为什么我无法在asp.net上的服务器上找到要下载的文件？

Question

I'm beginner in asp.net and want to write simple web application to end user can download any file,write this code for that purpose:

string filePath = "~/beh/" + query[0].OstFileName;
FileInfo file = new FileInfo(filePath);
if (file.Exists) {

    Response.ContentType = "application/octet-stream";
    Response.AppendHeader("Content-Disposition", "attachment; filename=" + query[0].OstFileName.Trim());
    Response.TransmitFile(Server.MapPath("~/beh/" + query[0].OstFileName.Trim()));
    Response.End();
} else {
    Response.Write("<script>alert('File Not Found 1')</script>");
}

but when run that code i get else block alert,means get File Not Found 1 message,Where is my fault?thanks all.

Answer 1

Your issue is in the following lines.

string filePath = "~/beh/" + query[0].OstFileName;
FileInfo file = new FileInfo(filePath);

You're giving the FileInfo class a virtual path which the FileInfo cannot map to a local physical path on its own. You are however correctly mapping the virtual path to the local file path when you call Response.TransmitFile.

Change your code to the following:

string filePath = "~/beh/" + query[0].OstFileName;
FileInfo file - new FileInfo(Server.MapPath(filePath));

See: https://msdn.microsoft.com/en-us/library/ms524632(v=vs.90).aspx

Answer 2

string filePath = "~/beh/" + query[0].OstFileName;

In this line you specify the path to search for, including the filename.

The next line you check if this file exists and if so save the file from the query result.

However if you check if the file exists before you actually save the file it will never exist.

Change the path to read: string filePath = Server.MapPath("~\\beh").

Then add the filename to that once you save the file.

Hope this makes sense.