UUID 重复？

小_Y 2013-12-31 05:48:35



import java.util.ArrayList;

import java.util.HashSet;

import java.util.List;

public class UUID {

	public static void main(String[] args) {

		final int x = Integer.parseInt(args[0]);

		final int y = Integer.parseInt(args[1]);

		final String[][] uuids = new String[x][y];

		final int[] ks = new int[x];

		for(int j = 0; j < x; j++) {

			final int k = j;

			new Thread(new Runnable(){

				public void run() {

					for(int i = 0; i < y ; i++) {

						uuids[k][i] = getUUID();

					}

					System.out.println(k + "  Over.");

					ks[k] = 1;

				}

				

			}).start();

		}

		while(true) {

			try {

				Thread.sleep(50);

			} catch (InterruptedException e) {

				e.printStackTrace();

			}

			boolean flag = true;

			for(int i = 0; i < ks.length; i++) {

				if(ks[i] == 0) {

					flag = false;

				}

			}

			if(flag) {

				break;

			}	

		}

		System.out.println("Process UUID");

		HashSet<String> set = new HashSet<String>(uuids.length);

		List<String> list = new ArrayList<String>();

		for(int i = 0; i < uuids.length; i++) {

			for(int j = 0; j < uuids[i].length; j++) {

				if(!set.add(uuids[i][j])) {

					list.add(i + "#" + j + "#" + uuids[i][j]);

					System.out.print(uuids[i][j] + "|   ");

				} else {

					System.out.print(uuids[i][j] + "|   ");

				}

			}

			System.out.println();

		}

		System.out.println("Process UUID ["+set.size()+"]");

		System.out.println(list);	

	}

	public static String getUUID() {

		String s = java.util.UUID.randomUUID().toString();

		return s.substring(0, 8) + s.substring(9, 13) + s.substring(14, 18)

				+ s.substring(19, 23) + s.substring(24);

	}

	

}

执行 java -Xms512m -Xmx512m UUID 10 10 有可能会重复，



5  Over.

0  Over.

8  Over.

4  Over.

6  Over.

9  Over.

2  Over.

3  Over.

7  Over.

1  Over.

Process UUID

111a259c52fb4ea7b313fe33cd2b1a56|   def2c8f802e546b49594498809349d9f|   89c3b3bb1772471d9275f763cc82a655|   e1af69b5744d4bf69b19b3425c5ac355|   a46218ea0f574444b3c8af738e6d05cc|   d8df2b2741b24d3ca672d7f9bc78e3c1|   4223d0ca2bf944bb8d64a7867e150dd3|   023deb9163784ccebb0703a778fa03eb|   96763ee8c91c45b1a21435c1031dcbde|   033070ce7d2f4614b700a1ffaffaaa3e|

333bf61aa8634e47b2d1f7df150d979f|   ec2d4226cf3c4299aad3e97f246f0142|   073aed8d9d8748668c377875bf7e9a6e|   fe87c53421cc4505b75dacc3b7928fa5|   1c9a6af7699d433ea4652c3514c4cfc6|   f0d74353fa8946a19803609f06d32865|   9ccda1bce1ec4de08751a764f75bc8b0|   e98cac7671ab4e1fa345cb5ebbf5f2da|   324089828b4a419e9c2487f2e2ea4f24|   a6ec9e64bae24ea0a710d58e522b4de2|

cf2bf25509014e52982807c5a8d9c5d4|   cdb6b5324f854b9d83d9c13c132e77f1|   2e1744970d2c4c3484743b3e0a147e99|   33009f87cde14e12ad59687acf7ec9e7|   e4c133edc254472dba68853a50428d79|   89c833fef714490ea3f381843ae2e551|   8c1ea95e616f477383e4d7176b759da0|   f4459e074ade466683433d1dc594fc5a|   11ef5a7199f24372ad88db69d68faac8|   df197fdee0d74602809e76b965ebeb7f|

c4c2a850be104db9b7d41160534938c5|   f2bb56c27f884cfcb31e218de6d6e4b2|   1bd40a566ca94f0b804d7c9531174874|   be9dac6ce5ed44868044d1064fc56dc8|   d5c1e4c19d1d41169e4d660e90a537b6|   85ba87dc52af4b648d671da289f1bfb9|   19229b03f5974c7c93918979029d41fd|   eed6b3f6a8ea4e84b14d29dc3733523c|   86b962d554094bddafe3f271fe0b63a4|   59ebdc9463fd4ba0ad8ed7c1f36632f9|

