public static class CallWebAPI
    {
        public static async Task<string> APIPost(string url, string data)
        {
            string result = string.Empty;
            //设置HttpClientHandler的AutomaticDecompression
            var handler = new HttpClientHandler() { AutomaticDecompression = DecompressionMethods.GZip };
            //创建HttpClient（注意传入HttpClientHandler）
            using (var http = new HttpClient(handler))
            {
                //使用FormUrlEncodedContent做HttpContent
                var content = new FormUrlEncodedContent(new Dictionary<string, string>()       
                {
//传递单个值
                  {"", data}//键名必须为空
//传递对象
//{"name","hello"},
//{"age","16"}
                 });

                //await异步等待回应
                var response = await http.PostAsync(url, content);
                //确保HTTP成功状态值
                response.EnsureSuccessStatusCode();
                //await异步读取最后的JSON（注意此时gzip已经被自动解压缩了，因为上面的AutomaticDecompression = DecompressionMethods.GZip）
                result = await response.Content.ReadAsStringAsync();
            }
            return result;
        }

        static async void APIGet(string url)
        {
            //创建HttpClient（注意传入HttpClientHandler）
            var handler = new HttpClientHandler() { AutomaticDecompression = DecompressionMethods.GZip };

            using (var http = new HttpClient(handler))
            {
                //await异步等待回应
                var response = await http.GetAsync(url);
                //确保HTTP成功状态值
                response.EnsureSuccessStatusCode();

                //await异步读取最后的JSON（注意此时gzip已经被自动解压缩了，因为上面的AutomaticDecompression = DecompressionMethods.GZip）
                Console.WriteLine(await response.Content.ReadAsStringAsync());
            }
        }
    }

public static class RequestUtility
    {
        #region 同步方法

        /// <summary>
        /// 使用Get方法获取字符串结果（没有加入Cookie）
        /// </summary>
        /// <param name="url"></param>
        /// <returns></returns>
        public static string HttpGet(string url, Encoding encoding = null)
        {
            WebClient wc = new WebClient();
            wc.Encoding = encoding ?? Encoding.UTF8;
            //if (encoding != null)
            //{
            //    wc.Encoding = encoding;
            //}
            return wc.DownloadString(url);
        }

        /// <summary>
        /// 使用Get方法获取字符串结果（加入Cookie）
        /// </summary>
        /// <param name="url"></param>
        /// <param name="cookieContainer"></param>
        /// <param name="encoding"></param>
        /// <returns></returns>
        public static string HttpGet(string url, CookieContainer cookieContainer = null, Encoding encoding = null, int timeOut = 10000)
        {
            HttpWebRequest request = (HttpWebRequest)WebRequest.Create(url);
            request.Method = "GET";
            request.Timeout = timeOut;

            if (cookieContainer != null)
            {
                request.CookieContainer = cookieContainer;
            }

            HttpWebResponse response = (HttpWebResponse)request.GetResponse();

            if (cookieContainer != null)
            {
                response.Cookies = cookieContainer.GetCookies(response.ResponseUri);
            }

            using (Stream responseStream = response.GetResponseStream())
            {
                using (StreamReader myStreamReader = new StreamReader(responseStream, encoding ?? Encoding.GetEncoding("utf-8")))
                {
                    string retString = myStreamReader.ReadToEnd();
                    return retString;
                }
            }
        }

        /// <summary>
        /// 使用Post方法获取字符串结果，常规提交
        /// </summary>
        /// <returns></returns>
        public static string HttpPost(string url, CookieContainer cookieContainer = null, Dictionary<string, string> formData = null, Encoding encoding = null, int timeOut = 10000)
        {
            MemoryStream ms = new MemoryStream();
            formData.FillFormDataStream(ms);//填充formData
            return HttpPost(url, cookieContainer, ms, null, null, encoding, timeOut);
        }

        /// <summary>
        /// 使用Post方法获取字符串结果
        /// </summary>
        /// <param name="url"></param>
        /// <param name="cookieContainer"></param>
        /// <param name="postStream"></param>
        /// <param name="fileDictionary">需要上传的文件，Key：对应要上传的Name，Value：本地文件名</param>
        /// <param name="timeOut"></param>
        /// <returns></returns>
        public static string HttpPost(string url, CookieContainer cookieContainer = null, Stream postStream = null, Dictionary<string, string> fileDictionary = null, string refererUrl = null, Encoding encoding = null, int timeOut = 10000)
        {
            HttpWebRequest request = (HttpWebRequest)WebRequest.Create(url);
            request.Method = "POST";
            request.Timeout = timeOut;

