java生成GUID与UUID

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     GUID是一个128位长的数字,一般用16进制表示。算法的核心思想是结合机器的网卡、当地时间、一个随机数来生成GUID。从理论上讲,如果一台机器每秒产生10000000个GUID,则可以保证(概率意义上)3240年不重复。

    UUID是1.5中新增的一个类,在java.util下,用它可以产生一个号称全球唯一的ID
Java代码
import java.util.UUID; 
public class Test { 
 public static void main(String[] args) { 
  UUID uuid = UUID.randomUUID();  
  System.out.println (uuid); 


编译运行输出:
07ca3dec-b674-41d0-af9e-9c37583b08bb


两种方式生成guid 与uuid

需要comm log 库

Java代码
/**
 * @author Administrator
 *
 * TODO To change the template for this generated type comment go to
 * Window - Preferences - Java - Code Style - Code Templates
 */ 
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()); 
       } 
     } 
 
 


同样

Java代码
UUID uuid = UUID.randomUUID(); 
System.out.println("{"+uuid.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)。

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