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import java.net.DatagramSocket;
import java.net.InetSocketAddress;
import java.net.SocketAddress;
import java.nio.ByteBuffer;
import java.nio.ByteOrder;
import java.nio.channels.DatagramChannel;
public class UDPTimeClient {
public static void main(String[] args) throws Exception {
DatagramChannel channel = DatagramChannel.open();
// port 0 selects any available port
SocketAddress address = new InetSocketAddress(0);
DatagramSocket socket = channel.socket();
socket.setSoTimeout(5000);
socket.bind(address);
SocketAddress server = new InetSocketAddress("time.nist.gov", 37);
ByteBuffer buffer = ByteBuffer.allocate(8192);
// time protocol always uses big-endian order
buffer.order(ByteOrder.BIG_ENDIAN);
// Must put at least one byte of data in the buffer;
// it doesn't matter what it is.
buffer.put((byte) 65);
buffer.flip();
channel.send(buffer, server);
buffer.clear();
buffer.put((byte) 0).put((byte) 0).put((byte) 0).put((byte) 0);
channel.receive(buffer);
buffer.flip();
long secondsSince1970 = buffer.getLong();
System.out.println(secondsSince1970);
channel.close();
}
}
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