AbstractUUIDGenerator.java

/**********************************************************************
Copyright (c) 2005 Andy Jefferson and others. All rights reserved.
Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at

    http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License. 


Contributors:
    ...
**********************************************************************/
package org.datanucleus.store.valuegenerator;

import java.net.InetAddress;
import java.util.Properties;

import org.datanucleus.util.Localiser;
import org.datanucleus.util.NucleusLogger;
import org.datanucleus.util.TypeConversionHelper;

/**
 * Value generator for a UUID format. To be extended by implementations giving the UUID in particular forms.
 */
public abstract class AbstractUUIDGenerator extends AbstractGenerator<String>
{
    /** IP Address of local machine. */
    static final int IP_ADDRESS;

    static 
    {
        // Calculate the IP address of this machine for use in the UUID
        int ipAddr = 0;
        try
        {
            ipAddr = TypeConversionHelper.getIntFromByteArray(InetAddress.getLocalHost().getAddress());
        }
        catch (Exception e)
        {
            ipAddr = 0;
        }

        IP_ADDRESS = ipAddr;
    }

    /** Unique value across JVMs on this machine. */
    static final int JVM_UNIQUE = (int) (System.currentTimeMillis() >>> 8);

    static short counter = (short) 0;

    /**
     * Constructor.
     * @param name Symbolic name for this generator
     * @param props Properties controlling its behaviour
     */
    public AbstractUUIDGenerator(String name, Properties props)
    {
        super(name, props);
    }

    /**
     * Accessor for the storage class for values generated with this generator.
     * @return Storage class (in this case String.class)
     */
    public static Class getStorageClass()
    {
        return String.class;
    }

    /**
     * Method to reserve "size" values to the block.
     * @param size The block size
     * @return The reserved block
     */
    protected ValueGenerationBlock<String> reserveBlock(long size)
    {
        Object[] ids = new Object[(int) size];
        for (int i = 0; i < size; i++)
        {
            ids[i] = getIdentifier();
        }
        if (NucleusLogger.VALUEGENERATION.isDebugEnabled())
        {
            NucleusLogger.VALUEGENERATION.debug(Localiser.msg("040004", "" + size));
        }
        return new ValueGenerationBlock(ids);
    }

    /**
     * Create an identifier in the required UUID format required.
     * @return The identifier
     */
    protected abstract String getIdentifier();

    /**
     * Simple counter for identities.
     * @return The next count value
     */
    protected short getCount() 
    {
        // We could move this to the individual implementing classes
        // so they have their own count
        synchronized(AbstractUUIDGenerator.class) 
        {
            if (counter < 0)
            {
                counter = 0;
            }
            return counter++;
        }
    }
}