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);
        }

    }