C#中HttpWebRequest、WebClient、HttpClient 、HttpClientFactory Flurl、的使用总结

C#中HttpWebRequest、WebClient、HttpClient 、HttpClientFactory Flurl、的使用总结三者的区别HttpWebRequest命名空间:System.Net,这是.NET创建者最初开发用于使用HTTP请求的标准类。使用HttpWebRequest可以让开发者控制请求/响应流程的各个方面,如timeouts,cookies,headers,protocols。另一个好处是HttpWebRequest类不会阻塞UI线程。例如,当您从响应很慢的API服务器下载大文件时,您的应用程序的UI不会停止响应。HttpWebRequest通常和WebResponse一起使用,一个发送请求,一个获

C#中HttpWebRequest、WebClient、HttpClient 、HttpClientFactory、 Flurl的使用总结

三者的区别三者的区别

HttpWebRequest

命名空间: System.Net,这是.NET创建者最初开发用于使用HTTP请求的标准类。使用HttpWebRequest可以让开发者控制请求/响应流程的各个方面,如 timeouts, cookies, headers, protocols。另一个好处是HttpWebRequest类不会阻塞UI线程。例如,当您从响应很慢的API服务器下载大文件时,您的应用程序的UI不会停止响应。HttpWebRequest通常和WebResponse一起使用,一个发送请求,一个获取数据。HttpWebRquest更为底层一些,能够对整个访问过程有个直观的认识,但同时也更加复杂一些。在framework中,

  • 大量并发 HttpWebRequest 需要设置一个最大连接数,
  • 如果第一次访问很慢,取消代理检查
  • .Net中并发连接限制数量默认是2,哪怕你开100条线程同时进行请求,有效的连接数仍是2条,解决办法就是在App.config中修改配置.
  <system.net>
    <defaultProxy enabled="false">
      <proxy/>
      <bypasslist/>
      <module/>
    </defaultProxy>
    <connectionManagement>
      <!-- address:要限制的地址 maxconnection:最大连接数 -->
      <add address="*" maxconnection="512"/>
    </connectionManagement>

ServicePointManager.DefaultConnectionLimit = 200;
WebClient.Proxy = null; 或 HttpWebRequest.Proxy = null;

     //POST方法
    public static string HttpPost(string Url, string postDataStr)
    { 
   
      HttpWebRequest request = (HttpWebRequest)WebRequest.Create(Url);
      request.Method = "POST";
      request.ContentType = "application/x-www-form-urlencoded";
      Encoding encoding = Encoding.UTF8;
      byte[] postData = encoding.GetBytes(postDataStr);
      request.ContentLength = postData.Length;
      Stream myRequestStream = request.GetRequestStream();
      myRequestStream.Write(postData, 0, postData.Length);
      myRequestStream.Close();
      HttpWebResponse response = (HttpWebResponse)request.GetResponse();
      Stream myResponseStream = response.GetResponseStream();
      StreamReader myStreamReader = new StreamReader(myResponseStream, encoding);
      string retString = myStreamReader.ReadToEnd();
      myStreamReader.Close();
      myResponseStream.Close();

      return retString;
    }
    //GET方法
    public static string HttpGet(string Url, string postDataStr)
    { 
   
      HttpWebRequest request = (HttpWebRequest)WebRequest.Create(Url + (postDataStr == "" ? "" : "?") + postDataStr);
      request.Method = "GET";
      request.ContentType = "text/html;charset=UTF-8";
      HttpWebResponse response = (HttpWebResponse)request.GetResponse();
      Stream myResponseStream = response.GetResponseStream();
      StreamReader myStreamReader = new StreamReader(myResponseStream, Encoding.GetEncoding("utf-8"));
      string retString = myStreamReader.ReadToEnd();
      myStreamReader.Close();
      myResponseStream.Close();
      return retString;
    }

WebClient

命名空间System.Net,WebClient是一种更高级别的抽象,是HttpWebRequest为了简化最常见任务而创建的,使用过程中你会发现他缺少基本的header,timeoust的设置,不过这些可以通过继承httpwebrequest来实现。相对来说,WebClient比WebRequest更加简单,它相当于封装了request和response方法,不过需要说明的是,Webclient和WebRequest继承的是不同类,两者在继承上没有任何关系。使用WebClient可能比HttpWebRequest直接使用更慢(大约几毫秒),但却更为简单,减少了很多细节,代码量也比较少。

public class WebClientHelper
  { 
   
    public static string DownloadString(string url)
    { 
   
      WebClient wc = new WebClient();
      //wc.BaseAddress = url; //设置根目录
      wc.Encoding = Encoding.UTF8;  //设置按照何种编码访问,如果不加此行,获取到的字符串中文将是乱码
      string str = wc.DownloadString(url);
      return str;
    }
    public static string DownloadStreamString(string url)
    { 
   
