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 -->agp138/168.9.201.138:1354181875222:2617300098220936058
valueAfterMD5 -->ea1d90c35ad3662aeadf585c1d6ecd02
RandomGUID=EA1D90C3-5AD3-662A-EADF-585C1D6ECD02