c# – 如何在asp.net上传之前检查文件类型？

我们怎样才能在不使用文件扩展名的情况下检查文件类型(如jpg等格式),然后再使用asp.net& C# ？

我正在使用vs 2008 asp.net c#TELERIK Controls(RadUpload)

想象一些正文将文本文件扩展名更改为jpg并在上传控件中选择它,例如radupload …

我们怎么能认识到这个文件是不是真的jpg？

例：

// generate new Guid
Guid fileguid = Guid.NewGuid();

// set limit for images, 1920x1200 pixels
int imageWidth = 1920;
int imageHeight = 1200;
int maxFileSize = 8388608;
// web.config - httpRuntime - maxRequestLength="8192"
// 8,388,608 Bytes 
// 8,192 KB ( / 1024 ) 
// 8.00 MB ( / 1024 / 1024 )

string sConn = ConfigurationManager.ConnectionStrings["AssetsDBCS"].ConnectionString;
SqlConnection objConn = new SqlConnection(sConn);
objConn.Open();
SqlCommand objCmd = new SqlCommand("sp_FileStorage_New", objConn);
objCmd.CommandType = CommandType.StoredProcedure;

SqlParameter paramFileGuid = objCmd.Parameters.Add("@FileGuid", SqlDbType.UniqueIdentifier);
SqlParameter paramFileSubject = objCmd.Parameters.Add("@Subject", SqlDbType.VarChar);
SqlParameter paramFileContentType = objCmd.Parameters.Add("@ContentType", SqlDbType.VarChar);
SqlParameter paramFileData = objCmd.Parameters.Add("@BinaryData", SqlDbType.VarBinary);
SqlParameter paramFileSize = objCmd.Parameters.Add("@Filesize", SqlDbType.BigInt);
SqlParameter paramFileDesc = objCmd.Parameters.Add("@Description", SqlDbType.VarChar);
SqlParameter paramIsSLAFile = objCmd.Parameters.Add("@IsSLAFile", SqlDbType.Bit);
SqlParameter paramUserStamp = objCmd.Parameters.Add("@UserStamp", SqlDbType.VarChar);

paramFileGuid.Direction = ParameterDirection.Input;
paramFileSubject.Direction = ParameterDirection.Input;
paramFileContentType.Direction = ParameterDirection.Input;
paramFileData.Direction = ParameterDirection.Input;
paramFileSize.Direction = ParameterDirection.Input;
paramFileDesc.Direction = ParameterDirection.Input;
paramIsSLAFile.Direction = ParameterDirection.Input;
paramUserStamp.Direction = ParameterDirection.Input;

// read data
byte[] bData = new byte[fuOne.PostedFile.ContentLength];
Stream objStream = fuOne.PostedFile.InputStream;
objStream.Read(bData, 0, fuOne.PostedFile.ContentLength);

paramFileSubject.Value = txtSubject.Text;

objCmd.Parameters.Add("@FileName", SqlDbType.VarChar).Value = Path.GetFileName(fuOne.PostedFile.FileName);
objCmd.Parameters.Add("@Extension", SqlDbType.VarChar).Value = Path.GetExtension(fuOne.PostedFile.FileName);

paramFileGuid.Value = fileguid;

paramFileContentType.Value = fuOne.PostedFile.ContentType;
paramFileData.Value = bData;
paramFileSize.Value = fuOne.PostedFile.ContentLength;
paramFileDesc.Value = fuOne.PostedFile.FileName;
paramIsSLAFile.Value = cbIsSLAFile.Checked;
paramUserStamp.Value = ac.getUser();

if (fuOne.PostedFile.ContentLength < maxFileSize)
{

    switch (fuOne.PostedFile.ContentType)
    {
        case "image/pjpeg":
            {

                System.Drawing.Image iImage = System.Drawing.Image.FromStream(new MemoryStream(bData));

                if (iImage.Width > imageWidth || iImage.Height > imageHeight)
                {
                    lblStatus.Text = "The image width or height cannot be greater than " + imageHeight + " x " + imageWidth + " pixels";
                }
                else
                {
                    objCmd.ExecuteNonQuery();
                    objConn.Close();

                    hlDownload.Visible = true;
                    hlDownload.NavigateUrl = "Download.aspx?DownloadFileGuid=" + fileguid.ToString();
                    hlDownload.Text = "Click here to download the uploaded file";

                    hlShowFile.Visible = true;
                    hlShowFile.NavigateUrl = "Download.aspx?ShowFileGuid=" + fileguid.ToString();
                    hlShowFile.Text = "Click here to view the uploaded file";

                    lblStatus.Text = showUploadFileInfo(Path.GetFileName(fuOne.PostedFile.FileName), fuOne.PostedFile.ContentType, fuOne.PostedFile.ContentLength, iImage.Width, iImage.Height);
                }
                break;
            }
    }
}