Getting Date in HTTP format in Java

问题:

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/?

回答1:

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.

回答2:

java.time

If you're using Java 8 and later you can the predefined formatter for RFC 1123, DateTimeFormatter.RFC_1123_DATE_TIME.

java.time.format.DateTimeFormatter.RFC_1123_DATE_TIME.format(ZonedDateTime.now(ZoneOffset.UTC))

回答3:

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())

回答4:

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.

回答5:

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

回答6:

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

回答7:

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.

回答8:

Two-digit day-of-month

Some applications require the RFC1123 format to include a two digit day-of-month. 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.