static void Main(string[] args)
{
    var a1= Encoding.UTF8.GetBytes("<");
    var a2 = Encoding.UTF8.GetBytes("<");
    Console.WriteLine("去除utf-8 bom之前");
    Console.WriteLine(Encoding.UTF8.GetString(a1));
    Console.WriteLine(Encoding.UTF8.GetString(a2));

    //如果是utf-8 BOM则去除utf-8 bom头
    if (a2.Length >= 3&& a2[0] == 239 && a2[1] == 187 && a2[2] == 191)
    {
        var a2Tmp = a2.ToList();
        a2Tmp.RemoveRange(0, 3);
        a2 = a2Tmp.ToArray();
    }
    Console.WriteLine("去除utf-8 bom之后");
    Console.WriteLine(Encoding.UTF8.GetString(a1));
    Console.WriteLine(Encoding.UTF8.GetString(a2));
}