How to generate a lot of unique random strings in Scala

Question

I want to generate a lot of random strings that unique of each other and unique in MySQL with specify the number of generated like 10,000.

I could make sure the strings are unique each other in every time generated strings, just check if the List[String] contains the string in each time generate.
But I don't know how to make sure its unique in MySQL, I have been set the unique index in MySQL like ALTER TABLE Code ADD UNIQUE INDEX `codeUnique` (`code`);

But if the unique guarantee is when inserting data into MySQL, insert will failure.
And if check the insert failure in each time insert, generating will take a very very long time when the number of generated is large.

Answer 1

Use List.fill and randomUUID as @Sudhir notes:

scala> List.fill(10000)(java.util.UUID.randomUUID.toString)
res0: List[String] = List(
  3c789851-975c-499d-8b0b-5bc60dee7497, 
  9511fb41-a42e-47d8-a5f3-ba1a6f3847f2,
  61263421-59de-4538-87c6-eb98ccf1e19d, 
 ...)

You can double check they are unique by converting it to a set and checking the size:

scala> List.fill(10000)(randomUUID.toString).toSet.size
res1: Int = 10000

Answer 2

You can simply use Java's java.util.UUID.randomUUID.toString method to get unique String . See doc here . Chances of getting duplicate keys using this method is very low (I never got duplicate keys). So you don't have to maintain a collection either.

If you want to use your own random key generator and want to make sure it's unique, you should not go for List[String] because List can have duplicates and for checking if a key already exists, you need to iterate over each elements, which is a costly operation. You should use Set[String] instead and then use Set 's contains() method to check if key is already present.

Answer 3

循环遍历10000个整数，取每个数字的MD5或SHA1。