Your Plug-in file should be generated at the “target” folder under the Astah Plug-in project as “[artifactId] - [version].jar”. Copy this file to “plugins” folder under Astah Install folder and then launch Astah, and go to [Help] - [Plugin List].
If you see your new Plug-in in the list, congratulations! That means your Plug-in has been installed successfully in Astah.