C# HttpClient类库

示例代码：

using System.Net.Http;
using System.Net.Http.Headers;
using System.Threading.Tasks;

namespace MachineServer
{
    public static class HttpHelper
    {
        public static HttpClient HttpClient { get; set; }

        public static void InitializeClient()
        {
            //单例模式
            if (HttpClient == null)
            {
                HttpClient = new HttpClient();
            }

            HttpClient.DefaultRequestHeaders.Accept.Clear();
            HttpClient.DefaultRequestHeaders.Accept.Add(new MediaTypeWithQualityHeaderValue("application/json"));

            //能解读https类型
            //ServicePointManager.SecurityProtocol = SecurityProtocolType.Tls12;
        }

        /// <summary>
        /// Get方法
        /// </summary>
        /// <param name="url">目标链接(含参数)</param>
        /// <returns>返回的字符串</returns>
        public static async Task<string> GetAsync(string url)
        {
            using (HttpResponseMessage response = await HttpClient.GetAsync(url))
            {
                response.EnsureSuccessStatusCode();
                string result = await response.Content.ReadAsStringAsync();
                return result;
            }
        }

        /// <summary>
        /// Post方法
        /// </summary>
        /// <param name="url">目标链接</param>
        /// <param name="json">发送的json格式的参数字符串</param>
        /// <returns>返回的字符串</returns>
        public static async Task<string> PostAsync(string url, string json)
        {
            StringContent content = new StringContent(json);
            content.Headers.ContentType = new MediaTypeHeaderValue("application/json");

            using (HttpResponseMessage response = await HttpClient.PostAsync(url, content))
            {
                response.EnsureSuccessStatusCode();
                string result = await response.Content.ReadAsStringAsync();
                return result;
            }
        }

        /// <summary>
        /// Post方法
        /// </summary>
        /// <param name="url">目标链接</param>
        /// <param name="json">发送的json格式的参数字符串</param>
        /// <returns>返回的字符串</returns>
        public static async Task<string> PostAsync(string url, HttpContent content)
        {
            //HttpContent content = new FormUrlEncodedContent(new Dictionary<string, string>()
            //       {
            //           { "token", token},
            //           { "orderNo", orderNo}
            //       });
            content.Headers.ContentType = new MediaTypeHeaderValue("application/x-www-form-urlencoded") { CharSet = "utf-8" };

            using (HttpResponseMessage response = await HttpClient.PostAsync(url, content))
            {
                response.EnsureSuccessStatusCode();
                string result = await response.Content.ReadAsStringAsync();
                return result;
            }
        }
    }
}

Get方法

get方法传递参数，是将参数及其值直接跟在url后面，以?开始，中间用&间隔，类似：

string tokenString = await HttpHelper.GetAsync($"https://er.com/Apps/Mes/getToken?appKey=11&nonce=22&timestamp=33&signature=44");

Post方法

post方法传递参数有几种形式，需要看HTTP服务端那边支持哪种，客户端用时，需要将Header的ContentType设置正确。

总结以下三种：

1. json格式：

content.Headers.ContentType = new MediaTypeHeaderValue("application/json");

对应Postman中：

2. form-data格式：

content.Headers.Remove("Content-Type");
content.Headers.TryAddWithoutValidation("Content-Type", "multipart/form-data; boundary=----WebKitFormBoundarypy5dIaqJBcHjn7sv");

对应Postman中：

3. x-www-form-urlencoded格式：

content.Headers.ContentType = new MediaTypeHeaderValue("application/x-www-form-urlencoded") { CharSet = "utf-8" };

对应Postman中：

已测试Post方法的x-www-form-urlencoded方式使用成功