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：

引用

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：

引用

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