Optaplanner: prevent custom List from beeing cloned by FieldAccessingSolutionCloner - optaplanner

Question

I have a #PlanningSolution class, that has one field with a custom List implementation as type.
When solving I run into the following issue (as described in the optaplanner documentation):
java.lang.IllegalStateException: The cloneCollectionClass (class java.util.ArrayList) created for originalCollectionClass (class Solution$1) is not assignable to the field's type (class CustomListImpl).
Maybe consider replacing the default SolutionCloner.
As this field has no impact on planning, can I prevent FieldAccessingSolutionCloner from trying to clone that particular field e.g. by adding some annotation? I dont want to provide a complete custom SolutionCloner.
When inspecting the sources of FieldAccessingSolutionCloner I found out that I only needed to override the method retrieveCachedFields(...) or constructCloneCollection(...) so I tried to extend FieldAccessingSolutionCloner but then I need a public no-args-constructor. There I dont know how to initialise the field solutionDescriptor in the no-args-constructor to use my ExtendedFieldAccessingSolutionCloner as solution cloner.

Answer 1

If the generic solution cloner decided to clone that List, there is probably a good reason for it do so: one of the the elements in that list probably has a reference to a planning entity or the planning solution - and therefore the entire list needs to be planning cloned.
If that's not the case, this is a bug in OptaPlanner. Please provide the classes source code of the class with that field and the CustomListImpl class too, so we can reproduce and fix it.
To supply a custom SolutionCloner, follow the docs which will show something like this (but this is a simple case without chained variables, so it's easy to get right, but solution cloning is notoriously difficult!).
#PlanningSolution(solutionCloner = VaccinationSolutionCloner.class)
public class VaccinationSolution {...}
public class VaccinationSolutionCloner implements SolutionCloner<VaccinationSolution> {
#Override
public VaccinationSolution cloneSolution(VaccinationSolution solution) {
List<PersonAssignment> personAssignmentList = solution.getPersonAssignmentList();
List<PersonAssignment> clonedPersonAssignmentList = new ArrayList<>(personAssignmentList.size());
for (PersonAssignment personAssignment : personAssignmentList) {
PersonAssignment clonedPersonAssignment = new PersonAssignment(personAssignment);
clonedPersonAssignmentList.add(clonedPersonAssignment);
}
return new VaccinationSolution(solution.getVaccineTypeList(), solution.getVaccinationCenterList(), solution.getAppointmentList(),
solution.getVaccinationSlotList(), clonedPersonAssignmentList, solution.getScore());
}
}