再也不用写请求HttpHelper了，HttpClient帮助你

前言

在C#7.1之后,net推出HttpClient类代替WebRequest, HttpWebRequest, ServicePoint, and WebClient ，先来看下他们在以前的作用

• HttpWebRequest和HttpWebResponse类是用于发送和接收HTTP数据的一种方式
• ServicePoint提供 HTTP 连接的连接管理
• WebClient 提供用于将数据发送到由 URI 标识的资源及从这样的资源接收数据的常用方法

相信大家都使用过http的帮助类，来帮助我们处理请求客户端。C#7.1版本推出 HttpClient ，现在有了HttpClient，完全可以不再使用帮助类了，HttpClient使用起来更方便，甚至你连请求方法是Post，Put,Get都不用写，功能十分强大。



WebRequest, HttpWebRequest, ServicePoint, and WebClient 已经过时，请使用 HttpClient

使用（异步请求，下载等）

属性

方法

GetAsync(String)以异步操作将 GET 请求发送给指定 URI。

普通的get请求获取请求消息 返回的HttpResponseMessage包含所有的响应信息，比如说状态码，响应的消息头，相应的json等都可以用这个来处理

GetByteArrayAsync(String)将 GET 请求发送到指定 URI 并在异步操作中以字节数组的形式返回响应正文

                using (var webClient = new System.Net.Http.HttpClient())
                {

                    var bytes = await webClient.GetByteArrayAsync(vodeourl.VideoUrl);
                    //var fileStream = new FileStream($"{videoid}.mp4", FileMode.Create, FileAccess.Write);
                    //fileStream.Write(stream, 0, stream.Length);
                    //fileStream.Dispose();
                }

添加cookies

var handler = new HttpClientHandler();
            var cookieContainer = new CookieContainer();
            cookieContainer.Add(new Uri(url), new Cookie("cookie_name", "cookie_value"));
            handler.CookieContainer = cookieContainer;

            using (var webClient = new System.Net.Http.HttpClient(handler))
            {
                webClient.DefaultRequestHeaders.Add("user-agent", "Mozilla/5.0 (Windows NT 6.1; Win64; x64; rv:57.0) Gecko/20100101 Firefox/57.0");
                webClient.DefaultRequestHeaders.Add("Connection", "Keep-Alive");
                webClient.DefaultRequestHeaders.Add("Keep-Alive", "timeout=600");

                var aa = webClient.GetStringAsync(url).Result;
                return aa.ToString();
                //await Console.Out.WriteLineAsync(str);
                //var fileStream = new FileStream($"{videoid}.mp4", FileMode.Create, FileAccess.Write);
                //fileStream.Write(stream, 0, stream.Length);
                //fileStream.Dispose();
            }

请求Json格式 或者 通过Post请求数据： application/x-www-form-urlencoded

var httpClient = new HttpClient();
var url = "http://192.168.0.9:9000/Demo/PostUrlCode";
var response = await httpClient.PostAsync(url, new FormUrlEncodedContent(new List<KeyValuePair<string, string>>()
{
    new KeyValuePair<string, string>("name","小明"),
    new KeyValuePair<string, string>("age","20")
}));
var str = await response.Content.ReadAsStringAsync();

上传文件

using (HttpClient client = new HttpClient())
{
    var content = new MultipartFormDataContent();
    //添加字符串参数，参数名为qq
    content.Add(new StringContent("123456"), "qq");

    string path = Path.Combine(System.Environment.CurrentDirectory, "1.png");
    //添加文件参数，参数名为files，文件名为123.png
    content.Add(new ByteArrayContent(System.IO.File.ReadAllBytes(path)), "file", "123.png");

    var requestUri = "http://192.168.1.108:56852/api/Test/SaveFile";
    var result = client.PostAsync(requestUri, content).Result.Content.ReadAsStringAsync().Result;

    Console.WriteLine(result);
}

请求超时

var httpClient = new HttpClient();
httpClient.Timeout = TimeSpan.FromSeconds(10); // 设置超时时间为10秒

var url = "xxxxxxxxxx";
List<KeyValuePair<string, string>> fromdic = dic.ToList();
var sign = Tool.Sign(dic, key);
fromdic.Add(new KeyValuePair<string, string>("sign", sign));

CancellationTokenSource cts = new CancellationTokenSource();
cts.CancelAfter(TimeSpan.FromSeconds(10)); // 设置取消请求的时间为10秒

发送 HEAD 请求来获取响应头信息，并检查状态码是否是成功的（如200）来判断文件是否存在

using System;
using System.Net.Http;

var url = "https://xxx.com/contract//55";

using (var httpClient = new HttpClient())
{
   var request = new HttpRequestMessage(HttpMethod.Head, url);
   var response = httpClient.SendAsync(request).GetAwaiter().GetResult();

   if (response.IsSuccessStatusCode)
   {
       Console.WriteLine("文件存在");
   }
   else
   {
       Console.WriteLine("文件不存在");
   }
}