Java: How to obtain all Fields from a class through an instance returned from a generic function?

Backstory: I have an external interface system that is based on JSON and GSON. The external interface receives a JSON string that always contains a key as String type and an dictionary with the data. The associated Message handler class is found in a lookup table based on the key. This all works.

Implementation example:

class Message
{
    public Class<?> payloadType;

    public Message(Class<?> type)
    {
        this.payloadType = type;
    }

    public abstract void handle(Gson gson, T json);
}


public class NotifyPlayer extends Message<NotifyPlayer.JSONStructure>
{
    public NotifyPlayer ()
    {
        super(JSONStructure.class);
    }

    @Override
    public void handle(Gson gson, JSONStructure object)
    {
        //impl
    }

    static class JSONStructure
    {
        int user_id;

        String message;

        String from;
    }
}

And the Message handler is registered in a map:

THashMap<String, Class<? extends Message>> messages
messages.add("notify", NotifyPlayer.class);

What I am trying to accomplish is to get all Fields from the JSONStructure and print the Field name, type and default value (if any).

What I am having trouble with is getting FieldUtils to use the JSONStructure class type instead of java.lang.Class

Class<? extends Message> command = Server.getCommand("notify");
Object dummy = command.newInstance();
Object json = command.getField("type").get(dummy);
Class jsonClass = json.getClass(); 
System.out.println("Json getClass() : " + json.getClass());
Field[] fields = FieldUtils.getAllFields(jsonClass); 

jsonClass ends up being of type Class instead of NotifyPlayer.JSONStructure