public List<A> daoMethod() {
    List<Object[]> dbResult = getDbResults();
    List<A> javaObjects = new ArrayList<>();

    // build nested Java objects
    for (Object[] line in dbResult) {
        A a = new A();
        a.setProp1(line[0]);
        a.setProp2(line[1]);
        // and so on...
        javaObjects.add(a);
        return javaObjects ;
    }
}

public ResponseEntity<A> controllerMethod() {
    List<A> javaObjects = myDao.daoMethod();
    return new ResponseEntity(javaObjects, HttpStatus.OK);
}

@JsonInclude(JsonInclude.Include.NON_NULL) // removes all fields having NULL value
public abstract class BaseDto implements Serializable{
    // some properties...
}

{
  prop1: "some string",
  prop2: [{},{},{}],
  prop3: [],
  prop4: {},
}

{
  prop1: "some string"
}