RFR: 8316235: Optimization for DateTimeFormatter::format

[ExE Boss]

On Wed, 13 Sep 2023 14:56:15 GMT, 温绍锦 <duke at openjdk.org> wrote:

> In many scenarios, DateTimeFormatter::format is a slower operation.  
> 
> For example, the following business scenarios
> 1. The json library gson/jackson/[fastjson2](https://github.com/alibaba/fastjson2) formats Instant/LocalDate/LocalTime/LocalDateTime/ZonedDateTim into strings.
> 2. In data integration scenarios, for projects like  [datax](https://github.com/alibaba/datax)/[canal](https://github.com/alibaba/canal), if the input type is Date/Instant and the output type is String, formatting is required.
> 
> This PR provides format performance optimization for commonly used date patterns.
> 
> ISO_INSTANT
> ISO_LOCAL_TIME
> ISO_LOCAL_DATE
> ISO_LOCAL_DATETIME
> HH:mm:ss
> HH:mm:ss.SSS
> yyyy-MM-dd
> yyyy-MM-dd HH:mm:ss
> yyyy-MM-dd'T'HH:mm:ss
> yyyy-MM-dd HH:mm:ss.SSS
> yyyy-MM-dd'T'HH:mm:ss.SSS

src/java.base/share/classes/java/time/format/DateTimeFormatterBuilder.java line 2594:

> 2592:             } else {
> 2593:                 return super.format(context, buf);
> 2594:             }

This can use `instanceof <pattern>`:
Suggestion:

            if (temporal instanceof LocalDateTime ldt) {
                date = ldt.toLocalDate();
            } else if (temporal instanceof LocalDate ld) {
                date = ld;
            } else if (temporal instanceof ZonedDateTime zdt) {
                date = zdt.toLocalDate();
            } else if (temporal instanceof OffsetDateTime odt) {
                date = odt.toLocalDate();
            } else {
                return super.format(context, buf);
            }


Or even a pattern switch:
Suggestion:

            switch (temporal) {
                case LocalDateTime ldt -> date = ldt.toLocalDate();
                case LocalDate ld -> date = ld;
                case ZonedDateTime zdt -> date = zdt.toLocalDate();
                case OffsetDateTime odt -> date = odt.toLocalDate();
                default -> {
                    return super.format(context, buf);
                }
            }

src/java.base/share/classes/java/time/format/DateTimeFormatterBuilder.java line 2661:

> 2659:             } else {
> 2660:                 return super.format(context, buf);
> 2661:             }

This can use `instanceof <pattern>`:
Suggestion:

            if (temporal instanceof LocalTime lt) {
                time = lt;
            } else if (temporal instanceof LocalDateTime ldt) {
                time = ldt.toLocalTime();
            } else if (temporal instanceof ZonedDateTime zdt) {
                time = zdt.toLocalTime();
            } else if (temporal instanceof OffsetDateTime odt) {
                time = odt.toLocalTime();
            } else if (temporal instanceof OffsetTime ot) {
                time = ot.toLocalTime();
            } else {
                return super.format(context, buf);
            }


Or even a pattern switch:
Suggestion:

            switch (temporal) {
                case LocalTime lt -> time = lt;
                case LocalDateTime ldt -> time = ldt.toLocalTime();
                case ZonedDateTime zdt -> time = zdt.toLocalTime();
                case OffsetDateTime odt -> time = odt.toLocalTime();
                case OffsetTime ot -> time = ot.toLocalTime();
                default -> {
                    return super.format(context, buf);
                }
            }

src/java.base/share/classes/java/time/format/DateTimeFormatterBuilder.java line 2683:

> 2681:      * Composite printer and parser.
> 2682:      */
> 2683:     static class CompositePrinterParser implements DateTimePrinterParser {

This class can be `sealed`:
Suggestion:

    static sealed class CompositePrinterParser implements DateTimePrinterParser {

-------------

PR Review Comment: https://git.openjdk.org/jdk/pull/15722#discussion_r1324933754
PR Review Comment: https://git.openjdk.org/jdk/pull/15722#discussion_r1324937172
PR Review Comment: https://git.openjdk.org/jdk/pull/15722#discussion_r1324941838