Try this:
https://github.com/tbroyer/gwt-maven-archetypes
https://stackoverflow.com/questions/13933957/remoteserviceservlet-with-filter-in-gwt
https://medium.com/@AlexeyBalchunas/make-any-java-web-app-serverless-786119ffdf83
Can I import sources and generate the necessary XML file to make it a GWT module? Gradle source dependencies could help