使用Java设置系统时间的毫秒数

Question

Would it be possible to set system time with milliseconds component on Windows OS using Java? I am trying to synchronize clocks between couple of computers but the OS API seems to offer only set time in format: HH:MM:SS .

This is what i tried:

public static void main(String[] args) throws InterruptedException, IOException {


    String time="10:00:20"; // this works

    String timeWithMiliseconds = "10:00:20.100"; // this doesn't change time at all

    Runtime rt = Runtime.getRuntime();
    rt.exec("cmd /C time " + time);


}

I am wondering how do NTP clients work if it's not possible to set milliseconds component ?

One way to deal with this issue could be to calculate time in milliseconds when server should reach next second, and sleep for that time. Is there a better, more direct way to achieve this ?

Answer 1

As mentioned by immibis you could use the Windows function SetSystemTime to set the time.

Find below a snippet which call the Windows function using JNA 4.2

Kernel32 kernel = Kernel32.INSTANCE;
WinBase.SYSTEMTIME newTime = new WinBase.SYSTEMTIME();
newTime.wYear = 2015; 
newTime.wMonth = 11;
newTime.wDay = 10;
newTime.wHour = 12;
newTime.wMinute = 0;
newTime.wSecond = 0;
newTime.wMilliseconds = 0;
kernel.SetSystemTime(newTime);

For further information have a look into the sources of JNA and on those links SetSystemTime Windows function and SYSTEMTIME structure .

An introduction to JNA from 2009. Simplify Native Code Access with JNA