Time Server NIO Example

This example listens for connections and tells callers what time it is. Is a simple, blocking program that demonstrates NIO socket channels (accepting and writing), buffer handling, charsets, and regular expressions.

public class TimeServer {

    // We can't use the normal daytime port (unless we're running as root,
    // which is unlikely), so we use this one instead
    private static int PORT = 8013;

    // The port we'll actually use
    private static int port = PORT;

    // Charset and encoder for US-ASCII
    private static Charset charset = Charset.forName("US-ASCII");
    private static CharsetEncoder encoder = charset.newEncoder();

    // Direct byte buffer for writing
    private static ByteBuffer dbuf = ByteBuffer.allocateDirect(1024);

    // Open and bind the server-socket channel

    private static ServerSocketChannel setup() throws IOException {
        ServerSocketChannel ssc = ServerSocketChannel.open();
        InetSocketAddress isa = new InetSocketAddress(
            InetAddress.getLocalHost(), port);
        ssc.socket().bind(isa);
        return ssc;
    }

    // Service the next request to come in on the given channel

    private static void serve(ServerSocketChannel ssc) throws IOException {
        try (SocketChannel sc = ssc.accept()) { 
            String now = new Date().toString();
            System.out.println("now: " + now);
            sc.write(encoder.encode(CharBuffer.wrap(now + "\r\n")));
            System.out.println(sc.socket().getInetAddress() + " : " + now);
        }
    }

    public static void main(String[] args) {
        if (args.length > 1) {
            System.err.println("Usage: java TimeServer [port]");
            return;
        }

        // If the first argument is a string of digits then we take that
        // to be the port number
        if ((args.length == 1) && Pattern.matches("[0-9]+", args[0]))
            port = Integer.parseInt(args[0]);
        
        try {
            ServerSocketChannel ssc = setup();
            for (;;) {
                serve(ssc);
            }
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}