org.josef.jpa

Class ObjectIdDispenser

java.lang.Object

org.josef.jpa.ObjectIdDispenser

public final class ObjectIdDispenser
extends Object

Dispenses unique object identifiers which can be used as primary keys.
This class is based upon an article by Scott Ambler Called: Enterprise-Ready Object IDs. For performance reasons however we do not use a UUID or GUID but a simple long. Using 8 bits for the low value we have 2^56=72057594037927936 unique numbers which is more than enough for our purposes.
This class assumes that a properties file exists with the same name as this class. The properties files should have a key: oidSequenceName. It's value determines the name of the sequence used to generate object id's. See the class SequentialIdGenerator for further details.

Version:

1.0 $Revision: 6298 $

Author:

Kees Schotanus

Method Summary

Modifier and Type	Method and Description
static ObjectIdDispenser	getInstance() Simply returns the one and only dispenser object.
long	getNextObjectID() Retrieves the next unique object identifier.
static void	main(String[] args) Gets and prints the next object ID.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Method Detail

getInstance

public static ObjectIdDispenser getInstance()

Simply returns the one and only dispenser object.
Note: different classloaders may return different instances, even though it's hard to speak of a singleton it really doesn't matter since the database lock mechanism is used for synchronization.

Returns:

Single object ID dispenser instance.

getNextObjectID

public long getNextObjectID()
                     throws SequentialIdGeneratorException

Retrieves the next unique object identifier.

Returns:

Unique object identifier.
The identifier is not globally unique but it is unique to all entity beans stored in the database that use this mechanism.

Throws:

SequentialIdGeneratorException - When the next object ID could not be obtained.
This exception can only occur when the database has to be accessed to get the next ID.

main

public static void main(String[] args)
                 throws SequentialIdGeneratorException

Gets and prints the next object ID.

Parameters:

args - Not used.

Throws:

SequentialIdGeneratorException - When the next object id could not be fetched.