<i18n dev> RFR: 8276220: Reduce excessive allocations in DateTimeFormatter [v7]

[Naoto Sato]

On Wed, 3 Nov 2021 17:23:51 GMT, Claes Redestad <redestad at openjdk.org> wrote:

>> Prompted by a request from Volkan Yazıcı I took a look at why the java.time formatters are less efficient for some common patterns than custom formatters in apache-commons and log4j. This patch reduces the gap, without having looked at the third party implementations. 
>> 
>> When printing times:
>> - Avoid turning integral values into `String`s before appending them to the buffer 
>> - Specialize `appendFraction` for `NANO_OF_SECOND` to avoid use of `BigDecimal`
>> 
>> This means a speed-up and reduction in allocations when formatting almost any date or time pattern, and especially so when including sub-second parts (`S-SSSSSSSSS`).
>> 
>> Much of the remaining overhead can be traced to the need to create a `DateTimePrintContext` and adjusting `Instant`s into a `ZonedDateTime` internally. We could likely also win performance by specializing some common patterns.
>> 
>> Testing: tier1-3
>
> Claes Redestad has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Minor cleanup

test/jdk/java/time/test/java/time/format/TestFractionPrinterParser.java line 80:

> 78: 
> 79: /**
> 80:  * Test FractionPrinterParser.

OK, then I'd add some comments that the test covers `NanoPrinterParser` as well.

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PR: https://git.openjdk.java.net/jdk/pull/6188