JAVA UUID生成

2015年8月11日 由 Creater 留言 »

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,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、一个随即数来生成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。

package com.mytest;
import java.util.UUID;
public class UTest {
    public static void main(String[] args) {
        UUID uuid = UUID.randomUUID();
        System.out.println(uuid);
    }
}

UUID(Universally Unique Identifier)全局唯一标识符,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。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。

在Java中生成UUID主要有以下几种方式:
1.JDK1.5
如果使用的JDK1.5的话,那么生成UUID变成了一件简单的事,以为JDK实现了UUID:
java.util.UUID,直接调用即可.

UUID uuid  =  UUID.randomUUID(); 
String s = UUID.randomUUID().toString();//用来生成数据库的主键id非常不错

UUID是由一个十六位的数字组成,表现出来的形式例如
550E8400-E29B-11D4-A716-446655440000

//下面就是实现为数据库获取一个唯一的主键id的代码 
public class UUIDGenerator { 
    public UUIDGenerator() { 
    } 
    /** 
     * 获得一个UUID 
     * @return String UUID 
     */ 
    public static String getUUID(){ 
        String s = UUID.randomUUID().toString(); 
        //去掉“-”符号 
        return s.substring(0,8)+s.substring(9,13)+s.substring(14,18)+s.substring(19,23)+s.substring(24); 
    } 
    /** 
     * 获得指定数目的UUID 
     * @param number int 需要获得的UUID数量 
     * @return String[] UUID数组 
     */ 
    public static String[] getUUID(int number){ 
        if(number < 1){ 
            return null; 
        } 
        String[] ss = new String[number]; 
        for(int i=0;i<number;i++){ 
            ss[i] = getUUID(); 
        } 
        return ss; 
    } 
    public static void main(String[] args){ 
        String[] ss = getUUID(10); 
        for(int i=0;i<ss.length;i++){ 
            System.out.println(ss[i]); 
        } 
    } 
}   

2.手动生成

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());
       }
     }
}
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