如何使用时区偏移量将日期转换为时间？

Question

How can I print a Date into format HH:mm+-GMT using SimpleDateFormat ?

"EEE, d MMM yyyy HH:mm:ss Z"    Wed, 4 Jul 2001 12:08:56 -0700
"yyMMddHHmmssZ"                 010704120856-0700

How could I just print: 13:01-7 for the above example? So, the timezone offset to be represented with the shortest possible value?

Answer 1

If you are on Java 7, you could use the X flag to get the timezone.

Java 7 SimpleDateFormat javadoc:

X Time zone ISO 8601 time zone -08; -0800; -08:00

Answer 2

Try below:

import java.util.Date;
import java.text.SimpleDateFormat;

class array05{
  public static void main(String[] args){
      SimpleDateFormat sf = new SimpleDateFormat("EEE, d MMM yyyy HH:mm:ss Z");
      System.out.println(sf.format(new Date()));
  }
}

For me it have been printing Вт, 12 ноя 2013 14:22:24 +0200

Answer 3

Understanding how computer time is works is very important. With that said I agree that if an API is created to help you process computer time like real time then it should work in such a way that allows you to treat it like real time. For the most part this is the case but there are some major oversights which do need attention.

Anyway I digress!! If you have your UTC offset (better to work in UTC than GMT offsets) you can calculate the time in milliseconds and add that to your timestamp. Note that an SQL Timestamp may vary from a Java timestamp as the way the elapse from the epoch is calculated is not always the same - dependant on database technologies and also operating systems.

I would advise you to use System.currentTimeMillis() as your time stamps as these can be processed more consistently in java without worrying about converting SQL Timestamps to java Date objects etc.

To calculate your offset you can try something like this:

Long gmtTime =1317951113613L; // 2.32pm NZDT
Long timezoneAlteredTime = 0L;

if (offset != 0L) {
    int multiplier = (offset*60)*(60*1000);
    timezoneAlteredTime = gmtTime + multiplier;
} else {
    timezoneAlteredTime = gmtTime;
}

Calendar calendar = new GregorianCalendar();
calendar.setTimeInMillis(timezoneAlteredTime);

DateFormat formatter = new SimpleDateFormat("dd MMM yyyy HH:mm:ss z");

formatter.setCalendar(calendar);
formatter.setTimeZone(TimeZone.getTimeZone(timeZone));

String newZealandTime = formatter.format(calendar.getTime());

I hope this is helpful!

Answer 4

Try this, the shortest possible as you quoted in question,

long millis = new Date().getTime();
System.out.println(SimpleDateFormat.getTimeInstance(SimpleDateFormat.SHORT).format(millis));