In AEM, the Overlay and Sling Resource Merger are two approaches for customizing the behavior of existing components or templates without modifying the original code.
Overlay
The Overlay approach involves copying the entire structure of an existing component or template to a new location in the /apps folder. You can then modify the copied files to achieve the desired functionality.
For example, if you want to modify the behavior of the “title” component in AEM, you would create a new folder structure in /apps with the same name and path as the original component (e.g., /apps/components/core/title). You can then modify the copied files to add your custom functionality.
One drawback of the Overlay approach is that it can create maintenance issues when new versions of AEM or the component/template are released. You will need to manually update your Overlay files to stay up-to-date with any changes.
Sling Resource Merger
The Sling Resource Merger approach involves selectively merging specific resources (e.g., CSS files, scripts, properties, etc.) from the original component/template with the resources in your custom code. This approach is more flexible and efficient than the Overlay approach, but requires more careful management.
For example, if you want to modify the styles of the “title” component in AEM, you would create a new folder structure in /apps with a different name (e.g., /apps/myproject/components/title). You can then create a new CSS file in this folder with your custom styles.
To merge your custom styles with the original styles from the “title” component, you can add a “.content.xml” file to your folder with the following code:
<?xml version="1.0" encoding="UTF-8"?>
<jcr:root xmlns:sling="http://sling.apache.org/jcr/sling/1.0"
xmlns:jcr="http://www.jcp.org/jcr/1.0"
jcr:primaryType="sling:OrderedFolder"
sling:resourceSuperType="core/wcm/components/title/v2/title"
/>
This code sets the “sling:resourceSuperType” property to the path of the original “title” component. This tells AEM to merge any resources in your custom component with the corresponding resources in the original component.
Note that the Sling Resource Merger approach requires a more detailed understanding of the AEM component architecture and configuration. It is also more efficient than the Overlay approach since it only merges specific resources instead of copying entire component structures.
Both Overlay and Sling Resource Merger approaches have their own advantages and disadvantages, and the choice depends on the specific requirements and constraints of your project.
