如何在.net core 下進行http請求

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本文章是在VS2017的環境下，.net core 1.1版本以上。

在這期間，由于.net core 并不基于IIS，我們的過去的網絡請求代碼在.net core框架下，有可能會出現不兼容，報錯的現象。這里大致介紹下在.net core 下如何進行http請求，主要仍然是GET和POST方法，有錯誤的地方，歡迎指正！

先來說POST,POST我實現了三種方法，前兩種基于的原理是完全一致的，后面的有些小小的差異，但他們的本質都是http請求，本質上是無區別的，只是實現方法有所不同。

廢話不多說，上代碼：

POST異步方法：

 /// <summary>
    /// 異步請求post（鍵值對形式,可等待的）
    /// </summary>
    /// <param name="uri">網絡基址("http://localhost:59315")</param>
    /// <param name="url">網絡的地址("/api/UMeng")</param>
    /// <param name="formData">鍵值對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">編碼格式</param>
    /// <param name="mediaType">頭媒體類型</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>
    /// 同步請求post（鍵值對形式）
    /// </summary>
    /// <param name="uri">網絡基址("http://localhost:59315")</param>
    /// <param name="url">網絡的地址("/api/UMeng")</param>
    /// <param name="formData">鍵值對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">編碼格式</param>
    /// <param name="mediaType">頭媒體類型</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;
    }

遺憾的是，同步方法也是基于異步實現的，個人認為這樣做會加大系統開銷。如果各位有其他的高效實現，請不吝賜教！

接下來是通過流的方式進行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
      {
        // 以字符流的方式讀取HTTP響應
        stream = rsp.GetResponseStream();
        reader = new StreamReader(stream, encoding);
        return reader.ReadToEnd();
      }
      finally
      {
        // 釋放資源
        if (reader != null) reader.Dispose();
        if (stream != null) stream.Dispose();
        if (rsp != null) rsp.Dispose();
      }
    }

這種方式的POST還是將數據寫入到流里面，進行POST,之所以寫前兩個key-value的形式，是為了符合java或者oc的風格，在c#書寫的webapi中，由于接收形式是{=value}而不是{key=value}(由webapi的性質決定)，后續我會說如何在webapi中接收（key-value）的形式，適當避免.net后臺人員與android和ios的矛盾，從而達到社會主義民主社會的長治久安。

接下來是get，同樣同步異步都是由異步實現的，還請各位看官輕噴。

GET：

 /// <summary>
    /// 異步請求get(UTF-8)
    /// </summary>
    /// <param name="url">鏈接地址</param>    
    /// <param name="formData">寫在header中的內容</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請求
    /// </summary>
    /// <param name="url">鏈接地址</param>    
    /// <param name="formData">寫在header中的鍵值對</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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