UUIDGenerator.java

/*
 * Copyright 2004-2009 the original author or authors.
 * 
 * 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.
 */

package org.compass.core.id;

import java.io.Serializable;
import java.net.InetAddress;

/**
 * @author kimchy
 */
public class UUIDGenerator implements IdentifierGenerator {

    private static int toInt(byte[] bytes) {
        int result = 0;
        for (int i = 0; i < 4; i++) {
            result = (result << 8) - Byte.MIN_VALUE + (int) bytes[i];
        }
        return result;
    }

    private static final int IP;
    static {
        int ipadd;
        try {
            ipadd = toInt(InetAddress.getLocalHost().getAddress());
        } catch (Exception e) {
            ipadd = 0;
        }
        IP = ipadd;
    }

    private static short counter = (short) 0;

    private static final int JVM = (int) (System.currentTimeMillis() >>> 8);

    /**
     * Unique across JVMs on this machine (unless they load this class in the
     * same quater second - very unlikely)
     */
    protected int getJVM() {
        return JVM;
    }

    /**
     * Unique in a millisecond for this JVM instance (unless there are >
     * Short.MAX_VALUE instances created in a millisecond)
     */
    protected short getCount() {
        synchronized (UUIDGenerator.class) {
            if (counter < 0)
                counter = 0;
            return counter++;
        }
    }

    /**
     * Unique in a local network
     */
    protected int getIP() {
        return IP;
    }

    /**
     * Unique down to millisecond
     */
    protected short getHiTime() {
        return (short) (System.currentTimeMillis() >>> 32);
    }

    protected int getLoTime() {
        return (int) System.currentTimeMillis();
    }

    private String sep = "";

    protected String format(int intval) {
        String formatted = Integer.toHexString(intval);
        StringBuffer buf = new StringBuffer("00000000");
        buf.replace(8 - formatted.length(), 8, formatted);
        return buf.toString();
    }

    protected String format(short shortval) {
        String formatted = Integer.toHexString(shortval);
        StringBuffer buf = new StringBuffer("0000");
        buf.replace(4 - formatted.length(), 4, formatted);
        return buf.toString();
    }

    public Serializable generate() {
        return new StringBuffer(36).append(format(getIP())).append(sep).append(format(getJVM())).append(sep).append(
                format(getHiTime())).append(sep).append(format(getLoTime())).append(sep).append(format(getCount()))
                .toString();
    }

}