Question

How can I inject dependencies into objects that weren’t created by a DI framework?

I am running an application on Google App Engine using Objectify, so POJOs are created by Objectify when data is fetched from the datastore. Personally i like having convenience methods to get related objects, like car.getOwner().getName() The car object is created by Objectify. The code of getOwner() owner would be something like

public Person getOwner(){
    return PersonService.getById(this.ownerId);
}

I could improve it with a ServiceLocator

public Person getOwner(){
    return ServiceLocator.getService(PersonService.class).getById(this.ownerId);
}

But how would I do this with DI?

I looked at Guice, but i can only think of putting the Injector in a singleton and access it from the getOwner method.

Is my thinking flawed?

Answer 1

If you are using Objectify4 you can subclass ObjectifyFactory and override the construct() method. This will allow you to inject your entity classes.

You can see an example here: https://github.com/stickfigure/motomapia/blob/master/java/com/motomapia/OfyFactory.java