NTPClientpublic final class NTPClient extends Object | This is an example program demonstrating how to use the NTPUDPClient
class. This program sends a Datagram client request packet to a
Network time Protocol (NTP) service port on a specified server,
retrieves the time, and prints it to standard output along with
the fields from the NTP message header (e.g. stratum level, reference id,
poll interval, root delay, mode, ...)
See the spec
for details.
Usage: NTPClient
Example: NTPClient clock.psu.edu |
| Fields Summary |
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| private static final NumberFormat | numberFormat |
| Methods Summary |
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| public static final void | main(java.lang.String[] args)
if (args == null || args.length == 0) {
System.err.println("Usage: NTPClient <hostname-or-address-list>");
System.exit(1);
}
NTPUDPClient client = new NTPUDPClient();
// We want to timeout if a response takes longer than 10 seconds
client.setDefaultTimeout(10000);
try {
client.open(NtpV3Packet.NTP_PORT);
for (int i = 0; i < args.length; i++)
{
System.out.println();
try {
InetAddress hostAddr = InetAddress.getByName(args[i]);
System.out.println("> " + hostAddr.getHostName() + "/" + hostAddr.getHostAddress());
TimeInfo info = client.getTime(hostAddr);
processResponse(info);
} catch (IOException ioe) {
ioe.printStackTrace();
}
}
} catch (SocketException e) {
e.printStackTrace();
}
client.close();
| | public static void | processResponse(TimeInfo info)Process TimeInfo object and print its details.
NtpV3Packet message = info.getMessage();
int stratum = message.getStratum();
String refType;
if (stratum <= 0)
refType = "(Unspecified or Unavailable)";
else if (stratum == 1)
refType = "(Primary Reference; e.g., GPS)"; // GPS, radio clock, etc.
else
refType = "(Secondary Reference; e.g. via NTP or SNTP)";
// stratum should be 0..15...
System.out.println(" Stratum: " + stratum + " " + refType);
int version = message.getVersion();
int li = message.getLeapIndicator();
System.out.println(" leap=" + li + ", version="
+ version + ", precision=" + message.getPrecision());
System.out.println(" mode: " + message.getModeName() + " (" + message.getMode() + ")");
int poll = message.getPoll();
// poll value typically btwn MINPOLL (4) and MAXPOLL (14)
System.out.println(" poll: " + (poll <= 0 ? 1 : (int) Math.pow(2, poll))
+ " seconds" + " (2 ** " + poll + ")");
double disp = message.getRootDispersionInMillisDouble();
System.out.println(" rootdelay=" + numberFormat.format(message.getRootDelayInMillisDouble())
+ ", rootdispersion(ms): " + numberFormat.format(disp));
int refId = message.getReferenceId();
String refAddr = NtpUtils.getHostAddress(refId);
String refName = null;
if (refId != 0) {
if (refAddr.equals("127.127.1.0")) {
refName = "LOCAL"; // This is the ref address for the Local Clock
} else if (stratum >= 2) {
// If reference id has 127.127 prefix then it uses its own reference clock
// defined in the form 127.127.clock-type.unit-num (e.g. 127.127.8.0 mode 5
// for GENERIC DCF77 AM; see refclock.htm from the NTP software distribution.
if (!refAddr.startsWith("127.127")) {
try {
InetAddress addr = InetAddress.getByName(refAddr);
String name = addr.getHostName();
if (name != null && !name.equals(refAddr))
refName = name;
} catch (UnknownHostException e) {
// some stratum-2 servers sync to ref clock device but fudge stratum level higher... (e.g. 2)
// ref not valid host maybe it's a reference clock name?
// otherwise just show the ref IP address.
refName = NtpUtils.getReferenceClock(message);
}
}
} else if (version >= 3 && (stratum == 0 || stratum == 1)) {
refName = NtpUtils.getReferenceClock(message);
// refname usually have at least 3 characters (e.g. GPS, WWV, LCL, etc.)
}
// otherwise give up on naming the beast...
}
if (refName != null && refName.length() > 1)
refAddr += " (" + refName + ")";
System.out.println(" Reference Identifier:\t" + refAddr);
TimeStamp refNtpTime = message.getReferenceTimeStamp();
System.out.println(" Reference Timestamp:\t" + refNtpTime + " " + refNtpTime.toDateString());
// Originate Time is time request sent by client (t1)
TimeStamp origNtpTime = message.getOriginateTimeStamp();
System.out.println(" Originate Timestamp:\t" + origNtpTime + " " + origNtpTime.toDateString());
long destTime = info.getReturnTime();
// Receive Time is time request received by server (t2)
TimeStamp rcvNtpTime = message.getReceiveTimeStamp();
System.out.println(" Receive Timestamp:\t" + rcvNtpTime + " " + rcvNtpTime.toDateString());
// Transmit time is time reply sent by server (t3)
TimeStamp xmitNtpTime = message.getTransmitTimeStamp();
System.out.println(" Transmit Timestamp:\t" + xmitNtpTime + " " + xmitNtpTime.toDateString());
// Destination time is time reply received by client (t4)
TimeStamp destNtpTime = TimeStamp.getNtpTime(destTime);
System.out.println(" Destination Timestamp:\t" + destNtpTime + " " + destNtpTime.toDateString());
info.computeDetails(); // compute offset/delay if not already done
Long offsetValue = info.getOffset();
Long delayValue = info.getDelay();
String delay = (delayValue == null) ? "N/A" : delayValue.toString();
String offset = (offsetValue == null) ? "N/A" : offsetValue.toString();
System.out.println(" Roundtrip delay(ms)=" + delay
+ ", clock offset(ms)=" + offset); // offset in ms
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