Getting Date in HTTP format in Java

I'm trying to get a String of a date in Java in the format specified in HTTP 1.1. Which, as far as I can tell, is:

> Fri, 31 Dec 1999 23:59:59 GMT

With the time always being GMT.

What would be the easiest way to get this from Date/Calendar/?

java.time

EDIT:

DateTimeFormatter.ofPattern("EEE, dd MMM yyyy HH:mm:ss z", Locale.ENGLISH).withZone(ZoneId.of("GMT"))

is the way to do it with pure java.time. HTTP 1.1 is to not a 100% match with RFC 1123, so using the java.time.format.DateTimeFormatter.RFC_1123_DATE_TIME formatter will fail for day-of-month less than 10. (thanks to @PavanKamar and @ankon for pointing that out)

Note: to be backwards compliant, you would need to also support the other two formats specified by RFC 2616

In case someone else will try to find the answer here (like I did) here's what will do the trick:

String getServerTime() {
    Calendar calendar = Calendar.getInstance();
    SimpleDateFormat dateFormat = new SimpleDateFormat(
        "EEE, dd MMM yyyy HH:mm:ss z", Locale.US);
    dateFormat.setTimeZone(TimeZone.getTimeZone("GMT"));
    return dateFormat.format(calendar.getTime());
}

in order to set the server to speak English and give time in GMT timezone.

If you're using Joda-Time (which I would highly recommend for any handling of dates and times in Java), you can do:

import org.joda.time.DateTime;
import org.joda.time.format.DateTimeFormat;
import org.joda.time.format.DateTimeFormatter;

...

private static final DateTimeFormatter RFC1123_DATE_TIME_FORMATTER = 
    DateTimeFormat.forPattern("EEE, dd MMM yyyy HH:mm:ss 'GMT'")
    .withZoneUTC().withLocale(Locale.US);

...

RFC1123_DATE_TIME_FORMATTER.print(new DateTime())

Two-digit day-of-month

Some applications require the format to include a two digit day-of-month as per RFC7231. The Java 8 DateTimeFormatter.RFC_1123_DATE_TIME uses a single digit:

System.out.println(DateTimeFormatter.RFC_1123_DATE_TIME.format(ZonedDateTime.now(ZoneOffset.UTC)));

Output: Wed, 1 Aug 2018 14:56:46 GMT

Some applications don't like that. Before you use the old answers that use Joda-time or a pre-java8 SimpleDateFormat, here's a working Java-8 DateTimeFormatter:

DateTimeFormatter.ofPattern("EEE, dd MMM yyyy HH:mm:ss O")

Now, when you do this:

DateTimeFormatter formatter = DateTimeFormatter.ofPattern("EEE, dd MMM yyyy HH:mm:ss O");
System.out.println(formatter.format(ZonedDateTime.now(ZoneOffset.UTC)));

You get Wed, 01 Aug 2018 14:56:46 GMT - note the leading zero in the day-of-month field.

If you, like me, are trying to format a Java 8 java.time.Instant you need to explicitly add the time zone to the formatter. Like this:

Instant instant = Instant.now();
String formatted = DateTimeFormatter.RFC_1123_DATE_TIME
		.withZone(ZoneOffset.UTC)
		.format(instant);
System.out.println(formatted);

Which prints: > Tue, 15 Mar 2016 14:45:34 GMT

If you are not afraid of additional dependencies, you can use apache DateUtils:

import org.apache.http.impl.cookie.DateUtils;
DateUtils.formatDate(new Date(System.currentTimeMillis()));
// Tue, 17 Apr 2012 18:59:02 GMT

This will format your date with respect to RFC 822 RFC1123.

Calendar calendar = Calendar.getInstance();
SimpleDateFormat dateFormat = new SimpleDateFormat("EEE, dd MMM yyyy HH:mm:ss z");
System.out.println("Date: " + dateFormat.format(calendar.getTime()));

You can play with it. The documentation is here: http://download.oracle.com/javase/7/docs/api/java/text/SimpleDateFormat.html

I know this is a late response but just wanted to add it for completeness.

You did not mention what you need the string for. But if you need it for an HTTP response header, you can use HttpServletResponse.setDateHeader(). It does all the formatting for you.