AEM Interview Questions: Essential Topics to Master

Sling Models in AEM

1. What are Sling Models in AEM?

   - Sling Models in AEM are a Java-based framework that provides a convenient way to map AEM's JCR resources to POJO (Plain Old Java Object) representations. They act as a bridge between the resource-oriented approach of AEM and the object-oriented approach of Java.

2. How do Sling Models work in AEM?

   - Sling Models work in AEM by leveraging the adaptable concept provided by the Sling framework. Sling Models use annotations to define and map the properties of AEM resources to fields within a Java class. They can be automatically adapted to different resource types based on the resource's adaptable hierarchy.

3. What are the advantages of using Sling Models in AEM?

   - The advantages of using Sling Models in AEM include:

     - Easy mapping of resource properties to Java fields.

     - Improved code readability and maintainability.

     - Reduction in boilerplate code.

     - Automatic adaptation to different resource types.

     - Dependency injection of services and resources.

     - Enhanced testability and easier unit testing.

4. How do you define a Sling Model in AEM?

   - To define a Sling Model in AEM, you need to create a Java class and annotate it with the `@Model` annotation. This annotation identifies the class as a Sling Model. The class should also extend the `WCMUsePojo` class or implement the `org.apache.sling.models.annotations.Model` interface.

5. What is the purpose of the @Model annotation in AEM Sling Models?

   - The `@Model` annotation in AEM Sling Models is used to mark a class as a Sling Model. It informs the AEM framework that the class should be treated as a Sling Model and enables the Sling Model functionality for the annotated class.

6. How do you inject resources or services into a Sling Model?

   - To inject resources or services into a Sling Model, you can use the `@Inject` annotation. You can annotate fields, constructor parameters, or setter methods with `@Inject` to indicate the dependencies that should be automatically injected by the AEM framework.

7. What is the difference between @Inject and @Self annotations in AEM Sling Models?

   - The `@Inject` annotation is used to inject services or resources into a Sling Model, while the `@Self` annotation is used to inject the current resource into a Sling Model. The `@Inject` annotation allows you to inject any available service or resource, while `@Self` specifically injects the resource associated with the Sling Model instance.

8. How do you use Sling Models to map properties from a resource to the model fields?

   - To map properties from a resource to model fields, you can use the `@Inject` or `@ValueMapValue` annotations. The `@Inject` annotation injects individual properties, while the `@ValueMapValue` annotation injects a `ValueMap` object containing all the properties of the resource.

9. How can you use Sling Models to adapt to different resource types in AEM?

   - Sling Models automatically adapt to different resource types based on the resource's adaptable hierarchy. By creating different Sling Model classes and defining them to adapt to specific resource types, you can ensure that the appropriate Sling Model is used based on the resource being adapted.

10. Can you explain the concept of Sling Model Exporters in AEM?

    - Sling Model Exporters allow you to expose Sling Models as different output formats, such as JSON, XML, or custom formats. By defining export annotations (`@Exporter` and `@Exporters`) on Sling Models, you can control the serialization and provide custom mappings for the exported output.

11. How do you handle nested resources or child resources using Sling Models?

    - To handle nested resources or child resources using Sling Models, you can use the `@ChildResource` or `@ChildResources` annotation. These annotations allow you to inject child resources as separate Sling Model instances or as a collection of Sling Model instances.

12. What is the purpose of the @PostConstruct annotation in AEM Sling Models?

    - The `@PostConstruct` annotation is used in Sling Models to mark a method that should be invoked after the Sling Model instance has been constructed and all dependencies have been injected. It allows you to perform initialization or setup tasks that require the Sling Model to be fully constructed.

13. How can you handle request-specific data in Sling Models?

    - To handle request-specific data in Sling Models, you can use the `@SlingObject` annotation to inject the `SlingHttpServletRequest` or `RequestContext` object. These objects provide access to the current request and can be used to retrieve request-specific data, such as request parameters or headers.

14. Can you explain the concept of Sling Model inheritance and how it works?

    - Sling Model inheritance allows you to define a base Sling Model class and have other Sling Model classes inherit its properties and behavior. Inheritance is achieved by extending a base Sling Model class using the `@Model` annotation. The child Sling Models inherit the fields, methods, and annotations of the base class.

15. How do you handle multivalue properties in Sling Models?

    - To handle multivalue properties in Sling Models, you can use the `@ValueMapValue` annotation with the `defaultValue` attribute set to an array. This allows you to inject a property as an array or `List` of values. Alternatively, you can use the `@Inject` annotation with the `@Named` annotation to inject multivalue properties as an array or `List` directly.

These answers should give you a good understanding of AEM Sling Models and help you prepare for an interview on this topic.