6654487027d34877af2baedefa90f59a|   f0af4400bae34ee9b3aaa26f5eb5b7d1|   771d748b63ac4e2c9ac822199c984667|   3d8f4443720245d9a2b4f822ad8ae5d0|   513d79eeb16b461ca1ec549fd54ec709|   6fc2a02fc70c4f15baa0316d4901d74d|   fea0ef82baf442e4bd2931e002e95dae|   200cd15ac49446e0abfec9d5526cd5b6|   48e2b7118cfe4f96b2f513b9ba9871bb|   a167bb66880d4ce38779a64439255673|

9b5c9f50fdfa4414b1180a0bbed9b34f|   43156bc3897a4156a3d2e9d2a73b6677|   510d51eff3204412af4f2b2b18030aba|   0dfe8dca76464a7ab1705691df9e8370|   81da5ae024244fdaacc1b92104956f4e|   dd2c42697c924b47a23099db3b1afc35|   aab508823d174939b9c48030c25536d7|   cea7d8f6700c424ea7ab03d923147c8a|   8b69c816c1e547769341cde9c8d78453|   6ee86e999ab04c9d947bf4f722474b0e|

a8e6a1c6db68473ea6a795735ece1706|   855237a44dc04af4a64e5e4c42622061|   5be2750e59a64808a8fda49a07322adf|   305d02aba2154164bf0d22d7b7ca9843|   5a0c48ff4df24628b6c0c672d80a6564|   a2477102c63e49748baa7b6e129f36a7|   a002680eb3cf4d7ba0a05bed454f91fa|   5e653a6c826548139af0622486131674|   3ee588f2d65143c5bcb7eb45d7989834|   456c3f6b7e104801bfb2721897066585|

fa505f3f6de146e7bbf0ddf1dc9e5ab0|   6c3ab749c7b347bb889e56a37537b8ce|   145215b900774154b5bbc657190a8461|   ce4bc81f84fe4104bfc5fd5ad74b30dc|   3ccedac3e0984e87af06dbb47408549c|   a5151cb341844ade99f2d33b8ff7a0cb|   b0f5e188cc674a78b8171824c6d8a89e|   49761db468d94ffe8f794277dfc3e30a|   f52922151bd34c94bead9918788ca094|   eae9b4153ff74779b2fd99d5436bdbe6|

111a259c52fb4ea7b313fe33cd2b1a56|   b162447a84b149caa53c21bea7f66125|   574d68eb825c406681698beecdf79f68|   af4780ee2bd849b3a1edfb6bfa7b17c6|   6b19a03fd4744d7a8681f66a4560e612|   b0da2834af384b318d491026840c1a78|   106a084b0d70480a8ddec98ddd25f7aa|   81f17d11ea52415abecdbd26471b8a16|   d32a6dcc477643d18627f65721753a92|   fc3d1d68cdca47e9b973d36dab0845c0|

dbaa05fe045b452792c36d6285e8dde1|   7af895e5734b4ef5bf639ec6a2c5c7d7|   0a5aef1b9b434fac9dcad6d5c6e3c30a|   99dff71b520643328ec3dae601848362|   42b8b812a81d4292a771b0a98a495ca1|   4bc57d3dd04241599088a751ea9d0b62|   83ea97cec9ea459eaac1fe632eaca957|   3775f3835347404ca62d277053acb953|   bf69fc6c2c3949fc8e0cc59bbcdd35a4|   6689217ab4454b9fab162c56293adacb|

Process UUID [99]

[8#0#111a259c52fb4ea7b313fe33cd2b1a56]

其中 uuids[0][0] 和 uuids[8][0] 重复，是代码有问题么？
但是执行 java UUID 10 10 却不会重复，这是什么情况啊？

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潇水汀寒 2014-01-02

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跟并发没有关系只能说你脸黑了不过还是要自信以后不会碰到这种情况了,UUID没这么逊的

小_Y 2014-01-02

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基本上都是每个线程的第0个是重复的，应该是代码有问题？一定要加上同步么？那位大神能把这个翻译下？ http://kaqi.iteye.com/blog/1976723

