GUID生成类一例

这是以前在网上找到的一个例子，具体网址忘了。所以不能给出引用链接，向作者致歉！

import java.net.InetAddress;import java.net.UnknownHostException;import java.security.MessageDigest;import java.security.NoSuchAlgorithmException;import java.security.SecureRandom;import java.util.Random;public class RandomGUID extends Object {     public String valueBeforeMD5 = "";    public String valueAfterMD5 = "";    private static Random myRand;    private static SecureRandom mySecureRand;     private static String s_id;     /*     * 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 RandomGUID() {        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 RandomGUID(boolean secure) {        getRandomGUID(secure);    }     /*     * Method to generate the random GUID     */    private void getRandomGUID(boolean secure) {        MessageDigest md5 = null;        StringBuffer sbValueBeforeMD5 = new StringBuffer();         try {            md5 = MessageDigest.getInstance("MD5");        } catch (NoSuchAlgorithmException e) {            System.out.println("Error: " + e);        }         try {            long time = System.currentTimeMillis();            long rand = 0;             if (secure) {                rand = mySecureRand.nextLong();            } else {                rand = myRand.nextLong();            }             // This StringBuffer can be a long as you need; the MD5            // hash will always return 128 bits.  You can change            // the seed to include anything you want here.            // You could even stream a file through the MD5 making            // the odds of guessing it at least as great as that            // of guessing the contents of the file!            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();            for (int j = 0; j < array.length; ++j) {                int b = array[j] & 0xFF;                if (b < 0x10) sb.append('0');                sb.append(Integer.toHexString(b));            }             valueAfterMD5 = sb.toString();         } catch (Exception e) {            System.out.println("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();        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[]) {        RandomGUID myGUID = new RandomGUID();        System.out.println("valueBeforeMD5 -->" + myGUID.valueBeforeMD5);        System.out.println("valueAfterMD5 -->" + myGUID.valueAfterMD5);        System.out.println("RandomGUID=" + myGUID.toString());    }}

控制台打印：

valueBeforeMD5 -->agp138/168.9.201.138:1354181875222:2617300098220936058valueAfterMD5 -->ea1d90c35ad3662aeadf585c1d6ecd02RandomGUID=EA1D90C3-5AD3-662A-EADF-585C1D6ECD02