Consider introducing Printer/Parser specializations of Formatter [SPR-6272]

[spring-projects-issues]

Keith Donald opened SPR-6272 and commented

Formatter is a convenient interface to implement for parsing and printing objects. However, there could be cases where you want to register specific Printer or Parser functions for certain types for more flexibility. For example, consider Joda Time DateTimeFormatter. Such a Formatter can parse/format a Joda DateTime object, which is nice and useful. However, the Joda format library can actually print any ReadableInstant (which includes DateTime) and ReadablePartial, while only being able to parse DateTime objects. In this case, it would make logical sense to have separate ReadableInstantPrinter, ReadablePartialPrinter, and DateTimeParser classes. For the current DateTimeFormatter, ReadablePartial implementations such as LocalDate must first be coersed to DateTime before they can be printed. Having a separate Printer interface that accepted a ReadablePartial would not require such a coersion step.

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Affects: 3.0 RC1

[spring-projects-issues]

Keith Donald commented

Some code ideas showing formatting rules registered for a @ShortDate annotation where any @ShortDate property that is a ReadablePartial, ReadableInstant, or Long can be printed, and DateTime objects will be parsed. This will require no coersion to print; a coersion from DateTime to the target @ShortDate property type may still be required.

[spring-projects-issues]

Keith Donald commented

addFormatter(ShortDate.class).
	printer(new Printer<ReadablePartial>() {
		String print(ReadablePartial partial, Locale locale) {
			return DateTimeFormat.shortDate().withLocale(locale).print(partial);
		}
	}).
	printer(new Printer<ReadableInstant>() {
		String print(ReadableInstant instant, Locale locale) {
			return DateTimeFormat.shortDate().withLocale(locale).print(instant);
		}		
	}).
	printer(new Printer<Long>() {
		String print(Long instant, Locale locale) {
			return DateTimeFormat.shortDate().withLocale(locale).print(instant);
		}
	}).
	parser(new Parser<DateTime>() {
		DateTime parse(String printed, Locale locale) {
			return DateTimeFormat.shortDate().withLocale(locale).parse(printed);
		}
	});