Java SDK snippet to do also the Service Worker Integration

I´m looking for a Java SDK snippet to paste at the web site pages and serve also as the Service Worker Integration.
I want to connect a Progressive Web App to a Push notification service (WonderPush). But such PWA was developed under a CMS (Mobilverse). The Javascript code is publicly available at : https://docs.wonderpush.com/docs/service-worker-integration but I guess it is thought for files to be uploaded within the software code, and not to be pasted.