How to assure reliable message delivery of websockets?

Question

I am developing a simple server whose primary task is to push notifications to users like a typical Push Notification Server. I have used java websockets

Answer 1

The websockets specification is really low level and does not provide a confirmation for send messages. You have to either implement this yourself as an application-level protocol or use an existing protocol on top of websockets.

Stomp is a popular protocol which defines an "ACK" reply for consumed messages: Stomp specification