使用.NET 4.0任务模式使用HTTPClient .ReadAsAsync将JSON反序列化为数组或列表

Question

我正在尝试反序列化http://api.usa.gov/jobs/search.json?query=nursing+jobs使用.NET 4.0任务模式返回的JSON .它返回此JSON('加载JSON数据'@ http://jsonviewer.stack.hu/).

[
  {
    "id": "usajobs:353400300",
    "position_title": "Nurse",
    "organization_name": "Indian Health Service",
    "rate_interval_code": "PA",
    "minimum": 42492,
    "maximum": 61171,
    "start_date": "2013-10-01",
    "end_date": "2014-09-30",
    "locations": [
      "Gallup, NM"
    ],
    "url": "https://www.usajobs.gov/GetJob/ViewDetails/353400300"
  },
  {
    "id": "usajobs:359509200",
    "position_title": "Nurse",
    "organization_name": "Indian Health Service",
    "rate_interval_code": "PA",
    "minimum": 42913,
    "maximum": 61775,
    "start_date": "2014-01-16",
    "end_date": "2014-12-31",
    "locations": [
      "Gallup, NM"
    ],
    "url": "https://www.usajobs.gov/GetJob/ViewDetails/359509200"
  },
  ...
]

指数行动:

  public class HomeController : Controller
  {
    public ActionResult Index()
    {
      Jobs model = null;
      var client = new HttpClient();
      var task = client.GetAsync("http://api.usa.gov/jobs/search.json?query=nursing+jobs")
        .ContinueWith((taskwithresponse) =>
        {
          var response = taskwithresponse.Result;
          var jsonTask = response.Content.ReadAsAsync<Jobs>();
          jsonTask.Wait();
          model = jsonTask.Result;
        });
      task.Wait();
      ...
     }

工作和工作类:

  [JsonArray]
  public class Jobs { public List<Job> JSON; }

  public class Job
  {
    [JsonProperty("organization_name")]
    public string Organization { get; set; }
    [JsonProperty("position_title")]
    public string Title { get; set; }
  }

当我设置断点jsonTask.Wait();并检查jsonTask状态是Faulted.InnerException是"Type ProjectName.Jobs不是集合".

我开始使用没有JsonArray属性的Jobs类型和作为数组的Job(Job [])并得到了这个错误.

  public class Jobs { public Job[] JSON; }

    +       InnerException  {"Cannot deserialize the current JSON array (e.g. [1,2,3]) into type 'ProjectName.Models.Jobs' because the type requires a JSON object (e.g. {\"name\":\"value\"}) to deserialize correctly.\r\n
    To fix this error either change the JSON to a JSON object (e.g. {\"name\":\"value\"}) or change the deserialized type to an array or a type that implements a collection interface
 (e.g. ICollection, IList) like List<T> that can be deserialized from a JSON array. JsonArrayAttribute can also be added to the type to force it to deserialize from a JSON array.\r\n
Path '', line 1, position 1."}  System.Exception {Newtonsoft.Json.JsonSerializationException}

我如何使用.NET 4.0任务模式处理此站点的JSON？await async在使用.NET 4.5中的模式之前,我想让它工作.

答案更新:

这是使用.NET 4.5异步等待模式和brumScouse的答案的示例.

 public async Task<ActionResult>Index()
 {
    List<Job> model = null;
    var client = newHttpClient();

    // .NET 4.5 async await pattern
    var task = await client.GetAsync(http://api.usa.gov/jobs/search.json?query=nursing+jobs);
    var jsonString = await task.Content.ReadAsStringAsync();
    model = JsonConvert.DeserializeObject<List<Job>>(jsonString);
    returnView(model);
 }

您需要引入System.Threading.Tasks命名空间.
注意:没有.ReadAsString可用的方法,.Content这就是我使用该.ReadAsStringAsync方法的原因.

Answer 1

您可以尝试使用Json2csharp.com网站之类的东西,而不是手工制作模型.粘贴在示例JSON响应中,越大越好,然后拉入生成的类.这至少会带走一些移动部件,在csharp中为您提供JSON的形状,为序列化器提供更简单的时间,您不必添加属性.

只需使其工作,然后修改您的类名,以符合您的命名约定,并在以后添加属性.

编辑:好的,有点搞乱我已经成功地将结果反序列化为一个工作列表(我使用Json2csharp.com为我创建类)

public class Job
{
        public string id { get; set; }
        public string position_title { get; set; }
        public string organization_name { get; set; }
        public string rate_interval_code { get; set; }
        public int minimum { get; set; }
        public int maximum { get; set; }
        public string start_date { get; set; }
        public string end_date { get; set; }
        public List<string> locations { get; set; }
        public string url { get; set; }
}

并编辑您的代码:

        List<Job> model = null;
        var client = new HttpClient();
        var task = client.GetAsync("http://api.usa.gov/jobs/search.json?query=nursing+jobs")
          .ContinueWith((taskwithresponse) =>
          {
              var response = taskwithresponse.Result;
              var jsonString = response.Content.ReadAsStringAsync();
              jsonString.Wait();
              model = JsonConvert.DeserializeObject<List<Job>>(jsonString.Result);

          });
        task.Wait();

这意味着你可以摆脱你的包含对象.值得注意的是,这不是与任务相关的问题,而是反序列化问题.

编辑2:

有一种方法可以获取JSON对象并在Visual Studio中生成类.只需复制选择的JSON,然后编辑>选择性粘贴>将JSON粘贴为类.这里有一整页专门介绍:

http://blog.codeinside.eu/2014/09/08/Visual-Studio-2013-Paste-Special-JSON-And-Xml/

Answer 2

var response = taskwithresponse.Result;
          var jsonString = response.ReadAsAsync<List<Job>>().Result;

Answer 3

返回类型取决于服务器，有时响应确实是一个 JSON 数组，但作为文本/纯文本发送

在请求中设置接受头应该得到正确的类型：

client.DefaultRequestHeaders.Accept.Add(new MediaTypeWithQualityHeaderValue("application/json")); 

然后可以将其序列化为 JSON 列表或数组。感谢@svick 的评论，这让我很好奇它应该可以工作。

我在没有配置接受标头的情况下得到的异常是 System.Net.Http.UnsupportedMediaTypeException。

以下代码更清晰，应该可以工作（未经测试，但在我的情况下有效）：

    var client = new HttpClient();
    client.DefaultRequestHeaders.Accept.Add(new MediaTypeWithQualityHeaderValue("application/json"));
    var response = await client.GetAsync("http://api.usa.gov/jobs/search.json?query=nursing+jobs");
    var model = await response.Content.ReadAsAsync<List<Job>>();