目录

• 1、遇到的问题
• ① 远程主机强迫关闭了一个现有的连接
• ② POST请求某种情况下请求会失败的解决方案
• 2、使用HttpClient为什么建议使用单例
• 3、基础代码实现

1、遇到的问题

① 远程主机强迫关闭了一个现有的连接

相信大家在使用 HttpClient 的时候遇到过 远程主机强迫关闭了一个现有的连接 的错误，一般的解决方法就是下面这种

解决办法：在请求方法中指定 ServicePoint 安全协议

System.Net.ServicePointManager.SecurityProtocol = System.Net.SecurityProtocolType.Tls11 | System.Net.SecurityProtocolType.Tls12;

② POST请求某种情况下请求会失败的解决方案

工作中遇到写正常的 http post 请求会失败的问题，于是就在原有的基础上改动了写代码使用HttpRequestMessage 指定 标头、HTTP 谓词和潜在数据，详情见代码第二个 post 请求方法。

2、使用HttpClient为什么建议使用单例

HttpClient 旨在被实例化一次并在应用程序的整个生命周期中重复使用。为每个请求实例化一个 HttpClient 类将耗尽重负载下可用的套接字数量。将导致 SocketException 错误。

3、基础代码实现

using System;
using System.Net.Http;
using System.Net.Http.Headers;
using System.Reflection;
using System.Text;

namespace Clear.DataServices.HttpHelper
{
    public class HttpClientService
    {
        private static HttpClientService _instance;

        private static readonly object _lock = new object();
        
        private static HttpClient _client;
        
        public HttpClientService() { }
        
        public static HttpClientService GetInstance()
        {
            if (_instance == null)
            {
                lock (_lock)
                {
                    if (_instance == null)
                    {
                        _instance = new HttpClientService();
                    }
                    
                    if (_client is null)
					{
					    _client = new HttpClient();
					}
                }
            }
            return _instance;
        }
      
        /// <summary>
        /// HttpClient Get请求
        /// </summary>
        /// <param name="url">请求地址</param>
        /// <returns></returns>
        public string HttpGet(string url)
        {
            try
            {
                if (_client.BaseAddress is null)
				{
				    _client.BaseAddress = new Uri(url);
				}
              
                client.DefaultRequestHeaders.Accept.Clear();
                HttpResponseMessage response = client.GetAsync(url).Result;

                response.EnsureSuccessStatusCode();
                string responseBody = response.Content.ReadAsStringAsync().Result;

                return responseBody;                
            }
            catch (Exception e)
            {                
                object errorMessage = new
                {
                    code = "-",
                    message = e.Message
                };
                return JsonConvert.SerializeObject(errorMessage);
            }
        }

        /// <summary>
        /// HttpClient Post请求
        /// </summary>
        /// <param name="url">请求地址</param>
        /// <param name="content">HttpContent</param>
        /// <returns></returns>
        public string HttpPost(string url, string content, string token = null)
        {
            try
            {
                if (_client.BaseAddress is null)
				{
				    _client.BaseAddress = new Uri(url);
				}
				
                // System.Net.ServicePointManager.SecurityProtocol = System.Net.SecurityProtocolType.Tls | System.Net.SecurityProtocolType.Tls12;

                client.DefaultRequestHeaders.Accept.Clear();
                client.DefaultRequestHeaders.Connection.Add("keep-alive");
                if (!token.IsNullOrEmpty())
                {
                    client.DefaultRequestHeaders.Add("Authorization-Token", token);
                }
                client.DefaultRequestHeaders.Accept.Add(new MediaTypeWithQualityHeaderValue("application/json"));
             
                HttpResponseMessage response = client.PostAsync(url, new StringContent(content, Encoding.UTF, "application/json")).Result;
                response.EnsureSuccessStatusCode();
                string responseBody = response.Content.ReadAsStringAsync().Result;
             
                return responseBody;                
            }
            catch (Exception e)
            {                
                object errorMessage = new
                {
                    code = "-",
                    message = e.Message
                };
                return JsonConvert.SerializeObject(errorMessage);
            }
        }

        /// <summary>
        /// HttpClient Post请求
        /// </summary>
        /// <remarks>
        /// 用于非正常http请求
        /// </remarks>
        /// <param name="url"></param>
        /// <param name="content"></param>
        /// <returns></returns>
        public string HttpPost(string url, string content)
        {
            try
            {
                using (var request = new HttpRequestMessage(new HttpMethod("Post"), url))
                {
                    // System.Net.ServicePointManager.SecurityProtocol = System.Net.SecurityProtocolType.Tls | System.Net.SecurityProtocolType.Tls12;

                    request.Headers.TryAddWithoutValidation("Content-Type", "application/json");

                    request.Content = new StringContent(content);

                    request.Content.Headers.ContentType = MediaTypeHeaderValue.Parse("application/json");
                    var response = _client.SendAsync(request).Result;
                    return response.Content.ReadAsStringAsync().Result;
                }
            }
            catch (Exception e)
            {
                object errorMessage = new
                {
                    code = "-",
                    message = e.Message
                };
                return JsonConvert.SerializeObject(errorMessage);
            }
        }

        /// <summary>
        /// Model对象转换为uri网址参数形式
        /// </summary>
        /// <param name="obj">Model对象</param>
        /// <param name="url">前部分网址</param>
        /// <returns></returns>
        public string GetUriParam(object obj, string url = "")
        {
            PropertyInfo[] propertis = obj.GetType().GetProperties(BindingFlags.Instance | BindingFlags.Public);
            StringBuilder sb = new StringBuilder();
            sb.Append(url);
            sb.Append("?");
            foreach (var p in propertis)
            {
                var v = p.GetValue(obj, null);
                if (v == null) continue;

                sb.Append(p.Name);
                sb.Append("=");
                sb.Append(Uri.EscapeDataString(v.ToString()));//将字符串转换为它的转义表示形式，HttpUtility.UrlEncode是小写
                sb.Append("&");
            }
            sb.Remove(sb.Length -, 1);

            return sb.ToString();
        }
    }
}