@BsonDiscriminator
public interface Pet {
    String getType();
}

public class Cat implements Pet {

    private String name;
    // ...
}

MongoCollection<Pet>.find() throws:
Cannot find a public constructor for 'Pet'.  Please ensure the class has a public, empty constructor with no arguments, or else a constructor with a BsonCreator annotation

@BsonDiscriminator
public abstract class Pet {
    abstract String getType();
}

public class Cat extends Pet {

    private String name;
    // ...
}

MongoCollection<Pet>.insertOne(cat) and MongoCollection<Pet>.find() throws: 
Can't find a codec for CodecCacheKey{clazz=class tour.Pet, types=null}.