如何使用C#调用雅虎REST服务

 .NET Framework提供类处理HTTP请求。这篇文章讲述一下处理GET和POST请求。

概述

简单GET请求

简单POST请求

HTTP授权请求

错误处理

深入阅读

概述

System.Net命名空间包含 HttpWebRequest和 HttpWebResponse类，这两个类可以从web服务器获取数据和使用基于HTTP的服务。通常你需要添加System.Web的引用，这样就可以使用HttpUtility类，这个类可以提供方法对 HTML 和URL的文本进行编码或者解码。

雅虎web服务返回XML数据。有些web服务返回其他格式的数据，比如JSON和序列化的PHP，.NET Framework自从扩展支持处理xml数据之后，处理这种格式的数据就特别简单了。

简单GET请求

接下来的例子获取网页并打印出源码。

C# GET 例1

using System;  using System.IO;  using System.Net;  using System.Text;    // Create the web request  HttpWebRequest request = WebRequest.Create("https://developer.yahoo.com/") as HttpWebRequest;    // Get response  using (HttpWebResponse response = request.GetResponse() as HttpWebResponse)  {      // Get the response stream      StreamReader reader = new StreamReader(response.GetResponseStream());        // Console application output      Console.WriteLine(reader.ReadToEnd());  }  

简单POST请求

有些APIs要求你使用POST请求。为了实现这个功能，我们改变请求方法和内容类型，然后将请求的数据写入到数据流（stream）中。

C# POST例1

// We use the HttpUtility class from the System.Web namespace  using System.Web;    Uri address = new Uri("http://api.search.yahoo.com/ContentAnalysisService/V1/termExtraction");    // Create the web request  HttpWebRequest request = WebRequest.Create(address) as HttpWebRequest;    // Set type to POST  request.Method = "POST";  request.ContentType = "application/x-www-form-urlencoded";    // Create the data we want to send  string appId = "YahooDemo";  string context = "Italian sculptors and painters of the renaissance"                      + "favored the Virgin Mary for inspiration";  string query = "madonna";    StringBuilder data = new StringBuilder();  data.Append("appid=" + HttpUtility.UrlEncode(appId));  data.Append("&context=" + HttpUtility.UrlEncode(context));  data.Append("&query=" + HttpUtility.UrlEncode(query));    // Create a byte array of the data we want to send  byte[] byteData = UTF8Encoding.UTF8.GetBytes(data.ToString());    // Set the content length in the request headers  request.ContentLength = byteData.Length;    // Write data  using (Stream postStream = request.GetRequestStream())  {      postStream.Write(byteData, 0, byteData.Length);  }    // Get response  using (HttpWebResponse response = request.GetResponse() as HttpWebResponse)  {      // Get the response stream      StreamReader reader = new StreamReader(response.GetResponseStream());        // Console application output      Console.WriteLine(reader.ReadToEnd());  }  

HTTP授权请求

del.icio.us API要求你使用授权的请求，使用HTTP授权传递用户名和密码。这个很容易实现的，只要在请求的时候增加NetworkCredentials 就可以了。

C# HTTP AUTHENTICATION

// Create the web request  HttpWebRequest request       = WebRequest.Create("https://api.del.icio.us/v1/posts/recent") as HttpWebRequest;    // Add authentication to request  request.Credentials = new NetworkCredential("username", "password");    // Get response  using (HttpWebResponse response = request.GetResponse() as HttpWebResponse)  {      // Get the response stream      StreamReader reader = new StreamReader(response.GetResponseStream());        // Console application output      Console.WriteLine(reader.ReadToEnd());  }  

错误处理

雅虎提供众多基于REST的web服务，不全是使用相同的错误处理方式。有些web服务返回状态码200（表示OK），详细的错误信息在返回来的xml里面，但是有些web服务使用标准的HTTP状态码表示错误信息。请阅读您使用的web服务的文档，了解你所遇到的响应的错误类型。请记住，雅虎基于浏览器授权和HTTP授权是不一样的。调用 HttpRequest.GetResponse() 方法在服务器没有返回状态码200（表示OK），请求超时和网络错误的时候，会引发错误。但是，重定向会自动处理的。

这是一个典型的例子，打印一个网页的内容和基本的HTTP错误代码处理错误。

C# GET 例2

public static void PrintSource(Uri address)  {      HttpWebRequest request;      HttpWebResponse response = null;      StreamReader reader;      StringBuilder sbSource;        if (address == null) { throw new ArgumentNullException("address"); }        try      {          // Create and initialize the web request          request = WebRequest.Create(address) as HttpWebRequest;          request.UserAgent = ".NET Sample";          request.KeepAlive = false;          // Set timeout to 15 seconds          request.Timeout = 15 * 1000;            // Get response          response = request.GetResponse() as HttpWebResponse;            if (request.HaveResponse == true && response != null)          {              // Get the response stream              reader = new StreamReader(response.GetResponseStream());                // Read it into a StringBuilder              sbSource = new StringBuilder(reader.ReadToEnd());                // Console application output              Console.WriteLine(sbSource.ToString());          }      }      catch (WebException wex)      {          // This exception will be raised if the server didn't return 200 - OK          // Try to retrieve more information about the network error          if (wex.Response != null)          {              using (HttpWebResponse errorResponse = (HttpWebResponse)wex.Response)              {                  Console.WriteLine(                      "The server returned '{0}' with the status code {1} ({2:d}).",                      errorResponse.StatusDescription, errorResponse.StatusCode,                      errorResponse.StatusCode);              }          }      }      finally      {          if (response != null) { response.Close(); }      }  }  

深入阅读

网上相关信息。

• HttpWebRequest 类 文档
• HttpWebResponse 类 文档
• A Deeper Look at Performing HTTP Requests in an ASP.NET Page
• .NET Screen Scraping in depth

翻译这篇文章其实是自己想学习如何使用C#调用REST服务。