引用 Newtonsoft.Json

        // Post請求
        public string PostResponse(string url,string postData,out string statusCode)
        {
            string result = string.Empty;
            //設置Http的正文
            HttpContent httpContent = new StringContent(postData);
            //設置Http的內容標頭
            httpContent.Headers.ContentType = new
 
 System.Net.Http.Headers.MediaTypeHeaderValue("application/json");
            //設置Http的內容標頭的字符
            httpContent.Headers.ContentType.CharSet = "utf-8";
            using(HttpClient httpClient=new HttpClient())
            {
                //異步Post
                HttpResponseMessage response = httpClient.PostAsync(url, httpContent).Result;
                
 
//輸出Http響應狀態碼
                statusCode = response.StatusCode.ToString();
                //確保Http響應成功
                if (response.IsSuccessStatusCode)
                {
                    //異步讀取json
                    result = response.Content.ReadAsStringAsync().Result;
                }
            }
            
 
return result;
        }


        // 泛型：Post請求
        public T PostResponse<T>(string url,string postData) where T:class,new()
        {
            T result = default(T);
 
            HttpContent httpContent = new StringContent(postData);
            httpContent.Headers.ContentType = new System.Net.Http.Headers.MediaTypeHeaderValue("application/json");
            httpContent.Headers.ContentType.CharSet = "utf-8";
            using(HttpClient httpClient=new HttpClient())
            {
                HttpResponseMessage response = httpClient.PostAsync(url, httpContent).Result;
 
                if (response.IsSuccessStatusCode)
                {
                    Task<string> t = response.Content.ReadAsStringAsync();
                    string s = t.Result;
                    //Newtonsoft.Json
                    string json = JsonConvert.DeserializeObject(s).ToString();
                    result = JsonConvert.DeserializeObject<T>(json); 
                }
            }
            return result;
        }

參數為鍵值對：var content = new FormUrlEncodedContent(postData);

使用HttpClient 請求的時候碰到個問題不知道是什麽異常，用HttpWebResponse請求才獲取到異常，設置ServicePointManager可以用，參考下面這個

        /// <summary>
        /// http請求接口
        /// </summary>
        /// <typeparam name="T"></typeparam>
        /// <param name="url"></param>
        /// <param name="postData"></param>
        /// <returns></returns>
        public T httpClientPost<T>(string url, string postData) where T : class, new()
        {
            
            T result = default(T);
            ServicePointManager.ServerCertificateValidationCallback = new RemoteCertificateValidationCallback(CheckValidationResult);
            System.Net.ServicePointManager.SecurityProtocol = SecurityProtocolType.Ssl3 | SecurityProtocolType.Tls | SecurityProtocolType.Tls11 | SecurityProtocolType.Tls12;
            HttpContent httpContent = new StringContent(postData);
            httpContent.Headers.ContentType = new System.Net.Http.Headers.MediaTypeHeaderValue("application/json");
            httpContent.Headers.ContentType.CharSet = "utf-8";
            using (HttpClient httpClient = new HttpClient())
            {
                HttpResponseMessage response = httpClient.PostAsync(url, httpContent).Result;

                if (response.IsSuccessStatusCode)
                {
                    Task<string> t = response.Content.ReadAsStringAsync();
                    string s = t.Result;
                    //Newtonsoft.Json
                    string json = JsonConvert.DeserializeObject(s).ToString();
                    result = JsonConvert.DeserializeObject<T>(json);
                }

            }

            return result;

        }


        public bool CheckValidationResult(object sender, X509Certificate certificate, X509Chain chain, SslPolicyErrors errors)
        {  // 總是接受  
            return true;
        }


