学步园

    public static bool IsAllowedExtension(FileUpload hifile)
    {
        //System.IO.FileStream fs = new System.IO.FileStream(hifile.PostedFile.FileName, System.IO.FileMode.Open, System.IO.FileAccess.Read);
        //System.IO.BinaryReader r = new System.IO.BinaryReader(fs);
        int fileLen = hifile.PostedFile.ContentLength;
        byte[] imgArray = new byte[fileLen];
        hifile.PostedFile.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();

        /*文件扩展名说明
        jpg：255216
        bmp：6677
        gif：7173
        xls,doc,ppt：208207
        rar：8297
        zip：8075
        txt：98109
        pdf：3780
        */

        bool ret = false;
        String[] fileType = { "255216", "6677", "7173", "208207", "8297", "8075", "98109", "3780" };
        for (int i = 0; i < fileType.Length; i++)
        {
            if (fileclass == fileType[i])
            {
                ret = true;
                break;
            }
        }
        return ret;
    }

ref:http://www.cnblogs.com/jueban/archive/2009/03/06/933121.html