How to deny connection to a server in Java

How to deny connection to a server in Java

If this question is general, don't just down vote it please. Tell me how
to make it better, and bare with me, because I am fairly new to the site.
Ok, so here it goes:
How can I deny connecting to a server in Java.
I have made a chat client in Java. The server and client work, but I want
to implement kicking and banning.
Does this have to do with Sockets, ServerSockets, or something else.
Please help me!
Thanks.