        /// <summary>
        /// http請求接口
        /// </summary>
        /// <typeparam name="T"></typeparam>
        /// <param name="url"></param>
        /// <param name="bodyString"></param>
        /// <returns></returns>
        public VMDataResponse<T> HttpPost<T>(string url, string bodyString)
        {
            var result = new VMDataResponse<T>();
            try
            {
                ServicePointManager.ServerCertificateValidationCallback = new RemoteCertificateValidationCallback(CheckValidationResult);
                var request = WebRequest.Create(url);
                request.Method = "POST";
                request.ContentType = "application/json; charset=utf-8";
                byte[] buffer = Encoding.UTF8.GetBytes(bodyString);
                request.ContentLength = buffer.Length;
                System.Net.ServicePointManager.SecurityProtocol = SecurityProtocolType.Ssl3 | SecurityProtocolType.Tls | SecurityProtocolType.Tls11 | SecurityProtocolType.Tls12;
                request.GetRequestStream().Write(buffer, 0, buffer.Length);
                var response = (HttpWebResponse)request.GetResponse();
                if (response.StatusCode != HttpStatusCode.OK)
                {
                    result.msg = "錯誤：Respose返回不是StatusCode!=OK";
                    result.status = 500;
                    logger.Error(result.msg);
                    return result;
                }
                using (var ss = response.GetResponseStream())
                {
                    byte[] rbs = new byte[4096];
                    int count = 0;
                    string str = "";
                    while (ss != null && (count = ss.Read(rbs, 0, rbs.Length)) > 0)
                    {
                        str += Encoding.UTF8.GetString(rbs, 0, count);
                    }
                    var msg = str;
                    //logger.Error("返回信息" + msg);
                    if (!string.IsNullOrWhiteSpace(msg))
                    {
                        result.data = JsonConvert.DeserializeObject<T>(msg);
                        return result;
                    }
                }
            }
            catch (Exception ex)
            {
                result.msg = "錯誤：請求出現異常消息：" + ex.Message;
                result.status = 600;
                logger.Error(result.msg);
                return result;
            }
            return result;
        }

get:

        // 泛型：Get請求
        public T GetResponse<T>(string url) where T :class,new()
        {
            T result = default(T);
 
            using (HttpClient httpClient=new HttpClient())
            {
                httpClient.DefaultRequestHeaders.Accept.Add(new System.Net.Http.Headers.MediaTypeWithQualityHeaderValue("application/json"));
                HttpResponseMessage response = httpClient.GetAsync(url).Result;
 
                if (response.IsSuccessStatusCode)
                {
                    Task<string> t = response.Content.ReadAsStringAsync();
                    string s = t.Result;
                    string json = JsonConvert.DeserializeObject(s).ToString();
                    result = JsonConvert.DeserializeObject<T>(json);
                }
            }
            return result;
        }

        // Get請求
        public string GetResponse(string url, out string statusCode)
        {
            string result = string.Empty;
 
            using (HttpClient httpClient = new HttpClient())
            {
                httpClient.DefaultRequestHeaders.Accept.Add(new System.Net.Http.Headers.MediaTypeWithQualityHeaderValue("application/json"));
 
                HttpResponseMessage response = httpClient.GetAsync(url).Result;
                statusCode = response.StatusCode.ToString();
 
                if (response.IsSuccessStatusCode)
                {
                    result = response.Content.ReadAsStringAsync().Result;
                }
            }
            return result;
        }

put:

        // Put請求
        public string PutResponse(string url, string putData, out string statusCode)
        {
            string result = string.Empty;
            HttpContent httpContent = new StringContent(putData);
            httpContent.Headers.ContentType = new System.Net.Http.Headers.MediaTypeHeaderValue("application/json");
            httpContent.Headers.ContentType.CharSet = "utf-8";
            using (HttpClient httpClient = new HttpClient())
            {
                HttpResponseMessage response = httpClient.PutAsync(url, httpContent).Result;
                statusCode = response.StatusCode.ToString();
                if (response.IsSuccessStatusCode)
                {
                    result = response.Content.ReadAsStringAsync().Result;
                }
            }
            return result;
        }


        // 泛型：Put請求
        public T PutResponse<T>(string url, string putData) where T : class, new()
        {
            T result = default(T);
            HttpContent httpContent = new StringContent(putData);
            httpContent.Headers.ContentType = new System.Net.Http.Headers.MediaTypeHeaderValue("application/json");
            httpContent.Headers.ContentType.CharSet = "utf-8";
            using(HttpClient httpClient=new HttpClient())
            {
                HttpResponseMessage response = httpClient.PutAsync(url, httpContent).Result;
 
                if (response.IsSuccessStatusCode)
                {
                    Task<string> t = response.Content.ReadAsStringAsync();
                    string s = t.Result;
                    string json = JsonConvert.DeserializeObject(s).ToString();
                    result = JsonConvert.DeserializeObject<T>(json);
                }
            }
            return result;
        }

