Java将毫秒时间戳转换为与给定时区相关的日期

Question

I have seen many resources on this but one thing I cant get is when converting the millisecond timestamp, how I add a corresponding time zone, during the conversion process.

Date date = new Date(Long.valueOf(dateInMil*1000L);
SimpleDateFormat myDate = new SimpleDateFormat("EEE, MMM d, ''yy");
String formatted = myDate.format(date);

Now if I have a time zone/offset in string formate ie "-04:00" or "+2:00" how to apply it to the above so I can get the proper date ?

Answer 1

tl;dr

Instant.ofEpochMilli( myCountOfMilliseconds ) 
       .atZone( ZoneId.of( "Africa/Tunis" ) )
       .toString()

java.time

The modern approach uses the java.time classes rather than the troublesome old Calendar / Date classes that are now legacy.

Assuming your count of milliseconds is a count since the epoch reference of first moment of 1970 in UTC (1970-01-01T00:00), then parse as a Instant .

The Instant class represents a moment on the timeline in UTC with a resolution of nanoseconds (up to nine (9) digits of a decimal fraction).

Instant instant = Instant.ofEpochMilli( myCountOfMilliseconds ) ;

To move from UTC to another time zone, apply a ZoneId to get a ZonedDateTime .

Specify a proper time zone name in the format of continent/region , such as America/Montreal , Africa/Casablanca , or Pacific/Auckland . Never use the 3-4 letter abbreviation such as EST or IST as they are not true time zones, not standardized, and not even unique(!).

ZoneId z = ZoneId.of( "Africa/Tunis" ) ;
ZonedDateTime zdt = instant.atZone( z ) ;

Objects vs text

After assigning the time zone, then generate a string in your desired format (not before). You may be conflating date-time values (objects) with strings representing their value textually. Learn to think of smart objects, not dumb strings.

DateTimeFormatter

To generate a String in a particular format, use a DateTimeFormatter . Search Stack Overflow as this been covered many many times, as have the other concepts shown here. Of special note are the DateTimeFormatter.ofLocalized… methods.

---

About java.time

The java.time framework is built into Java 8 and later. These classes supplant the troublesome old legacy date-time classes such as java.util.Date , Calendar , & SimpleDateFormat .

The Joda-Time project, now in maintenance mode , advises migration to the java.time classes.

To learn more, see the Oracle Tutorial . And search Stack Overflow for many examples and explanations. Specification is JSR 310 .

Where to obtain the java.time classes?

• Java SE 8 , Java SE 9 , and later
  • Built-in.
  • Part of the standard Java API with a bundled implementation.
  • Java 9 adds some minor features and fixes.
• Java SE 6 and Java SE 7
  • Much of the java.time functionality is back-ported to Java 6 & 7 in ThreeTen-Backport .
• Android
  • Later versions of Android bundle implementations of the java.time classes.
  • For earlier Android, the ThreeTenABP project adapts ThreeTen-Backport (mentioned above). See How to use ThreeTenABP… .

The ThreeTen-Extra project extends java.time with additional classes. This project is a proving ground for possible future additions to java.time. You may find some useful classes here such as Interval , YearWeek , YearQuarter , and more .

Answer 2

I was doing a similar thing in my previous project.You can use setTimeZone method of SimpleDateFormat class. Something like this :

mydate.setTimeZone(TimeZone.getTimeZone("GMT -0400"));

Answer 3

    DateTimeFormatter myDateFormatter
            = DateTimeFormatter.ofPattern("EEE, MMM d, ''yy", Locale.ENGLISH);
    long dateInSec = 1_554_321_098L;
    String utcOffsetString = "-04:00";
    ZoneOffset offset = ZoneOffset.of(utcOffsetString);
    String date = Instant.ofEpochSecond(dateInSec)
            .atOffset(offset)
            .format(myDateFormatter);
    System.out.println(date);

This prints

Wed, Apr 3, '19

The other example offset you gave, +2:00 , is slightly more difficult since ZoneOffset.of requires either only hours ( +2 ) or two-digit hours before the colon ( +02:00 ). One solution is to fix the string before handing it to ZoneOffset :

    String utcOffsetString = "+2:00";
    utcOffsetString = utcOffsetString.replaceFirst("([-+])(\\d:\\d{2})", "$10$2");
    ZoneOffset offset = ZoneOffset.of(utcOffsetString);

The result is still Wed, Apr 3, '19 . If there were already 2-digit hours in the string, replaceFirst won't replace anything, so you just get the same string back.

If I change the offset to +08:00 , I get Thu, Apr 4, '19 instead.

Edit: I frankly find the regular expression I use for fixing the offset string quite unreadable. Here's a simpler way of fixing it:

    DateTimeFormatter offsetFormatter = DateTimeFormatter.ofPattern("O", Locale.ENGLISH);
    ZoneOffset offset = ZoneOffset.from(offsetFormatter.parse("GMT" + utcOffsetString));

Like Basil Bourque I am using java.time . See all the details in his answer .

Answer 4

Not exactly what your looking for but close

String timeZone = "America/Los_Angeles"
TimeZone tz = TimeZone.getTimeZone(timeZone);
SimpleDateFormat sdf = new SimpleDateFormat("EEEEE MMMMM d hh:mm a");
sdf.setTimeZone(tz);

Date localizedTime = sdf.format(new Date());

If you keep the localization strings instead of the offsets this will work. Or you can make a map.