This video shows you how to create a websocket server in java

Links:

https://www.javainuse.com/spring/boot-websocket

https://start.spring.io/

https://www.websocket.org/echo.html

Azure:
https://azure.microsoft.com/en-us/services/web-pubsub/
https://azure.microsoft.com/en-us/services/signalr-service/

AWS:
https://docs.aws.amazon.com/apigateway/latest/developerguide/apigateway-websocket-api.html