File	Doc	Category	Size	Date	Package
TimeService.java	API Doc	Example	8231	Mon May 20 00:24:28 BST 2002	com.ronsoft.books.nio.channels

TimeService

• java.lang.Object

Fields Summary
private static final int	DEFAULT_TIME_PORT
private static final long	DIFF_1900
protected DatagramChannel	channel
protected boolean	listening

Constructors Summary
public TimeService(int port) this.channel = DatagramChannel.open(); if (port != 0) { System.out.println ("Listening on port " + port + " for time requests"); channel.socket().bind (new InetSocketAddress (port)); listening = true; }

Methods Summary
public static long	currentTimeSecs() return (System.currentTimeMillis() / 1000); // secs/1970
public static java.lang.String	hostInfo(java.net.InetSocketAddress sa) return (sa.getHostName() + ":" + sa.getPort());
public static void	main(java.lang.String[] argv) if (argv.length == 0) { System.out.println ("Usage: [ -s | -l port ] [ -p port ] host ..."); return; } List hosts = new LinkedList(); int listenPort = 0; int port = DEFAULT_TIME_PORT; for (int i = 0; i < argv.length; i++) { String arg = argv [i]; // listen as a server, on the default port if (arg.equals ("-s")) { listenPort = DEFAULT_TIME_PORT; continue; } // listen as a server, on the given port if (arg.equals ("-l")) { i++; listenPort = Integer.parseInt (argv [i]); continue; } // send client requests to the given port if (arg.equals ("-p")) { i++; port = Integer.parseInt (argv [i]); continue; } // create an address object for the host name InetSocketAddress sa = new InetSocketAddress (arg, port); // validate that it has an address if (sa.getAddress() == null) { System.out.println ("Cannot resolve address: " + arg); continue; } hosts.add (sa); } TimeService timeService = newInstance (listenPort); // send time requests to all the supplied hosts Iterator it = hosts.iterator(); while (it.hasNext()) { InetSocketAddress sa = (InetSocketAddress) it.next(); System.out.println ("Requesting time from " + hostInfo (sa)); timeService.requestTime (sa); } System.out.println (""); System.out.println ("Waiting for replies..."); timeService.run (hosts.size());
public static com.ronsoft.books.nio.channels.TimeService	newInstance(int listenPort) return (new TimeService (listenPort));
protected void	printTime(long remote1900, java.net.InetSocketAddress sa) long remote = remote1900 - DIFF_1900; long local = currentTimeSecs(); Date remoteDate = new Date (remote * 1000); Date localDate = new Date (local * 1000); long skew = remote - local; System.out.println ("Reply from " + hostInfo (sa)); System.out.println (" there: " + remoteDate); System.out.println (" here: " + localDate); System.out.print (" skew: "); if (skew == 0) { System.out.println ("none"); } else { System.out.println (skew + " seconds " + ((skew < 0) ? "behind" : "ahead")); }
protected java.net.InetSocketAddress	receivePacket(java.nio.channels.DatagramChannel channel, java.nio.ByteBuffer buffer) buffer.clear(); // receive a 32-bit, big-endian, unsigned value return ((InetSocketAddress) channel.receive (buffer));
public void	requestTime(java.net.InetSocketAddress sa) ByteBuffer buffer = ByteBuffer.allocate (1); buffer.flip(); // make it empty, see RFC868 // fire and forget channel.send (buffer, sa);
public void	run(int expect) // allocate a buffer to hold a long value ByteBuffer longBuffer = ByteBuffer.allocate (8); // assure big-endian (network) byte order longBuffer.order (ByteOrder.BIG_ENDIAN); // zero the whole buffer to be sure longBuffer.putLong (0, 0); // position to first byte of the low-order 32 bits longBuffer.position (4); // slice the buffer, gives view of the low-order 32 bits ByteBuffer buffer = longBuffer.slice(); int replies = 0; while (true) { InetSocketAddress sa; sa = receivePacket (channel, buffer); if (sa == null) { // only get here if receivePacket timed out if (listening) { continue; } System.out.println ("Time's up, " + (expect - replies) + " replies never arrived"); break; } buffer.flip(); if (buffer.remaining() == 0) { // empty packet, someone requesting our time System.out.println ("Time request from " + hostInfo (sa)); serveTimeRequest (sa); } else { // reply to a time request we sent replies++; printTime (longBuffer.getLong (0), sa); } if (expect == 0) { // running as pure server, carry on continue; } if (replies == expect) { // all request were answered System.out.println ("All packets answered"); expect = 0; if ( ! listening) { break; } } else { // some haven't shown up yet System.out.println ("Received " + replies + " of " + expect + " replies"); } }
protected void	serveTimeRequest(java.net.InetSocketAddress sa) ByteBuffer buffer = ByteBuffer.allocate (8); buffer.clear(); buffer.putLong (0, currentTimeSecs() + DIFF_1900); buffer.position (4); // low-order 32-bit int this.channel.send (buffer, sa);