CODEWITHSUNDEEP
javaandroidgson
Osiriz
Osiriz

Reputation: 218

GSON - the Array<>Object JSON-Conversion is not solved despite TypeAdapter

This is my class which represents the json-structure from the server:

ArrayList<EventWebInterface.Element> element;

public class Element {
    String id;
    String subtitle;
    String name;
    String subline;
    String count;
}

And this is the structure:

{
    element: [
    {
    id: "1985",
    subtitle: "01. August 2013 18:30 Uhr | Berlin",
    name: "blabla....",
subline: "blabla....",
    category_id: ""
    },
    {
    id: "1962",
    subtitle: "07. August 2013 19:00 Uhr | Cloppenburg",
    name: "blabla...",
    subline: "blabla....",
    category_id: ""
    },
    { ...

But sometimes the structure has only one element like:

{
    element: {
       id: "1985",
       subtitle: "01. August 2013 18:30 Uhr | Berlin",
       name: "blabla...",
       subline: "blabla....",
       category_id: ""
    }
}

For this case i've got a typeadapter for gson which looks like this:

public class EventWebTypeAdapter implements JsonDeserializer<List<EventWebInterface.Element>> {
public List<EventWebInterface.Element> deserialize(JsonElement json, Type typeOfT, JsonDeserializationContext ctx) {
    List<EventWebInterface.Element> vals = new ArrayList<EventWebInterface.Element>();
    if (json.isJsonArray()) {
        for (JsonElement e : json.getAsJsonArray()) {
            vals.add((EventWebInterface.Element) ctx.deserialize(e, EventWebInterface.Element.class));
        }
    } else if (json.isJsonObject()) {
        vals.add((EventWebInterface.Element) ctx.deserialize(json, EventWebInterface.Element.class));
    } else {
        throw new RuntimeException("Unexpected JSON type: " + json.getClass());
    }
    return vals;
}

public Type getType(){
    return new TypeToken<List<EventWebInterface.Element>>() {}.getType();
}

}

I use it this way:

EventWebTypeAdapter mTypeAdapter = new EventWebTypeAdapter();
Type mType = mTypeAdapter.getType();
Class<I> mInterface = EventWebInterface.class

Gson gson = new GsonBuilder().registerTypeAdapter(mType, mTypeadapter).create();
dataObject = gson.fromJson(data, mInterface);

But the Adapter doesn't work. It gives me:

com.google.gson.JsonSyntaxException: java.lang.IllegalStateException: Expected BEGIN_ARRAY but was BEGIN_OBJECT

I don't get it, why it doesn't work... =(

Upvotes: 1

Views: 1584

Answers (1)

MikO
MikO

Reputation: 18751

I myself find your code a bit messy, so I can't really find the error.

I'll explain what I'd do from the beginning and maybe you can compare it with your code and get some ideas...

First I'd create these 2 classes:

class Response
    List<Element> element;

class Element
    String id;
    String subtitle;
    String name;
    String subline;
    String count;

Then I'd create a TypeAdapter, and I think the easiest way is to create one for the Responseclass. Something like:

public class ResponseDeserializer implements JsonDeserializer<Response> {

    public Response deserialize(JsonElement json, Type typeOfT, JsonDeserializationContext ctx) {

        JsonElement elementField = json.getAsJsonObject().get("element");

        List<Element> elementList = new ArrayList<>();

        if (elementField.isJsonArray()) {
            for (JsonElement item : elementField.getAsJsonArray()) {
                elementList.add(ctx.deserialize(item, Element.class));
            }
        } else if (elementField.isJsonObject()) {
            elementList.add(ctx.deserialize(elementField, Element.class));
        }

        Response response = new Response(elementList);

        return response;
    }
}

Then you just need to register the adapter with:

GsonBuilder builder = new GsonBuilder().registerTypeAdapter(Response.class, new ResponseDeserializer());
Gson gson = builder.create();

And eventually parse the JSON with:

Response response = gson.fromJson(data, Response.class);

Upvotes: 3

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