How to convert .NET DateTime.toBinary() to java date

Question

I have a .NET INT64 value(result from DateTime.toBinary()) as -8586018589234214115 from JSON response. How do I convert that value into valid java Date?

Thanks, Sandeep

Answer 1

1. Convert the value (e.g. -8586018589234214115) to DateTime object (say, theDateTimeObject) using DateTime.FromBinary(Int64)
2. Convert theDateTimeObject to DateTimeOffset as DateTimeOffset dateTime = DateTime.SpecifyKind(theDateTimeObject, DateTimeKind.Utc)
3. Pass the value of DateTimeOffset.ToUnixTimeMilliseconds into java.time.Instant#ofEpochMilli to get an object of Instant which you can convert to other date-time types.

Demo:

import java.time.Instant;
import java.time.LocalDateTime;
import java.time.OffsetDateTime;
import java.time.ZoneOffset;
import java.time.ZonedDateTime;

public class Main {
    public static void main(String[] args) {
        long millis = 1608075095347L;
        Instant instant = Instant.ofEpochMilli(millis);
        System.out.println(instant);

        // You can derive other date-time objects from Instant e.g.
        OffsetDateTime odt = instant.atOffset(ZoneOffset.UTC);
        ZonedDateTime zdt = instant.atZone(ZoneOffset.UTC);
        LocalDateTime ldt = odt.toLocalDateTime();
        System.out.println(odt);
        System.out.println(zdt);
        System.out.println(ldt);
    }
}

Output:

2020-12-15T23:31:35.347Z
2020-12-15T23:31:35.347Z
2020-12-15T23:31:35.347Z
2020-12-15T23:31:35.347

Note that the date-time API of java.util and their formatting API, SimpleDateFormat are outdated and error-prone. It is recommended to stop using them completely and switch to the modern date-time API. Learn more about the modern date-time API at Trail: Date Time.

Note: For any reason, if you have to stick to Java 6 or Java 7, you can use ThreeTen-Backport which backports most of the java.time functionality to Java 6 & 7.

If you are working for an Android project and your Android API level is still not compliant with Java-8, check Java 8+ APIs available through desugaring and How to use ThreeTenABP in Android Project.

Answer 2

The Binary value is:

A 64-bit signed integer that encodes the Kind property in a 2-bit field and the Ticks property in a 62-bit field.

Since the Kind property is useless to us, we can simply mask it out using value & ((1L << 62) - 1) to get the Ticks property.

A Tick is:

A single tick represents one hundred nanoseconds or one ten-millionth of a second. There are 10,000 ticks in a millisecond (see TicksPerMillisecond) and 10 million ticks in a second.

The value of this property represents the number of 100-nanosecond intervals that have elapsed since 12:00:00 midnight, January 1, 0001.

Which means we can convert like this:

private static final long NANOS_PER_TICK = 100L;
private static final long TICKS_PER_SECOND = 1000000000L / NANOS_PER_TICK;
private static final long YEAR_OFFSET = -62135596800L;
// Seconds from Epoch to 12:00:00 midnight, January 1, 0001, calculated using:
//   OffsetDateTime.of(1, 1, 1, 0, 0, 0, 0, ZoneOffset.UTC).toEpochSecond()

static Instant fromDateTimeBinary(long value) {
    long ticks = value & ((1L << 62) - 1);
    return Instant.ofEpochSecond(ticks / TICKS_PER_SECOND + YEAR_OFFSET,
                                 ticks % TICKS_PER_SECOND * NANOS_PER_TICK);
}

Test

long dateTimeBinary = -8586018589234214115L;
System.out.println(dateTimeBinary + " -> " + fromDateTimeBinary(dateTimeBinary));

Output

-8586018589234214115 -> 2020-09-10T14:26:02.056169300Z

Warning: The -8586018589234214115 value specifies a Kind value of 2=Local (the time represented is local time), but we don't know what the "local" time zone was, so the result of converting to UTC may be wrong.

---

We can also convert the other way:

static long toDateTimeBinary(Instant dateTime) {
    long ticks = (dateTime.getEpochSecond() - YEAR_OFFSET) * TICKS_PER_SECOND
               + dateTime.getNano() / NANOS_PER_TICK;
    return (0x01L/*Kind=UTC*/ << 62) | ticks;
}

Test

Instant now = Instant.now();
System.out.println(now + " -> " + toDateTimeBinary(now));

Output

2020-12-16T01:51:17.066065200Z -> 5249122821198048556

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See also: Java 8 Time - Equivalent of .NET DateTime.MaxValue.Ticks

Answer 3

It would be better to convert to unix time .net DateTimeOffset.ToUnixTimeMilliseconds and then use the java.util.Date java constructor to parse it