UDown 2014-01-01

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         String s = java.util.UUID.randomUUID().toString();
        return s.substring(0, 8) + s.substring(9, 13) + s.substring(14, 18)
                + s.substring(19, 23) + s.substring(24);

改成

         String s = "";
    	synchronized (s) {
    		s = java.util.UUID.randomUUID().toString();
		}
        return s.substring(0, 8) + s.substring(9, 13) + s.substring(14, 18)
                + s.substring(19, 23) + s.substring(24);

getUUID() 方法

UDown 2014-01-01

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6  Over.
8  Over.
2  Over.
5  Over.
3  Over.
0  Over.
7  Over.
1  Over.
4  Over.
9  Over.
Process UUID
6356d81ec33446ceaf4c27301aadea15|   660d89f7e25e4fb790be2b8cf0b4d15f|   0c163aa5cbaa4b8fb19a844611736017|   a8399c4f864f4fb4b36e6df31b7c69fa|   153c11934fba44669987752156c58c4d|   b169a8af0a0e42c69b526d52544b6ede|   9c94f2bd4f984d119ca8540cfcce3878|   706dcb5c3a5744688d4e56c87878bdbd|   14c92280375f426bbd0147ad2a52d949|   827a61ca70a5492dad803fe9b50f3edf|   
f269d744d83f44dbba7a056fb9e738f2|   669bf01d808b44abaecefeade10e246c|   03fd19dbeebb42cd8dbde0b1bd226e30|   7c2609d7a14148649ae6ae1d0db513b3|   47a2144195734d0e914a3235ed3dac95|   0dc271a9892943999e06291fd539351a|   1a3d8c979c864f2d8eabb5cc6b2fadbe|   660dd077bc0f47e0b4ebf389ec3cb89c|   21e0d065429948518f137fef6c0c8177|   4aae77b036c54a0d999e42d9aeecbc12|   
6356d81ec33446ceaf4c27301aadea15|   c3f85398b5a34a719ea897868b0c7bc6|   22efb322209f465ca41dd93a7cb878ed|   deb38d0e2a9b4f26af94d4a854c40600|   f5bcd1f663ab4552b234e6a117e590e7|   9370eb8e2d9d48fa8c7a15d8e207915d|   9420af1d40b94986b565ebd2bedb552c|   2fcf4e33eb20432fa570696206b0dbf4|   e8e8e531547449928c50d5064f264f8c|   d462c881d6b343389ef24e72c51f67e3|   
596d087709194d88a8f06c3f48444208|   6172d1ac6a044969a26b1e838bc5960a|   763a96366a144ce683ce7dbfbdd5b569|   a7487ca688cd4bd781a6e72a705ef834|   98877b7473ec49a78e102821b38a4d37|   bb81a6ab783c4ac497dd3accedf822cc|   e3d0e647dc87470ba30b28752ef040f6|   91cf2f932c9d4a57b34d8dc89cd8f621|   61aa47b4b3b1426f8aadad0d5d6083f5|   e64f02a897894a65ab665db9058bfebf|   
8fab09b08d4541fc9d7e989701896afe|   43950dedebfa45e0896e005348650819|   b49ad6f3edd94c2f9fc0158987a77332|   77e137533dc847d89148bec3d2a4c2dd|   fbe7524a54044e2c994c985288e6547c|   6a72a933787e4b62a36440c4f459fa03|   6f030d3507a54bf492b5187d261f5475|   9a996131274f4e4882453a5e922ef518|   640ce7c2f77343d7b23cf871e3e6ecc3|   01188380cf1247839c25d1e8e2acb60a|   
f269d744d83f44dbba7a056fb9e738f2|   8d6b0208f3264fb9acb2a894f4faa67d|   5c6542acbebd4a2c9707cd4079d0a1c7|   4a09cd435db342198633581c0fd92a47|   08ca8d65a542488dbd72a59d2a9f12de|   d40e2a10fc3344d0a59efbf52a68a52e|   c2bdc96417054151bbe54b21d3ac242b|   1cb621657eee495d9d7faaa9affea50f|   29edf7de65724525869a8fd051586891|   0c0a37f1d9d14219a2887676aed9dd46|   
6356d81ec33446ceaf4c27301aadea15|   2df78fdf909f408485168693cc69e6d3|   2fc089771c934d20bf561650dd1e6990|   40328717e9ab4a2ea97bffe6444dc969|   a046dacf50e54279b26713a7822cea82|   062bc2fe07e64ef289d7c8d4ebf2e88f|   7788c441f5c5486aa33b39418c7955e2|   3aeabe9e88f3486db0c2a738600c91da|   0a087ce4c8094c30a8185883dd180b58|   9890182dcfac4509be0890125d57e91a|   
6356d81ec33446ceaf4c27301aadea15|   6c49b6205b6b42d78a12fee7ad9d6863|   c8f5afef0fe64e2ead5716e221f32a60|   7a793947e26849ac9cd68fb3046a5f48|   d1157f589c6f4455a62d38d160dbf02e|   f595f8d61cf8473c975b233ec4ea8971|   af31473dea014cf49278b224c2bc4dca|   66653cd1fc0447e2b3f51e7da99db26e|   04baad3118824899937374a4dc003c86|   a808ab650bc442d28901adb2e33b5986|   
6356d81ec33446ceaf4c27301aadea15|   bda1faff329d4ac1a8cff449edf9b425|   be27ee7afef142288e84f336b0b249b8|   2d672c6c16b847a09e32315916e184eb|   e84375c01a014a6b8a4211cface07f1d|   0ff67695eeac49a192d8c2bf5b9b40e8|   55d2e31337b2444793fb4a30bd2d7702|   39fa9392518d4573965e6e3ba2c75ca9|   2791886c88b84a9a94e6a1feb604c2f5|   cedec90389cf44e9a6d7ee4c00d3b394|   
e54065d557634b5492ad3ffe991450d8|   c09c252beeef42049e4bf9e071449086|   e3fad258f5e446ceaab25cc7da98a96d|   d5e89d29bb3743bfba17b7a7dd8ad97c|   ceaee7ac199b41e5858215636141029e|   b30a37a926b040a08f93eff9d64e2d1d|   5746f8e242af469696289eea597a6cb2|   fc62da22ce124546822b1042d6a80686|   0d7fc25c779f48e8949374ce7d1fcdef|   c9c8127adf26401081bb2842dc89ba14|   
Process UUID [95]
[2#0#6356d81ec33446ceaf4c27301aadea15, 5#0#f269d744d83f44dbba7a056fb9e738f2, 6#0#6356d81ec33446ceaf4c27301aadea15, 7#0#6356d81ec33446ceaf4c27301aadea15, 8#0#6356d81ec33446ceaf4c27301aadea15]

