In this example, the movie titles that appear in the drop-down control are returned by an AEM Sling Servlet. This article walks you through how to create an AEM component that uses Sling Servlets to populate fields that appear in component dialogs. By hooking into a Sling Servlet, you can dynamically populate dialog fields. For example, you can code the Servlet to call an external web service, and populate a dialog field with the data returned by the external service.
To read this development article, click https://helpx.adobe.com/experience-manager/using/dialog_fields_servlets.html.