Module com.github.f4b6a3.uuid
Package com.github.f4b6a3.uuid.factory

Class AbstTimeBasedFactory

  • All Implemented Interfaces:
    NoArgsFactory
    Direct Known Subclasses:
    DceSecurityFactory, TimeBasedFactory, TimeOrderedFactory
    public abstract class AbstTimeBasedFactory
extends UuidFactory
implements NoArgsFactory
    Abstract factory for creating time-based unique identifiers (UUIDv1, UUIDv2 and UUIDv6).

    The time stamp has 100-nanoseconds resolution, starting from 1582-10-15, which is a date known as Gregorian Epoch. The the time stamp rolls over around AD 5235 (1582 + 2^60 / 365.25 / 24 / 60 / 60 / 10000000).

    The node identifier can be:

    • A MAC address;
    • A hash of host name, MAC and IP;
    • A random number that always changes;
    • A specific number chosen by someone.

    The node identifier used by this factory can be controlled by defining a system property 'uuidcreator.node' or an environment variable 'UUIDCREATOR_NODE'. The system property has preference over the environment variable.

    Options accepted by the system property and the environment variable:

    • The string "mac" for using the MAC address;
    • The string "hash" for using a hash of host name, MAC and IP;
    • The string "random" for using a random number that always changes;
    • The string representation of a specific number between 0 and 2^48-1.

    If a property or variable is defined, all UUIDs generated by this factory will be based on it.

    Otherwise, if no property or variable is defined, a random node identifier is generated once at instantiation. This is the default.

    Example of system property definition: 

    
 # Append to VM arguments
 -Duuidcreator.node="mac"

    Example of environment variable definition: 

    
 # Append to ~/.profile
 export UUIDCREATOR_NODE="mac"
    See Also:
    TimeFunction, NodeIdFunction, ClockSeqFunction, RFC-4122 - 4.2. Algorithms for Creating a Time-Based UUID

    • Constructor Detail

      • AbstTimeBasedFactory

        protected AbstTimeBasedFactory​(UuidVersion version,
                               AbstTimeBasedFactory.Builder<?,​?> builder)
        A protected constructor that receives a builder object.
        Parameters:
        version - the version number (1, 2 or 6)
        builder - a builder object

    • Method Detail

      • create

        public UUID create()
        Returns a time-based UUID.
        Specified by:
        create in interface NoArgsFactory
        Returns:
        a time-based UUID

      • formatMostSignificantBits

        protected long formatMostSignificantBits​(long timestamp)
        Returns the most significant bits of the UUID.

        It implements the algorithm for generating UUIDv1.

        Parameters:
        timestamp - the number of 100-nanoseconds since 1970-01-01 (Unix epoch)
        Returns:
        the MSB

      • formatLeastSignificantBits

        protected long formatLeastSignificantBits​(long nodeIdentifier,
                                          long clockSequence)
        Returns the least significant bits of the UUID.
        Parameters:
        nodeIdentifier - a node identifier
        clockSequence - a clock sequence
        Returns:
        the LSB

      • selectNodeIdFunction

        protected static NodeIdFunction selectNodeIdFunction()
        Select the node identifier function. This method reads the system property 'uuidcreator.node' and the environment variable 'UUIDCREATOR_NODE' to decide what node identifier function must be used. 1. If it finds the string "mac", the generator will use the MAC address. 2. If it finds the string "hash", the generator will use the system data hash. 3. If it finds the string "random", the generator will use a random number that always changes. 4. If it finds the string representation of a specific number in octal, hexadecimal or decimal format, the generator will use the number represented. 5. Else, a random number will be used by the generator.

      • selectTimeFunction

        protected static TimeFunction selectTimeFunction()
        Select the time function. If the operating system is WINDOWS, it returns a function that is more efficient for its typical time granularity (15.6ms). Otherwise, it returns the default time function.
        Returns:
        a time function