Some example shortcuts for working with Java8 DateTime Api (java.time): e.g. Instant, LocalDateTime, ZonedDateTime, OffsetDateTime

InstantUtcUtil.groovy

package com.example.util

import groovy.transform.CompileStatic
import groovy.transform.TypeChecked

import java.time.*
import java.time.format.DateTimeFormatter

@CompileStatic
@TypeChecked
class InstantUtcUtil {

    public static final List<Closure<Instant>> PARSERS_DEFAULT = [
            {
                String text -> return Instant.parse(text)
            },
            {
                String text ->

                    return ZonedDateTime.parse(text)
                            .toInstant()
            },
            {
                String text ->

                    return OffsetDateTime.parse(text)
                            .toInstant()
            },
            {
                String text ->

                    return LocalDateTime.parse(text)
                            .toInstant(ZoneOffset.UTC)
            },
            {
                String text ->

                    return LocalDateTime.parse(text, DateTimeFormatter.ISO_ZONED_DATE_TIME)
                            .toInstant(ZoneOffset.UTC)
            },
            {
                String text ->

                    return LocalDateTime.parse(text, DateTimeFormatter.ofPattern("yyyyMMdd'T'HHmmX"))
                            .toInstant(ZoneOffset.UTC)
            }
    ];


    public static Instant parseOrElseGet(String value, List<Closure<Instant>> parserList, Closure<Instant> orElse) {
        Objects.requireNonNull(value, "value")
        Objects.requireNonNull(parserList, "matchers")
        Objects.requireNonNull(orElse, "orElse")

        for (parser in parserList) {
            try {
                Instant instant = (Instant) parser(value)
                if (instant != null) {

                    return instant
                }
            } catch (all) {
                // ignore, handled graceful
            }
        }

        return orElse()
    }

    public static Instant toInstant(LocalDateTime localDateTime) {
        Objects.requireNonNull("localDateTime")

        return localDateTime.toInstant(ZoneOffset.UTC)
    }

    public static Instant toInstant(ZonedDateTime zonedDateTime) {
        Objects.requireNonNull("zonedDateTime")

        return zonedDateTime.toInstant()
    }

    public static Instant toInstant(OffsetDateTime offsetDateTime) {
        Objects.requireNonNull("offsetDateTime")

        return offsetDateTime.toInstant()
    }

    public static LocalDateTime toLocalDateTime(Instant instant) {
        Objects.requireNonNull("instant")

        return LocalDateTime.ofInstant(instant, ZoneOffset.UTC)
    }

    public static ZonedDateTime toZonedDateTime(Instant instant) {
        Objects.requireNonNull("instant")

        return ZonedDateTime.ofInstant(instant, ZoneOffset.UTC)
    }

    public static OffsetDateTime toOffsetDateTime(Instant instant) {
        Objects.requireNonNull("instant")

        return OffsetDateTime.ofInstant(instant, ZoneOffset.UTC)
    }

    public static Instant withEpochSecondPrecision(Instant source) {
        Objects.requireNonNull(source, "source")

        return Instant.ofEpochSecond(source.getEpochSecond(), 0)
    }

    public static Instant requireNonEmpty(Object source, String message) {
        boolean isValid = source instanceof Instant && source.getEpochSecond() > 0;

        boolean hasMessage = message instanceof String && !(message.trim().isEmpty());
        String finalMessage = "Parameter must be Instant, not empty!";
        if (hasMessage) {
            finalMessage += " " + message
        }

        if (!isValid) {
            throw new RuntimeException(finalMessage);
        }

        return (Instant) source;
    }

}

System.out.println(ZonedDateTime.parse("2016-08-17T22:00:00Z").toString()); // 2016-08-17T22:00Z
System.out.println(ZonedDateTime.parse("2016-08-17T22:00:00.123Z").toString()); // 2016-08-17T22:00:00.123Z
System.out.println(ZonedDateTime.parse("2016-08-17T22:00:00+02:00").toString()); // 2016-08-17T22:00+02:00
System.out.println(ZonedDateTime.parse("2016-08-17T22:00:00+02:00").withZoneSameInstant(ZoneId.of("UTC")).toString()); // 2016-08-17T20:00Z[UTC]
System.out.println(ZonedDateTime.parse("2016-08-17T22:00:00").toString()); // exception, weil ZeitZoneInfo fehlt.