Get nested JSON object with GSON using retrofit

Question

I\'m consuming an API from my android app, and all the JSON responses are like this:

{
    \'status\': \'OK\',
    \'reason\': \'Everything was fine\',
    \         


        

Answer 1

Another simple solution:

JsonObject parsed = (JsonObject) new JsonParser().parse(jsonString);
Content content = gson.fromJson(parsed.get("content"), Content.class);

Answer 2

Continuing Brian's idea, because we almost always have many REST resources each with it's own root, it could be useful to generalize deserialization:

 class RestDeserializer<T> implements JsonDeserializer<T> {

    private Class<T> mClass;
    private String mKey;

    public RestDeserializer(Class<T> targetClass, String key) {
        mClass = targetClass;
        mKey = key;
    }

    @Override
    public T deserialize(JsonElement je, Type type, JsonDeserializationContext jdc)
            throws JsonParseException {
        JsonElement content = je.getAsJsonObject().get(mKey);
        return new Gson().fromJson(content, mClass);

    }
}

Then to parse sample payload from above, we can register GSON deserializer:

Gson gson = new GsonBuilder()
    .registerTypeAdapter(Content.class, new RestDeserializer<>(Content.class, "content"))
    .build();

Answer 3

@BrianRoach's solution is the correct solution. It is worth noting that in the special case where you have nested custom objects that both need a custom TypeAdapter, you must register the TypeAdapter with the new instance of GSON, otherwise the second TypeAdapter will never be called. This is because we are creating a new Gson instance inside our custom deserializer.

For example, if you had the following json:

{
    "status": "OK",
    "reason": "some reason",
    "content": {
        "foo": 123,
        "bar": "some value",
        "subcontent": {
            "useless": "field",
            "data": {
                "baz": "values"
            }
        }
    }
}

And you wanted this JSON to be mapped to the following objects:

class MainContent
{
    public int foo;
    public String bar;
    public SubContent subcontent;
}

class SubContent
{
    public String baz;
}

You would need to register the SubContent's TypeAdapter. To be more robust, you could do the following:

public class MyDeserializer<T> implements JsonDeserializer<T> {
    private final Class mNestedClazz;
    private final Object mNestedDeserializer;

    public MyDeserializer(Class nestedClazz, Object nestedDeserializer) {
        mNestedClazz = nestedClazz;
        mNestedDeserializer = nestedDeserializer;
    }

    @Override
    public T deserialize(JsonElement je, Type type, JsonDeserializationContext jdc) throws JsonParseException {
        // Get the "content" element from the parsed JSON
        JsonElement content = je.getAsJsonObject().get("content");

        // Deserialize it. You use a new instance of Gson to avoid infinite recursion
        // to this deserializer
        GsonBuilder builder = new GsonBuilder();
        if (mNestedClazz != null && mNestedDeserializer != null) {
            builder.registerTypeAdapter(mNestedClazz, mNestedDeserializer);
        }
        return builder.create().fromJson(content, type);

    }
}

and then create it like so:

MyDeserializer<Content> myDeserializer = new MyDeserializer<Content>(SubContent.class,
                    new SubContentDeserializer());
Gson gson = new GsonBuilder().registerTypeAdapter(Content.class, myDeserializer).create();

This could easily be used for the nested "content" case as well by simply passing in a new instance of MyDeserializer with null values.

Answer 4

A better solution could be this..

public class ApiResponse<T> {
    public T data;
    public String status;
    public String reason;
}

Then, define your service like this..

Observable<ApiResponse<YourClass>> updateDevice(..);

Answer 5

Don't forget @SerializedName and @Expose annotations for all Class members and Inner Class members that most deserialized from JSON by GSON.

Look at https://stackoverflow.com/a/40239512/1676736

Answer 6

There is a simpler way, just consider content sub object as another class:

class Content {
    var foo = 0
    var bar: String? = null
}

class Response {
    var statis: String? = null
    var reason: String? = null
    var content: Content? = null
} 

and now you can use Response type to deserialize json.