//abstract generic class for accessing collection
@BsonDiscriminator
public abstract class GenericContainer<T> {
  private ObjectId id;
  private InnerModel<T> inner;

  public ObjectId getId() {
    return id;
  }
  public void setId(final ObjectId id) {
    this.id = id;
  }
  public InnerModel<T> getInner() {
    return inner;
  }
  void setInner(final InnerModel<T> inner) {
    this.inner = inner;
  }
}

// class for property in GenericContainer
public class InnerModel<T> {
  private T field;

  public T getField() {
    return field;
  }
  public void setField(final T field) {
    this.field = field;
  }
}

public class IntContainer extends GenericContainer<Integer> {}

public class StringContainer extends GenericContainer<String> {}

public void test(final MongoDatabase database) {
  @SuppressWarnings("unchecked")
  final MongoCollection<GenericContainer<?>>  collection =
    (MongoCollection<GenericContainer<?>>) (MongoCollection<?>)
    database.getCollection("genericCollection", GenericContainer.class);

  final IntContainer intContainer = new IntContainer();
  intContainer.setInner(new InnerModel<>());
  intContainer.getInner().setField(3);

  final InsertOneResult insertResult = collection.insertOne(intContainer);
  System.out.println(insertResult.getInsertedId());
}