Investigate requirement for reflective access to convert date/time values.

[christophstrobl]

The ElasticsearchDateConverter is making use of reflection to access the from method for eg. java.time.Instant. This requires additional configuration for GraalVM native image.
Currently we are adding the required configuration for java.time types via the general processing of Spring Data repositories, but it would be nice to get rid of that extra bit of reflection config if possible.

[sothawo]

We could create a list of all implementations of TemporalAccessor that have a static method from(Temporal) from the JDK and then replace that reflection code with something like

if(type instanceof LocalDate) {
  return LocalDate.from(template);
} else if (type instance of SomeOtherTemporalAccessor.class) {
  return SomeOtherTemporalAccessor.from(temporal);
} else ...

[sothawo]

I wrote a small program that gets all the relevant classes from the java.time package and that spits out the following code that could replace the existing one:

@SuppressWarnings("unchecked")
private static <T extends TemporalAccessor> TemporalQuery<T> getTemporalQuery(Class<T> type) {
	return temporal -> {
		if (type == java.time.chrono.HijrahDate.class) {
			return (T) java.time.chrono.HijrahDate.from(temporal);
		}
		if (type == java.time.chrono.JapaneseDate.class) {
			return (T) java.time.chrono.JapaneseDate.from(temporal);
		}
		if (type == java.time.ZonedDateTime.class) {
			return (T) java.time.ZonedDateTime.from(temporal);
		}
		if (type == java.time.LocalDateTime.class) {
			return (T) java.time.LocalDateTime.from(temporal);
		}
		if (type == java.time.chrono.ThaiBuddhistDate.class) {
			return (T) java.time.chrono.ThaiBuddhistDate.from(temporal);
		}
		if (type == java.time.LocalTime.class) {
			return (T) java.time.LocalTime.from(temporal);
		}
		if (type == java.time.ZoneOffset.class) {
			return (T) java.time.ZoneOffset.from(temporal);
		}
		if (type == java.time.OffsetTime.class) {
			return (T) java.time.OffsetTime.from(temporal);
		}
		if (type == java.time.chrono.ChronoLocalDate.class) {
			return (T) java.time.chrono.ChronoLocalDate.from(temporal);
		}
		if (type == java.time.Month.class) {
			return (T) java.time.Month.from(temporal);
		}
		if (type == java.time.chrono.ChronoLocalDateTime.class) {
			return (T) java.time.chrono.ChronoLocalDateTime.from(temporal);
		}
		if (type == java.time.MonthDay.class) {
			return (T) java.time.MonthDay.from(temporal);
		}
		if (type == java.time.Instant.class) {
			return (T) java.time.Instant.from(temporal);
		}
		if (type == java.time.OffsetDateTime.class) {
			return (T) java.time.OffsetDateTime.from(temporal);
		}
		if (type == java.time.chrono.ChronoZonedDateTime.class) {
			return (T) java.time.chrono.ChronoZonedDateTime.from(temporal);
		}
		if (type == java.time.chrono.MinguoDate.class) {
			return (T) java.time.chrono.MinguoDate.from(temporal);
		}
		if (type == java.time.Year.class) {
			return (T) java.time.Year.from(temporal);
		}
		if (type == java.time.DayOfWeek.class) {
			return (T) java.time.DayOfWeek.from(temporal);
		}
		if (type == java.time.LocalDate.class) {
			return (T) java.time.LocalDate.from(temporal);
		}
		if (type == java.time.YearMonth.class) {
			return (T) java.time.YearMonth.from(temporal);
		}
		throw new ConversionException("could not create object of class " + type.getName());
	};
}

Looks a little ugly, but should do. The only thing we'd loose is the ability to have a user have her own implementation of TemporalAccessor providing a from() method, but I guess this is a rather hypthetical problem.

[christophstrobl]

thanks @sothawo! You could leave the reflection variant in as a fallback. In that case users could still manually register a TypeHint for their implementation if needed.

[sothawo]

ok, though I think that will never happen ;-)