Can you suggest me a good java based chat server?

Like real Java (the compiled kind) or a ajax one that uses javascript? Big difference.

If it the second look at this

Most use PHP and MySQL. You need to at least be able to make a database.

This took about four seconds. example

It is three files.

http://www.linuxuser.at/chat/ajax_chat.zip

quick google search lead me to: http://www.tigase.org/

looking for real java not javascript

The java requirement may be a little tricky. Most chat servers (irc or other) that I know of offhand are either C or C++.

See:
http://en.wikipedia.org/wiki/List_of_XMPP_server_software
http://en.wikipedia.org/wiki/Comparison_of_IRC_daemons

although, looks like openfire might also be an option.

You might want to check out theserverside.com and ask ths question.