How to generate a GUID/UUID in Apex?

Question:

What is the best way to generate a GUID/UUID in Apex, particularly in the format nnnnnnnn-nnnn-nnnn-nnnn-nnnnnnnnnnnn?

For example, a valid UUID might look like 13219ec0-3a81-44c5-a300-de14b7d0235f. This functionality would be useful in scenarios like assigning unique identifiers to records in triggers.

Answer:

Below is a reusable class in Apex for generating GUIDs/UUIDs. The class uses random number generation to create a unique string formatted according to the requested structure.

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Sample Usage:

You can generate a GUID-like string by creating an MD5 hash of the current timestamp. The timestamp is retrieved using DateTime.now().getTime(), ensuring that each generated string is unique, with a resolution down to 1 millisecond.

if (acct.AccountUuid__c == null) {
    acct.AccountUuid__c = GuidUtil.NewGuid();
}

code explanation: The code checks if the AccountUuid__c field on the acct record is null. If it is, it assigns a newly generated UUID from the GuidUtil.NewGuid() method to ensure the record has a unique identifier.

Apex Class:

global class GuidUtil {

    private static String kHexChars = '0123456789abcdef';

    global static String NewGuid() {
        String returnValue = '';
        Integer nextByte = 0;

        for (Integer i = 0; i < 16; i++) {
            if (i == 4 || i == 6 || i == 8 || i == 10) 
                returnValue += '-';

            nextByte = (Math.round(Math.random() * 255) - 128) & 255;

            if (i == 6) {
                nextByte = nextByte & 15;
                nextByte = nextByte | (4 << 4);
            }

            if (i == 8) {
                nextByte = nextByte & 63;
                nextByte = nextByte | 128;
            }

            returnValue += getCharAtIndex(kHexChars, nextByte >> 4);
            returnValue += getCharAtIndex(kHexChars, nextByte & 15);
        }

        return returnValue;
    }

    global static String getCharAtIndex(String str, Integer index) {
        if (str == null) return null;
        if (str.length() <= 0) return str;    
        if (index == str.length()) return null;    
        return str.substring(index, index + 1);
    }
}

code explanation: The GuidUtil class generates a random UUID in Apex using a loop to construct a 16-byte identifier, inserting hyphens at specific positions to match the UUID format. It ensures compliance with UUID version 4 by setting specific bits and uses a helper method to extract hexadecimal characters for the final string.

This implementation ensures compliance with the UUID version 4 standard, where the sixth octet indicates the UUID version, and the eighth octet indicates the variant. It creates a unique identifier every time it is called.

Summing up

In Apex, a GUID/UUID can be generated using either a timestamp-based or a randomness-based approach. The timestamp method leverages DateTime.now().getTime(), creating a unique 128-bit string hashed with MD5, ensuring uniqueness at the millisecond level but requiring careful timing to avoid duplicates. Alternatively, Crypto.getRandomLong() generates a random long value, which is then hashed using MD5 for higher entropy, though it may be slightly slower due to additional computation. Both methods can format the result into a standard GUID structure using string manipulation techniques like toUpperCase() and insert() to add dashes, ensuring the output follows the typical nnnnnnnn-nnnn-nnnn-nnnn-nnnnnnnnnnnn format.

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