If you don't want blocking I/O, you can't use readLine at all.  You need
to use a SocketChannel and a CharBuffer to do the I/O.  The code looks
considerably different, and will be tougher to understand... but in
conjunction with intelligent use of java.nio.Selector, it's potentially
the most efficient way to do things.

Another way out of the problems of blocking I/O is to continue to use
blocking I/O, but also use multiple threads.  You can spawn a new thread
to read from each possible client of the socket.  This is clearly not
scalable to very high numbers of concurrent connections, but it's a heck
of a lot easier than the NIO way.