HttpClient介绍

使用RestSharp 库消费Restful Service http://www.zzzyk.com/kf/201203/124274.html 中介绍了一个开源的Http Client库RestSharp。在ASP.NET MVC 4中也带来.NET框架中的Http Client。它提供了一个灵活的、可扩展的API来访问一切通过HTTP公开的RESTful服务。HttpClient是ASP.NET Web API 的一部分，直接包含在.NET 4.5中，也可以单独安装ASP.NET MVC4,可以通过Nuget包获取，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和发送HttpRequestMessages的主要类，如果你习惯了使用WebClient或者是HttpWebRequest，需要注意HttpClient和他们不同的地方：

1、在HttpClient实例上配置扩展，设置默认的头部，取消未完成的请求和更多的设置。

2、你通过一个单一的HttpClient实例，它有自己的连接池。

3、HttpClients不与特定的HTTP服务器绑定,你可以使用相同的HttpClient实例提交任何HTTP请求。

4、你可以用HttpClient为特定的站点创建特殊的Client

5、HttpClient采用新的型模式处理异步请求使它更容易管理和协调更多的请求。

下面我们看下具体的代码， MSDN code gallery 有个很详细Get操作的示例，这个示例是向World Bank Data Web API 发送一个Get请求，获取到Json格式的数据

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();
        }
    }
}
下面介绍一个发送Post 请求的示例，示例代码使用默认创建的ASP.NET Web API模板项目：

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)

补充：Web开发 , ASP.Net ,