Is there any way to generate the same UUID from a String

Question

I am wondering if there is a way to generate the same UUID based on a String. I tried with UUID, it looks like it does not provide this feature.

Answer 1

You can use UUID this way to get always the same UUID for your input String:

 String aString="JUST_A_TEST_STRING";
 String result = UUID.nameUUIDFromBytes(aString.getBytes()).toString();

Answer 2

UUID.nameUUIDFromBytes() only generates MD5 UUIDs. However, SHA1 is preferred over MD5, if backward compatibility is not an issue.

The utility class below generates MD5 UUIDs and SHA-1 UUIDs. Feel free to use and share.

package com.example;

import java.nio.ByteBuffer;
import java.nio.charset.StandardCharsets;
import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;
import java.util.UUID;

/**
 * Generates UUIDv3 (MD5) and UUIDv5 (SHA1).
 *
 * It is fully compliant with RFC-4122.
 */
public class HashUuid {

    private static final int V3 = 3; // MD5
    private static final int V5 = 5; // SHA-1

    private static final String HASH_V3 = "MD5";
    private static final String HASH_V5 = "SHA-1";

    public static final UUID NAMESPACE_DNS = new UUID(0x6ba7b8109dad11d1L, 0x80b400c04fd430c8L);
    public static final UUID NAMESPACE_URL = new UUID(0x6ba7b8119dad11d1L, 0x80b400c04fd430c8L);
    public static final UUID NAMESPACE_OID = new UUID(0x6ba7b8129dad11d1L, 0x80b400c04fd430c8L);
    public static final UUID NAMESPACE_X500 = new UUID(0x6ba7b8149dad11d1L, 0x80b400c04fd430c8L);

    public static UUID v3(String name) {
        return generate(V3, HASH_V3, null, name);
    }

    public static UUID v5(String name) {
        return generate(V5, HASH_V5, null, name);
    }

    public static UUID v3(UUID namespace, String name) {
        return generate(V3, HASH_V3, namespace, name);
    }

    public static UUID v5(UUID namespace, String name) {
        return generate(V5, HASH_V5, namespace, name);
    }

    private static UUID generate(int version, String algorithm, UUID namespace, String name) {

        MessageDigest hasher = hasher(algorithm);

        if (namespace != null) {
            ByteBuffer ns = ByteBuffer.allocate(16);
            ns.putLong(namespace.getMostSignificantBits());
            ns.putLong(namespace.getLeastSignificantBits());
            hasher.update(ns.array());
        }

        hasher.update(name.getBytes(StandardCharsets.UTF_8));
        ByteBuffer hash = ByteBuffer.wrap(hasher.digest());

        final long msb = (hash.getLong() & 0xffffffffffff0fffL) | (version & 0x0f) << 12;
        final long lsb = (hash.getLong() & 0x3fffffffffffffffL) | 0x8000000000000000L;

        return new UUID(msb, lsb);
    }

    private static MessageDigest hasher(String algorithm) {
        try {
            return MessageDigest.getInstance(algorithm);
        } catch (NoSuchAlgorithmException e) {
            throw new RuntimeException(String.format("%s not supported.", algorithm));
        }
    }

    /**
     * For tests!
     */
    public static void main(String[] args) {

        UUID namespace = UUID.randomUUID();
        String name = "JUST_A_TEST_STRING";

        System.out.println(String.format("UUID.nameUUIDFromBytes():     '%s'", UUID.nameUUIDFromBytes(name.getBytes())));
        System.out.println();
        System.out.println(String.format("HashUuid.v3(name):            '%s'", HashUuid.v3(name)));
        System.out.println(String.format("HashUuid.v5(name):            '%s'", HashUuid.v5(name)));
        System.out.println(String.format("HashUuid.v3(namespace, name): '%s'", HashUuid.v3(namespace, name)));
        System.out.println(String.format("HashUuid.v5(namespace, name): '%s'", HashUuid.v5(namespace, name)));
    }
}

This is the output:

UUID.nameUUIDFromBytes():     '9e120341-627f-32be-8393-58b5d655b751'

HashUuid.v3(name):            '9e120341-627f-32be-8393-58b5d655b751'
HashUuid.v5(name):            'e4586bed-032a-5ae6-9883-331cd94c4ffa'
HashUuid.v3(namespace, name): 'f0043437-723b-308f-a6c0-74ec36ddf9c2'
HashUuid.v5(namespace, name): '18a45fd8-8fab-5647-aad7-1d3264932180'

Alternatively, you can also use uuid-creator. See this example:

// Create a UUIDv5 (SHA1)
String name = "JUST_A_TEST_STRING";
UUID uuid = UuidCreator.getNameBasedSha1(name);

Answer 3

You should use UUID v5.

Version-3 and version-5 UUIDs are generated by hashing a namespace identifier and name. Version 3 uses MD5 as the hashing algorithm, and version 5 uses SHA-1.1 - wikipedia

UUID v5 requires a namespace. That namespace should be a UUID v4, which you can just generate online. The namespace assures that for a given input, the output will always be the same.

A possible implementation of UUID v5 can be found here:

<!-- https://search.maven.org/artifact/com.github.f4b6a3/uuid-creator -->
<dependency>
  <groupId>com.github.f4b6a3</groupId>
  <artifactId>uuid-creator</artifactId>
  <version>3.6.0</version>
</dependency>

It can be used as follows:

UUID namespace = ; // todo generate a UUID v4.
String input = "input";
UUID uuid = UuidCreator.getNameBasedSha1(namespace, input);

(In a way, the namespace acts like a seed would, for a random number generator. By contrast, while a seed is supposed to be random, our namespace is a constant. And that forces our generator to always produce the same value for a given input.)

Answer 4

If you are looking for a Javascript alternative, look at uuid-by-string which also gives option to use SHA-1 or MD5 hash functions.