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可以利用HttpClient来进行Web Api的调用。由于WebA Api的调用本质上就是一次普通的发送请求与接收响应的过程，

所有HttpClient其实可以作为一般意义上发送HTTP请求的工具。

using System;using System.Collections.Generic;using System.Linq;using System.Net.Http;using System.Text;using System.Threading.Tasks;namespace 自己的名称空间{    public class ApiHelper    {        /// 
        /// api调用方法/注意一下API地址        /// 
        /// 控制器名称--自己所需调用的控制器名称        /// 请求方式--get-post-delete-put        /// 方法名称--如需一个Id(方法名/ID)(方法名/?ID)根据你的API灵活运用        /// 方法参数--如提交操作传整个对象        /// 
   
    json字符串--可以反序列化成你想要的
           public static string GetApiMethod(string controllerName, string overb, string action, object obj = null)        {            Task
   
     task = null;            string json = "";            HttpClient client = new HttpClient();            client.BaseAddress = new Uri("http://localhost:****/api/" + controllerName + "/");            switch (overb)            {                case "get":                    task = client.GetAsync(action);                    break;                case "post":                    task = client.PostAsJsonAsync(action, obj);                    break;                case "delete":                    task = client.DeleteAsync(action);                    break;                case "put":                    task = client.PutAsJsonAsync(action, obj);                    break;                default:                    break;            }            task.Wait();            var response = task.Result;            if (response.IsSuccessStatusCode)            {                var read = response.Content.ReadAsStringAsync();                read.Wait();                json = read.Result;            }            return json;        }    }}
   

可能需要以下引用集:

System.Net.Http.Formatting.dll

System.Web.Http.dll

*************************************************

引用 Newtonsoft.Json  

// Post请求        public string PostResponse(string url,string postData,out string statusCode)        {            string result = string.Empty;            //设置Http的正文            HttpContent httpContent = new StringContent(postData);            //设置Http的内容标头            httpContent.Headers.ContentType = new System.Net.Http.Headers.MediaTypeHeaderValue("application/json");            //设置Http的内容标头的字符            httpContent.Headers.ContentType.CharSet = "utf-8";            using(HttpClient httpClient=new HttpClient())            {                //异步Post                HttpResponseMessage response = httpClient.PostAsync(url, httpContent).Result;                //输出Http响应状态码                statusCode = response.StatusCode.ToString();                //确保Http响应成功                if (response.IsSuccessStatusCode)                {                    //异步读取json                    result = response.Content.ReadAsStringAsync().Result;                }            }            return result;        }        // 泛型：Post请求        public T PostResponse
   
    (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
    
      t = response.Content.ReadAsStringAsync();                    string s = t.Result;                    //Newtonsoft.Json                    string json = JsonConvert.DeserializeObject(s).ToString();                    result = JsonConvert.DeserializeObject
     
      (json);                 }            }            return result;        }        // 泛型：Get请求        public T GetResponse
      
       (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
       
         t = response.Content.ReadAsStringAsync();                    string s = t.Result;                    string json = JsonConvert.DeserializeObject(s).ToString();                    result = JsonConvert.DeserializeObject
        
         (json); } } return result; } // Get请求 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请求 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请求 public T PutResponse
         
          (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
          
            t = response.Content.ReadAsStringAsync(); string s = t.Result; string json = JsonConvert.DeserializeObject(s).ToString(); result = JsonConvert.DeserializeObject
           
            (json); } } return result; }
           
          
         
        
       
      
     
    
   

出处：

========================================================

我自己把上面的修改下，可以不引用 Newtonsoft.Json  ，在POST模式的方法PostWebAPI增加了GZip的支持，请求超时设置，其他的功能可以自己去扩展，增加了简单调用的方式。

后续可以扩展异步方式、HttpWebRequest方式调用Webapi（待完成。。。）

using System;using System.Collections.Generic;using System.IO;using System.Linq;using System.Net;using System.Net.Http;using System.Net.Http.Headers;using System.Text;using System.Threading.Tasks;using System.Web.Script.Serialization;namespace Car.AutoUpdate.Comm{    public class WebapiHelper    {        #region HttpClient        /// 
        /// Get请求指定的URL地址        /// 
        /// URL地址        /// 
           public static string GetWebAPI(string url)        {            string result = "";            string strOut = "";            try            {                result = GetWebAPI(url, out strOut);            }            catch (Exception ex)            {                LogHelper.Error("调用后台服务出现异常！", ex);            }            return result;        }        /// 
        /// Get请求指定的URL地址        /// 
        /// URL地址        /// Response返回的状态        /// 
           public static string GetWebAPI(string url, out string statusCode)        {            string result = string.Empty;            statusCode = string.Empty;            try            {                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;                    }                    else                    {                        LogHelper.Warn("调用后台服务返回失败：" + url + Environment.NewLine + SerializeObject(response));                    }                }            }            catch (Exception ex)            {                LogHelper.Error("调用后台服务出现异常！", ex);            }            return result;        }        /// 
        /// Get请求指定的URL地址        /// 
        /// 
   
