如何在 Android Studio 中使用 Retrofit 2 解析复杂的 JSON

Question

I am trying to get the stopId from this API but I am having a hard time parsing it using retrofit 2 + gson. I've only got experience with less complicated JSON API's. Could anyone help me?

{
    "direction": "inbound",
    "timetable": {
        "$type": "Tfl.Api.Presentation.Entities.Timetable, Tfl.Api.Presentation.Entities",
        "departureStopId": "940GZZCRECR",
        "routes": [{
            "$type": "Tfl.Api.Presentation.Entities.TimetableRoute, Tfl.Api.Presentation.Entities",
            "stationIntervals": [{
                "$type": "Tfl.Api.Presentation.Entities.StationInterval, Tfl.Api.Presentation.Entities",
                "id": "0",
                "intervals": [{
                    "$type": "Tfl.Api.Presentation.Entities.Interval, Tfl.Api.Presentation.Entities",
                    "stopId": "940GZZCRLEB",
                    "timeToArrival": 2
                }, {
                    "$type": "Tfl.Api.Presentation.Entities.Interval, Tfl.Api.Presentation.Entities",
                    "stopId": "940GZZCRSAN",
                    "timeToArrival": 3
                }]
            }, {

            }, {

            }],
            "schedules": [

            ]
        }]
    }
}

Answer 1

Create your models automatically with this tool. Just paste an example json response. http://pojo.sodhanalibrary.com

Remember to check and edit types of your variables, sometimes they can be null. After that make your call as usual.

Answer 2

You have to create proper models hierarchy, for example:

BaseModel :

public class BaseModel {
    String direction;
    Timetable timetable;
}

Timetable :

public class Timetable {
    String $type;
    String departureStopId;
    List<Route> routes;
}

Route :

public class Route {
    String $type;
    List<StationInterval> stationIntervals;
    List<Integer> schedules;
}

StationInterval :

public class StationInterval {
    String $type;
    int id;
    List<Interval> intervals;
}

Interval :

public class Interval {
    String $type;
    String stopId;
    int timeToArrival;
}

And make retrofit call as usual:

 @GET("some_url")
 Call<BaseModel> loadSomeData();

Answer 3

A simple and efficient way of generating POJO from JSON is http://www.jsonschema2pojo.org/ After you have included the models generated from the above link, you can continue reading this if you need some info setting up Retrofit 2.0.

Now, you would have to define a interface for the APIs

public interface MyAPI {
    @GET("/url")
    Call<ResponseModel> getData();
}

Then create a class to get the retrofit client

public class MyDataClient {

    public static final String BASE_URL = "";
    private static Retrofit retrofit = null;


    public static Retrofit getClient() {
        if (retrofit==null) {
            HttpLoggingInterceptor logging = new HttpLoggingInterceptor();
            logging.setLevel(HttpLoggingInterceptor.Level.BODY);
            OkHttpClient.Builder httpClient = new OkHttpClient.Builder();
            httpClient.addInterceptor(logging);

            retrofit = new Retrofit.Builder()
                    .baseUrl(BASE_URL)
                    .addConverterFactory(GsonConverterFactory.create())
                    .client(httpClient.build())
                    .build();
        }
        return retrofit;
    }
}

Then when you need to call the API do this,

     MyAPI apiService =MyDataClient.getClient().create(MyAPI.class);
     Call<ResponseModel> call = apiService.getData();
     call.enqueue(new Callback<ResponseModel>() {
                @Override
                public void onResponse(Call<ResponseModel> call, Response<ResponseModel> response) {
                }
                @Override
               public void onFailure(Call<ResponseModel> call, Throwable t){
                }
        });