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用Jva生成GUID

 2009-03-24 20:51:30 来源:WEB开发网   
核心提示:在项目里加入common-loging.jar /*** @author ccadmin** TODO To change the template for this generated type comment go to*/import java.net.InetAddress;import java.net.Un

在项目里加入common-loging.jar

 /**
* @author ccadmin
*
* TODO To change the template for this generated type comment go to
*/
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 {
   PRotected final org.apache.commons.logging.Log logger = org.apache.commons.logging.LogFactory
    .getLog(getClass());

   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 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(128);

  try {
      md5 = MessageDigest.getInstance("MD5");
    } catch (NoSuchAlgorithmException e) {
      logger.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) {
      logger.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++) {
      RandomGUID myGUID = new RandomGUID();
      System.out.println("Seeding String=" + myGUID.valueBeforeMD5);
      System.out.println("rawGUID=" + myGUID.valueAfterMD5);
      System.out.println("RandomGUID=" + myGUID.toString());
     }
    }


}

UUID是指在一台机器上生成的数字,它保证对在同一时空中的所有机器都是唯一的。通常平台会提供生成UUID的API。UUID按照开放软件基金会 (OSF)制定的标准计算,用到了以太网卡地址、纳秒级时间、芯片ID码和许多可能的数字。由以下几部分的组合:当前日期和时间(UUID的第一个部分与时间有关,如果你在生成一个UUID之后,过几秒又生成一个UUID,则第一个部分不同,其余相同),时钟序列,全局唯一的IEEE机器识别号(如果有网卡,从网卡获得,没有网卡以其他方式获得),UUID的唯一缺陷在于生成的结果串会比较长。关于UUID这个标准使用最普遍的是微软的 GUID(Globals Unique Identifiers)。

Tags:Jva 生成 GUID

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