在.NET中发送HTTP POST请求

技术背景

在.NET开发中，经常需要与外部服务进行交互，发送HTTP POST请求是常见的需求之一。例如，向服务器提交表单数据、调用API接口等。不同的.NET版本和场景下，有多种方式可以实现HTTP POST请求。

实现步骤

方法A：HttpClient（推荐）

适用范围：.NET Framework 4.5+、.NET Standard 1.1+ 和 .NET Core 1.0+。
设置：建议在应用程序的生命周期内实例化一个 HttpClient 并共享它。

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using System.Net.Http;

private static readonly HttpClient client = new HttpClient();

POST请求示例

var values = new Dictionary<string, string>
{
    { "thing1", "hello" },
    { "thing2", "world" }
};

var content = new FormUrlEncodedContent(values);
var response = await client.PostAsync("http://www.example.com/recepticle.aspx", content);
var responseString = await response.Content.ReadAsStringAsync();

方法B：第三方库

RestSharp

var client = new RestClient("http://example.com");
// client.Authenticator = new HttpBasicAuthenticator(username, password);
var request = new RestRequest("resource/{id}");
request.AddParameter("thing1", "Hello");
request.AddParameter("thing2", "world");
request.AddHeader("header", "value");
request.AddFile("file", path);
var response = client.Post(request);
var content = response.Content; // Raw content as string

Flurl.Http

using Flurl.Http;

var responseString = await "http://www.example.com/recepticle.aspx"
    .PostUrlEncodedAsync(new { thing1 = "hello", thing2 = "world" })
    .ReceiveString();

方法C：HttpWebRequest（不推荐用于新开发）

using System.Net;
using System.Text;  // For class Encoding
using System.IO;    // For StreamReader

var request = (HttpWebRequest)WebRequest.Create("http://www.example.com/recepticle.aspx");
var postData = "thing1=" + Uri.EscapeDataString("hello");
postData += "&thing2=" + Uri.EscapeDataString("world");
var data = Encoding.ASCII.GetBytes(postData);

request.Method = "POST";
request.ContentType = "application/x-www-form-urlencoded";
request.ContentLength = data.Length;

using (var stream = request.GetRequestStream())
{
    stream.Write(data, 0, data.Length);
}

var response = (HttpWebResponse)request.GetResponse();
var responseString = new StreamReader(response.GetResponseStream()).ReadToEnd();

方法D：WebClient（不推荐用于新开发）

using System.Net;
using System.Collections.Specialized;

using (var client = new WebClient())
{
    var values = new NameValueCollection();
    values["thing1"] = "hello";
    values["thing2"] = "world";

    var response = client.UploadValues("http://www.example.com/recepticle.aspx", values);
    var responseString = Encoding.Default.GetString(response);
}

核心代码

通用的HttpClient POST请求

using System.Net.Http;

private static readonly HttpClient client = new HttpClient();

var values = new Dictionary<string, string>
{
    { "key1", "value1" },
    { "key2", "value2" }
};

var content = new FormUrlEncodedContent(values);
var response = await client.PostAsync("http://example.com/api", content);
var responseString = await response.Content.ReadAsStringAsync();

发送JSON数据的POST请求

using System;
using System.Net.Http;
using System.Text;
using System.Threading.Tasks;
using System.Web.Script.Serialization;

namespace ConsoleApplication1
{
    class Customer
    {
        public string Name { get; set; }
        public string Address { get; set; }
        public string Phone { get; set; }
    }

    public class Program
    {
        private static readonly HttpClient _Client = new HttpClient();
        private static JavaScriptSerializer _Serializer = new JavaScriptSerializer();

        static async Task Run()
        {
            string url = "http://www.example.com/api/Customer";
            Customer cust = new Customer() { Name = "Example Customer", Address = "Some example address", Phone = "Some phone number" };
            var json = _Serializer.Serialize(cust);
            var response = await Request(HttpMethod.Post, url, json, new Dictionary<string, string>());
            string responseText = await response.Content.ReadAsStringAsync();
        }

        static async Task<HttpResponseMessage> Request(HttpMethod pMethod, string pUrl, string pJsonContent, Dictionary<string, string> pHeaders)
        {
            var httpRequestMessage = new HttpRequestMessage();
            httpRequestMessage.Method = pMethod;
            httpRequestMessage.RequestUri = new Uri(pUrl);
            foreach (var head in pHeaders)
            {
                httpRequestMessage.Headers.Add(head.Key, head.Value);
            }
            switch (pMethod.Method)
            {
                case "POST":
                    HttpContent httpContent = new StringContent(pJsonContent, Encoding.UTF8, "application/json");
                    httpRequestMessage.Content = httpContent;
                    break;
            }

            return await _Client.SendAsync(httpRequestMessage);
        }
    }
}