    返回的json转换成指定实体对象
           /// URL地址        /// 
           public static T GetWebAPI
   
    (string url) where T : class, new()        {            T result = default(T);            try            {                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
    
      t = response.Content.ReadAsStringAsync();                        string s = t.Result;                        string jsonNamespace = DeserializeObject
     
      (s).ToString();                        result = DeserializeObject
      
       (s);                    }                    else                    {                        LogHelper.Warn("调用后台服务返回失败：" + url + Environment.NewLine + SerializeObject(response));                    }                }            }            catch (Exception ex)            {                LogHelper.Error("调用后台服务出现异常！", ex);            }            return result;        }        /// 
       
        /// Post请求指定的URL地址        /// 
        /// 
       URL地址        /// 
       提交到Web的Json格式的数据：如:{"ErrCode":"FileErr"}        /// 
               public static string PostWebAPI(string url, string postData)        {            string result = "";            HttpStatusCode strOut = HttpStatusCode.BadRequest;            try            {                result = PostWebAPI(url, postData, out strOut);            }            catch (Exception ex)            {                LogHelper.Error("调用后台服务出现异常！", ex);            }            return result;        }        /// 
       
        /// Post请求指定的URL地址        /// 
        /// 
       URL地址        /// 
       提交到Web的Json格式的数据：如:{"ErrCode":"FileErr"}        /// 
       Response返回的状态        /// 
               public static string PostWebAPI(string url, string postData, out HttpStatusCode httpStatusCode)        {            string result = string.Empty;            httpStatusCode = HttpStatusCode.BadRequest;            //设置Http的正文            HttpContent httpContent = new StringContent(postData);            //设置Http的内容标头            httpContent.Headers.ContentType = new System.Net.Http.Headers.MediaTypeHeaderValue("application/json");            //设置Http的内容标头的字符            httpContent.Headers.ContentType.CharSet = "utf-8";            HttpClientHandler httpHandler = new HttpClientHandler() { AutomaticDecompression = DecompressionMethods.GZip };            try            {                //using (HttpClient httpClient = new HttpClient(httpHandler))                using (HttpClient httpClient = new HttpClient())                {                    httpClient.Timeout = new TimeSpan(0, 0, 5);                    //异步Post                    HttpResponseMessage response = httpClient.PostAsync(url, httpContent).Result;                    //输出Http响应状态码                    httpStatusCode = response.StatusCode;                    //确保Http响应成功                    if (response.IsSuccessStatusCode)                    {                        //异步读取json                        result = response.Content.ReadAsStringAsync().Result;                    }                    else                    {                        LogHelper.Warn("调用后台服务返回失败：" + url + Environment.NewLine + SerializeObject(response));                    }                }            }            catch (Exception ex)            {                LogHelper.Error("调用后台服务出现异常！", ex);            }            return result;        }        /// 
       
        /// Post请求指定的URL地址        /// 
        /// 
       
        返回的json转换成指定实体对象
               /// 
       URL地址        /// 
       提交到Web的Json格式的数据：如:{"ErrCode":"FileErr"}        /// 
               public static T PostWebAPI
       
        (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";            HttpClientHandler httpHandler = new HttpClientHandler() { AutomaticDecompression = DecompressionMethods.GZip };            try            {                using (HttpClient httpClient = new HttpClient(httpHandler))                {                    HttpResponseMessage response = httpClient.PostAsync(url, httpContent).Result;                    if (response.IsSuccessStatusCode)                    {                        Task
        
          t = response.Content.ReadAsStringAsync(); string s = t.Result; //Newtonsoft.Json string jsonNamespace = DeserializeObject
         
          (s).ToString(); result = DeserializeObject
          
           (s); } else { LogHelper.Warn("调用后台服务返回失败：" + url + Environment.NewLine + SerializeObject(response)); } } } catch (Exception ex) { LogHelper.Error("调用后台服务出现异常！", ex); } return result; } /// 
           
 /// Put请求指定的URL地址 /// 
 /// 
           URL地址 /// 
           提交到Web的Json格式的数据：如:{"ErrCode":"FileErr"} /// 
            public static string PutWebAPI(string url, string putData) { string result = ""; string strOut = ""; result = PutWebAPI(url, putData, out strOut); return result; } /// 
           
