UUIDGenerator生成唯一编码

生成唯一编码

 

import java.net.InetAddress;

public class UUIDGenerator {

    /** 
     * @param 通过处理Ip得到的整数值 
     */
    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);

    /** 
     * 或得该类加载时jvm的时间唯一的(除非加载该类在相同的四分之一秒-几乎不可能) 
     * 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();
    }

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

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

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

    public 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;
    }
//    public static void main(String[] args) {
//        UUIDGenerator uuid = new UUIDGenerator();
//        for (int i = 0; i < 100; i++) {
//            System.out.println(uuid.generate());
//        }
//    }
}