Efficient method to generate UUID String in JAVA UUID randomUUID toString without the dashes

Question

I would like an efficient utility to generate unique sequences of bytes  UUID is a good candidate but UUID randomUUID   toString   generates stuff like 44e128a5-ac7a-4c9a-be4c-224b6bf81b20 which is good  but I would prefer dash-less string   I m looking for an efficient way to generate a random strings  only from alphanumeric characters  no dashes or any other special symbols

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Dashes don t need to be removed from HTTP request as you can see in URL of this thread  But if you want to prepare well-formed URL without dependency on data you should use URLEncoder encode  String data  String encoding   instead of changing standard form of you data  For UUID string representation dashes is normal

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This does it   public static void main String   args        final String uuid   UUID randomUUID   toString   replace  -            System out println  uuid       uuid

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I have just copied UUID toString   method and just updated it to remove  -  from it  It will be much more faster and straight forward than any other solution  public String generateUUIDString UUID uuid        return  digits uuid getMostSignificantBits    gt  gt  32  8                digits uuid getMostSignificantBits    gt  gt  16  4                digits uuid getMostSignificantBits    4                digits uuid getLeastSignificantBits    gt  gt  48  4                digits uuid getLeastSignificantBits    12           Returns val represented by the specified number of hex digits     private String digits long val  int digits        long hi   1L  lt  lt   digits   4       return Long toHexString hi    val  amp   hi - 1    substring 1       Usage   generateUUIDString UUID randomUUID     Another implementation using reflection  public String generateString UUID uuid  throws NoSuchMethodException  InvocationTargetException  IllegalAccessException        if  uuid    null            return                Method digits   UUID class getDeclaredMethod  digits   long class  int class       digits setAccessible true        return    String  digits invoke uuid  uuid getMostSignificantBits    gt  gt  32  8                digits invoke uuid  uuid getMostSignificantBits    gt  gt  16  4                digits invoke uuid  uuid getMostSignificantBits    4                digits invoke uuid  uuid getLeastSignificantBits    gt  gt  48  4                digits invoke uuid  uuid getLeastSignificantBits    12

