使用RestSharp 庫消費Restful Service 中介紹了一個開源的Http Client庫RestSharp。在ASP.NET MVC 4中也帶來.NET框架中的Http Client。它提供了一個靈活的、可擴展的API來訪問一切通過HTTP公開的RESTful服務。HttpClient是ASP.NET Web API 的一部分，直接包含在.NET 4.5中，也可以單獨安裝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和發送HttpRequestMessages的主要類，如果你習慣了使用WebClient或者是HttpWebRequest， 需要注意HttpClient和他們不同的地方：
1、在HttpClient實例上配置擴展，設置默認的頭部，取消未完成的請求和更多的設置。
2、你通過一個單一的HttpClient實例，它有自己的連接池。
3、HttpClients不與特定的HTTP服務器綁定,你可以使用相同的HttpClient實例提交任何HTTP請求。
4、你可以用HttpClient為特定的站點創建特殊的Client
5、HttpClient采用新的型模式處理異步請求使它更容易管理和協調更多的請求。
下面我們看下具體的代碼， MSDN code gallery 有個很詳細Get操作的示例，這個示例是向World Bank Data Web API 發送一個Get請求，獲取到Json格式的數據
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();
}
}
}
下面介紹一個發送Post 請求的示例，示例代碼使用默認創建的ASP.NET Web API模板項目：
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);
});
});
上面代碼首先是創建一個HttpClient實例，設置要Post的數據的格式，然后調用HttpClient的異步請求，獲取到的是一個HttpResponseMessage實例，可以在這個實例中檢查請求的狀態，調用的是一個擴展方法EnsureSuccessStatusCode，如果不是HttpStatusCode.OK，就會拋出一個異常。通過HttpResponseMessage的Content屬性獲取HttpContent，HttpContent有一些方法輔助處理接收的內容。
對應於使用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);
}
上面是通過代碼發送的Http請求，也可以用Fiddlers來驗證請求，例如：
