asp.net判断上传图片是否合法

private bool IsAllowedExtension(HttpPostedFile postfile)

{

int fileLen = postfile.ContentLength;

byte[] imgArray = new byte[fileLen];

postfile.InputStream.Read(imgArray, 0, fileLen);

System.IO.MemoryStream fs = new System.IO.MemoryStream(imgArray);

System.IO.BinaryReader r = new System.IO.BinaryReader(fs);

string fileclass = "";

byte buffer;

try

{

buffer = r.ReadByte();

fileclass = buffer.ToString();

buffer = r.ReadByte();

fileclass += buffer.ToString();

}

catch

{

return false;

}

r.Close();

fs.Close();

String[] fileType = { "255216", "6677", "7173", "13780" };

for (int i = 0; i < fileType.Length; i++)

{

if (fileclass == fileType[i])

{

return true;

}

}

return false;

}