Как я могу получить элементы из поддокумента mongodb в java?

Question

У меня есть база данных mongodb ("тестирование"), в которой есть несколько коллекций. Я использую один с именем "Pelis3", который содержит документы. Документы содержат типичные элементы и вложенный документ под названием "принадлежит коллекции", к которому я буду обращаться. Проблема в том, что я могу печатать только элементы 1-го уровня и вложенный документ как документ.

Как я могу получить один за другим элементы вложенного документа "ведомый_колебанием"?

Это мой код Java. Я вызываю функцию saveJson:

public class mongoDB {

    private MongoClient mongoClient;
    private MongoDatabase mongodb;
    private MongoCollection<Document> collection;

    public MongoDatabase selectDatabase() {
        setMongoClient(new MongoClient());
        setMongodb(getMongoClient().getDatabase("testing"));
        return getMongodb();
    }

    public MongoClient getMongoClient() {
        return mongoClient;
    }

    public void setMongoClient(MongoClient mongoClient) {
        this.mongoClient = mongoClient;
    }

    public MongoDatabase getMongodb() {
        return mongodb;
    }

    public void setMongodb(MongoDatabase mongodb) {
        this.mongodb = mongodb;
    }

    public MongoCollection<Document> getCollection() {
        return collection;
    }

    public void setCollection(String col) {
        this.collection = (selectDatabase().getCollection(col));
    }

    public void saveJson(JsonObject json) {
        setCollection("Pelis3");
        Document document = Document.parse(json.toString());
        getCollection().insertOne(document);

        for (Document doc : getCollection().find()) {

            System.out.println(doc.getBoolean("adult"));
            Object ob = doc.get("belongs_to_collection");
            System.out.println(ob);


        }
    }
}

Это содержание коллекции:

{
  "adult": false,
  "backdrop_path": "/8SqBiesvo1rh9P1hbJTmnVum6jv.jpg",
  "belongs_to_collection": {
    "id": 304378,
    "name": "Independence Day Collection",
    "poster_path": "/diCxphvzqas0Tr5eq7tLUzg5M7d.jpg",
    "backdrop_path": "/p7oqa94XgNGVMazXwR49QfyGgtx.jpg"
  },
  "budget": 165000000,
  "genres": [
    {
      "id": 28,
      "name": "Action"
    },
    {
      "id": 12,
      "name": "Adventure"
    },
    {
      "id": 878,
      "name": "Science Fiction"
    }
  ],
  "homepage": "http://www.warof1996.com",
  "id": 47933,
  "imdb_id": "tt1628841",
  "original_language": "en",
  "original_title": "Independence Day: Resurgence",
  "overview": "We always knew they were coming back. Using recovered alien technology, the nations of Earth have collaborated on an immense defense program to protect the planet. But nothing can prepare us for the aliens’ advanced and unprecedented force. Only the ingenuity of a few brave men and women can bring our world back from the brink of extinction.",
  "popularity": 5.163195,
  "poster_path": "/5CHJs479xWnm3zMDOl94VkKS7MZ.jpg",
  "production_companies": [
    {
      "name": "Twentieth Century Fox Film Corporation",
      "id": 306
    },
    {
      "name": "Centropolis Entertainment",
      "id": 347
    },
    {
      "name": "TSG Entertainment",
      "id": 22213
    },
    {
      "name": "Stereo D",
      "id": 86561
    }
  ],
  "production_countries": [
    {
      "iso_3166_1": "US",
      "name": "United States of America"
    }
  ],
  "release_date": "2016-06-22",
  "revenue": 389681935,
  "runtime": 120,
  "spoken_languages": [
    {
      "iso_639_1": "en",
      "name": "English"
    }
  ],
  "status": "Released",
  "tagline": "We had twenty years to prepare. So did they.",
  "title": "Independence Day: Resurgence",
  "video": false,
  "vote_average": 4.9,
  "vote_count": 2236
}

И это выход, когда я запускаю программу de:

jfx-project-run:
Executing /media/daniel/WD_1TB/Programación/proyectos personales/Gestor de colecciones/dist/run1943415091/Gestor de colecciones.jar using platform /usr/lib/jvm/java-8-oracle/jre/bin/java
jul 02, 2017 5:51:56 PM com.mongodb.diagnostics.logging.JULLogger log
INFORMACIÓN: Cluster created with settings {hosts=[127.0.0.1:27017], mode=SINGLE, requiredClusterType=UNKNOWN, serverSelectionTimeout='30000 ms', maxWaitQueueSize=500}
jul 02, 2017 5:51:56 PM com.mongodb.diagnostics.logging.JULLogger log
INFORMACIÓN: No server chosen by ReadPreferenceServerSelector{readPreference=primary} from cluster description ClusterDescription{type=UNKNOWN, connectionMode=SINGLE, serverDescriptions=[ServerDescription{address=127.0.0.1:27017, type=UNKNOWN, state=CONNECTING}]}. Waiting for 30000 ms before timing out
jul 02, 2017 5:51:56 PM com.mongodb.diagnostics.logging.JULLogger log
INFORMACIÓN: Opened connection [connectionId{localValue:1, serverValue:50}] to 127.0.0.1:27017
jul 02, 2017 5:51:56 PM com.mongodb.diagnostics.logging.JULLogger log
INFORMACIÓN: Monitor thread successfully connected to server with description ServerDescription{address=127.0.0.1:27017, type=STANDALONE, state=CONNECTED, ok=true, version=ServerVersion{versionList=[2, 6, 10]}, minWireVersion=0, maxWireVersion=2, maxDocumentSize=16777216, roundTripTimeNanos=579216}
jul 02, 2017 5:51:56 PM com.mongodb.diagnostics.logging.JULLogger log
INFORMACIÓN: Opened connection [connectionId{localValue:2, serverValue:51}] to 127.0.0.1:27017
false
Document{{id=304378, name=Independence Day Collection, poster_path=/diCxphvzqas0Tr5eq7tLUzg5M7d.jpg, backdrop_path=/p7oqa94XgNGVMazXwR49QfyGgtx.jpg}}
false
Document{{id=304378, name=Independence Day Collection, poster_path=/diCxphvzqas0Tr5eq7tLUzg5M7d.jpg, backdrop_path=/p7oqa94XgNGVMazXwR49QfyGgtx.jpg}}
Java Result: 1
Deleting directory /media/daniel/WD_1TB/Programación/proyectos personales/Gestor de colecciones/dist/run1943415091
jfxsa-run:
BUILD SUCCESSFUL (total time: 3 seconds)