Get field from model in JSON view

[Guillaume Lucazeau]

Hello,

I have a class model where I generate a value for a property from two other
properties, something like that:

@Model(adaptables = Resource.class)
public class MyModel extends AbstractResource implements Resource {

  @Inject
  private int valueOne;

  @Inject
  private int valueTwo;

  private int sum;

  public getSum() {
    return sum;
  }

  @PostConstruct
  public void calculateScore() {
    sum = valueOne + valueTwo;
  }
}

I'd like to see this "sum" property when I call the JSON view:
{
  "sling:resourceType": "model/myModel",
  "jcr:createdBy": "admin",
  "jcr:created": "Mon Dec 07 2015 17:11:31 GMT+0100",
  "jcr:primaryType": "sling:Folder",
  "valueOne": 10,
  "valueTwo": 5,
  "sum": 15
  }

I tried to save it in a ModifiableValueMap properties that I get with
adaptTo() and display it with new JSONObject(properties) but it requires an
administrative authentication, or now a service with a special user.

I don't mind trying to do that but it seems a bit heavy as a solution, I
was wondering if there would be something easier to do such thing?

Thank you
Guillaume