programming-examples/java/Basics/TimeQuery.java

TimeQuery



import java.io.*;
import java.net.*;
import java.nio.*;
import java.nio.channels.*;
import java.nio.charset.*;
import java.util.regex.*;


public class TimeQuery {

    // The standard daytime port
    private static int DAYTIME_PORT = 13;

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

    // Charset and decoder for US-ASCII
    private static Charset charset = Charset.forName("US-ASCII");
    private static CharsetDecoder decoder = charset.newDecoder();

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

    // Ask the given host what time it is
    //
    private static void query(String host) throws IOException {
    InetSocketAddress isa
        = new InetSocketAddress(InetAddress.getByName(host), port);
    SocketChannel sc = null;

    try {

        // Connect
        sc = SocketChannel.open();
        sc.connect(isa);

        // Read the time from the remote host.  For simplicity we assume
        // that the time comes back to us in a single packet, so that we
        // only need to read once.
        dbuf.clear();
        sc.read(dbuf);

        // Print the remote address and the received time
        dbuf.flip();
        CharBuffer cb = decoder.decode(dbuf);
        System.out.print(isa + " : " + cb);

    } finally {
        // Make sure we close the channel (and hence the socket)
        if (sc != null)
        sc.close();
    }
    }

    public static void main(String[] args) {
    if (args.length < 1) {
        System.err.println("Usage: java TimeQuery [port] host...");
        return;
    }
    int firstArg = 0;

    // If the first argument is a string of digits then we take that
    // to be the port number
    if (Pattern.matches("[0-9]+", args[0])) {
        port = Integer.parseInt(args[0]);
        firstArg = 1;
    }

    for (int i = firstArg; i < args.length; i++) {
        String host = args[i];
        try {
        query(host);
        } catch (IOException x) {
        System.err.println(host + ": " + x);
        }
    }
    }

}