      WebClient wc = new WebClient();
      wc.Headers.Add("User-Agent", "Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/76.0.3809.132 Safari/537.36");
      Stream objStream = wc.OpenRead(url);
      StreamReader _read = new StreamReader(objStream, Encoding.UTF8);  //新建一个读取流,用指定的编码读取,此处是utf-8
      string str = _read.ReadToEnd();
      objStream.Close();
      _read.Close();
      return str;
    }

    public static void DownloadFile(string url, string filename)
    { 
   
      WebClient wc = new WebClient();
      wc.DownloadFile(url, filename);   //下载文件
    }

    public static void DownloadData(string url, string filename)
    { 
   
      WebClient wc = new WebClient();
      byte [] bytes = wc.DownloadData(url);  //下载到字节数组
      FileStream fs = new FileStream(filename, FileMode.Create);
      fs.Write(bytes, 0, bytes.Length); 
      fs.Flush();
      fs.Close();
    }

    public static void DownloadFileAsync(string url, string filename)
    { 
   
      WebClient wc = new WebClient();
      wc.DownloadFileCompleted += DownCompletedEventHandler;
      wc.DownloadFileAsync(new Uri(url), filename);
      Console.WriteLine("下载中。。。");
    }
    private static void DownCompletedEventHandler(object sender, AsyncCompletedEventArgs e)
    { 
   
      Console.WriteLine(sender.ToString());  //触发事件的对象
      Console.WriteLine(e.UserState);
      Console.WriteLine(e.Cancelled);
      Console.WriteLine("异步下载完成!");
    }

    public static void DownloadFileAsync2(string url, string filename)
    { 
   
      WebClient wc = new WebClient();
      wc.DownloadFileCompleted += (sender, e) =>
      { 
   
        Console.WriteLine("下载完成!");
        Console.WriteLine(sender.ToString());
        Console.WriteLine(e.UserState);
        Console.WriteLine(e.Cancelled);
      };
      wc.DownloadFileAsync(new Uri(url), filename);
      Console.WriteLine("下载中。。。");
    }
  }

HttpClient

HttpClient是.NET4.5引入的一个HTTP客户端库,其命名空间为 System.Net.Http ,.NET 4.5之前我们可能使用WebClient和HttpWebRequest来达到相同目的。HttpClient利用了最新的面向任务模式,使得处理异步请求非常容易。它适合用于多次请求操作,一般设置好默认头部后,可以进行重复多次的请求,基本上用一个实例可以提交任何的HTTP请求。HttpClient有预热机制,第一次进行访问时比较慢,所以不应该用到HttpClient就new一个出来,应该使用单例或其他方式获取HttpClient的实例

public class HttpClientHelper
  { 
   
    private static readonly object LockObj = new object();
    private static HttpClient client = null;
    public HttpClientHelper() { 
   
      GetInstance();
    }
    public static HttpClient GetInstance()
    { 
   

      if (client == null)
      { 
   
        lock (LockObj)
        { 
   
          if (client == null)
          { 
   
            client = new HttpClient();
          }
        }
      }
      return client;
    }
    public async Task<string> PostAsync(string url, string strJson)//post异步请求方法
    { 
   
      try
      { 
   
        HttpContent content = new StringContent(strJson);
        content.Headers.ContentType = new System.Net.Http.Headers.MediaTypeHeaderValue("application/json");
        //由HttpClient发出异步Post请求
        HttpResponseMessage res = await client.PostAsync(url, content);
        if (res.StatusCode == System.Net.HttpStatusCode.OK)
        { 
   
          string str = res.Content.ReadAsStringAsync().Result;
          return str;
        }
        else
          return null;
      }
      catch (Exception ex)
      { 
   
        return null;
      }
    }

    public string Post(string url, string strJson)//post同步请求方法
    { 
   
      try
      { 
   
        HttpContent content = new StringContent(strJson);
        content.Headers.ContentType = new System.Net.Http.Headers.MediaTypeHeaderValue("application/json");
        //client.DefaultRequestHeaders.Connection.Add("keep-alive");
        //由HttpClient发出Post请求
        Task<HttpResponseMessage> res = client.PostAsync(url, content);
        if (res.Result.StatusCode == System.Net.HttpStatusCode.OK)
        { 
   
          string str = res.Result.Content.ReadAsStringAsync().Result;
          return str;
        }
        else
          return null;
      }
      catch (Exception ex)
      { 
   
        return null;
      }
    }

    public string Get(string url)
    { 
   
      try
      { 
   
        var responseString = client.GetStringAsync(url);
        return responseString.Result;
      }
      catch (Exception ex)
      { 
   
        return null;
      }
    }

  }

HttpClient有预热机制,第一次请求比较慢;可以通过初始化前发送一次head请求解决:

