how do i get the date/time back from a UUID type 1

问题

I have included the following UUID library compile group: 'com.fasterxml.uuid', name: 'java-uuid-generator', version: '3.1.5' in my build.

i have some code like this

        NoArgGenerator timeBasedGenerator = Generators.timeBasedGenerator()
        UUID tuid = timeBasedGenerator.generate()
        Timestamp timestamp = new Timestamp ((tuid.timestamp()/1000) as Long)
        Date dateTime = new Date (timestamp.getTime())

however when itry and look at the date its nothing like what it should be so for example i get 'uid fef57eca-7c8b-11e8-bedd-992c2ac3197a was Sun Feb 06 07:55:54 GMT 6327' when today is 30/06/2018

Does anyone know how to correctly extract the real date and time from a time based UUID using the fasterxml.uuid library?

but stumped

ps tried this instead

        UUID tuid = timeBasedGenerator.generate()
        Long t = tuid.timestamp()
        Timestamp timestamp = new Timestamp (t)
        Date dateTime = new Date (timestamp.getTime())

which gives a uid ff79d7d9-7cb5-11e8-976c-6ba57a5e9636 and date of Thu Aug 14 11:11:40 BST 4359073

回答1:

I did some more searching on the web.

I built the following 'simple utility' class that can be expanded as required:

import com.fasterxml.uuid.Generators
import com.fasterxml.uuid.NoArgGenerator

class UuidUtil {

    static final NoArgGenerator timeBasedGenerator = Generators.timeBasedGenerator()


    /**
     * From UUID javadocs the resulting timestamp is measured in 100-nanosecond units since midnight, October 15, 1582 UTC
     * timestamp() from UUID is measured in 100-nanosecond units since midnight, October 15, 1582 UTC
     *
     * The Java timestamp in milliseconds since 1970-01-01 as baseline
     *
     * @return
     */
    static long getStartOfUuidRelativeToUnixEpochInMilliseconds () {
        Calendar c = Calendar.getInstance(TimeZone.getTimeZone("GMT-0"))
        c.set(Calendar.YEAR, 1582)
        c.set(Calendar.MONTH, Calendar.OCTOBER)
        c.set(Calendar.DAY_OF_MONTH, 15)
        c.set(Calendar.HOUR_OF_DAY, 0)
        c.set(Calendar.MINUTE, 0)
        c.set(Calendar.SECOND, 0)
        c.set(Calendar.MILLISECOND, 0)

        return c.getTimeInMillis()
    }

    //https://www.wolframalpha.com/input/?i=convert+1582-10-15+UTC+to+unix+time
    final static long START_OF_UUID_RELATIVE_TO_UNIX_EPOCH_SECONDS = -12219292800L
    final static long START_OF_UUID_RELATIVE_TO_UNIX_EPOCH_MILLIS = -12219292800L * 1000L

    /**
     * timestamp() from UUID is measured in 100-nanosecond units since midnight, October 15, 1582 UTC,
     * so we must convert for 100ns units to millisecond procession
     * @param tuid
     * @return
     */
    static long getMillisecondsFromUuid (UUID tuid) {

        assert tuid.version() == 1      //ensure its a time based UUID

        // timestamp returns in 10^-7 (100 nano second chunks), 
        // java Date constructor  assumes 10^-3 (millisecond precision)
        // so we have to divide by 10^4 (10,000) to get millisecond precision  
        long milliseconds_since_UUID_baseline = tuid.timestamp() /10000L

    }

    static getDateFromUuid (UUID tuid) {
        // Allocates a Date object and initializes it to represent the specified number of milliseconds since the 
        // standard java (unix) base time known as "the epoch", namely January 1, 1970, 00:00:00 GMT
        // have to add relative offset from UUID start date of unix epoch to get start date in unix time milliseconds 
        new Date (getMillisecondsFromUuid (tuid) + START_OF_UUID_RELATIVE_TO_UNIX_EPOCH_MILLIS )
    }

    static UUID getTimeBasedUuid () {
        UUID tuid = timeBasedGenerator.generate()
    }

}

I've added explanatory comment so that you can follow what you had to do to process the UUID timestamp() method into a format that works for normal Java date and time processing.

Why the Java UUID class can't provide the methods one might expect to make a time-based UUID interoperable with the normal java date/time formats based on normal unix epoch is a mystery to me.

I ran a little test script using the above static methods:

println "get start of epoch in milliseconds " + UuidUtil.getStartOfUuidRelativeToUnixEpochInMilliseconds()
assert UuidUtil.START_OF_UUID_RELATIVE_TO_UNIX_EPOCH_MILLIS == UuidUtil.startOfUuidRelativeToUnixEpochInMilliseconds

UUID tuid = UuidUtil.timeBasedUuid

println "uid : $tuid"

Date date = UuidUtil.getDateFromUuid(tuid)
println "extracted date from uid is " + UuidUtil.getDateFromUuid(tuid)

and got this

get start of epoch in milliseconds -12219292800000
uid : 43acb588-7d39-11e8-b37b-59f77bf2d333
extracted date from uid is Sun Jul 01 15:15:53 BST 2018

which looked correct for time the script was run.

回答2:

The library 'uuid-creator' has a utility class that helps to exctract UUID parts like time and node id. See this exemple:

long milliseconds = UuidUtil.extractUnixMilliseconds(uuid);

Project: https://github.com/f4b6a3/uuid-creator

来源：https://stackoverflow.com/questions/51117194/how-do-i-get-the-date-time-back-from-a-uuid-type-1

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