关于Java的UUID

UUID或者UNID或者UID，是一个统一唯一标识，可以用来标记文档、数据或其它需要唯一标识的东西。Java 5.0内置UUID的实现，见java.util.UUID. 下面代码是找到的2种实现方式，随手测了一下，两者时间效率居然出奇的相似，在10000000次循环中，均在660秒左右。

import java.math.BigInteger;  
import java.util.Random;  
import java.util.UUID;  
  
public class UUIDTest {  
    private static UUID uid = null;  
    private static final Random RANDOM = new Random();  
      
    public static String getUUID() {  
        uid = UUID.randomUUID();   
        String idstr = uid.toString().replace("-", "");  
        return idstr.toUpperCase();  
    }  
      
      
    public static String generateGUID(){  
        return new BigInteger(165, RANDOM).toString(36).toUpperCase();  
    }  
      
    /** 
     * @param args 
     */  
    public static void main(String[] args) {  
        int cycles = 100000000;   
          
        long start = System.currentTimeMillis();  
        for (int i = 0; i < cycles; i++) {  
            //System.out.println(getUUID());  

            getUUID();  
        }  
        long end = System.currentTimeMillis();  
        String msg = "Time(ms) of getUUID() " + cycles + " times: " ;  
        System.out.println (msg + (end - start));  
          
          
        long start1 = System.currentTimeMillis();  
        for (int i = 0; i < cycles; i++) {  
            //System.out.println(generateGUID());  

            generateGUID();  
        }  
        long end1 = System.currentTimeMillis();  
        msg = "Time(ms) of generateGUID() " + cycles + " times: " ;  
        System.out.println (msg + (end1 - start1));  
    }  
}  

2者所生成ID字串如下：

FB0F88715B564691A85F28DBFDD57D90
E50999DA27624D7E81B89C47DF02DA92
E601B3C99AC4490E97EA0174860EEFDF
839DF94E497E45D09D5D7F34C531511F
54459B4DACF94097962A1C6017A35882
6A6CAF5667F74C24A28141CD287C44BE
7DF3E7F386934C4E9842E980E9E4C652
3370A0549E3C4C5EA3A5EFC53E5DC9B6
563F56BA980F43D3A07DF58B9F95F2EC
0968563C99E046B9944DFDD36CDDF5E2
GV9VQMTJC4NDFV5IB7N5IDWABQWF8M4M
LD0U9UKFPGG9LKKYHEWJSJ40OC57JHIQ
J9KTPM0Y9676256UNQTO7HFQG0G0CBDK
H0B4IVYNO99N918YIJ12PKA4T0R6P394
CTYE9DTF9IBUXXOR1SYCJYCRXD9H6KO9
2ZQ1CH3MGP5M3AOTFH1VJ3ZQ8M0CH2I5
MDGHQLHQ34A0Q9JNJ7S6WFAN8YV0M652
HVC2R84PT2ZKABL2FSSR84K9N5IG98WP
MGZ3NZJ5RS51KCL12KHLGURXCHZK8YNK
129RZPH0UPQO8SMCZZJFTY37G47T19KL

时间测试结果：

Time(ms) of getUUID() 100000000 times: 669516
Time(ms) of generateGUID() 100000000 times: 663656