Java GUID

code example:

public class GUID {    public String valueBeforeMD5 = "";    public String valueAfterMD5 = "";    private static Random myRand;    private static SecureRandom mySecureRand;    private static String s_id;    private static final int PAD_BELOW = 0x10;    private static final int TWO_BYTES = 0xFF;    /*     * Static block to take care of one time secureRandom seed. It takes a few     * seconds to initialize SecureRandom. You might want to consider removing     * this static block or replacing it with a "time since first loaded" seed     * to reduce this time. This block will run only once per JVM instance.     */    static {        mySecureRand = new SecureRandom();        long secureInitializer = mySecureRand.nextLong();        myRand = new Random(secureInitializer);        try {            s_id = InetAddress.getLocalHost().toString();        } catch (UnknownHostException e) {            e.printStackTrace();        }    }    /*     * Default constructor. With no specification of security option, this     * constructor defaults to lower security, high performance.     */    public GUID() {        getRandomGUID(false);    }    /*     * Constructor with security option. Setting secure true enables each random     * number generated to be cryptographically strong. Secure false defaults to     * the standard Random function seeded with a single cryptographically     * strong random number.     */    public GUID(boolean secure) {        getRandomGUID(secure);    }    /*     * Method to generate the random GUID     */    private void getRandomGUID(boolean secure) {        MessageDigest md5 = null;        StringBuffer sbValueBeforeMD5 = new StringBuffer(128);        try {            md5 = MessageDigest.getInstance("MD5");        } catch (NoSuchAlgorithmException e) {            log.error("Error: " + e);        }        try {            long time = System.currentTimeMillis();            long rand = 0;            if (secure) {                rand = mySecureRand.nextLong();            } else {                rand = myRand.nextLong();            }            sbValueBeforeMD5.append(s_id);            sbValueBeforeMD5.append(":");            sbValueBeforeMD5.append(Long.toString(time));            sbValueBeforeMD5.append(":");            sbValueBeforeMD5.append(Long.toString(rand));            valueBeforeMD5 = sbValueBeforeMD5.toString();            md5.update(valueBeforeMD5.getBytes());            byte[] array = md5.digest();            StringBuffer sb = new StringBuffer(32);            for (int j = 0; j < array.length; ++j) {                int b = array[j] & TWO_BYTES;                if (b < PAD_BELOW)                    sb.append('0');                sb.append(Integer.toHexString(b));            }            valueAfterMD5 = sb.toString();        } catch (Exception e) {            log.error("Error:" + e);        }    }    /*     * Convert to the standard format for GUID (Useful for SQL Server     * UniqueIdentifiers, etc.) Example: C2FEEEAC-CFCD-11D1-8B05-00600806D9B6     */    public String toString() {        String raw = valueAfterMD5.toUpperCase();        StringBuffer sb = new StringBuffer(64);        sb.append(raw.substring(0, 8));        sb.append("-");        sb.append(raw.substring(8, 12));        sb.append("-");        sb.append(raw.substring(12, 16));        sb.append("-");        sb.append(raw.substring(16, 20));        sb.append("-");        sb.append(raw.substring(20));        return sb.toString();    }    // Demonstraton and self test of class    public static void main(String args[]) {        for (int i = 0; i < 100; i++) {            GUID myGUID = new GUID();            log.info("Seeding String=" + myGUID.valueBeforeMD5);            log.info("rawGUID=" + myGUID.valueAfterMD5);            log.info("RandomGUID=" + myGUID.toString());            log.info("----------------------------------------");        }    }}