how push notification (java/ servlet) for web application?

Question

In my application I have to show a notification on a particular action taken place ?

I have to show logged in user a notification then. .

1-One way to get no

Answer 1

Nowadays a promising way of client-server communication is to use Websockets.

See What are Long-Polling, Websockets, Server-Sent Events (SSE) and Comet to see some other ways together with the Websockets and for an advantages of Websockets with an introduction see An Introduction To WebSockets