            #region 处理Form表单文件上传
            var formUploadFile = fileDictionary != null && fileDictionary.Count > 0;//是否用Form上传文件
            if (formUploadFile)
            {
                //通过表单上传文件
                postStream = postStream ?? new MemoryStream();

                string boundary = "----" + DateTime.Now.Ticks.ToString("x");
                //byte[] boundarybytes = Encoding.ASCII.GetBytes("\r\n--" + boundary + "\r\n");
                string fileFormdataTemplate = "\r\n--" + boundary + "\r\nContent-Disposition: form-data; name=\"{0}\"; filename=\"{1}\"\r\nContent-Type: application/octet-stream\r\n\r\n";
                string dataFormdataTemplate = "\r\n--" + boundary +
                                              "\r\nContent-Disposition: form-data; name=\"{0}\"\r\n\r\n{1}";
                foreach (var file in fileDictionary)
                {
                    try
                    {
                        var fileName = file.Value;
                        //准备文件流
                        using (var fileStream = FileHelper.GetFileStream(fileName))
                        {
                            string formdata = null;
                            if (fileStream != null)
                            {
                                //存在文件
                                formdata = string.Format(fileFormdataTemplate, file.Key, /*fileName*/ Path.GetFileName(fileName));
                            }
                            else
                            {
                                //不存在文件或只是注释
                                formdata = string.Format(dataFormdataTemplate, file.Key, file.Value);
                            }

                            //统一处理
                            var formdataBytes = Encoding.ASCII.GetBytes(postStream.Length == 0 ? formdata.Substring(2, formdata.Length - 2) : formdata);//第一行不需要换行
                            postStream.Write(formdataBytes, 0, formdataBytes.Length);

                            //写入文件
                            if (fileStream != null)
                            {
                                byte[] buffer = new byte[1024];
                                int bytesRead = 0;
                                while ((bytesRead = fileStream.Read(buffer, 0, buffer.Length)) != 0)
                                {
                                    postStream.Write(buffer, 0, bytesRead);
                                }
                            }
                        }
                    }
                    catch (Exception ex)
                    {
                        throw ex;
                    }
                }
                //结尾
                var footer = Encoding.ASCII.GetBytes("\r\n--" + boundary + "--\r\n");
                postStream.Write(footer, 0, footer.Length);

                request.ContentType = string.Format("multipart/form-data; boundary={0}", boundary);
            }
            else
            {
                request.ContentType = "application/x-www-form-urlencoded";
            }
            #endregion

            request.ContentLength = postStream != null ? postStream.Length : 0;
            request.Accept = "text/html,application/xhtml+xml,application/xml;q=0.9,image/webp,*/*;q=0.8";
            request.KeepAlive = true;

            if (!string.IsNullOrEmpty(refererUrl))
            {
                request.Referer = refererUrl;
            }
            request.UserAgent = "Mozilla/5.0 (Windows NT 6.1; WOW64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/31.0.1650.57 Safari/537.36";

            if (cookieContainer != null)
            {
                request.CookieContainer = cookieContainer;
            }

            #region 输入二进制流
            if (postStream != null)
            {
                postStream.Position = 0;

                //直接写入流
                Stream requestStream = request.GetRequestStream();

                byte[] buffer = new byte[1024];
                int bytesRead = 0;
                while ((bytesRead = postStream.Read(buffer, 0, buffer.Length)) != 0)
                {
                    requestStream.Write(buffer, 0, bytesRead);
                }


                //debug
                postStream.Seek(0, SeekOrigin.Begin);
                StreamReader sr = new StreamReader(postStream);
                var postStr = sr.ReadToEnd();


                postStream.Close();//关闭文件访问
            }
            #endregion

            HttpWebResponse response = (HttpWebResponse)request.GetResponse();

            if (cookieContainer != null)
            {
                response.Cookies = cookieContainer.GetCookies(response.ResponseUri);
            }

            using (Stream responseStream = response.GetResponseStream())
            {
                using (StreamReader myStreamReader = new StreamReader(responseStream, encoding ?? Encoding.GetEncoding("utf-8")))
                {
                    string retString = myStreamReader.ReadToEnd();
                    return retString;
                }
            }
        }

        #endregion

        /// <summary>
        /// 组装QueryString的方法
        /// 参数之间用&连接，首位没有符号，如：a=1&b=2&c=3
        /// </summary>
        /// <param name="formData"></param>
        /// <returns></returns>
        public static string GetQueryString(this Dictionary<string, string> formData)
        {
            if (formData == null || formData.Count == 0)
            {
                return "";
            }

