java UUID.randomUUID() 与 SecureRandom
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UUID.randomUUID() vs SecureRandom
提问by User3518958
I am trying to understand the advantages of using UUID.randomUUID() over SecureRandom generator as the former uses securerandom internally.
我试图了解使用 UUID.randomUUID() 而不是 SecureRandom 生成器的优势，因为前者在内部使用 securerandom。
回答by uoyilmaz
Well, the source codeshows UUID.randomUUIDuses SecureRandom.
好吧，源代码显示UUID.randomUUID使用SecureRandom.
public static UUID [More ...] randomUUID() {
SecureRandom ng = numberGenerator;
if (ng == null) {
numberGenerator = ng = new SecureRandom();
}
byte[] randomBytes = new byte[16];
ng.nextBytes(randomBytes);
randomBytes[6] &= 0x0f; /* clear version */
randomBytes[6] |= 0x40; /* set to version 4 */
randomBytes[8] &= 0x3f; /* clear variant */
randomBytes[8] |= 0x80; /* set to IETF variant */
return new UUID(randomBytes);
}
As you can see, you can use either, but in a secure UUID you have 6 non-random bits, which can be considered a disadvantage if you are picky.
如您所见，您可以使用任何一种，但在安全的 UUID 中，您有 6 个非随机位，如果您很挑剔，这可以被认为是一个缺点。
回答by Peter Lawrey
Random numbers have a random chance of being repeated. The lower the randomness (unless there is some co-ordination), the greater the chance of producing the same number twice.
随机数有随机重复的机会。随机性越低（除非有一些协调），产生相同数字两次的机会就越大。
https://en.wikipedia.org/wiki/Birthday_problem
As you produce more random numbers the chance of the same number being repeated increases as every id must be different to every other id.
https://en.wikipedia.org/wiki/Birthday_problem
随着您生成更多随机数，重复相同数字的机会会增加，因为每个 id 必须与其他每个 id 不同。
SecureRandom allows you to choose how many bit of randomness you want. Make it too small and there is a good chance they will be repeated. You can get duplicate random 32-bit id in a fraction of a second.
SecureRandom 允许您选择所需的随机数。让它太小，它们很有可能会重复。您可以在几分之一秒内获得重复的随机 32 位 ID。
UUID sets the standard at 128 bits (or as uoyilmaz points out, 122 bits are random) This is enough for most use cases. However if you want a random String, I would be tempted to use more bits and/or a higher base than 16. Java for example support base 36 and 64 which means you can have shorter ids, or more randomness for the same length ID.
UUID 将标准设置为 128 位（或者正如 uoyilmaz 指出的那样，122 位是随机的）这对于大多数用例来说已经足够了。但是，如果您想要一个随机字符串，我会倾向于使用更多位和/或比 16 更高的基数。例如，Java 支持基数 36 和 64，这意味着您可以拥有更短的 ID，或者相同长度 ID 的更多随机性。
Note: UUID format has multiple -in it's dump though I don't see the value of them, they just make the string longer.
注意：UUID 格式-在它的转储中有多个，尽管我没有看到它们的值，它们只是使字符串更长。
回答by typelogic
Thanks for all the provided technical answers. I, myself, was also baffled by the difference between the two which led me here. But then, a thought dawned on me: If you only call the function once, then there is no difference as both method generates a number that could not be pre-calculated. But if call the function several times, then they differ here because a statistical normal distribution is a property of a random number generator whereas this is not a property of a UUID. UUID strives for uniqueness and in fact it derives the provided number using your computer's MAC hardware address, the current epoch seconds etc. And eventually, if you for-loop call the UUID values it will not be statistically normally distributed.
感谢您提供的所有技术答案。我自己也对导致我来到这里的两者之间的差异感到困惑。但是，我突然想到：如果你只调用一次函数，那么没有区别，因为这两种方法都会生成一个无法预先计算的数字。但是，如果多次调用该函数，则它们在这里有所不同，因为统计正态分布是随机数生成器的属性，而这不是 UUID 的属性。UUID 力求唯一性，实际上它使用您计算机的 MAC 硬件地址、当前纪元秒等得出提供的数字。最终，如果您循环调用 UUID 值，它将不会在统计上呈正态分布。
回答by sandromark78
The UUID is not a random number: it is a universal unique ID. You can be sure that no one can generate the same hexadecimal string.
UUID 不是随机数：它是通用唯一 ID。您可以确定没有人可以生成相同的十六进制字符串。
A random number is another story: it is not an hexadecimal string and it is not universally unique.
随机数是另一回事：它不是十六进制字符串，也不是普遍唯一的。
A more efficient and completed generator of UUIDs is provided by this library.
这个库提供了一个更高效、更完整的 UUID 生成器。
