如何使用 GSON 解析接口

Question

I've have an interface model with nested interfaces. For each interface there is also mainly 1 concrete implementation class like:

public interface Book {

    String getTitle();
}

public class BookImpl implements Book {

    private String title;

    @Override
    public String getTitle() {
        return title;
    }

    public void setTitle(String title) {
        this.title = title;
    }
}

Now to parse the json like:

gson.fromJson(json, Book.class);

Does not work as it does not know the implementation class.

So I created a custom deserializer like:

public class BookDeserializer implements JsonDeserializer<Book> {

    @Override
    public Book deserialize(final JsonElement json, final Type typeOfT, final JsonDeserializationContext context) throws JsonParseException {
        return context.deserialize(json, BookImpl.class);
    }
}

But I do this for each interface in my model.

Is that the proper way to this? Creating such a simplistic deserializer? I feel there should be an easier way.

Like with Jackson I would create a custom Jackson Module and register the type mapping like:

.addAbstractTypeMapping(Book.class, BookImpl.class)

Is this also possible with GSON?

Answer 1

You can use generic version of JsonDeserializer

public static class MyDeserializer implements JsonDeserializer {
    private Class<?> implClass;

    public MyDeserializer(Class<?> c) {
        implClass = c;
    }

    @Override
    public Object deserialize(JsonElement json, Type typeOfT, 
            JsonDeserializationContext context) throws JsonParseException {
        return context.deserialize(json, implClass);
    }
}

And register it pretty much like in Jackson with one line

builder.registerTypeAdapter(A.class, new MyDeserializer(AImpl.class));
builder.registerTypeAdapter(B.class, new MyDeserializer(BImpl.class));

---

Or just use lambda like

builder.registerTypeAdapter(G.class, (JsonDeserializer) (json, typeOfT, context)
                -> context.deserialize(json, H.class));