Deserializing custom exceptions in Newtonsoft.Json

Question

I\'ve been having trouble deserializing custom exceptions in Newtonsoft.Json version 11.0.2. It works fine in Newtonsoft.Json version 10.0.3.

I serialize and deseria

Answer 1

In Json.NET 11 a change was made to how ISerializable types are serialized. According to the release notes:

• Change - Types that implement ISerializable but don't have [SerializableAttribute] are not serialized using ISerializable

Thus you must now mark your exception types with SerializableAttribute:

[Serializable]
public sealed class MyHttpException : MyBaseException
{
}

[Serializable]
public abstract class MyBaseException : Exception
{
}

Alternatively, you could create a custom contract resolver that restores the old behavior:

public class PreferISerializableContractResolver : DefaultContractResolver
{
    protected override JsonContract CreateContract(Type objectType)
    {
        var contract = base.CreateContract(objectType);

        if (!IgnoreSerializableInterface
            && contract is JsonObjectContract
            && typeof(ISerializable).IsAssignableFrom(objectType)
            && !objectType.GetCustomAttributes(true).OfType<JsonContainerAttribute>().Any())
        {
            contract = CreateISerializableContract(objectType);
        }

        return contract;
    }
}

(You may want to cache the contract resolver for best performance.)

Why was this change made? According to Issue #1622: classes deriving from System.Exception do not serialize/deserialize properly:

Json.NET previous wasn't serializing ISerializable types correctly. The SerializableAttribute is required.

See here for more info dotnet/corefx#23415.

And in turn the linked issue dotnet/corefx Issue #23415: PlatformNotSupportedException when attempting to serialize DirectoryInfo instance with Newtonsoft.Json indicates that the change was made at the request of the .NET Core team:

JamesNK commented on Aug 29, 2017

So the issue is Json.NET is checking that a type implements ISerializable but not also checking for the SerialiazableAttribute?

ViktorHofer commented on Aug 29, 2017

Correct :)

Thus if you do use PreferISerializableContractResolver instead of marking your ISerializable types with [Serializable], you might encounter this very issue in .NET Core.