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javaaemslingsling-models

AEM slingmodels - why do we need unused adaptables in each model? Why need both Resource & SlingHTTPRequest?

I am working on a project where every model has this line:

@Model(adaptables = { SlingHttpServletRequest.class,Resource.class },
 defaultInjectionStrategy = DefaultInjectionStrategy.OPTIONAL)

In my understanding:

  1. If Resource or SlingHTTPRequest is not to be used, this dependency injection must be removed from the model
  2. SlingHTTPRequest can help obtain resource with the use of .getResource method anyway, so using SlingHTTPServeltRequest class alone, with required dependencyInjectionStrategy should be sufficient, and Resource class as an adaptable is never needed?

Please share your thoughts. Thanks in advance!

Solution

  • Question 1)

    • A SlingModel MUST be either created/adapted from SlingHttpServletRequest or a Resource. It cannot be created from nothing.

    • The the adaptables-property specifies, from which object it can be created.

    • If the SlingModel can be created from both, the scripting-environment (e.g. HTL scripts) will use the Resource. But SlingModels can be used elsewhere too, so the source will be random.

    Hint 1: Do not use both adaptables. So either decide for SlingHttpServletRequest or Resource. Because both will work, but the injecting will be different - and can cause weird bugs (at least it is thin ice, and hard to test). The example with @Self is simple, but some other injectors are even more complicated, as the implicitly the @Via changes.

    @Model(adaptables = { SlingHttpServletRequest.class, Resource.class },
                      defaultInjectionStrategy = DefaultInjectionStrategy.OPTIONAL)
public class MySlingModel {

@Self
// will be null, if adapted from Resource!!!
private SlingHttpServletRequest request;

@Self
// will be null, if adapted from SlingHttpServletRequest!!!
private Resource resource;

    Question 2

    Components (and so SlingModels) should be context-free, and be represented by a Resource (= JCR node and evtl. some sub-nodes). So a SlingModel should normally adapted from a Resource. It is also easier to use elsewhere (in other services or sling-models).

    Only, if you need something from the request, then switch to the SlingHttpServletRequest. Unfortunately this is often needed for URL mapping. But limit yourself to access RequestAttributes. Even something like WcmMode should not be used in a SlingModel. It is better to see SlingModels as a Wrapper around a Resource, a small Java-Layer to access data.

    Hint 2: Not everything is a SlingModel! You can create Services, Servlets, AdapterFactories, Filters, Rewriter, ...