Java Instant.parse on Date java 8

问题

I have some legacy KML documents which includes a time stamp entry. Why is the below date not valid when using Instant to parse? Both methods are suppose to parse ISO 8601 formatted dates.

String dateString = "2017-12-04T08:06:60Z"

Using

java.time.Instant.parse(dateString)

throws an error

"DateTimeParseException Text 2017-12-04T08:06:60Z could not be parsed at index 0."

However, when using

Date myDate =   javax.xml.bind.DatatypeConverter.parseDateTime( dateString )

myDate is parsed correctly....

回答1:

60 seconds isn't a valid time. Meaning that this is invalid 2017-12-04T08:06:60Z, if it was 60 seconds then the minute should have incremented and your time would be 2017-12-04T08:07:00Z

Using a valid date and then parsing the String would work just fine:

String date = "2017-12-04T08:07:00Z";
System.out.println(Instant.parse(date));

Also java.time ignores leap seconds. From the docs:

Implementations of the Java time-scale using the JSR-310 API are not required to provide any clock that is sub-second accurate, or that progresses monotonically or smoothly. Implementations are therefore not required to actually perform the UTC-SLS slew or to otherwise be aware of leap seconds. JSR-310 does, however, require that implementations must document the approach they use when defining a clock representing the current instant. See Clock for details on the available clocks.

回答2:

The accepted answer is fine. I just have two things to add:

You can parse the string with the invalid second value of 60 by using ResolverStyle.LENIENT.
Since Jon Skeet in a comment mentioned a possible leap second: It’s not a valid leap second. java.time does support the parsing of a (valid) leap second.

Parsing your string

    DateTimeFormatter lenientFormatter
            = DateTimeFormatter.ISO_OFFSET_DATE_TIME
                    .withResolverStyle(ResolverStyle.LENIENT);
    String dateString = "2018-12-04T08:06:60Z";
    Instant myInstant = lenientFormatter.parse(dateString, Instant::from);
    System.out.println(myInstant);

Output:

2018-12-04T08:07:00Z

So the overflowing second value of 60 has been rolled into a full minute.

By the way, javax.xml.bind.DatatypeConverter.parseDateTime parses into a Calendar (not a Date), which is how the returned object can in fact hold a second value of 60. It seems that it generally accepts a second value of 60, but throws an exception on 61.

Parsing a valid leap second

This does in no way answer your question, but I thought that it might be useful for future readers. A leap second is always the last second of the day, so 23:59:60. An Instant cannot hold this value, but you can query whether one was parsed. It’s supported via DateTimeFormatterBuilder.appendInstant(), and DateTimeFormatter.parsedLeapSecond().

    DateTimeFormatter leapSecondFormatter = new DateTimeFormatterBuilder()
            .appendInstant()
            .toFormatter();
    Instant myInstant
            = leapSecondFormatter.parse("2018-12-04T23:59:60Z", Instant::from);
    System.out.println(myInstant);

    TemporalAccessor parsed = leapSecondFormatter.parse("2018-12-04T23:59:60Z");
    System.out.println("Instant: " + parsed.query(Instant::from));
    System.out.println("Was a leap second parsed? "
            + parsed.query(DateTimeFormatter.parsedLeapSecond()));

Output:

2018-12-04T23:59:59Z
Instant: 2018-12-04T23:59:59Z
Was a leap second parsed? true

I don’t know why it had to be this complicated, but it works.

Link: Documentation of DateTimeFormatter.parsedLeapSecond

来源：https://stackoverflow.com/questions/55304194/java-instant-parse-on-date-java-8

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