Efficient method to generate UUID String in JAVA (UUID.randomUUID().toString() without the dashes)

Question

Hello,

I would like an efficient utility to generate Unique sequences of bytes. UUID is a good candidate but UUID.randomUUID().toString() generates stuff like 44e128a5-ac7a-4c9a-be4c-224b6bf81b20 which is good as long as you don't need to transmit it over http, in which casa the dashes need to be removed.

I'm looking for an efficient way to generate a random strings, only from alphanumeric characters (no dashes or any other special symbols).

Thanks for helping, Maxim.

Answer 1

This does it:

public static void main(String[] args) {
    final String uuid = UUID.randomUUID().toString().replaceAll("-", "");
    System.out.println("uuid = " + uuid);
}

But I don't understand fully why you want to remove the dashes.

Answer 2

Dashes don't need to be removed from HTTP request as you can see in URL of this thread. But if you want to prepare well-formed URL without dependency on data you should use URLEncoder.encode( String data, String encoding ) instead of changing standard form of you data. For UUID string representation dashes is normal.

Answer 3

I used JUG (Java UUID Generator) to generate unique ID. It is unique across JVMs. Pretty good to use. Here is the codes for your reference.

private static final SecureRandom secureRandom = new SecureRandom();
private static final UUIDGenerator generator = UUIDGenerator.getInstance();

public synchronized static String generateUniqueId() {
  UUID uuid = generator.generateRandomBasedUUID(secureRandom);

  return uuid.toString().replaceAll("-", "").toUpperCase();
}

You could download the library from: http://jug.safehaus.org/

Answer 4

Hey guys,

Just wanted to update that I've ended up writing something of my own (after reading UUID.java implementation). Note that I'm not generating a UUID, instead just a random 32 bytes hex string in the most efficient way I could think of.

import java.security.SecureRandom;
import java.util.UUID;

public class RandomUtil {
    // Maxim: Copied from UUID implementation :)
    private static volatile SecureRandom numberGenerator = null;
    private static final long MSB = 0x8000000000000000L;

    public static String genRandom32Hex() {
        SecureRandom ng = numberGenerator;
        if (ng == null) {
            numberGenerator = ng = new SecureRandom();
        }

        return Long.toHexString(MSB | ng.nextLong()) + Long.toHexString(MSB | ng.nextLong());
    }

    public static void main(String[] args) {
        System.out.println(UUID.randomUUID().toString());
        System.out.println(RandomUtil.genRandom32Hex());

        System.out.println();
        System.out.println(Long.toHexString(0x8000000000000000L |21));
        System.out.println(Long.toBinaryString(0x8000000000000000L |21));
        System.out.println(Long.toHexString(Long.MAX_VALUE + 1));
    }
}