_httpClient = new HttpClient() { 
    BaseAddress = new Uri(BASE_ADDRESS) };

    //帮HttpClient热身
    _httpClient.SendAsync(new HttpRequestMessage { 
   
        Method = new HttpMethod("HEAD"), 
        RequestUri = new Uri(BASE_ADDRESS + "/") })
      .Result.EnsureSuccessStatusCode();

HttpClient 日常使用及坑点:

我们先来用个简单的例子做下测试,看为什么不要每次RPC请求都实例化一个HttpClient:

  public class Program
    { 
   
        static void Main(string[] args)
        { 
   
            HttpAsync();
            Console.WriteLine("Hello World!");
            Console.Read();
        }

        public static async void HttpAsync()
        { 
   
            for (int i = 0; i < 10; i++)
            { 
   
                using (var client = new HttpClient())
                { 
   
                    var result = await client.GetAsync("http://www.baidu.com");
                    Console.WriteLine($"{i}:{result.StatusCode}");
                }
            }
        }
    }

通过netstat查看下TCP连接情况:
在这里插入图片描述

默认在windows下,TIME_WAIT状态将会使系统将会保持该连接240s

这里也就引出了我上面说的载过的一次坑:在高并发的情况下,连接来不及释放,socket被耗尽,耗尽之后就会出现喜闻乐见的一个错误:

#使用jemter压测复现错误信息:
Unable to connect to the remote serverSystem.Net.Sockets.SocketException: Only one usage of each socket address (protocol/network address/port) is normally permitted.

复用了HttpClient,每次RPC请求的时候,实际上还节约了创建通道的时间,在性能压测的时候也是很明显的提升。

因为是复用的HttpClient,那么一些公共的设置就没办法灵活的调整了,如请求头的自定义。
因为HttpClient请求每个url时,会缓存该url对应的主机ip,从而会导致DNS更新失效(TTL失效了)

HttpClientFactory优势:

HttpClientFactory 是ASP.NET CORE 2.1中新增加的功能。

Factory,顾名思义HttpClientFactory就是HttpClient的工厂,内部已经帮我们处理好了对HttpClient的管理,不需要我们人工进行对象释放,同时,支持自定义请求头,支持DNS更新等等等。

HttpClientFactory使用方法:

从微软源码分析,HttpClient继承自HttpMessageInvoker,而HttpMessageInvoker实质就是HttpClientHandler。

HttpClientFactory 创建的HttpClient,也即是HttpClientHandler,只是这些个HttpClient被放到了“池子”中,工厂每次在create的时候会自动判断是新建还是复用。(默认生命周期为2min)

  public class Startup
    { 
   
        public Startup(IConfiguration configuration)
        { 
   
            Configuration = configuration;
        }

        public IConfiguration Configuration { 
    get; }

        // This method gets called by the runtime. Use this method to add services to the container.
        public void ConfigureServices(IServiceCollection services)
        { 
   
            //other codes
            
            services.AddHttpClient("client_1",config=>  //这里指定的name=client_1,可以方便我们后期服用该实例
            { 
   
                config.BaseAddress= new Uri("http://client_1.com");
                config.DefaultRequestHeaders.Add("header_1","header_1");
            });
            services.AddHttpClient("client_2",config=>
            { 
   
                config.BaseAddress= new Uri("http://client_2.com");
                config.DefaultRequestHeaders.Add("header_2","header_2");
            });
            services.AddHttpClient();

            //other codes
            services.AddMvc().AddFluentValidation();
        }
      }

这里直接以controller为例,其他地方自行DI

    public class TestController : ControllerBase
    { 
   
        private readonly IHttpClientFactory _httpClient;
        public TestController(IHttpClientFactory httpClient)
        { 
   
            _httpClient = httpClient;
        }

        public async Task<ActionResult> Test()
        { 
   
            var client = _httpClient.CreateClient("client_1"); //复用在Startup中定义的client_1的httpclient
            var result = await client.GetStringAsync("/page1.html");

            var client2 = _httpClient.CreateClient(); //新建一个HttpClient
            var result2 = await client.GetStringAsync("http://www.site.com/XXX.html");

            return null;
        }
    }

flurl

参考:

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