1.1.4 利用HttpClient调用 WebApi

　　　　对于一个.net客户端程序，它可以利用HttpClient来进行Web Api的调用。由于WebA Api的调用本质上就是一次普通的发送请求与接收响应的过程，

所有HttpClient其实可以作为一般意义上发送HTTP请求的工具。

　　　　在ConsoleApp代表的控制台应用中，我们利用HttpClient来调用以Self Host方式寄宿的Web Api。

　　　　为该项目引用Common， System.Net.Http

class Program
    {
        static void Main(string[] args)
        {
            Process();
            Console.Read();
        }

        private async static void Process()
        {
            //获取当前联系人列表
            HttpClient httpClient = new HttpClient();
            HttpResponseMessage response = await httpClient.GetAsync("http://localhost/selfhost/api/contacts");
            IEnumerable<Contact> contacts = await response.Content.ReadAsAsync<IEnumerable<Contact>>();
            Console.WriteLine("当前联系人列表：");
            ListContacts(contacts);

            //添加新的联系人
            Contact contact = new Contact { Name = "王五", PhoneNo = "17712348765", EmailAddress = "wangwuEmali@123.com", Address = "天津" };
            await httpClient.PostAsJsonAsync<Contact>("http://localhost/selfhost/api/contacts", contact);
            Console.WriteLine("添加联系人：王五");
            response = await httpClient.GetAsync("http://localhost/selfhost/api/contacts");
            contacts = await response.Content.ReadAsAsync<IEnumerable<Contact>>();
            ListContacts(contacts);

            //修改现有的某个联系人
            response = await httpClient.GetAsync("http://localhost/selfhost/api/contacts/001");
            contact = (await response.Content.ReadAsAsync<IEnumerable<Contact>>()).First();
            contact.Name = "修改过的张三";
            await httpClient.PutAsJsonAsync<Contact>("http://localhost/selfhost/api/contacts", contact);
            Console.WriteLine("修改联系人001的信息");
            response = await httpClient.GetAsync("http://localhost/selfhost/api/contacts");
            contacts = await response.Content.ReadAsAsync<IEnumerable<Contact>>();
            ListContacts(contacts);

            //删除现有的某个联系人
            response = await httpClient.DeleteAsync("http://localhost/selfhost/api/contacts/002");
            Console.WriteLine("删除联系人“002”");
            response = await httpClient.GetAsync("http://localhost/selfhost/api/contacts");
            contacts = await response.Content.ReadAsAsync<IEnumerable<Contact>>();
            ListContacts(contacts);

        }

        private static void ListContacts(IEnumerable<Contact> contacts)
        {
            foreach (Contact item in contacts)
            {
                Console.WriteLine("{0,-6}{1,-6}{2,-20}{3,-10}", item.ID, item.Name, item.EmailAddress, item.Address);
                Console.WriteLine();
            }
        }
    }

　　　　效果如下