HttpClient實現同步異步GET,POST

        /// <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 ??= "";
            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 = "application/json", int timeOut = 30, Dictionary<string, string> headers = null)
        {
            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();
        }