Storing UUID as base64 String

Question

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 

Answer 1

I was also trying to do something similar. I am working with a Java application which uses UUIDs of the form 6fcb514b-b878-4c9d-95b7-8dc3a7ce6fd8 (which are generated with the standard UUID lib in Java). In my case I needed to be able to get this UUID down to 30 characters or less. I used Base64 and these are my convenience functions. Hopefully they will be helpful for someone as the solution was not obvious to me right away.

Usage:

String uuid_str = "6fcb514b-b878-4c9d-95b7-8dc3a7ce6fd8"; String uuid_as_64 = uuidToBase64(uuid_str); System.out.println("as base64: "+uuid_as_64); System.out.println("as uuid: "+uuidFromBase64(uuid_as_64)); 

Output:

as base64: b8tRS7h4TJ2Vt43Dp85v2A as uuid  : 6fcb514b-b878-4c9d-95b7-8dc3a7ce6fd8 

Functions:

import org.apache.commons.codec.binary.Base64;  private static String uuidToBase64(String str) {     Base64 base64 = new Base64();     UUID uuid = UUID.fromString(str);     ByteBuffer bb = ByteBuffer.wrap(new byte[16]);     bb.putLong(uuid.getMostSignificantBits());     bb.putLong(uuid.getLeastSignificantBits());     return base64.encodeBase64URLSafeString(bb.array()); } private static String uuidFromBase64(String str) {     Base64 base64 = new Base64();      byte[] bytes = base64.decodeBase64(str);     ByteBuffer bb = ByteBuffer.wrap(bytes);     UUID uuid = new UUID(bb.getLong(), bb.getLong());     return uuid.toString(); } 

Answer 2

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.