Determine the internet time of another country in Java

问题

I am developing a Java application that will be used by people from around the world. One feature requires it to display the current time in Melbourne, Australia.

I have found this answer and adapted the code as follows, but it returns my current time (as expected). It uses the Apache Commons Net library:

    try {
        String TIME_SERVER = "time-a.nist.gov";   
        NTPUDPClient timeClient = new NTPUDPClient();
        InetAddress inetAddress = InetAddress.getByName(TIME_SERVER);
        TimeInfo timeInfo = timeClient.getTime(inetAddress);
        long returnTime = timeInfo.getMessage().getTransmitTimeStamp().getTime();
        return new Date(returnTime);
    } catch (Exception e) {
        System.out.println(e.getMessage());
        return null;
    }

How can I modify this code to return the time in Melbourne, rather than my time? I am open to other solutions to solve this problem as well.

Thank you!

EDIT:

Taking Jon's advice, I have used the JodaTime library and built the following code to solve the problem. It can be used for other time zones by changing Australia/Melbourne to any timezone found here.

    try {
        //Get the time for the current time zone.
        String TIME_SERVER = "time-a.nist.gov";   
        NTPUDPClient timeClient = new NTPUDPClient();
        InetAddress inetAddress = InetAddress.getByName(TIME_SERVER);
        TimeInfo timeInfo = timeClient.getTime(inetAddress);
        long returnTime = timeInfo.getMessage().getTransmitTimeStamp().getTime();

        //Format it to the Melbourne TimeZone.
        DateTimeZone tzMelbourne = DateTimeZone.forID("Australia/Melbourne");
        return new DateTime(returnTime).toDateTime(tzMelbourne);
    } catch (Exception e) {
        System.out.println(e.getMessage());
        return null;
    }

回答1:

You're currently returning a java.util.Date - that doesn't have a time zone. It's just an instant in time. It's not in your time zone, or some other time zone - it's just an instant. When you call toString(), that will give you a textual representation in your local time zone, but that's not part of the data in the object.

If you need to represent "a date/time in a particular time zone" then you should use the Calendar class, or ideally use Joda Time which is a much better date/time API.

Alternatively, if you're just trying to format the date/time in a particular time zone, you can use SimpleDateFormat - set the time zone, and then format the Date value you're already returning.

回答2:

Instead of looking up from an NTP server, you can use java.util.TimeZoneto get time of a specific place in the world.(It also knows about day-light savings) Your timezone ID is 'Australia/Melbourne'.

TimeZone australiaMelbourneTimeZone = TimeZone.getTimeZone("Australia/Melbourne");

Calendar dateTime = Calendar.getInstance(tz);

//Use this Calendar instance to print time

Not: I have found the Timezone ID Australia/Melbourne by dumping all avaliable time zone IDs supported by the java.util.TimeZone as follows:

   for(String timeZoneID: TimeZone.getAvailableIDs()) {
            System.out.println(timeZoneID);
   }

The output included 'Australia/Melbourne' as follows:

... Australia/Brisbane Australia/Canberra Australia/Currie Australia/Hobart Australia/Lindeman Australia/Melbourne Australia/NSW Australia/Queensland Australia/Sydney Australia/Tasmania

回答3:

Check this. You can get a calendar instance and change its timezone.

来源：https://stackoverflow.com/questions/20743368/determine-the-internet-time-of-another-country-in-java