            StringBuilder sb = new StringBuilder();

            var i = 0;
            foreach (var kv in formData)
            {
                i++;
                sb.AppendFormat("{0}={1}", kv.Key, kv.Value);
                if (i < formData.Count)
                {
                    sb.Append("&");
                }
            }

            return sb.ToString();
        }

        /// <summary>
        /// 填充表单信息的Stream
        /// </summary>
        /// <param name="formData"></param>
        /// <param name="stream"></param>
        public static void FillFormDataStream(this Dictionary<string, string> formData, Stream stream)
        {
            string dataString = GetQueryString(formData);
            var formDataBytes = formData == null ? new byte[0] : Encoding.UTF8.GetBytes(dataString);
            stream.Write(formDataBytes, 0, formDataBytes.Length);
            stream.Seek(0, SeekOrigin.Begin);//设置指针读取位置
        }

        /// <summary>
        /// 封装System.Web.HttpUtility.HtmlEncode
        /// </summary>
        /// <param name="html"></param>
        /// <returns></returns>
        public static string HtmlEncode(this string html)
        {
            return System.Web.HttpUtility.HtmlEncode(html);
        }
        /// <summary>
        /// 封装System.Web.HttpUtility.HtmlDecode
        /// </summary>
        /// <param name="html"></param>
        /// <returns></returns>
        public static string HtmlDecode(this string html)
        {
            return System.Web.HttpUtility.HtmlDecode(html);
        }
        /// <summary>
        /// 封装System.Web.HttpUtility.UrlEncode
        /// </summary>
        /// <param name="url"></param>
        /// <returns></returns>
        public static string UrlEncode(this string url)
        {
            return System.Web.HttpUtility.UrlEncode(url);
        }
        /// <summary>
        /// 封装System.Web.HttpUtility.UrlDecode
        /// </summary>
        /// <param name="url"></param>
        /// <returns></returns>
        public static string UrlDecode(this string url)
        {
            return System.Web.HttpUtility.UrlDecode(url);
        }
    }

public class FileHelper
    {
        /// <summary>
        /// 根据完整文件路径获取FileStream
        /// </summary>
        /// <param name="fileName"></param>
        /// <returns></returns>
        public static FileStream GetFileStream(string fileName)
        {
            FileStream fileStream = null;
            if (!string.IsNullOrEmpty(fileName) && File.Exists(fileName))
            {
                fileStream = new FileStream(fileName, FileMode.Open);
            }
            return fileStream;
        }
    }

/// <summary>
        /// Post获取信息
        /// </summary>
        /// <typeparam name="T">实体对象</typeparam>
        /// <param name="url">post url</param>
        /// <param name="data">post json data</param>
        /// <returns></returns>
        public static T PostOfUrl<T>(string url, string data)
        {
            System.Net.HttpWebRequest httpWebRequest = (HttpWebRequest)System.Net.WebRequest.Create(url);
            httpWebRequest.Method = "POST";

            httpWebRequest.Headers.Add("Accept-Charset", "utf-8");

            byte[] postBytes = Encoding.UTF8.GetBytes(data);
            //httpWebRequest.ContentType = "text/xml"; 
            httpWebRequest.ContentType = "application/json; charset=utf-8";// httpWebRequest.ContentLength = Encoding.UTF8.GetByteCount(data);//strJson为json字符串 
            Stream stream = httpWebRequest.GetRequestStream();
            stream.Write(postBytes, 0, postBytes.Length);
            stream.Close();//发送完毕，接受返回值 
            var response = httpWebRequest.GetResponse();
            Stream streamResponse = response.GetResponseStream();
            StreamReader streamRead = new StreamReader(streamResponse);
            String responseString = streamRead.ReadToEnd();
            JavaScriptSerializer js = new JavaScriptSerializer();
            var list = js.Deserialize<T>(responseString);
            return list;
        }

        public static T GetOfUrl<T>(string url)
        {
            HttpWebRequest req = (HttpWebRequest)WebRequest.Create(url);
            req.Method = "GET";
            HttpWebResponse resp = (HttpWebResponse)req.GetResponse();

            StreamReader sr = new StreamReader(resp.GetResponseStream(), Encoding.UTF8);
            string respHtml = sr.ReadToEnd();
            JavaScriptSerializer js = new JavaScriptSerializer();
            var list = js.Deserialize<T>(respHtml);
            return list;
        }