">缩略图文件保存路径</param>
    /// <param name="fileStream">原始文件流</param>
    /// <param name="width">缩略图宽</param>
    /// <param name="height">缩略图高</param>
    private void CreateThumbnail(string thumbFilePath, Stream fileStream, int width, int height)
    {
      using (Image image = Image.FromStream(fileStream))
      {
        using (Image thumbnail = image.GetThumbnailImage(width, height, null, IntPtr.Zero))
        {
          thumbnail.Save(thumbFilePath);
        }
      }

    }

  }

var upFileMsg = new UpFileMessage()
          {
            IsImage = true,
            OriginalFileName = platformImg[i].FileName,
            FileStream = platformImg[i].InputStream,
            ThumbWidth = ThumbWidth,
            Mode = "W"
          };
         var  upFileResultMsg = new FileUtil().UpLoadFile(upFileMsg);