RFR: 8315999: Improve Date toString performance [v9]

[Claes Redestad]

On Tue, 12 Sep 2023 13:10:42 GMT, 温绍锦 <duke at openjdk.org> wrote:

>> Of course, the optimization of DateTimeFormatter is more general, and we can spend time doing it later. The format of toString is fixed, we can not use DateTimeFormatter.
>
>> Have you considered potentially more generalizable optimizations to `DateTimeFormatter.ISO_INSTANT.format(this)` here?
>> 
>> Hand-rolling a fixed-length buffer, skipping the `StringBuilder` .. understandably this can have a performance edge, but perhaps a `DateTimeFormatter` like `ISO_INSTANT` can be optimized to get closer to whatever speed-up this gets you - with broader implications.
> 
> I submitted an optimization for the commonly used format of DateTimeFormatter::format

Do you have a link to that PR? Is there an RFE filed for it?

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PR Review Comment: https://git.openjdk.org/jdk/pull/15658#discussion_r1323705970