如何在.net core 下进行http请求

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本文章是在VS2017的环境下，.net core 1.1版本以上。

在这期间，由于.net core 并不基于IIS，我们的过去的网络请求代码在.net core框架下，有可能会出现不兼容，报错的现象。这里大致介绍下在.net core 下如何进行http请求，主要仍然是GET和POST方法，有错误的地方，欢迎指正！

先来说POST,POST我实现了三种方法，前两种基于的原理是完全一致的，后面的有些小小的差异，但他们的本质都是http请求，本质上是无区别的，只是实现方法有所不同。

废话不多说，上代码：

POST异步方法：

 /// <summary>
    /// 异步请求post（键值对形式,可等待的）
    /// </summary>
    /// <param name="uri">网络基址("http://localhost:59315")</param>
    /// <param name="url">网络的地址("/api/UMeng")</param>
    /// <param name="formData">键值对List<KeyValuePair<string, string>> formData = new List<KeyValuePair<string, string>>();formData.Add(new KeyValuePair<string, string>("userid", "29122"));formData.Add(new KeyValuePair<string, string>("umengids", "29122"));</param>
    /// <param name="charset">编码格式</param>
    /// <param name="mediaType">头媒体类型</param>
    /// <returns></returns>
    public async Task<string> HttpPostAsync(string uri, string url, List<KeyValuePair<string, string>> formData = null, string charset = "UTF-8", string mediaType = "application/x-www-form-urlencoded")
    {
      
      string tokenUri = url;
      var client = new HttpClient();
      client.BaseAddress = new Uri(uri);
      HttpContent content = new FormUrlEncodedContent(formData);
      content.Headers.ContentType = new MediaTypeHeaderValue(mediaType);
      content.Headers.ContentType.CharSet = charset;
      for (int i = 0; i < formData.Count; i++)
      {
        content.Headers.Add(formData[i].Key, formData[i].Value);
      }
      
      HttpResponseMessage resp = await client.PostAsync(tokenUri, content);
      resp.EnsureSuccessStatusCode();
      string token = await resp.Content.ReadAsStringAsync();
      return token;
    }

POST同步方法：

/// <summary>
    /// 同步请求post（键值对形式）
    /// </summary>
    /// <param name="uri">网络基址("http://localhost:59315")</param>
    /// <param name="url">网络的地址("/api/UMeng")</param>
    /// <param name="formData">键值对List<KeyValuePair<string, string>> formData = new List<KeyValuePair<string, string>>();formData.Add(new KeyValuePair<string, string>("userid", "29122"));formData.Add(new KeyValuePair<string, string>("umengids", "29122"));</param>
    /// <param name="charset">编码格式</param>
    /// <param name="mediaType">头媒体类型</param>
    /// <returns></returns>
    public string HttpPost(string uri, string url, List<KeyValuePair<string, string>> formData = null, string charset = "UTF-8", string mediaType = "application/x-www-form-urlencoded")
    {      
      string tokenUri = url;
      var client = new HttpClient();
      client.BaseAddress = new Uri(uri);
      HttpContent content = new FormUrlEncodedContent(formData);
      content.Headers.ContentType = new MediaTypeHeaderValue(mediaType);
      content.Headers.ContentType.CharSet = charset;
      for (int i = 0; i < formData.Count; i++)
      {
        content.Headers.Add(formData[i].Key, formData[i].Value);
      }

      var res = client.PostAsync(tokenUri, content);
      res.Wait();
      HttpResponseMessage resp = res.Result;
      
      var res2 = resp.Content.ReadAsStringAsync();
      res2.Wait();

      string token = res2.Result;
      return token;
    }

遗憾的是，同步方法也是基于异步实现的，个人认为这样做会加大系统开销。如果各位有其他的高效实现，请不吝赐教！

接下来是通过流的方式进行POST：

public string Post(string url, string data, Encoding encoding, int type)
    {
      try
      {
        HttpWebRequest req = WebRequest.CreateHttp(new Uri(url));
        if (type == 1)
        {
          req.ContentType = "application/json;charset=utf-8";
        }
        else if (type == 2)
        {
          req.ContentType = "application/xml;charset=utf-8";
        }
        else
        {
          req.ContentType = "application/x-www-form-urlencoded;charset=utf-8";
        }

        req.Method = "POST";
        //req.Accept = "text/xml,text/javascript";
        req.ContinueTimeout = 60000;

        byte[] postData = encoding.GetBytes(data);
        Stream reqStream = req.GetRequestStreamAsync().Result;
        reqStream.Write(postData, 0, postData.Length);
        reqStream.Dispose();

        var rsp = (HttpWebResponse)req.GetResponseAsync().Result;
        var result = GetResponseAsString(rsp, encoding);
        return result;
        
