format as GMT/UTC time when default timezone is something else

I have a program which needs to run under my loca开发者_JAVA技巧l timezone for other reasons, but for one procedure i need to output dates using a SimpleDateFormat in GMT.

what is the tidiest way to do this?

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Using the standard API:

Instant now = Instant.now();
String result = DateTimeFormatter.ofLocalizedDateTime(FormatStyle.LONG)
                                 .withZone(ZoneId.of("GMT"))
                                 .format(now);
System.out.println(result);

The new DateTimeFormatter instances are immutable and can be used as static variables.

Using the old standard API:

TimeZone gmt = TimeZone.getTimeZone("GMT");
DateFormat formatter = DateFormat.getTimeInstance(DateFormat.LONG);
formatter.setTimeZone(gmt);
System.out.println(formatter.format(new Date()));

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Given that SimpleDateFormat isn't thread-safe, I'd say that the tidiest way is to use Joda Time instead. Then you can create a single formatter (calling withZone(DateTimeZones.UTC) to specify that you want UTC) and you're away:

private static DateTimeFormatter formatter = DateTimeFormat.forPattern(...)
    .withZone(DateTimeZone.UTC);

...

String result = formatter.print(instant);

This has the other benefit that you can use Joda Time elsewhere in your code, which is always a good thing :)