哈哈，lz代码的问题，问题见下楼

Inhibitory 2014-01-01

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如果每一次执行都会重复，那么就是代码问题了。

Inhibitory 2014-01-01

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还有，如果不用多线程去生成UUID看看会不会重复，有可能问题出现在这也说不定。

Inhibitory 2014-01-01

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UUID毕竟是有限的，所以从理论上来说出现重复是可以想像的。但是楼主才生成这么几个就重复了，机率和中500万的彩票差不多。

tony4geek 2014-01-01

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UUID 重复几率很小很小的。

长笛党希望 2014-01-01

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不会的，是不是代码的问题，楼主可以找一下，你用时间来做UUID，一定能保证不重复。。建议尝试下。

coolbamboo2008 2014-01-01

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楼主，这么小的概率都被你抓住了，你可以考虑买张彩票

teemai 2013-12-31

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不会吧，这么低得概率都能被你逮到？？参考老帖：http://bbs.csdn.net/topics/390045377?page=1#post-393556750

花谢尊前不敢香 2013-12-31

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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的API。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
UUID由以下几部分的组合：
（1）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。
（2）时钟序列。
（3）全局唯一的IEEE机器识别号，如果有网卡，从网卡MAC地址获得，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)。在ColdFusion中可以用CreateUUID()函数很简单地生成UUID，其格式为：xxxxxxxx-xxxx- xxxx-xxxxxxxxxxxxxxxx(8-4-4-16)，其中每个 x 是 0-9 或 a-f 范围内的一个十六进制的数字。而标准的UUID格式为：xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxx (8-4-4-4-12)，可以从cflib 下载CreateGUID() UDF进行转换。