Json 如何用接口序列化一个类

I have never done much with serialization, but am trying to use Google's gson to serialize a Java object to a file. Here is an example of my issue:

public interface Animal {
    public String getName();
}


 public class Cat implements Animal {

    private String mName = "Cat";
    private String mHabbit = "Playing with yarn";

    public String getName() {
        return mName;
    }

    public void setName(String pName) {
        mName = pName;
    }

    public String getHabbit() {
        return mHabbit;
    }

    public void setHabbit(String pHabbit) {
        mHabbit = pHabbit;
    }

}

public class Exhibit {

    private String mDescription;
    private Animal mAnimal;

    public Exhibit() {
        mDescription = "This is a public exhibit.";
    }

    public String getDescription() {
        return mDescription;
    }

    public void setDescription(String pDescription) {
        mDescription = pDescription;
    }

    public Animal getAnimal() {
        return mAnimal;
    }

    public void setAnimal(Animal pAnimal) {
        mAnimal = pAnimal;
    }

}

public class GsonTest {

public static void main(String[] argv) {
    Exhibit exhibit = new Exhibit();
    exhibit.setAnimal(new Cat());
    Gson gson = new Gson();
    String jsonString = gson.toJson(exhibit);
    System.out.println(jsonString);
    Exhibit deserializedExhibit = gson.fromJson(jsonString, Exhibit.class);
    System.out.println(deserializedExhibit);
}
}

所以这很好地序列化了——但可以理解的是，删除了关于动物的类型信息:

{"mDescription":"This is a public exhibit.","mAnimal":{"mName":"Cat","mHabbit":"Playing with yarn"}}

This causes real problems for deserialization, though:

Exception in thread "main" java.lang.RuntimeException: No-args constructor for interface com.atg.lp.gson.Animal does not exist. Register an InstanceCreator with Gson for this type to fix this problem.

I get why this is happening, but am having trouble figuring out the proper pattern for dealing with this. I did look in the guide but it didn't address this directly.