如何从 Windows 服务调用 REST API

Question

我正在尝试从 Windows 服务调用 Rest API。 我以前从未尝试过。 我不知道为什么我不能打这个电话。

我的代码：

    string urlParameter = "posts/1";
    var client = new HttpClient();
    client.BaseAddress = new Uri("http://jsonplaceholder.typicode.com/");
    client.DefaultRequestHeaders.Accept.Add(new MediaTypeWithQualityHeaderValue("application/json"));

    HttpResponseMessage response = client.GetAsync(urlParameter).Result;
    if (response.IsSuccessStatusCode)
    {
        var dataObj = response.Content.ReadAsAsync<IEnumerable<MyType>>().Result;
    }

我收到以下错误：

• 消息：发送请求时出错。

• 内部异常消息：{“底层连接已关闭：连接意外关闭。”}

• System.Net.HttpWebRequest.EndGetResponse(IAsyncResult asyncResult) 处的内部异常堆栈跟踪
  在 System.Net.Http.HttpClientHandler.GetResponseCallback(IAsyncResult ar)

此错误是在以下行上生成的：

HttpResponseMessage response = client.GetAsync(urlParameter).Result;

任何建议，将不胜感激。

编辑：（更新代码）

    string urlParameter = "posts/1";
    var client = new HttpClient();
    client.BaseAddress = new Uri("http://jsonplaceholder.typicode.com/");
    client.DefaultRequestHeaders.Accept.Add(new MediaTypeWithQualityHeaderValue("application/json"));

    try
    {
        //var response = await client.GetAsync(urlParameter);
        var task = client.GetAsync(urlParameter);
        task.Wait();
        var response = task.Result;

        if (response.IsSuccessStatusCode)
        {
            var dataObj = response.Content.ReadAsAsync<IEnumerable<MyType>>().Result;
        }
    }
    catch (Exception ex)
    {
        string a = ex.Message;
        string b = ex.ToString();
    }

编辑2：（仍然得到同样的错误）

private static async void TestAPI2()
{
    using (HttpClient client = new HttpClient())
    {
        client.DefaultRequestHeaders.Add("Get", "application/json");

        var response = await client.GetAsync("http://jsonplaceholder.typicode.com/posts/1");

        string context = await response.Content.ReadAsStringAsync();

    }
}

Answer 1

你的问题是...

var response = client.GetAsync(urlParameter);

...返回一个任务，您需要先等待它完成。

打这个电话的最干净的方法是这样的......

var response = await client.GetAsync(urlParameter);

...这需要代码以这样的异步方法运行...

public async Task Foo() 
{
   var response = await client.GetAsync(urlParameter);
}

...或者您可以简单地告诉编译器使用 ...

var task = client.GetAsync(urlParameter);
task.Wait();

var response = task.Result;

……或者更紧凑的版本可能是使用这样的延续……

var result = await client.GetAsync(urlParameter)
    .ContinueWith(t => t.Result.Content.ReadAsAsync<IEnumerable<MyType>>())
    .Unwrap();

...这将执行请求，然后当请求返回时为您异步解析它并解包任务返回“内部结果”，因为此代码创建了一个 Task>> 并且您只想要 IEnumerable 所以等待解包的任务让你2个任务一个接一个执行的结果:)

...我查看了您的特定代码并在新的控制台应用程序中运行该代码，请将其更新为...

 class MyType
        {
          public int userId { get; set; }
          public int id { get; set; }
          public string title { get; set; }
          public string body { get; set; }
        }

        static void TestAnApiCall()
        {
            string urlParameter = "posts/1";
            var client = new HttpClient();
            client.BaseAddress = new Uri("http://jsonplaceholder.typicode.com/");
            client.DefaultRequestHeaders.Accept.Add(new MediaTypeWithQualityHeaderValue("application/json"));

            try
            {
                //var response = await client.GetAsync(urlParameter);
                var task = client.GetAsync(urlParameter);
                task.Wait();
                var response = task.Result;

                if (response.IsSuccessStatusCode)
                {
                    var readTask = response.Content.ReadAsAsync<MyType>();
                    readTask.Wait();
                    var dataObj = readTask.Result;
                    Console.WriteLine(JsonConvert.SerializeObject(dataObj));
                }
            }
            catch (Exception ex)
            {
                string a = ex.Message;
                string b = ex.ToString();
            }
        }

Answer 2

是的，它确实在“控制台应用程序”中工作，但是相同的代码在窗口服务中不起作用。 – 约翰·多伊

想回复此评论。 我确实遇到过类似的问题。 Rest API 无法从 Windows 服务进行调用，但它在控制台应用程序中工作。 显示为

{System.Net.Http.HttpRequestException: An error occurred while sending the request. ---> System.Net.WebException: Unable to connect to the remote server ---> System.Net.Sockets.SocketException: A connection attempt failed because the connected party did not properly respond after a period of time, or established connection failed because connected host has failed to respond 80.228.241.59:443
   at System.Net.Sockets.Socket.InternalEndConnect(IAsyncResult asyncResult)
   at System.Net.Sockets.Socket.EndConnect(IAsyncResult asyncResult)
   at System.Net.ServicePoint.ConnectSocketInternal(Boolean connectFailure, Socket s4, Socket s6, Socket& socket, IPAddress& address, ConnectSocketState state, IAsyncResult asyncResult, Exception& exception)
   --- End of inner exception stack trace ---

由于防火墙问题，这一切都发生在我身上。 最后能够使用 RestClient 中的代理设置解决这个问题并且它起作用了。