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
You can use WebSockets for this purpose. There are multiple implementations available like jwebsocket.
Take a look at the Comet model and Servlet 3.0 specification.
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
You can try Servlet3.0 Async functionality.
Here is an Chat example which does push : Servlet 3.0 Async Example