Generating 8-character only UUIDs

Question

UUID libraries generate 32-character UUIDs   I want to generate 8-character only UUIDs  is it possible

User · Answer

How about this one  Actually  this code returns 13 characters max  but it shorter than UUID   import java nio ByteBuffer  import java util UUID          Generate short UUID  13 characters          return short UUID     public static String shortUUID       UUID uuid   UUID randomUUID      long l   ByteBuffer wrap uuid toString   getBytes    getLong      return Long toString l  Character MAX RADIX

User · Answer

As  Cephalopod stated it isn t possible but you can shorten a UUID to 22 characters  public static String encodeUUIDBase64 UUID uuid            ByteBuffer bb   ByteBuffer wrap new byte 16            bb putLong uuid getMostSignificantBits             bb putLong uuid getLeastSignificantBits             return StringUtils trimTrailingCharacter BaseEncoding base64Url   encode bb array

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I do not think that it is possible but you have a good workaround    cut the end of your UUID using substring   use code new Random System currentTimeMillis    nextInt 99999999   this will generate random ID up to 8 characters long   generate alphanumeric id   char   chars    abcdefghijklmnopqrstuvwxyzABSDEFGHIJKLMNOPQRSTUVWXYZ1234567890  toCharArray    Random r   new Random System currentTimeMillis     char   id   new char 8   for  int i   0   i  lt  8   i          id i    chars r nextInt chars length      return new String id

User · Answer

Not a UUID  but this works for me  UUID randomUUID   toString   replace  quot - quot   quot  quot   substring 0 8

User · Answer

It is not possible since a UUID is a 16-byte number per definition  But of course  you can generate 8-character long unique strings  see the other answers    Also be careful with generating longer UUIDs and substring-ing them  since some parts of the ID may contain fixed bytes  e g  this is the case with MAC  DCE and MD5 UUIDs

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Actually I want timestamp based shorter unique identifier  hence tried the below program   It is guessable with nanosecond     endians length   endians length   combinations   public class TimStampShorterUUID        private static final Character    endians                 a    b    c    d    e    f    g    h    i    j                 k    l    m    n    o    p    q    r    s    t                 u    v    w    x    y    z                 A    B    C    D    E    F    G    H    I    J                 K    L    M    N    O    P    Q    R    S    T                 U    V    W    X    Y    Z                0    1    2    3    4    5    6    7    8    9                     private static ThreadLocal lt Character gt  threadLocal    new ThreadLocal lt Character gt         private static AtomicLong iterator   new AtomicLong -1         public static String generateShorterTxnId                Keep this as secure random when we want more secure  in distributed systems         int firstLetter   ThreadLocalRandom current   nextInt 0   endians length               Sometimes your randomness and timestamp will be same value            when multiple threads are trying at the same nano second           time hence to differentiate it  utilize the threads requesting           for this value  the possible unique thread numbers    endians length         Character secondLetter   threadLocal get            if  secondLetter    null                synchronized  threadLocal                    if  secondLetter    null                        threadLocal set endians  int   iterator incrementAndGet     endians length                                                 secondLetter   threadLocal get                      return      endians firstLetter    secondLetter   System nanoTime                public static void main String   args             Map lt String  String gt  uniqueKeysTestMap   new ConcurrentHashMap lt  gt              Thread t1   new Thread                    Override             public void run                     while true                        String time   generateShorterTxnId                        String result   uniqueKeysTestMap put time                           if result    null                            System out println  failed  -     time                                                                                    Thread t2   new Thread                    Override             public void run                     while true                        String time   generateShorterTxnId                        String result   uniqueKeysTestMap put time                           if result    null                            System out println  failed  -     time                                                                                    Thread t3   new Thread                    Override             public void run                     while true                        String time   generateShorterTxnId                        String result   uniqueKeysTestMap put time                           if result    null                            System out println  failed  -     time                                                                                    Thread t4   new Thread                    Override             public void run                     while true                        String time   generateShorterTxnId                        String result   uniqueKeysTestMap put time                           if result    null                            System out println  failed  -     time                                                                                    Thread t5   new Thread                    Override             public void run                     while true                        String time   generateShorterTxnId                        String result   uniqueKeysTestMap put time                           if result    null                            System out println  failed  -     time                                                                             Thread t6   new Thread                    Override             public void run                     while true                        String time   generateShorterTxnId                        String result   uniqueKeysTestMap put time                           if result    null                            System out println  failed  -     time                                                                                Thread t7   new Thread                    Override             public void run                     while true                        String time   generateShorterTxnId                        String result   uniqueKeysTestMap put time                           if result    null                            System out println  failed  -     time                                                                             t1 start            t2 start            t3 start            t4 start            t5 start            t6 start            t7 start              UPDATE  This code will work on single JVM  but we should think on distributed JVM  hence i am thinking two solutions one with DB and another one without DB   with DB   Company name  shortname 3 chars  ---- Random Number ---- Key specific redis COUNTER   3 char  ------------------------------------------------  2 char  ----------------  11 char   without DB  IPADDRESS ---- THREAD NUMBER ---- INCR NUMBER ---- epoch milliseconds   5 chars  -----------------  2char  -----------------------  2 char  -----------------  6 char   will update you once coding is done

