RFR: 8276766: Enable jar and jmod to produce deterministic timestamped content [v4]

[John Neffenger]

On Thu, 25 Nov 2021 10:55:45 GMT, Andrew Leonard <aleonard at openjdk.org> wrote:

> Please consider providing a more general option, say `--date`, which takes an [ISO 8601 date/time string](https://docs.oracle.com/en/java/javase/17/docs/api/java.base/java/time/format/DateTimeFormatter.html#ISO_DATE_TIME).

The `jar` and `jmod` tools will need to truncate, restrict, or convert the time zone and fractional seconds permitted by the ISO 8601 date and time format.

The only way I found to store a timestamp using the methods of `java.util.zip.ZipEntry` that was independent of the system's time zone was by passing a local date and time in UTC to `setTimeLocal(LocalDateTime)`, truncated to seconds.

You can store a zoned date and time indirectly (in seconds) by adding an extra extended timestamp field to each entry with `setLastModifiedTime(FileTime)`. Unfortunately, that method also stores the "MS-DOS date and time" as the local date and time in the default time zone of the JVM (the time zone of the build machine). Furthermore, the extra field added to each entry increases the size of the archive.

The beauty of the `SOURCE_DATE_EPOCH` value is that it avoids any confusion in its interpretation while providing a straightforward solution to the only users ever known to need it.

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PR: https://git.openjdk.java.net/jdk/pull/6481