Asp.Net文件流IO异常：由于另一个进程正在使用该进程，因此无法访问文件

Question

I have a problem about one of my Asp.Net applications. I am creating an excel file from a DataTable that I use. Here is the related function :

public static void ExportToExcel(System.Data.DataTable Tbl, string ExcelFilePath)
        {
            try
            {
                if (Tbl == null || Tbl.Columns.Count == 0)
                    throw new Exception("ExportToExcel: Null or empty input table!\n");

                // load excel, and create a new workbook
                Microsoft.Office.Interop.Excel.Application excelApp = new Microsoft.Office.Interop.Excel.Application();
                excelApp.Workbooks.Add();

                // single worksheet
                Microsoft.Office.Interop.Excel._Worksheet workSheet = excelApp.ActiveSheet;

                // column headings
                for (int i = 0; i < Tbl.Columns.Count; i++)
                {
                    workSheet.Cells[1, (i + 1)] = Tbl.Columns[i].ColumnName;
                }

                // rows
                for (int i = 0; i < Tbl.Rows.Count; i++)
                {
                    // to do: format datetime values before printing
                    for (int j = 0; j < Tbl.Columns.Count; j++)
                    {
                        workSheet.Cells[(i + 2), (j + 1)] = Tbl.Rows[i][j];
                    }
                }

                // check fielpath
                if (ExcelFilePath != null && ExcelFilePath != "")
                {
                    try
                    {
                        workSheet.SaveAs(ExcelFilePath);
                        excelApp.Quit();
                    }
                    catch (Exception ex)
                    {
                        throw new Exception("ExportToExcel: Excel file could not be saved! Check filepath.\n"
                            + ex.Message);
                    }
                }
                else    // no filepath is given
                {
                    excelApp.Visible = true;
                }
            }
            catch (Exception ex)
            {
                throw new Exception("ExportToExcel: \n" + ex.Message);
            }
        } 

Than I need to send this 'new created' excel file to the user's computer. The user downloads this file. And here is the 'download function' :

   public void FileDownload(string fileName)
        {
            Session["dosya"] = fileName;
            string dosyaUrl = @Server.MapPath("/") + Session["dosya"].ToString() + ".xlsx"; //buradan sonra dosyamızı indirme işlemine başlıyoruz.
            string yeni_dosya = Session["dosya"].ToString() + ".xlsx"; //biz işlem yapılacak dosyanın adını sessina attık oyle kullandık siz istediğiniz yolla yapabilirsiniz.
            FileStream fs;
            if (File.Exists(dosyaUrl))
            {
                fs = new FileStream(dosyaUrl, FileMode.Open, FileAccess.Read, FileShare.Read); 
            }
            else
            {
                return;
            }
            byte[] buffer = new byte[(int)fs.Length];
            fs.Read(buffer, 0, (int)fs.Length);
            fs.Flush();
            fs.Close();
            fs.Dispose();
            Response.Clear();
            Response.AddHeader("Content-Length", buffer.Length.ToString());//içeriğin uzunluğu AddHeader fonksiyonuna gonderiliyor...
            Response.AddHeader("Content-Disposition", "attachment; filename=" + yeni_dosya);
            Response.BinaryWrite(buffer);
            File.Delete(dosyaUrl);
            Response.End();

        }

And this two functions is controlling by a button on my web page.

When the code line comes to the line

fs.Read(buffer, 0, (int)fs.Length);

I am getting the exception :

IO Exception was unhandled by the user code : Cannot access the file because the process is being used by another process

I don't understand the cause of the problem. Cause I am saving and closing the file. And on the task manager I can't see a task about an excel file. And the exception is not handling when I got a breakpoint on the function lines and proceed the code line by line.

So what can be the problem ?

Answer 1

You should not attempt to automate Office in a server application .

In your case, you'll probably find an orphaned Excel process is running, and has the workbook open.

I'd suggest you use a third party component such as EPPlus or Aspose to create the workbook.