https://blog.csdn.net/sun_zeliang/article/details/81587835

https://blog.csdn.net/baidu_32739019/article/details/78679129

ASP.NET Core使用HttpClient的同步和異步請求

ASP.NET Core使用HttpClient的同步和異步請求

using System;
using System.Collections.Generic;
using System.Collections.Specialized;
using System.IO;
using System.Linq;
using System.Net;
using System.Net.Http;
using System.Text;
using System.Threading.Tasks;
using System.Web;

namespace Common
{
    public class HttpHelper
    {/// <summary>
        /// 發起POST同步請求
        /// 
        /// </summary>
        /// <param name="url"></param>
        /// <param name="postData"></param>
        /// <param name="contentType">application/xml、application/json、application/text、application/x-www-form-urlencoded</param>
        /// <param name="headers">填充消息頭</param>        
        /// <returns></returns>
        public static string HttpPost(string url, string postData = null, string contentType = null, int timeOut = 30, Dictionary<string, string> headers = null)
        {
            postData = postData ?? "";
            using (HttpClient client = new HttpClient())
            {
                if (headers != null)
                {
                    foreach (var header in headers)
                        client.DefaultRequestHeaders.Add(header.Key, header.Value);
                }
                using (HttpContent httpContent = new StringContent(postData, Encoding.UTF8))
                {
                    if (contentType != null)
                        httpContent.Headers.ContentType = new System.Net.Http.Headers.MediaTypeHeaderValue(contentType);

                    HttpResponseMessage response = client.PostAsync(url, httpContent).Result;
                    return response.Content.ReadAsStringAsync().Result;
                }
            }
        }


        /// <summary>
        /// 發起POST異步請求
        /// </summary>
        /// <param name="url"></param>
        /// <param name="postData"></param>
        /// <param name="contentType">application/xml、application/json、application/text、application/x-www-form-urlencoded</param>
        /// <param name="headers">填充消息頭</param>        
        /// <returns></returns>
        public static async Task<string> HttpPostAsync(string url, string postData = null, string contentType = null, int timeOut = 30, Dictionary<string, string> headers = null)
        {
            postData = postData ?? "";
            using (HttpClient client = new HttpClient())
            {
                client.Timeout = new TimeSpan(0, 0, timeOut);
                if (headers != null)
                {
                    foreach (var header in headers)
                        client.DefaultRequestHeaders.Add(header.Key, header.Value);
                }
                using (HttpContent httpContent = new StringContent(postData, Encoding.UTF8))
                {
                    if (contentType != null)
                        httpContent.Headers.ContentType = new System.Net.Http.Headers.MediaTypeHeaderValue(contentType);

                    HttpResponseMessage response = await client.PostAsync(url, httpContent);
                    return await response.Content.ReadAsStringAsync();
                }
            }
        }

        /// <summary>
        /// 發起GET同步請求
        /// </summary>
        /// <param name="url"></param>
        /// <param name="headers"></param>
        /// <param name="contentType"></param>
        /// <returns></returns>
        public static string HttpGet(string url, string contentType = null, Dictionary<string, string> headers = null)
        {
            using (HttpClient client = new HttpClient())
            {
                if (contentType != null)
                    client.DefaultRequestHeaders.Add("ContentType", contentType);
                if (headers != null)
                {
                    foreach (var header in headers)
                        client.DefaultRequestHeaders.Add(header.Key, header.Value);
                }
                HttpResponseMessage response = client.GetAsync(url).Result;
                return response.Content.ReadAsStringAsync().Result;
            }
        }

        /// <summary>
        /// 發起GET異步請求
        /// </summary>
        /// <param name="url"></param>
        /// <param name="headers"></param>
        /// <param name="contentType"></param>
        /// <returns></returns>
        public static async Task<string> HttpGetAsync(string url, string contentType = null, Dictionary<string, string> headers = null)
        {
            using (HttpClient client = new HttpClient())
            {
                if (contentType != null)
                    client.DefaultRequestHeaders.Add("ContentType", contentType);
                if (headers != null)
                {
                    foreach (var header in headers)
                        client.DefaultRequestHeaders.Add(header.Key, header.Value);
                }
                HttpResponseMessage response = await client.GetAsync(url);
                return await response.Content.ReadAsStringAsync();
            }
        }
    }
}

調用異步請求方法：

var result = await HttpHelper.HttpPostAsync("http://www.baidu.com/api/getuserinfo", "userid=23456798"); 

https://www.cnblogs.com/pudefu/p/7581956.html

https://blog.csdn.net/slowlifes/article/details/78504782

C# ASP.NET Core使用HttpClient的同步和異步請求