反序列化 Json Web API 响应 - 嵌套对象

Question

我通过 SSIS 脚本组件获得了一个 Web API JSON 响应，它以以下格式返回：

    {
  "Success": true,
  "Response": {
    "Applications": [
      {
        "App_ID": 1638486,
        "App_Ref": "Test Example",
        "Status": "Complete",
        "Error_Code": null,
        "Error_Message": null,
        "Create_Dt": "2014-05-14 03:09:01.030 +00:00",
        "Modify_Dt": "2014-05-14 03:10:59.757 +00:00",
        "Client_Name": "Silver Chef",
        "Client_Code": "SLVC01",
        "Centrelink_Status": "Receiving_Logons"
      },
      {
        "App_ID": 1637906,
        "App_Ref": "SME Demo",
        "Status": "Complete",
        "Error_Code": null,
        "Error_Message": null,
        "Create_Dt": "2015-10-08 03:07:26.793 +00:00",
        "Modify_Dt": "2015-10-08 03:23:32.833 +00:00",
        "Client_Name": "Silver Chef",
        "Client_Code": "SLVC01",
        "Centrelink_Status": "Receiving_Logons"
      },
      {
        "App_ID": 1585286,
        "App_Ref": "Test",
        "Status": "Receiving_Logons",
        "Error_Code": null,
        "Error_Message": null,
        "Create_Dt": "2015-12-04 03:12:49.617 +00:00",
        "Modify_Dt": "2015-12-04 03:12:49.617 +00:00",
        "Client_Name": "Silver Chef",
        "Client_Code": "SLVC01",
        "Centrelink_Status": "Receiving_Logons"
      }
],
    "Current_Dt": "2016-11-11 01:01:01.743 +00:00",
    "Last_App_Dt": "2016-10-03 22:48:56.397 +00:00",
    "Count": 500,
    "Total": 1870
  }
}

我已经声明了以下类：

     public class Application
        {
            public int App_ID { get; set; }
            public string App_Ref { get; set; }
            public string Status { get; set; }
            public int Error_Code { get; set; }
            public string Error_Message { get; set; }
            public DateTime Create_Dt { get; set; }
            public DateTime Modify_Dt { get; set; }
            public string Client_Name { get; set; }
            public string Client_Code { get; set; }
            public int Centrelink_Status { get; set; }

        }
        public class Response
        {
            public List<Application> Applications { get; set; }
            public string Current_Dt { get; set; }
            public string Last_App_Dt { get; set; }
            public int Count { get; set; }
            public int Total { get; set; }
        }

        public class RootObject
        {
            public bool Success { get; set; }
            public Response Response { get; set; }
        }

And this is the method that I am using to get the response. 
private RootObject GetWebServiceResult(string vAPIUrl)
    {

        string vAPIToken = Variables.APIToken;

        //Create Web Request
        HttpWebRequest apireq = (HttpWebRequest)WebRequest.Create(vAPIUrl);
        apireq.ContentType = "application/json";
        apireq.Method = "POST";

        string jsonPostStr = "{\"Settings\": {\"API_Token\": \"" + vAPIToken + "\"}, \"Payload\": {}}";
        byte[] postString = Encoding.UTF8.GetBytes(jsonPostStr);

        apireq.ContentLength = postString.Length;

        Stream jsonStream = apireq.GetRequestStream();

        jsonStream.Write(postString, 0, postString.Length);
        jsonStream.Close();

        // Get Web Response        
        HttpWebResponse apirsp = (HttpWebResponse)apireq.GetResponse();
        RootObject jsonResponse = null;

        Stream jsonRspStream = apirsp.GetResponseStream();
        string apiResponseString = null;

        using (StreamReader reader = new StreamReader(jsonRspStream)) 
        {
            apiResponseString = reader.ReadToEnd(); 
            Console.WriteLine(apiResponseString);
            reader.Close();
        }


        JavaScriptSerializer returnJson = new JavaScriptSerializer();

        //var serialJsonStr = returnJson.Serialize(apiResponseString);
        System.Windows.Forms.MessageBox.Show(apiResponseString);

        jsonResponse = returnJson.Deserialize<RootObject>(apiResponseString);

        return jsonResponse;

    }

我的问题是 returnJson.Deserialize(apiResponseString); 似乎返回 null 并随后使其失败。

我错过了什么？我想我在这个阶段有点代码盲。

提前致谢

Answer 1

Application 类有几个问题：

• 您已将Application.Error_Code 定义为整数：

  public int Error_Code { get; set; }
  

  但实际上，在JSON中，它有一个空值：

  "Error_Code": null,
  

  因此，Error_Code 需要是引用类型 (string) 或可空值类型 (int?)，具体取决于它在非空时所持有的内容。

• 您已将 Centrelink_Status 定义为 int，但在 JSON 中它是一个字符串：

  "Centrelink_Status": "Receiving_Logons"
  

  因此它也需要是数据模型中的字符串。

因此，您的 Application 类应如下所示：

public class Application
{
    public int App_ID { get; set; }
    public string App_Ref { get; set; }
    public string Status { get; set; }
    public int? Error_Code { get; set; } // Or string, if not numeric
    public string Error_Message { get; set; }
    public DateTime Create_Dt { get; set; }
    public DateTime Modify_Dt { get; set; }
    public string Client_Name { get; set; }
    public string Client_Code { get; set; }
    public string Centrelink_Status { get; set; }
}

如果有可能在 JSON 中出现 null 值，您可能还想让这些 DateTime 属性为空。

顺便说一句，当我试图反序列化这个 JSON 时，我得到了一个异常抛出，而不是返回一个空值：

System.InvalidOperationException was unhandled
  Message="Cannot convert null to a value type."
  Source="System.Web.Extensions"
  StackTrace:

在您的实际代码中，您是否捕获并吞下了异常？这正是一个坏主意，因为它往往会隐藏诸如此类的错误。至少，在调试时，无论何时抛出任何异常，包括第一次机会异常，您都应该中断 - 即使这 不是 默认行为。见Managing Exceptions with the Debugger。如果您发现某些类型的异常经常被抛出并且与调试无关，您可以选择性地重新忽略它们。如果你这样做了，这个错误会更容易追踪。诚然，该错误不是很容易解释，但确实给出了提示。如果您要使用json.net 反序列化您的 JSON，错误消息会更清晰：

Newtonsoft.Json.JsonSerializationException occurred
  Message="Error converting value {null} to type 'System.Int32'. Path 'Response.Applications[0].Error_Code', line 9, position 26."
  Source="Newtonsoft.Json"
  StackTrace:
       at Newtonsoft.Json.Serialization.JsonSerializerInternalReader.EnsureType(JsonReader reader, Object value, CultureInfo culture, JsonContract contract, Type targetType) in C:\Development\Releases\Json\Working\Newtonsoft.Json\Working-Signed\Src\Newtonsoft.Json\Serialization\JsonSerializerInternalReader.cs:line 986
  InnerException: System.InvalidCastException
       Message="Null object cannot be converted to a value type."
       Source="mscorlib"
       StackTrace:
            at System.Convert.ChangeType(Object value, Type conversionType, IFormatProvider provider)
            at Newtonsoft.Json.Serialization.JsonSerializerInternalReader.EnsureType(JsonReader reader, Object value, CultureInfo culture, JsonContract contract, Type targetType) in C:\Development\Releases\Json\Working\Newtonsoft.Json\Working-Signed\Src\Newtonsoft.Json\Serialization\JsonSerializerInternalReader.cs:line 979
       InnerException: