通过文件流判断文件编码

public static System.Text.Encoding GetFileEncode(Stream stream)
        {
            BinaryReader br = new BinaryReader(stream, Encoding.Default);
            byte[] bb = br.ReadBytes(3);
            br.Close();

            //通过头的前三位判断文件的编码
            if (bb[0] >= 0xFF)
            {
                if (bb[0] == 0xEF && bb[1] == 0xBB && bb[2] == 0xBF)
                {
                    return Encoding.UTF8;
                }
                else if (bb[0] == 0xFE && bb[1] == 0xFF)
                {
                    return Encoding.BigEndianUnicode;
                }
                else if (bb[0] == 0xFF && bb[1] == 0xFE)
                {
                    return Encoding.Unicode;
                }
                else
                {
                    return Encoding.Default;
                }
            }
            else
            {
                return Encoding.Default;
            }
        }