Cannot parse MapBox DirectionsRoute class from JSON

Question

I use MapBox REST API on backend side to create a route. Here is a simplified code:

public class MapBoxRequest {

  // using string pattern just for convenience
  private static final String PATTERN =
      "https://api.mapbox.com/directions/v5/mapbox/walking/%s,%s;%s,%s?alternatives=true&geometries=geojson&steps=true&access_token=%s";

  public static void main(String[] args) throws IOException, URISyntaxException {
    HttpRequestFactory requestFactory = new NetHttpTransport().createRequestFactory();

    String accessToken =
        "access_toekn";

    // set right location values
    String string = String.format(PATTERN, longitude1, latitude1, longitude2, latitude2, accessToken);

      URI uri = new URI(string);

    HttpRequest request = requestFactory.buildGetRequest(new GenericUrl(uri.toString()));
    String rawResponse = request.execute().parseAsString();

    
    // HERE I AM GETTING EXCEPTION, THIS CODE IS SUPPOSED TO BE CALLED IN ANDROID APP
    DirectionsResponse.fromJson(rawResponse);
  }
}

with these maven dependencies:

<dependency>
        <groupId>com.google.http-client</groupId>
        <artifactId>google-http-client</artifactId>
        <version>1.38.0</version>
 </dependency>

 <dependency>
       <groupId>com.mapbox.mapboxsdk</groupId>
       <artifactId>mapbox-sdk-services</artifactId>
       <version>5.6.0</version>
 </dependency>

But when I try to parse DirectionsResponse class from string I am getting the following exception:

Exception in thread "main" com.google.gson.JsonSyntaxException: java.lang.IllegalStateException: Expected 
a string but was BEGIN_OBJECT at line 1 column 546 path $.routes[0].legs[0].steps[0].geometry
    at com.google.gson.Gson.fromJson(Gson.java:939)
    at com.google.gson.Gson.fromJson(Gson.java:892)
    at com.google.gson.Gson.fromJson(Gson.java:841)
    at com.google.gson.Gson.fromJson(Gson.java:813)
    at com.mapbox.api.directions.v5.models.DirectionsResponse.fromJson(DirectionsResponse.java:133)
    at dating.walking.service.walking.setup.MapBoxRequest.main(MapBoxRequest.java:34)
Caused by: java.lang.IllegalStateException: Expected a string but was BEGIN_OBJECT at line 1 column 546 path $.routes[0].legs[0].steps[0].geometry
    at com.google.gson.stream.JsonReader.nextString(JsonReader.java:825)

The code above is for example. In practice Android/iOS clients are supposed to download that JSON, parse it and use it in navigation using MapBox Navigation SDK. The thing is in Android application I am getting the same exception as the one above.

My question is - how can I create a route on a backend side, send it to client as json and parse JSON and start navigation?

Answer 1

Using MapBox Java SDK instead of MapBox REST API and configuring Gson library helped me serialize and deserialize ReponseRoute class.

Here is a simplified code:

public class MapBoxSdkSample {

  public static void main(String[] args) {
    String accessToken = "*****";

    Point originPoint = Point.fromLngLat(**, **);
    Point destinationPoint = Point.fromLngLat(**, **);

    MapboxDirections client =
        MapboxDirections.builder()
            .origin(originPoint)
            .destination(destinationPoint)
            .overview(DirectionsCriteria.OVERVIEW_FULL)
            .profile(DirectionsCriteria.PROFILE_WALKING)
            .accessToken(accessToken)
            .build();

    client.enqueueCall(
        new Callback<>() {
          @Override
          public void onResponse(
              Call<DirectionsResponse> call, Response<DirectionsResponse> response) {

            // boilerplate code
            if (response.body() == null) {
              System.out.println(
                  "No routes found, make sure you set the right user and access token.");
              return;
            } else if (response.body().routes().size() < 1) {
              System.out.println("No routes found");
              return;
            }


            DirectionsRoute directionsRoute = response.body().routes().get(0);

            Gson gson =
                new GsonBuilder()
                    .registerTypeAdapterFactory(DirectionsAdapterFactory.create())
                    .create();
            String s1 = gson.toJson(directionsRoute);
            
            // I wasn't getting exceptions here and the object was populated with data
            DirectionsRoute parsedFromJsonRoute = gson.fromJson(s1, DirectionsRoute.class);
          }

          @Override
          public void onFailure(Call<DirectionsResponse> call, Throwable throwable) {
            System.out.println("Error: " + throwable.getMessage());
          }
        });
  }
}