 /// Put请求指定的URL地址 /// 
 /// 
           URL地址 /// 
           提交到Web的Json格式的数据：如:{"ErrCode":"FileErr"} /// 
           Response返回的状态 /// 
            public static string PutWebAPI(string url, string putData, out string statusCode) { string result = statusCode = string.Empty; HttpContent httpContent = new StringContent(putData); httpContent.Headers.ContentType = new System.Net.Http.Headers.MediaTypeHeaderValue("application/json"); httpContent.Headers.ContentType.CharSet = "utf-8"; try { using (HttpClient httpClient = new HttpClient()) { HttpResponseMessage response = httpClient.PutAsync(url, httpContent).Result; statusCode = response.StatusCode.ToString(); if (response.IsSuccessStatusCode) { result = response.Content.ReadAsStringAsync().Result; } else { LogHelper.Warn("调用后台服务返回失败：" + url + Environment.NewLine + SerializeObject(response)); } } } catch (Exception ex) { LogHelper.Error("调用后台服务出现异常！", ex); } return result; } /// 
           
 /// Put请求指定的URL地址 /// 
 /// 
           
            返回的json转换成指定实体对象
            /// 
           URL地址 /// 
           提交到Web的Json格式的数据：如:{"ErrCode":"FileErr"} /// 
            public static T PutWebAPI
           
            (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"; try { using (HttpClient httpClient = new HttpClient()) { HttpResponseMessage response = httpClient.PutAsync(url, httpContent).Result; if (response.IsSuccessStatusCode) { Task
            
              t = response.Content.ReadAsStringAsync(); string s = t.Result; string jsonNamespace = DeserializeObject
             
              (s).ToString(); result = DeserializeObject
              
               (s); } else { LogHelper.Warn("调用后台服务返回失败：" + url + Environment.NewLine + SerializeObject(response)); } } } catch (Exception ex) { LogHelper.Error("调用后台服务出现异常！", ex); } return result; } /// 
               
 /// 对象转JSON /// 
 /// 
               对象 /// 
               
                JSON格式的字符串
                public static string SerializeObject(object obj) { JavaScriptSerializer jss = new JavaScriptSerializer(); try { return jss.Serialize(obj); } catch (Exception ex) { LogHelper.Error("JSONHelper.SerializeObject 转换对象失败。", ex); throw new Exception("JSONHelper.SerializeObject(object obj): " + ex.Message); } } /// 
               
 /// 将Json字符串转换为对像 /// 
 /// 
                /// 
                /// 
                public static T DeserializeObject
               
                (string json) { JavaScriptSerializer Serializer = new JavaScriptSerializer(); T objs = default(T); try { objs = Serializer.Deserialize
                
                 (json); } catch (Exception ex) { LogHelper.Error("JSONHelper.DeserializeObject 转换对象失败。", ex); throw new Exception("JSONHelper.DeserializeObject
                 
                  (string json): " + ex.Message); } return objs; } #endregion private static HttpResponseMessage HttpPost(string url, HttpContent httpContent) { HttpResponseMessage response = null; HttpClientHandler httpHandler = new HttpClientHandler() { AutomaticDecompression = DecompressionMethods.GZip }; try { //using (HttpClient httpClient = new HttpClient(httpHandler)) using (HttpClient httpClient = new HttpClient()) { httpClient.Timeout = new TimeSpan(0, 0, 5); //异步Post response = httpClient.PostAsync(url, httpContent).Result; } } catch (Exception ex) { LogHelper.Error("调用后台服务出现异常！", ex); } return response; } }}
                 
                
               
              
             
            
           
          
         
        
       
      
     
    
   

下面再分享一个帮助类，有用到的做个参考吧

using HtmlAgilityPack;using System;using System.Collections.Generic;using System.Linq;using System.Net.Http;using System.Text;using System.Threading.Tasks;namespace WebCollect.CommonHelp{    public static class CommonHelper    {        #region HttpClient        private static HttpClient _httpClient;        public static HttpClient httpClient        {            get            {                if (_httpClient == null)                {                    _httpClient = new HttpClient();                    _httpClient.Timeout = new TimeSpan(0, 1, 0);                }                return _httpClient;            }            set { _httpClient = value; }        }        #endregion        #region get请求        /// 
        /// get请求返回的字符串        /// 
        ///         /// 
           public static string GetRequestStr(string url)        {            try            {                var response = httpClient.GetAsync(new Uri(url)).Result;                return response.Content.ReadAsStringAsync().Result;            }            catch (Exception)            {                return null;            }        }        /// 
        /// get请求返回的二进制        /// 
        ///         /// 
           public static byte[] GetRequestByteArr(string url)        {            try            {                var response = httpClient.GetAsync(new Uri(url)).Result;                return response.Content.ReadAsByteArrayAsync().Result;            }            catch (Exception)            {                return null;            }        }        #endregion        #region post请求        /// 
        /// post请求返回的字符串        /// 
        ///         /// 
           public static string PostRequestStr(string url)        {            try            {                string contentStr = "";                StringContent sc = new StringContent(contentStr);                sc.Headers.ContentType = new System.Net.Http.Headers.MediaTypeHeaderValue("application/x-www-form-urlencoded");//todo                var response = httpClient.PostAsync(new Uri(url), sc).Result;                return response.Content.ReadAsStringAsync().Result;            }            catch (Exception)            {                return null;            }        }        #endregion    }}

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