This week's book giveaway is in the OCAJP 8 forum. We're giving away four copies of OCA Java SE 8 Programmer I Study Guide and have Edward Finegan & Robert Liguori on-line! See this thread for details.
"Using the kill command", like, something built into your server protocol? Or "using the kill command" like, running the UNIX "kill" program? If it's the latter, then that's pretty much what you should expect -- "kill" isn't the right way to shut down a process cleanly. If you want a nice quiet way to turn your server off, provide another ServerSocket listening on a special port, and when that port receives a connection (or a connection followed by some special input sequence) then have the server exit.