RFR: 8315999: Improve Date toString performance [v13]

[Roger Riggs]

On Wed, 13 Sep 2023 14:22:35 GMT, 温绍锦 <duke at openjdk.org> wrote:

>> improve date toString performance, includes:
>> 
>> java.util.Date.toString
>> java.util.Date.toGMTString
>> java.time.Instant.toString
>> java.time.LocalDate.toString
>> java.time.LocalDateTime.toString
>> java.time.LocalTime.toString
>
> 温绍锦 has updated the pull request incrementally with one additional commit since the last revision:
> 
>   simplify LocalDate::getChars

Lots of adhoc changes bulk up the source and make it less maintainable.
Given the common element of time and date formatting strings as a domain specific language, there would be more benefit to leveraging one of several existing mechanisms to generate optimized formatters from application or library format strings.
For example, the general purpose [JEP 430: String Template](https://openjdk.org/jeps/430)s could be used to compose the string and leverage its optimizations of formatting the components.
Making improvements there either to performance or functionality would benefit more applications.

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PR Comment: https://git.openjdk.org/jdk/pull/15658#issuecomment-1726038572