User · Answer

First  Even the unique IDs generated by java UUID randomUUID or  net GUID are not 100  unique  Especialy UUID randomUUID is  only  a 128 bit  secure  random value  So if you reduce it to 64 bit  32 bit  16 bit  or even 1 bit  then it becomes simply less unique   So it is at least a risk based decisions  how long your uuid must be   Second  I assume that when you talk about  only 8 characters  you mean a String of 8 normal printable characters   If you want a unique string with length 8 printable characters you could use a base64 encoding  This means 6bit per char  so you get 48bit in total  possible not very unique - but maybe it is ok for you application   So the way is simple  create a 6 byte random array   SecureRandom rand           byte   randomBytes   new byte 16    rand nextBytes randomBytes     And then transform it to a Base64 String  for example by org apache commons codec binary Base64  BTW  it depends on your application if there is a better way to create  uuid  then by random   If you create a the UUIDs only once per second  then it is a good idea to add a time stamp   By the way  if you combine  xor  two random values  the result is always at least as random as the most random of the both

User · Answer

This is a similar way I m using here to generate an unique error code  based on Anton Purin answer  but relying on the more appropriate org apache commons text RandomStringGenerator instead of the  once  not anymore  deprecated org apache commons lang3 RandomStringUtils    Singleton  Component public class ErrorCodeGenerator implements Supplier lt String gt         private RandomStringGenerator errorCodeGenerator       public ErrorCodeGenerator             errorCodeGenerator   new RandomStringGenerator Builder                    withinRange  0    z                    filteredBy t - gt  t  gt    0   amp  amp  t  lt    9   t - gt  t  gt    A   amp  amp  t  lt    Z   t - gt  t  gt    a   amp  amp  t  lt    z                    build                Override     public String get             return errorCodeGenerator generate 8              All advices about collision still apply  please be aware of them

User · Answer

You can try RandomStringUtils class from apache commons   import org apache commons lang3 RandomStringUtils   final int SHORT ID LENGTH   8      all possible unicode characters String shortId   RandomStringUtils random SHORT ID LENGTH     Please keep in mind  that it will contain all possible characters which is neither URL nor human friendly    So check out other methods too      HEX  0-9  a-f  For example  6587fddb  c0f182c1 shortId   RandomStringUtils random 8   0123456789abcdef         a-z  A-Z  For example  eRkgbzeF  MFcWSksx shortId   RandomStringUtils randomAlphabetic 8        0-9  For example  76091014  03771122 shortId   RandomStringUtils randomNumeric 8        a-z  A-Z  0-9  For example  WRMcpIk7  s57JwCVA shortId   RandomStringUtils randomAlphanumeric 8      As others said probability of id collision with smaller id can be significant  Check out how birthday problem applies to your case  You can find nice explanation how to calculate approximation in this answer

[java] Generating 8-character only UUIDs

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