Deserializing to a templated class with Gson

Question

I have a class with a nested subclass

public class OuterClass {
class GenericClassHolder<R> {
    @SerializedName("results")
    List<R> results;

    public GenericClassHolder() {}

    public List<R> getResults() {
        return results;
    }
}

class ExampleClassA {
    @SerializedName("A")
    int a;

    public ExampleClassA() {}

    public int getA() {return a;}
}


class ExampleClassB {
    @SerializedName("B")
    String b;

    public ExampleClassA() {}

    public String getB() {return b;}
}
}

Currently I would like to be able to have a function that takes as a parameter the held class, and returns an appropriate instance of GenericClassHolder, ie something like my current code:

GenericClassHolder<ExampleClassA> genericA = parseJson(jsonString, ExampleClassA.class);

with

<T> GenericClassHolder<T> parseJson(final String jsonString, Class<T> variableClass) throws JsonSyntaxException {
    return GSON.fromJson(jsonString, new TypeToken<GenericClassHolder<T>>(){}.getType());
}

But this does not work in my current implementation, with the error

Unable to invoke no-args constructor for GenericClassHolder<T> . Register an InstanceCreator with Gson for this type may fix this problem.

How can I succinctly achieve my aforementioned goal of having a function that takes as input the specification for a class that may change and parses to this object accordingly? If it is not possible to achieve an elegant solution through a function, how can I achieve this goal without one?

Answer 1

I deployed this code in a Google Appengine instance, and due to some security reasons, I could not deserialize the way I was deserializing and replicate the same way on my local machine. The solution was to make the deserialized classes static; they were nested inside of an outer encapsulating class as well