带ZoneOffset的时间戳格式

Question

I want to print now() with different time offsets based on UTC:

offset=ZoneOffset.ofHours(-1);
zoneId=ZoneId.ofOffset("UTC", offset);
timeStampformater=DateTimeFormatter.ofPattern("yyyy.MM.dd.hh.mm.ss").withZone(zoneId);
System.out.println(LocalDateTime.now().format(timeStampformater));

offset=ZoneOffset.ofHours(0);
zoneId=ZoneId.ofOffset("UTC", offset);
timeStampformater=DateTimeFormatter.ofPattern("yyyy.MM.dd.hh.mm.ss").withZone(zoneId);
System.out.println(LocalDateTime.now().format(timeStampformater));

offset=ZoneOffset.ofHours(1);
zoneId=ZoneId.ofOffset("UTC", offset);
timeStampformater=DateTimeFormatter.ofPattern("yyyy.MM.dd.hh.mm.ss").withZone(zoneId);
System.out.println(LocalDateTime.now().format(timeStampformater));

However it always prints the same local time:

2015.12.15.09.56.00  -> should be 7:56
2015.12.15.09.56.00  -> should be 8:56
2015.12.15.09.56.00  -> OK because it is the local time.

Answer 1

The method DateTimeFormatter.withZone does not change the date/time. Internally, the formatter sets the timezone to the date/time to format and then formats it. Quoting its Javadoc:

In all other cases, the override zone is added to the temporal, replacing any previous zone, but without changing the date/time.

LocalDateTime.now() always returns the current date/time in your default timezone. Setting a timezone with a specific ZoneId or ZoneOffset (using atZone to create a ZonedDateTime ), you get the same date/time but in a different time zone (so it is a different instant in time).

Instead, you should construct the LocalDateTime by specifying the ZoneId or ZoneOffset using LocalDateTime.now(ZoneId) :

offset = ZoneOffset.ofHours(-1);
zoneId = ZoneId.ofOffset("UTC", offset);
timeStampformater = DateTimeFormatter.ofPattern("yyyy.MM.dd.hh.mm.ss");
System.out.println(LocalDateTime.now(zoneId).format(timeStampformater));

offset = ZoneOffset.ofHours(0);
zoneId = ZoneId.ofOffset("UTC", offset);
timeStampformater = DateTimeFormatter.ofPattern("yyyy.MM.dd.hh.mm.ss");
System.out.println(LocalDateTime.now(zoneId).format(timeStampformater));

offset = ZoneOffset.ofHours(1);
zoneId = ZoneId.ofOffset("UTC", offset);
timeStampformater = DateTimeFormatter.ofPattern("yyyy.MM.dd.hh.mm.ss");
System.out.println(LocalDateTime.now(zoneId).format(timeStampformater));

Note that you could simply your code by not using the ZoneId variable.

offset = ZoneOffset.ofHours(-1);
timeStampformater = DateTimeFormatter.ofPattern("yyyy.MM.dd.hh.mm.ss");
System.out.println(LocalDateTime.now(offset).format(timeStampformater));

Answer 2

You don't need the intermediate ZoneId object - and if you are interested in offset times, you could use an OffsetDateTime directly and apply an offset to that instead of applying an offset to the formatter (the rules for the application of the offset by the formatter are somewhat convoluted).

Something like:

DateTimeFormatter timeStampformater = DateTimeFormatter.ofPattern("yyyy.MM.dd.hh.mm.ss");

ZoneOffset offset = ZoneOffset.ofHours(-1);
System.out.println(OffsetDateTime.now(offset).format(timeStampformater));