AEM 6.3: Custom sling model injector, InjectionStrategy.OPTIONAL not working

[#1]

I've written my own custom annotation to find a property on the current resource and to return it. This annotation works fine when the property is available on the resource, things go wrong when it is not found:

Annotation:

@Target({ElementType.FIELD})
@Retention(RetentionPolicy.RUNTIME)
@InjectAnnotation
@Source(InheritedValueMapValueInjector.NAME)
public @interface InheritedValueMapValue {
  String property();
  InjectionStrategy injectionStrategy() default InjectionStrategy.DEFAULT;
}

Injector:

@Component(service = {Injector.class}, property = {
Constants.SERVICE_RANKING + ":Integer=" + 4300
})
public class InheritedValueMapValueInjector extends AbstractInjector implements Injector, StaticInjectAnnotationProcessorFactory {
public static final String NAME = "inherited-value-map-value";
@Override
public String getName() {
  return NAME;
}
@Override
public Object getValue(final Object adaptable, final String name, final Type type, final AnnotatedElement element,
   final DisposalCallbackRegistry callbackRegistry) {
  //CUSTOM LOGIC HERE
}
@Override
public InjectAnnotationProcessor2 createAnnotationProcessor(final AnnotatedElement element) {
  InheritedValueMapValue annotation = element.getAnnotation(InheritedValueMapValue.class);
  if (annotation != null) {
    return new InheritedValueAnnotationProcessor(annotation);
  }
  return null;
}
private static class InheritedValueAnnotationProcessor extends AbstractInjectAnnotationProcessor2 {
  private final InheritedValueMapValue annotation;
  InheritedValueAnnotationProcessor(final InheritedValueMapValue annotation) {
    this.annotation = annotation;
  }
    @Override
    public InjectionStrategy getInjectionStrategy() {
       return annotation.injectionStrategy();
    }
  }
}

Use in sling model:

@InheritedValueMapValue(property = "title", injectionStrategy = InjectionStrategy.OPTIONAL)
private String titleProperty;

This is what I see in my error logging:

Suppressed: org.apache.sling.models.factory.MissingElementException: Could not inject private java.lang.String com.company.platform.component.text.HeadingController.titleProperty
at org.apache.sling.models.impl.ModelAdapterFactory.createObject(ModelAdapterFactory.java:650)
... 223 common frames omitted
Caused by: org.apache.sling.models.factory.ModelClassException: No injector returned a non-null value!
at org.apache.sling.models.impl.ModelAdapterFactory.injectElement(ModelAdapterFactory.java:565)
at org.apache.sling.models.impl.ModelAdapterFactory.createObject(ModelAdapterFactory.java:648)

When I replace the strategy by an additional 'org.apache.sling.models.annotations.Optional' annotation it works, but I was wondering why it was not when using 'InjectionStrategy.OPTIONAL'? Thanks in advance!

NOTE: I am using AEM 6.3.1.2 uber-jar

[#2 · Accepted solution]

Hi, Jdruwe​.

The problem is @Component definition of your InheritedValueMapValueInjector. It should be registered for both interfaces - Injector and StaticInjectAnnotationProcessorFactory. For this, either remove "service" property from @Component (so it will automatically take all the implemented interfaces), either specify both of them.

[#3]

Thank you, it works now

[#4]

Thanks Alex for the great response!

[#5]

If I use @optitional instead of the strategy it works yes. I want it to work with the strategy

[#6]

To clarify - it works when you use - org.apache.sling.models.annotations.Optional.

To those reading this thread and want to know  how to use Align Model Injector with AEM -- see this article on the subject -- Creating a Sling Model Injector for Adobe Experience Manager