使用RestSharp 庫(kù)消費(fèi)Restful Service 中介紹了一個(gè)開源的Http Client庫(kù)RestSharp。在ASP.NET MVC 4中也帶來(lái).NET框架中的Http Client。它提供了一個(gè)靈活的、可擴(kuò)展的API來(lái)訪問一切通過HTTP公開的RESTful服務(wù)

使用RestSharp 庫(kù)消費(fèi)Restful Service 中介紹了一個(gè)開源的Http Client庫(kù)RestSharp。在ASP.NET MVC 4中也帶來(lái).NET框架中的Http Client。它提供了一個(gè)靈活的、可擴(kuò)展的API來(lái)訪問一切通過HTTP公開的RESTful服務(wù)。HttpClient是ASP.NET Web API 的一部分，直接包含在.NET 4.5中，也可以單獨(dú)安裝ASP.NET MVC4,可以通過Nuget包獲取，包里面包含以下3部分：

• System.Net.Http: The main NuGet package providing the basic HttpClient and related classes
• System.Net.Http.Formatting: Adds support for serialization, deserialization as well as for many additional features building on top of System.Net.Http
• System.Json: Adds support for JsonVaue which is a mechanism for reading and manipulating JSON documents

HttpClient是接收HttpResponseMessages和發(fā)送HttpRequestMessages的主要類，如果你習(xí)慣了使用WebClient或者是HttpWebRequest， 需要注意HttpClient和他們不同的地方：

1、在HttpClient實(shí)例上配置擴(kuò)展，設(shè)置默認(rèn)的頭部，取消未完成的請(qǐng)求和更多的設(shè)置。

2、你通過一個(gè)單一的HttpClient實(shí)例，它有自己的連接池。

3、HttpClients不與特定的HTTP服務(wù)器綁定,你可以使用相同的HttpClient實(shí)例提交任何HTTP請(qǐng)求。

4、你可以用HttpClient為特定的站點(diǎn)創(chuàng)建特殊的Client

5、HttpClient采用新的型模式處理異步請(qǐng)求使它更容易管理和協(xié)調(diào)更多的請(qǐng)求。

下面我們看下具體的代碼， MSDN code gallery 有個(gè)很詳細(xì)Get操作的示例，這個(gè)示例是向World Bank Data Web API 發(fā)送一個(gè)Get請(qǐng)求，獲取到Json格式的數(shù)據(jù)

namespace WorldBankSample 
{ 
    /// <summary> 
    /// Sample download list of countries from the World Bank Data sources at http://data.worldbank.org/ 
    /// </summary> 
    class Program 
    { 
        static string _address = "http://api.worldbank.org/countries?format=json"; 
 
        static void Main(string[] args) 
        { 
            // Create an HttpClient instance 
            HttpClient client = new HttpClient(); 
 
            // Send a request asynchronously continue when complete 
            client.GetAsync(_address).ContinueWith( 
                (requestTask) => 
                { 
                    // Get HTTP response from completed task. 
                    HttpResponseMessage response = requestTask.Result; 
 
                    // Check that response was successful or throw exception 
                    response.EnsureSuccessStatusCode(); 
 
                    // Read response asynchronously as JsonValue and write out top facts for each country 
                    response.Content.ReadAsAsync<JsonArray>().ContinueWith( 
                        (readTask) => 
                        { 
                            Console.WriteLine("First 50 countries listed by The World Bank..."); 
                            foreach (var country in readTask.Result[1]) 
                            { 
                                Console.WriteLine("   {0}, Country Code: {1}, Capital: {2}, Latitude: {3}, Longitude: {4}", 
                                    country.Value["name"], 
                                    country.Value["iso2Code"], 
                                    country.Value["capitalCity"], 
                                    country.Value["latitude"], 
                                    country.Value["longitude"]); 
                            } 
                        }); 
                }); 
 
