C# HttpClient使用 网络(一)

一、异步调用web服务  GetAsync（）

  static void Main(string[] args)
         {
             Console.WriteLine("In main before call to GetData!");
             GetData();
             Console.WriteLine("Back in main after call to GetData!");
             Console.ReadKey();
         }
         static  async void GetData()
         {
             HttpClient httpClient = new HttpClient();
             HttpResponseMessage response = null;

             response = await httpClient.GetAsync("http://www.baidu.com");
             if(response.IsSuccessStatusCode)
             {
                 Console.WriteLine("Response status Code :" + response.StatusCode + " " + response.ReasonPhrase);
                 string responseBodyAsText = response.Content.ReadAsStringAsync().Result;
                 Console.WriteLine("Received payload of " + responseBodyAsText.Length + " characters");
                 Console.WriteLine(responseBodyAsText);
             }
         }

二、设置或改变请求标题

    static void Main(string[] args)
         {
             GetData2();
             Console.ReadKey();
         }

 static  void GetData2()
         {
             HttpClient httpClient = new HttpClient();
             HttpResponseMessage response = null;
             httpClient.DefaultRequestHeaders.Add("Accept", "application/json;odata=verbose");
             Console.WriteLine("Request Headers:");
             EnumerateHeaders(httpClient.DefaultRequestHeaders);
             Console.WriteLine();
            response =  httpClient.GetAsync("http://www.baidu.com").Result;
             if (response.IsSuccessStatusCode)
             {
                 Console.WriteLine("Response Headers:");
                 EnumerateHeaders(response.Headers);
             }
         }
         private static void EnumerateHeaders(HttpHeaders headers)
         {
             foreach (var header in headers)
             {
                 var value = "";
                 foreach (var val in header.Value)
                 {
                     value = val + " ";
                 }
                 Console.WriteLine("Header: " + header.Key + " Value: " + value);
             }
         }

三、HttpMessageHandler

 class Program
     {

         static void Main(string[] args)
         {
             GetData();
             Console.ReadKey();
         }

         private static void GetData()
         {
             HttpClient httpClient = new HttpClient(new MessageHandler("error"));
             HttpResponseMessage response = null;
             Console.WriteLine();
             response = httpClient.GetAsync("http://services.odata.org/Northwind/Northwind.svc/Regions").Result;
             Console.WriteLine(response.StatusCode);
         }
     }

     public class MessageHandler : HttpClientHandler
     {
         string displayMessage = "";
         public MessageHandler(string message)
         {
             displayMessage = message;
         }

         protected override Task<HttpResponseMessage> SendAsync(HttpRequestMessage request, System.Threading.CancellationToken cancellationToken)
         {
             Console.WriteLine("In DisplayMessageHandler " + displayMessage);
             if (displayMessage == "error")
             {
                 var response = new HttpResponseMessage(System.Net.HttpStatusCode.BadRequest);
                 var tsc = new TaskCompletionSource<HttpResponseMessage>();
                 tsc.SetResult(response);
                 return tsc.Task;
             }
             return base.SendAsync(request, cancellationToken);
         }

     }