method to generating random UUID using Java

Question

I have a task to generate a unique string, the first thought which came to my mind was to use Java's UUID generator with additional improvements. And so my way of generating a random string looks something like this

public static String generateRandomString() {
    return "TEST" + 
            DateTimeFormatter.ofPattern("yyyyMMddHHmmssSSSSSS")
                    .format(LocalDateTime.now()) + UUID.randomUUID()
            .toString().replace("-", "");
}

would this method generating a random string would be sufficient to achieve uniqueness having in mind that I need to generate 10 000 000 of them on a daily basis for the next 20 years. Also, this piece of code will be spinning on different JVM and potentially on different servers.

To get/preserve an information on when approximately the string was generated. — miroana, Jan 11 '21 at 21:05
Just as an aside, all of the date/time formatting just gives the same uniqueness as using System.currentTimeMillis() — SJuan76, Jan 12 '21 at 00:31

score 3 · Answer 1 · answered Jan 11 '21 at 21:06

3

UUID.randomUUID() generates a type-4 UUID.

According to Wikipedia:

Thus, the probability to find a duplicate within 103 trillion version-4 UUIDs is one in a billion.

More info.

answered Jan 11 '21 at 21:06

Adrian Russo

546
4
16

score 2 · Answer 2 · answered Jan 11 '21 at 21:06

2

Just do the maths:

10000000*365*20 =                             73000000000
2^128           = 340282366920938463463374607431768211456

I'd say you can use it after comparing these numbers.

EDIT: I just saw a few other answers, definitely check if UUID.randomUUID() uses the full 128 bits or only some.

answered Jan 11 '21 at 21:06

recursive_tree

109
4

How this number 2^128 would be impacted knowing that multiple JVM could generate a random string using this very same method? – miroana Jan 11 '21 at 21:11
A version 4 UUID returned by `UUID.randomUUID()` has 122 random bits. https://en.wikipedia.org/wiki/Universally_unique_identifier#Version_4_(random) – dnault Jan 11 '21 at 21:18
2

@miroana Nothing to worry about, see https://stackoverflow.com/questions/1155008/how-unique-is-uuid – Progman Jan 11 '21 at 21:18

method to generating random UUID using Java

2 Answers2