            Console.WriteLine("Hit ENTER to exit..."); 
            Console.ReadLine(); 
        } 
    } 
} 
下面介紹一個(gè)發(fā)送Post 請(qǐng)求的示例，示例代碼使用默認(rèn)創(chuàng)建的ASP.NET Web API模板項(xiàng)目：

public class ValuesController : ApiController
   {
       // GET /api/values
       public IEnumerable<string> Get()
       {
           return new string[] { "value1", "value2" };
       }

       // GET /api/values/5
       public string Get(int id)
       {
           return "value";
       }

       // POST /api/values
       public string Post(string value)
       {
           return value;
       }

       // PUT /api/values/5
       public void Put(int id, string value)
       {
       }

       // DELETE /api/values/5
       public void Delete(int id)
       {
       }
   }

使用HttpClient示例的代碼如下：

          string serviceAddress = "http://localhost:2650/api/values";
           HttpWebRequest request = (HttpWebRequest)HttpWebRequest.Create(serviceAddress);
           request.Method = "POST";
           request.ContentType = "application/json";
           string strContent = @"{ ""value"": ""test""}" ;
           using (StreamWriter dataStream = new StreamWriter(request.GetRequestStream()))
           {
               dataStream.Write(strContent);
               dataStream.Close();
           }
           HttpWebResponse response = (HttpWebResponse)request.GetResponse();
           using (StreamReader dataStream = new StreamReader(response.GetResponseStream()))
           {
               var result = dataStream.ReadToEnd();
               Console.WriteLine(result);
           }

            Uri serviceReq = new Uri(serviceAddress);
            HttpClient client = new HttpClient();
            HttpContent content = new StringContent(@"{ ""value"": ""test""}");
            content.Headers.ContentType = new MediaTypeHeaderValue("application/json");

            // Send a request asynchronously continue when complete
            client.PostAsync(serviceReq, content).ContinueWith(
                (requestTask) =>
                {
                    // Get HTTP response from completed task.
                    HttpResponseMessage response = requestTask.Result;

                    // Check that response was successful or throw exception
                    response.EnsureSuccessStatusCode();

                    // Read response asynchronously as JsonValue and write out top facts for each country
                    response.Content.ReadAsAsync<string>().ContinueWith(
                        (readTask) =>
                        {
                            Console.WriteLine(readTask.Result);

                        });
                });

上面代碼首先是創(chuàng)建一個(gè)HttpClient實(shí)例，設(shè)置要Post的數(shù)據(jù)的格式，然后調(diào)用HttpClient的異步請(qǐng)求，獲取到的是一個(gè)HttpResponseMessage實(shí)例，可以在這個(gè)實(shí)例中檢查請(qǐng)求的狀態(tài)，調(diào)用的是一個(gè)擴(kuò)展方法EnsureSuccessStatusCode，如果不是HttpStatusCode.OK，就會(huì)拋出一個(gè)異常。通過HttpResponseMessage的Content屬性獲取HttpContent，HttpContent有一些方法輔助處理接收的內(nèi)容。

對(duì)應(yīng)于使用HttpWebRequest的示例如下：

          string serviceAddress = "http://localhost:2650/api/values";
           HttpWebRequest request = (HttpWebRequest)HttpWebRequest.Create(serviceAddress);
           request.Method = "POST";
           request.ContentType = "application/json";
           string strContent = @"{ ""value"": ""test""}" ;
           using (StreamWriter dataStream = new StreamWriter(request.GetRequestStream()))
           {
               dataStream.Write(strContent);
               dataStream.Close();
           }
           HttpWebResponse response = (HttpWebResponse)request.GetResponse();
           using (StreamReader dataStream = new StreamReader(response.GetResponseStream()))
           {
               var result = dataStream.ReadToEnd();
               Console.WriteLine(result);
           }

上面是通過代碼發(fā)送的Http請(qǐng)求，也可以用Fiddlers來(lái)驗(yàn)證請(qǐng)求，例如：