@ScriptVariable resourceResolver vs @SlingObject resourceResolver

Question

Can anyone explain to me the difference between calling resourceResolver by annotating @ScriptVariable and by annotating @SlingObject? In what context do they behave differently?

Answer 1

The key difference is in the way the object is retrieved. @ScriptVariable and @SlingObject are injector-specific annotations. This means that you can use them to instruct Sling Models to use a particular injector.

The injector that recognises the @ScriptVariable annotation can inject objects available as Scripting Variables. In case ot the resourceResolver, it should be the one associated with the request. Same as slingRequest.getResourceResolver().

Looking at the code, the injector that kicks in on fields annotated with @SlingObject is a bit more interesting in that it will inspect the adaptable (from which your Sling Model is being adapted) and obtain the resolver accordingly:

• If the adaptable is a Resource, it'll return resource.getResourceResolver(), i.e. the resolver originally used to load the resource. This may be quite aribtrary.
• If the adaptable is a SlingHttpServletRequest, it'll return request.getResourceResolver(), i.e. the resolver instantiated by Sling in association with the request and the session of the user issuing the request.
• If the adaptable itself is a ResourceResolver, it will be returned directly.

In some cases, the difference between the three will be negligible, but sometimes it will be important which resolver you choose. If your model is, for example, supposed to be used outside the scope of a request (imagine it's instantiated by an OSGi service that runs on a schedule and there's no incoming request), you'll be better off using resource or resourceResolver as an adaptable.