c# - WCF JSON 反序列化中的空格问题

Question

我有一个 WCF REST 服务，它接受 JSON 形式的自定义 DataContract 参数，该参数可以是父类(super class)型或子类型。当我传递包含额外空格的 JSON 时，该对象始终反序列化为父类(super class)型。当我从 JSON 中删除所有空格时，对象会反序列化为子类型。

这是一个例子:

[DataContract]
[KnownType(typeof(SubClass))]
public class SuperClass
{
    [DataMember]
    public string Message { get; set; }
}

[DataContract]
public class SubClass : SuperClass
{
    [DataMember]
    public string Extra { get; set; }
}

[ServiceContract]
public interface IService1
{
    [OperationContract]
    [WebInvoke]
    void LogMessage(SuperClass arg);
}

public class Service1 : IService1
{
    public void LogMessage(SuperClass arg)
    {
        if (arg is SubClass)
        {
            Debug.WriteLine("SubClass");
        }
        else if (arg is SuperClass)
        {
            Debug.WriteLine("SuperClass");
        }
    }
}

如果我发送以下消息，该服务将打印 SuperClass:

POST http://localhost:5763/Service1.svc/LogMessage HTTP/1.1
User-Agent: Fiddler
Content-Type: text/json
Host: localhost:5763
Content-Length: 86

{    "__type":"SubClass:#WhitespaceTest",    "Message":"Message",    "Extra":"Extra" }

如果我也“漂亮地打印”数据包，以便将 JSOn 分成多行，我会得到相同的结果。但是，如果我按如下方式删除空格，该服务将打印 SubClass:

POST http://localhost:5763/Service1.svc/LogMessage HTTP/1.1
User-Agent: Fiddler
Content-Type: text/json
Host: localhost:5763
Content-Length: 73

{"__type":"SubClass:#WhitespaceTest","Message":"Message","Extra":"Extra"}

我已经调试了 System.ServiceModel.OperationContext.Current.RequestContext.RequestMessage.ToString() 的输出，并注意到从 JSON 生成的 XML 在 2 个数据包之间是不同的:

<!-- First packet, deserializes to SuperClass -->
<root type="object">
    <__type type="string">SubClass:#WhitespaceTest</__type>
    <Message type="string">Message</Message>
    <Extra type="string">Extra</Extra>
</root>

<!-- Second packet, deserializes to SubClass -->
<root type="object" __type="SubClass:#WhitespaceTest">
    <Message type="string">Message</Message> 
    <Extra type="string">Extra</Extra> 
</root>

因此，空白似乎混淆了 JSON 反序列化器。有谁知道为什么会发生这种情况以及我能做什么？

Answer 1

这是一个已知问题，已在 4.5 框架中修复。不幸的是，如果您想在当前框架版本中使用多态性，您实际上需要去除对象前面的空白。一种方法是使用 JsonReaderWriterFactory 创建的读取器/写入器读取/写入 JSON，因为它将去除元素周围的空白(或任何 pretty-print )。

public class StackOverflow_8661714
{
    [DataContract(Name = "SuperClass", Namespace = "WhitespaceTest")]
    [KnownType(typeof(SubClass))]
    public class SuperClass
    {
        [DataMember]
        public string Message { get; set; }
    }

    [DataContract(Name = "SubClass", Namespace = "WhitespaceTest")]
    public class SubClass : SuperClass
    {
        [DataMember]
        public string Extra { get; set; }
    }
    public static void Test()
    {
        string originalJson = "{    \"__type\":\"SubClass:WhitespaceTest\",    \"Message\":\"Message\",    \"Extra\":\"Extra\" }";
        byte[] originalJsonBytes = Encoding.UTF8.GetBytes(originalJson);
        MemoryStream writeStream = new MemoryStream();
        XmlDictionaryWriter jsonWriter = JsonReaderWriterFactory.CreateJsonWriter(writeStream, Encoding.UTF8, false);
        XmlDictionaryReader jsonReader = JsonReaderWriterFactory.CreateJsonReader(originalJsonBytes, 0, originalJsonBytes.Length, XmlDictionaryReaderQuotas.Max);
        jsonWriter.WriteNode(jsonReader, true);
        jsonWriter.Flush();
        Console.WriteLine(Encoding.UTF8.GetString(writeStream.ToArray()));
        writeStream.Position = 0;

        DataContractJsonSerializer dcjs = new DataContractJsonSerializer(typeof(SuperClass), new Type[] { typeof(SubClass) });
        object o = dcjs.ReadObject(writeStream);
        Console.WriteLine(o);
    }
}