java设置服务器NTP同步

要在Java程序中设置服务器NTP同步，可以使用以下代码：

import java.net.*;
import java.util.*;
import java.text.*;

public class NtpTime {
    private static final int NTP_PACKET_SIZE = 48;
    private static final int NTP_PORT = 123;
    private static final int TIMEOUT = 10000;

    public static void main(String[] args) throws Exception {
        String ntpServer = "ntp.example.com";
        Date ntpTime = getNtpTime(ntpServer);
        System.out.println("NTP time: " + ntpTime);
        setSystemTime(ntpTime);
    }

    public static Date getNtpTime(String ntpServer) throws Exception {
        DatagramSocket socket = new DatagramSocket();
        socket.setSoTimeout(TIMEOUT);
        InetAddress address = InetAddress.getByName(ntpServer);
        byte[] buf = new byte[NTP_PACKET_SIZE];
        buf[0] = (byte) 0x1B;
        DatagramPacket packet = new DatagramPacket(buf, buf.length, address, NTP_PORT);
        socket.send(packet);
        packet = new DatagramPacket(buf, buf.length);
        socket.receive(packet);
        socket.close();
        long seconds = getUnsignedInt(buf, 40);
        long fraction = getUnsignedInt(buf, 44);
        long ms = (seconds - 2208988800L) * 1000 + fraction * 1000 / 0x100000000L;
        return new Date(ms);
    }

    private static long getUnsignedInt(byte[] buf, int offset) {
        long n = 0;
        for (int i = offset; i < offset + 4; i++) {
            n = n << 8 | (buf[i] & 0xFF);
        }
        return n;
    }

    public static void setSystemTime(Date ntpTime) throws Exception {
        SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
        String command = "date " + sdf.format(ntpTime);
        Runtime.getRuntime().exec(command);
    }
}

该代码首先通过`getNtpTime`方法从指定的NTP服务器获取时间，然后通过`setSystemTime`方法设置系统时间。请注意，设置系统时间需要在管理员权限下运行程序。

以上是Java设置服务器NTP同步的基本方法，您可以根据实际情况进行调整和优化。