Map a collection with parameter with mapstruct

Question

To map a certain object with mapstruct I need some custom post processing which needs an additional parameter to do it's work:

@Mapper
public abstract class AlertConfigActionMapper {

    @Mappings({ @Mapping(target = "label", ignore = true)})
    public abstract AlertConfigActionTO map (AlertConfigAction action, Locale userLanguage);

    @AfterMapping
    public void setLabel (AlertConfigAction  action, @MappingTarget AlertConfigActionTO to, Locale userLanguage) {
        for (AlertConfigActionLabel label : action.getAlertConfigActionLabels()) {
            if (label.getLanguage().equals(userLanguage)) {
                to.setLabel(label.getLabel());
                break;
            } else if (label.getLanguage().equals(Locale.ENGLISH)) {
                to.setLabel(label.getLabel());
            }
        }

    }
}

This works just fine. The problem starts when I add following method to this mapper:

public abstract ArrayList<AlertConfigActionTO> mapList (List<AlertConfigAction> actions, Locale userLanguage);

I need to pass this parameter (userLanguage) as well but mapstruct seems to 'break down' in this case: I generates following code for this part (which naturally gives a compilation error):

@Override
public List<AlertConfigActionTO> mapList(List<AlertConfigAction> actions, Locale userLanguage) {
    if ( actions == null && userLanguage == null ) {
        return null;
    }

    List<AlertConfigActionTO> list = new List<AlertConfigActionTO>();

    return list;
}

I'm sure it is related to the parameter since if I remove it (from all mapping methods) then the mapList method is generated correctly.

What is needed to be done to allow custom parameters in this case?

Answer 1

What you describe is not possible (yet). Could you open a feature request in our issue tracker? We should provide means of denoting parameters as some sort of "context" which is passed down the call stack.

As a work-around for the time being, you might take a look at using a ThreadLocal which you set before invoking the mapping routine and which you access in your after-mapping customization. It's not elegant - and you need to make sure to clean up the thread local to avoid memory leaks - but it should do the trick.