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Asked: 2026-05-11T15:07:54+00:00

I have been experimenting with using UUIDs as database keys. I want to take

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I have been experimenting with using UUIDs as database keys. I want to take up the least amount of bytes as possible, while still keeping the UUID representation human readable.

I think that I have gotten it down to 22 bytes using base64 and removing some trailing ‘==’ that seem to be unnecessary to store for my purposes. Are there any flaws with this approach?

Basically my test code does a bunch of conversions to get the UUID down to a 22 byte String, then converts it back into a UUID.

import java.io.IOException; import java.util.UUID;  public class UUIDTest {      public static void main(String[] args){         UUID uuid = UUID.randomUUID();         System.out.println('UUID String: ' + uuid.toString());         System.out.println('Number of Bytes: ' + uuid.toString().getBytes().length);         System.out.println();          byte[] uuidArr = asByteArray(uuid);         System.out.print('UUID Byte Array: ');         for(byte b: uuidArr){             System.out.print(b +' ');         }         System.out.println();         System.out.println('Number of Bytes: ' + uuidArr.length);         System.out.println();           try {             // Convert a byte array to base64 string             String s = new sun.misc.BASE64Encoder().encode(uuidArr);             System.out.println('UUID Base64 String: ' +s);             System.out.println('Number of Bytes: ' + s.getBytes().length);             System.out.println();               String trimmed = s.split('=')[0];             System.out.println('UUID Base64 String Trimmed: ' +trimmed);             System.out.println('Number of Bytes: ' + trimmed.getBytes().length);             System.out.println();              // Convert base64 string to a byte array             byte[] backArr = new sun.misc.BASE64Decoder().decodeBuffer(trimmed);             System.out.print('Back to UUID Byte Array: ');             for(byte b: backArr){                 System.out.print(b +' ');             }             System.out.println();             System.out.println('Number of Bytes: ' + backArr.length);              byte[] fixedArr = new byte[16];             for(int i= 0; i<16; i++){                 fixedArr[i] = backArr[i];             }             System.out.println();             System.out.print('Fixed UUID Byte Array: ');             for(byte b: fixedArr){                 System.out.print(b +' ');             }             System.out.println();             System.out.println('Number of Bytes: ' + fixedArr.length);              System.out.println();             UUID newUUID = toUUID(fixedArr);             System.out.println('UUID String: ' + newUUID.toString());             System.out.println('Number of Bytes: ' + newUUID.toString().getBytes().length);             System.out.println();              System.out.println('Equal to Start UUID? '+newUUID.equals(uuid));             if(!newUUID.equals(uuid)){                 System.exit(0);             }           } catch (IOException e) {         }      }       public static byte[] asByteArray(UUID uuid) {          long msb = uuid.getMostSignificantBits();         long lsb = uuid.getLeastSignificantBits();         byte[] buffer = new byte[16];          for (int i = 0; i < 8; i++) {             buffer[i] = (byte) (msb >>> 8 * (7 - i));         }         for (int i = 8; i < 16; i++) {             buffer[i] = (byte) (lsb >>> 8 * (7 - i));         }          return buffer;      }      public static UUID toUUID(byte[] byteArray) {          long msb = 0;         long lsb = 0;         for (int i = 0; i < 8; i++)             msb = (msb << 8) | (byteArray[i] & 0xff);         for (int i = 8; i < 16; i++)             lsb = (lsb << 8) | (byteArray[i] & 0xff);         UUID result = new UUID(msb, lsb);          return result;     }  }

output:

UUID String: cdaed56d-8712-414d-b346-01905d0026fe Number of Bytes: 36  UUID Byte Array: -51 -82 -43 109 -121 18 65 77 -77 70 1 -112 93 0 38 -2  Number of Bytes: 16  UUID Base64 String: za7VbYcSQU2zRgGQXQAm/g== Number of Bytes: 24  UUID Base64 String Trimmed: za7VbYcSQU2zRgGQXQAm/g Number of Bytes: 22  Back to UUID Byte Array: -51 -82 -43 109 -121 18 65 77 -77 70 1 -112 93 0 38 -2 0 38  Number of Bytes: 18  Fixed UUID Byte Array: -51 -82 -43 109 -121 18 65 77 -77 70 1 -112 93 0 38 -2  Number of Bytes: 16  UUID String: cdaed56d-8712-414d-b346-01905d0026fe Number of Bytes: 36  Equal to Start UUID? true
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1 Answer

  1. You can safely drop the padding "==" in this application. If you were to decode the base-64 text back to bytes, some libraries would expect it to be there, but since you are just using the resulting string as a key, it’s not a problem.

    I’d use Base-64 because its encoding characters can be URL-safe, and it looks less like gibberish. But there’s also Base-85. It uses more symbols and codes 4 bytes as 5 characters, so you could get your text down to 20 characters.

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