如何从Windows服务调用REST API

John doe 发表于 Dev

约翰·杜

我试图从Windows服务中调用Rest API。我以前从未尝试过。我不确定为什么无法拨打此电话。

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：发送请求时发生错误。
内部异常消息：{“基础连接已关闭：连接意外关闭。”}
内部异常堆栈跟踪位于
System.Net.Http.HttpClientHandler.GetResponseCallback（IAsyncResult ar）处的System.Net.HttpWebRequest.EndGetResponse（IAsyncResult asyncResult ）

在以下行上生成此错误：

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

任何建议，将不胜感激。

编辑：（更新的代码）

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

    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：（仍然收到相同的错误）

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();

    }
}

战争

您的问题是...

var response = client.GetAsync(urlParameter);

...返回一个任务，您需要先等待它完成。

拨打电话的最干净的方法是这样的...

var response = await client.GetAsync(urlParameter);

...这需要代码在这样的异步方法中运行...

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;

...或更紧凑的版本可能是使用像这样的延续...

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

...它将执行请求，然后在请求返回时异步为您解析并解包该任务，并返回“内部结果”，因为此代码创建了Task >>，而您只希望IEnumerable，因此等待解包的Task得到您2个任务一个接一个地执行的结果:)

...我查看了您的特定代码，并在新的控制台应用程序中运行了该代码，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();
            }
        }