HttpClient替换HttpWebRequest--以GET和POST请求为例说明

首先说一下HttpRequest、WebClient和HttpClient的关系：HttpRequest是基层的请求方式，WebClient是对HttpRequest的简化封装，在WebClient中有对HttpRequest的默认设置；HttpClient是重写的请求方式，相对于HttpRequest更简单实现异步请求，是.NetCore中更推崇的方式。

说明：以下代码中 在GetAccessToken(Async)中调用了调用了PostMail(Async)方式,其中在GetAccessToken(Async)实现GET请求，在PostMail(Async)中实现POST请求

一、对比一下HttpRequest与HttpClient实现GET请求的过程区别（其实很相似，但HttpClient轻松实现了异步）

1）HttpRequest的GET请求

 public ActionResult<string> GetAccessToken()
        {  //GET获取accessToken的参数 corid
            string uri = "你的URL";
            //创建请求
  //HttpWebRequest request = (HttpWebRequest)WebRequest.Create(uri);
            //WebClient是对HttpWebRequest的抽象,WebClient使用简单，但速度慢;Restsharp兼具WebClient和HttpWebClient的优点；HttpClient是.NetCore中的概念，更适合异步编程
            WebRequest request = WebRequest.Create(uri);
            //请求设置
            request.Credentials = CredentialCache.DefaultCredentials;
            //创建应答接收
            WebResponse response = request.GetResponse();
            //创建应答读写流
            string accessToken;
            using (Stream streamResponse=response.GetResponseStream())
            {
                StreamReader reader = new StreamReader(streamResponse);
                string responseFromServer = reader.ReadToEnd();
                JObject res = (JObject)JsonConvert.DeserializeObject(responseFromServer);
                 accessToken = res["access_token"].ToString();
                reader.Close();
            }
            //获得许可证凭证
            PostMail(accessToken);
            //关闭响应
            response.Close();
            return "success";
        }

2）HttpClient的GET请求

public async Task<ActionResult<string>> GetAccessTokenAsync()
        {
            string uri = "你的URL";
            HttpClientHandler handler = new HttpClientHandler
            {
                //设置是否发送凭证信息，有的服务器需要验证身份，不是所有服务器需要
                UseDefaultCredentials = false
                
            };
            HttpClient httpClient = new HttpClient(handler);
            HttpResponseMessage response = await httpClient.GetAsync(uri);
            response.EnsureSuccessStatusCode();
            string accessToken;
            //回复结果直接读成字符串
            string resp = await response.Content.ReadAsStringAsync();
            JObject json = (JObject)JsonConvert.DeserializeObject(resp);
            accessToken = json["access_token"].ToString();
            //采用流读数据
            //using (Stream streamResponse = await response.Content.ReadAsStreamAsync())
            //{
            //    StreamReader reader = new StreamReader(streamResponse);
            //    string responseFromServer = reader.ReadToEnd();
            //    JObject res = (JObject)JsonConvert.DeserializeObject(responseFromServer);
            //    accessToken = res["access_token"].ToString();
            //    reader.Close();
            //}
            //获得许可证凭证
            PostMailAsync(accessToken);
            //关闭响应
            return "success";
        }

二、对比一下HttpRequest与HttpClient实现POST请求的过程区别

1)HttpRequest的POST请求

  public void PostMail(string accessToken)
        {    //POST的API
            string uri = "https://qyapi.weixin.qq.com/cgi-bin/message/send?access_token=" + accessToken;
            //创建请求
            WebRequest myWebRequest = WebRequest.Create(uri);
            //请求设置
            myWebRequest.Credentials = CredentialCache.DefaultCredentials;
            myWebRequest.ContentType = "application/json;charset=UTF-8";
            myWebRequest.Method = "POST";
            //向服务器发送的内容
            using (Stream streamResponse = myWebRequest.GetRequestStream())
            {
                //创建JSON格式的发送内容
                JObject postedJObject = new JObject
                {
                    //在此处设置发送内容及对象
                    { "touser", "Heavy" },
                    { "msgtype", "text" },
                    { "agentid", 1000002 }
                };
                JObject text = new JObject
            {
                {"content","内容来自网站--内容可自行编辑--heavy"}
            };
                postedJObject.Add("text", text);
                postedJObject.Add("safe", 0);
                //将传送内容编码
                String paramString = postedJObject.ToString(Newtonsoft.Json.Formatting.None, null);
                byte[] byteArray = Encoding.UTF8.GetBytes(paramString);
                //向请求中写入内容
                streamResponse.Write(byteArray, 0, byteArray.Length);
            }
            //创建应答
            WebResponse myWebResponse = myWebRequest.GetResponse();
            //创建应答的读写流
            string responseFromServer;
            using (Stream streamResponse = myWebResponse.GetResponseStream())
            {
                StreamReader streamRead = new StreamReader(streamResponse);
                responseFromServer = streamRead.ReadToEnd();
            }
            //关闭应答
            myWebResponse.Close();
        }

2）HttpClient的POST请求

 public async void PostMailAsync(string accessToken)
        {
            string uri = "https://qyapi.weixin.qq.com/cgi-bin/message/send?access_token=" + accessToken;
            HttpClientHandler handler = new HttpClientHandler
            {
                UseDefaultCredentials = true,
               
            };
            HttpClient httpClient = new HttpClient(handler);
            JObject postedJObject = new JObject
                {
                    //在此处设置发送内容及对象
                    { "touser", "Heavy" },
                    { "msgtype", "text" },
                    { "agentid", 1000002 }
                };
            JObject text = new JObject
            {
                {"content","内容来自网站--内容可自行编辑--heavy"}
            };
            postedJObject.Add("text", text);
            postedJObject.Add("safe", 0);
            //将传送内容编码
            String paramString = postedJObject.ToString(Newtonsoft.Json.Formatting.None, null);
            //byte[] byteArray = Encoding.UTF8.GetBytes(paramString);
            HttpContent httpContent = new StringContent(paramString,Encoding.UTF8,"application/json");
            HttpResponseMessage response = await httpClient.PostAsync(uri, httpContent);
           //用来判断是否接收成功，否则抛出异常
            response.EnsureSuccessStatusCode();
        }