您可以像这样处理文件：

public void UploadFile(HttpRequestMessage request)
{
    HttpContext context = HttpContext.Current;
    HttpPostedFile postedFile = context.Request.Files["file"];
    // ...
}

另一种可能的解决方案。Web API方法使用ClosedXML nuget包来读取包含excel内容的流：

using ClosedXML.Excel;

public async void UploadFile()
{
    var context = HttpContext.Current;

    if (!Request.Content.IsMimeMultipartContent())
    {
        throw new HttpResponseException(HttpStatusCode.UnsupportedMediaType);
    }

    var provider = new MultipartMemoryStreamProvider();
    await Request.Content.ReadAsMultipartAsync(provider);

    foreach (HttpContent ctnt in provider.Contents)
    {
        //now read individual part into STREAM
        var stream = await ctnt.ReadAsStreamAsync();
        if (stream.Length != 0)
        {
            //handle the stream here
            using (XLWorkbook excelWorkbook = new XLWorkbook(stream))
            {
                var name = excelWorkbook.Worksheet(1).Name;
            }
        }
    }
}

我想分享另一种在WEB API中使用ExcelDataReader.DataSet库实现Upload and Read the EXCEL file的方法。

[Route("ReadFile")]
        [HttpPost]
        public string ReadFile()
        {
            try
            {
                #region Variable Declaration
                string message = "";
                HttpResponseMessage ResponseMessage = null;
                var httpRequest = HttpContext.Current.Request;
                DataSet dsexcelRecords = new DataSet();
                IExcelDataReader reader = null;
                HttpPostedFile Inputfile = null;
                Stream FileStream = null;
                #endregion
 
                #region Save Student Detail From Excel
                using (dbCodingvilaEntities objEntity = new dbCodingvilaEntities())
                {
                    if (httpRequest.Files.Count > 0)
                    {
                        Inputfile = httpRequest.Files[0];
                        FileStream = Inputfile.InputStream;
 
                        if (Inputfile != null && FileStream != null)
                        {
                            if (Inputfile.FileName.EndsWith(".xls"))
                                reader = ExcelReaderFactory.CreateBinaryReader(FileStream);
                            else if (Inputfile.FileName.EndsWith(".xlsx"))
                                reader = ExcelReaderFactory.CreateOpenXmlReader(FileStream);
                            else
                                message = "The file format is not supported.";
 
                            dsexcelRecords = reader.AsDataSet();
                            reader.Close();
 
                            if (dsexcelRecords != null && dsexcelRecords.Tables.Count > 0)
                            {
                                DataTable dtStudentRecords = dsexcelRecords.Tables[0];
                                for (int i = 0; i < dtStudentRecords.Rows.Count; i++)
                                {
                                    Student objStudent = new Student();
                                    objStudent.RollNo = Convert.ToInt32(dtStudentRecords.Rows[i][0]);
                                    objStudent.EnrollmentNo = Convert.ToString(dtStudentRecords.Rows[i][1]);
                                    objStudent.Name = Convert.ToString(dtStudentRecords.Rows[i][2]);
                                    objStudent.Branch = Convert.ToString(dtStudentRecords.Rows[i][3]);
                                    objStudent.University = Convert.ToString(dtStudentRecords.Rows[i][4]);
                                    objEntity.Students.Add(objStudent);
                                }
 
                                int output = objEntity.SaveChanges();
                                if (output > 0)
                                    message = "The Excel file has been successfully uploaded.";
                                else
                                    message = "Something Went Wrong!, The Excel file uploaded has fiald.";
                            }
                            else
                                message = "Selected file is empty.";
                        }
                        else
                            message = "Invalid File.";
                    }
                    else
                        ResponseMessage = Request.CreateResponse(HttpStatusCode.BadRequest);
                }
                return message;
                #endregion
            }
            catch (Exception)
            {
                throw;
            }
        }

您可以阅读此article，了解详细的逐步说明。