Question

I’m using gson to deserialize POJO objects from JSON representations.

I’d like one of the fields in one of my POJOs to contain arbitrary JSON data. For example:

class B {
    public String stringField;
    public JsonObject jsonField;
}

I’d like to be able to call Gson.fromJson(json, B.class) on the following JSON:

{
    "stringField": "booger",
    "jsonField" :
    {
        "arbitraryField1": "foo"
    }
}

and have the resulting B.jsonField contain a JsonObject with an arbitraryField of value foo.

However, when I attempt to do this, jsonField is always an empty object ({}). In fact, more generally, it appears that the following always returns an empty object:

new Gson().fromJson("{ foo: 1 }", JsonObject.class)

I would expect the above to return an object containing a field named foo of value 1.

How can I have gson preserve arbitrary json data when deserializing json to POJOS?

Answer 1

I was able to work around the problem by introducing a wrapper object that contains a JsonObject, and then writing a custom deserializer for that object that simply returns the original json. However, it seems like there must be a better way.

For posterity, the deserializer and the trivial wrapper object look like the following:

class MyJsonObjectWrapperDeserializer implements JsonDeserializer<MyJsonObjectWrapper> {
    @Override
    public MyJsonObjectWrapper deserialize(JsonElement json, Type typeOfT, JsonDeserializationContext context) throws JsonParseException {
        return new MyJsonObjectWrapper(json.getAsJsonObject());
    }
}

class MyJsonObjectWrapper {
    public JsonObject json;

    public MyJsonObjectWrapper(JsonObject json) {
        this.json = json;
    }
}