RFR JDK-8075526: Need a way to read and write time in UTC

[Xueming Shen]

Hi,

Please help review and comment on this rfe.

Issue: https://bugs.openjdk.java.net/browse/JDK-8075526
webrev: http://cr.openjdk.java.net/~sherman/8075526

Background info:

The title of the RFE is a little "mis-leading". All the existing set/get date-time
methods actually work with "UTC" time. Both the old pair

public void setTime(long time);
public long getTime();

and the newly introduced pair

pubic ZipEntry set/getLastModifiedTime(FileTime time);
public FileTime getLastModifiedTime();

are to set/get the last modified time in UTC time. However the ZIP specification
clearly specifies that the "normal" date and time fields in the zip file entry (loc and
cen) are defined as the date/time in dos format, which unfortunately is a "local"
date-time. Therefor timezone conversion must be applied before/after the utc time
can be set into/got from those fields (the UTC timestamps set/get by the new pair
are therefor being set into/got from the "extended timestamp fields" of the optional
extra data of each entry, those fields are specified as unix/utc timestamp)

We did not have an "local-date-time" abstract before the java.time.LocalDateTime
was introduced in jdk8, the epoc date/time is the only date/time abstract in java
vm.

The proposed change here is to add yet another pair of set/get modified time methods

public void setTimeLocale(LocalDateTime time);
public LocalDateTime getTimeLocal();

to use the java.time.LocalDateTime type to set/get the modified time into zip entry's
dos timestamp fields directly WITHOUT involving the timezone conversion (implied, with
default TimeZone).

Other than solving the pack/unpack problem raised in this RFE, it should also help improve
the performance when local-date-time is actually desired when interfacing with the ZipEntry
by eliminating the un-necessary/implied timezone conversion. For example, in our jar tool,
currently we are "printing" the timestamp for zip entry "e" as

     new Date(e.getTime()).toString();

in which we are converting the local-date-time (ms-dos-formatted in zip entry) to utc time
by using the default timezone (in ZipEntry), and then converting the utc time (in Date) back
to the printable "local date time" again.

It might be desired to format the "local-date-time" directly without involving the timezone
conversion now via the proposed method

java.time.format.DateTimeFormatter.ofPattern("EEE MMM dd HH:mm:ss zzz yyyy")
                                                        .withZone(java.time.ZoneId.systemDefault());
                                                        .format(e.getTimeLocal()

In above example, we still use the "system default timezone", however, it is used
purely to output the zone name for the "zzz" (which the Date.toString() does), not for conversion.
if the "zzz" is not required/needed, it can just be

java.time.format.DateTimeFormatter.ofPattern("EEE MMM dd HH:mm:ss yyyy").format(e.getTimeLocal());

Comment/Opinion please. If we agree the approach/webrev, I will submit the CCC before integration.

Thanks,
-Sherman