      }
      catch (Exception ex)
      {
        throw;
      }
    }

private string GetResponseAsString(HttpWebResponse rsp, Encoding encoding)
    {
      Stream stream = null;
      StreamReader reader = null;

      try
      {
        // 以字符流的方式读取HTTP响应
        stream = rsp.GetResponseStream();
        reader = new StreamReader(stream, encoding);
        return reader.ReadToEnd();
      }
      finally
      {
        // 释放资源
        if (reader != null) reader.Dispose();
        if (stream != null) stream.Dispose();
        if (rsp != null) rsp.Dispose();
      }
    }

这种方式的POST还是将数据写入到流里面，进行POST,之所以写前两个key-value的形式，是为了符合java或者oc的风格，在c#书写的webapi中，由于接收形式是{=value}而不是{key=value}(由webapi的性质决定)，后续我会说如何在webapi中接收（key-value）的形式，适当避免.net后台人员与android和ios的矛盾，从而达到社会主义民主社会的长治久安。

接下来是get，同样同步异步都是由异步实现的，还请各位看官轻喷。

GET：

 /// <summary>
    /// 异步请求get(UTF-8)
    /// </summary>
    /// <param name="url">链接地址</param>    
    /// <param name="formData">写在header中的内容</param>
    /// <returns></returns>
    public static async Task<string> HttpGetAsync(string url, List<KeyValuePair<string, string>> formData = null)
    {
      HttpClient httpClient = new HttpClient();
      HttpContent content = new FormUrlEncodedContent(formData);
      if (formData != null)
      {
        content.Headers.ContentType = new MediaTypeHeaderValue("application/x-www-form-urlencoded");
        content.Headers.ContentType.CharSet = "UTF-8";
        for (int i = 0; i < formData.Count; i++)
        {
          content.Headers.Add(formData[i].Key, formData[i].Value);
        }
      }
      var request = new HttpRequestMessage()
      {
        RequestUri = new Uri(url),
        Method = HttpMethod.Get,
      };
      for (int i = 0; i < formData.Count; i++)
      {
        request.Headers.Add(formData[i].Key, formData[i].Value);
      }
      var resp = await httpClient.SendAsync(request);
      resp.EnsureSuccessStatusCode();
      string token = await resp.Content.ReadAsStringAsync();

      return token;
    }

 /// <summary>
    /// 同步get请求
    /// </summary>
    /// <param name="url">链接地址</param>    
    /// <param name="formData">写在header中的键值对</param>
    /// <returns></returns>
    public string HttpGet(string url, List<KeyValuePair<string, string>> formData = null)
    {
      HttpClient httpClient = new HttpClient();
      HttpContent content = new FormUrlEncodedContent(formData);
      if (formData != null)
      {
        content.Headers.ContentType = new MediaTypeHeaderValue("application/x-www-form-urlencoded");
        content.Headers.ContentType.CharSet = "UTF-8";
        for (int i = 0; i < formData.Count; i++)
        {
          content.Headers.Add(formData[i].Key, formData[i].Value);
        }
      }
      var request = new HttpRequestMessage()
      {
        RequestUri = new Uri(url),
        Method = HttpMethod.Get,
      };
      for (int i = 0; i < formData.Count; i++)
      {
        request.Headers.Add(formData[i].Key, formData[i].Value);
      }
      var res = httpClient.SendAsync(request);
      res.Wait();
      var resp = res.Result;
      Task<string> temp = resp.Content.ReadAsStringAsync();
      temp.Wait();
      return temp.Result;
    }

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