C# HttpWebRequest post 请求传参数

Dictionary parameters = new Dictionary();    //参数列表
parameters.Add("paraName", "paraValue");
string url = "";

HttpWebRequest request = null;
HttpWebResponse response = null;
Stream reqStream = null;
request = (HttpWebRequest)WebRequest.Create(url);
request.Method = "post";    //设置为post请求
request.ReadWriteTimeout = 5000;
request.KeepAlive = false;
request.ContentType = "application/x-www-form-urlencoded;charset=utf-8";
byte[] postData = Encoding.UTF8.GetBytes(BuildQuery(parameters, "utf8"));   //使用utf-8格式组装post参数
reqStream=request.GetRequestStream();
reqStream.Write(postData, 0, postData.Length);     
response = (HttpWebResponse)request.GetResponse();


//组装请求参数
private string BuildQuery(IDictionary parameters, string encode)
{
    StringBuilder postData = new StringBuilder();
    bool hasParam = false;
    IEnumerator> dem = parameters.GetEnumerator();
    while (dem.MoveNext())
    {
        string name = dem.Current.Key;
        string value = dem.Current.Value;
        // 忽略参数名或参数值为空的参数
        if (!string.IsNullOrEmpty(name))
        {
            if (hasParam)
            {
                postData.Append("&");
            }
            postData.Append(name);
            postData.Append("=");
            if (encode == "gb2312")
            {
                postData.Append(HttpUtility.UrlEncode(value, Encoding.GetEncoding("gb2312")));
            }
            else if (encode == "utf8")
            {
                postData.Append(HttpUtility.UrlEncode(value, Encoding.UTF8));
            }
            else
            {
                postData.Append(value);
            }
            hasParam = true;
        }
    }
    return postData.ToString();
}