IDGenerator UUID

package com.joyveb.common.utils;

import java.net.InetAddress;

public class IDGenerator {
    /**
     * generateId，生成Id
     *
     * @return String 返回GUID字符串
     */
    public synchronized String generate() {
        return new StringBuffer(36).append(IPString).append(JVMString)
                .append(format(getHiTime())).append(format(getLoTime()))
                .append(format(getCount())).toString();
    }

    /**
     * 单例对象的获取函数
     *
     *
     * @return GUIDHexGenerator
     */
    public static IDGenerator getInstance() {
        if (instance == null) {
            synchronized (IDGenerator.class) {
                if (instance == null) {
                    instance = new IDGenerator();
                }
            }
        }
        return instance;
    }

    private static volatile IDGenerator instance;

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

    private final String IPString = format(IP);

    private static short counter = (short) 0;

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

    private final String JVMString = format(JVM);

    /**
     * 通过JVM使id好对于不同的JVM不重复，除非它们同时装载这个类 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() {
        counter++;
        if (counter < 0) {
            counter = 0;
        }
        return counter;
    }

    /**
     * IP地址使局域网内唯一，如果你用网卡物理号则全球唯一了：）
     */
    protected int getIP() {
        return IP;
    }

    /**
     * Unique down to millisecond
     */

    protected short getHiTime() {
        short hiTime = (short) ((System.currentTimeMillis() >>> 32) & 0xFFFF);
        return hiTime;
    }

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

    // private static final String SEPERATOR = "";

    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();
    }

    private 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;
    }

    public static byte[] toBytes(short value) {
        byte[] result = new byte[2];
        result[1] = (byte) ((0xFFl & value) + Byte.MIN_VALUE);
        result[0] = (byte) ((0xFFl & (value >>> 8)) + Byte.MIN_VALUE);
        return result;
    }

    public static void main(String[] str) {
        for (int i = 0; i <= 100; i++) {
            System.out.println(IDGenerator.getInstance().generate());
        }
    }
}