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Well  since an UUID gets added the hyphens  dashes  on toString   we can steal the implementation from Java s own implementation  shorting the byte array to 32 and adjusting the offset          public static String special                 UUID uuid   UUID randomUUID                return fastUUID uuid getLeastSignificantBits    uuid getMostSignificantBits                        private static String fastUUID long lsb  long msb                byte   buf   new byte 32               formatUnsignedLong0 lsb         4  buf  20  12               formatUnsignedLong0 lsb  gt  gt  gt  48  4  buf  16  4                formatUnsignedLong0 msb         4  buf  12  4               formatUnsignedLong0 msb  gt  gt  gt  16  4  buf  8   4               formatUnsignedLong0 msb  gt  gt  gt  32  4  buf  0   8                return new String buf  0                      private static final char   digits                      0     1     2     3     4     5                     6     7     8     9     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                     private static void formatUnsignedLong0 long val  int shift  byte   buf  int offset  int len                int charPos   offset   len              int radix   1  lt  lt  shift              int mask   radix - 1              do                   buf --charPos     byte digits   int  val   amp  mask                   val  gt  gt  gt   shift                while  charPos  gt  offset              Running it          public static void main String   args                IntStream range 0  100  forEach i- gt                    System out println special                                Generates  23f57da8a2784bb5acca553030f82e61 a14427efd8d147fdae315c1cf20fc53c ee972aa1cf85414ca364bef5c74a7e57 6877ef35eab94b9485c5dd7c8c5a8a56 578721476629422381c0f625e22564a8 dbf60f068b5443d7bc6e5280696fed9f dd611e870700480d81d394dd2125316c 04d71b9379ef4db49c28e113485ea76d fd4e8cf3f85a45ae8c1b9bfe3e489a4a 858c4e8297f849b784b65b6096dec4d4 b30a8ca318a349b486b5693814422555 351c2fab9bc1426fa3bb512484628f12 9ce59e01db38405aab82d46f2a236880 5ffb5acb547a4f15a4621b406391bc0d 541b5fba8ddb4f1ebbd59cdcd5f59f7c 77f9460c4baa43a7bbaaf7f2aff205bd 85fa5254305b4c72b1b7c0103aaee269 062d45aa86694b06aad841236b839341 7a265293560f4223ab8248fda502c89b b748c13ac45747b99aead4b0a2d7d179 cbcbf623c75d407fa3c88cfc89a90ed4 da263eed8771496faebb6290527f77fa 22231088dec04cffa40fb79ff56c6453 594a66de4b874b3491649c5d033917f6 4f6802ebd0cc4a39b25a67191c3af09d 8878b7ab8aa445cdadbef0f7c70d3deb 2c3ed0154f0c4ddbad498b7ae928b9bc cac1dcaa80e54e2db3248987d2dbda4a f9a3567e6dd54bf5900444c8b1c03815 f0d25d7b615a4495b51c01ab15093a88 243e45926311437c8b26cede2dc7de25 e4738c50e4cd448fbac252571c0907df 261d3593cc054569bcd645885d22c2ee 64a4796356a04cc4a09506aeb6f5b8fd 9aeebcbdde074ed69738589ca9bde0f1 ec040c956861466b84ed7f7cec601be0 18bd233781e44e7cb152800db4c4edc7 1b7b251df1244e8db46a45c186aada2b 3e32f644c9074cb3bbb15c5be1d9b95e 625309e3ffd14a90bfbd6d48142ac60e 664f0cf347ce4767add576da584526e7 fe3893fd376849fe9fed00e328e61470 254ce1441bbf4a7eae1cdf8d288e61e8 90896c6b309a49f48cc3b7a1570e1846 5f47acd1319245648098c1aec9b95f23 f798033052614b9eae8da7eba4ba3475 3471c4320e4e431eb1fa9f5eb5cb21e0 855f473fed034b1fa17f4f65b850e03b 1245de826d0d4373bdd4cf2157792954 543a8b16efca4fa2b5263315e8b21660 2dc186d699274257922853d783c0ec13 a92e6b1783db4b49a4aaa424b9e1b03f 16773feb48054cf0942a2a27204b3572 1e58da2107ac4ee39e28a93b32e1df1d 67622c19498d4178a1bab6b19087f2c2 412b6b4474fc43ccbeb1e7707b6420ee 7d0fd632913c425eb5f087600ccea870 439687baddb44852a43048b04d38427c 8b2dcc4e50464429a18b11e4aacf51a2 2fccb1c832894fe6b0b61bbdf175cd39 6d224b3d6e8747319fcf01b0309d8a0f b4982e3b4b594cb4b334c95c2c96355e c47fbaf90d1d4e9caf211f93b742631f 9440271e8ba6447d9a008e89a93016a6 8d24274b6a3f436a88362438aa6a221d 60452bd3f71747ed8c3706abb2235bd5 6fa93f2ee30740b89496439dd7227a4f cc17504cf80641f882c8665ae166ba44 743efe8eac6e47a789928da4fb5b6f70 4c4d2df3461448c4a3e934cf4a7ea74f b231eb3fb46240d38157764e8906aa7b a234ae65f7ed48f6b1887644eed36cc2 c9cd5ed3df3f4a27957b45498f0c48ef 3eb2fbbb0a714bb7986aef3ee34f0254 d15968e605f0440c9e740e3f4e498a9f 63a8d50e8db24b91a13d4ac2fb6f7d5b 5377df9296154c57926672ca8b3c9478 a4db4a3a9d5148648a23aa7f4f77f1e0 d0aee355a2ba42de89d659385514b0fa e92e7702481a4575a66d59c061459c5b 1b6c542d8f994d85a1312ab2cf4545ce 88e347a515474ec59013673e5402b97f 2187d9b2dc2b4d96baceade5ae99db44 4d641e69ca5b4acf90f8afe238d8a940 9c0f4c101c434831b928114c5fc0c401 140e16f6cf134785a98ae9baee5b9e7b 4dac5910f4d047e1b213c058e2230bf3 fb50a7e6333f49e4b469234426d5002f c96c5f2fa167458eaa6d01997d90a980 1e79721e587c4a92aa55cdf8195c8c55 0da27fc5d8384ce299197b4e06cda1d4 a5e32d9cf5834e86b3fe02bc0e3104d6 2dc1826647594b1fb728de67d3df363c 0276371815254198bd22cc76f901b332 bf9d77b7b4a64e7a97ade2a62af1f8e0 268cce3249f64895b6b47e86cf296e5b d523201fc950435f803bf89d5f042c45 607a4306b90b467f8b19c2c943bc92ef adfa9fb63a874ca1ad746ff573f03f28 fe88132c70d141e8839ce9e7f0308750  Should be just as efficient  more effecient  than Javas actually

User · Answer

I am amazed to see so many string replace ideas of UUID  How about this   UUID temp   UUID randomUUID    String uuidString   Long toHexString temp getMostSignificantBits           Long toHexString temp getLeastSignificantBits       This is the fasted way of doing it since the whole toString   of UUID is already more expensive not to mention the regular expression which has to be parsed and executed or the replacing with empty string

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A simple solution is  UUID randomUUID   toString   replace  -          Like the existing solutions  only that it avoids the String replaceAll call  Regular expression replacement is not required here  so String replace feels more natural  though technically it still is implemented with regular expressions  Given that the generation of the UUID is more costly than the replacement  there should not be a significant difference in runtime    Using the UUID class is probably fast enough for most scenarios  though I would expect that some specialized hand-written variant  which does not need the postprocessing  to be faster  Anyway  the bottleneck of the overall computation will normally be the random number generator  In case of the UUID class  it uses SecureRandom   Which random number generator to use is also a trade-off that depends on the application  If it is security-sensitive  SecureRandom is  in general  the recommendation  Otherwise  ThreadLocalRandom is an alternative  faster than SecureRandom or the old Random  but not cryptographically secure

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Ended up writing something of my own based on UUID java implementation  Note that I m not generating a UUID  instead just a random 32 bytes hex string in the most efficient way I could think of   Implementation  import java security SecureRandom  import java util UUID   public class RandomUtil          Maxim  Copied from UUID implementation        private static volatile SecureRandom numberGenerator   null      private static final long MSB   0x8000000000000000L       public static String unique             SecureRandom ng   numberGenerator          if  ng    null                numberGenerator   ng   new SecureRandom                       return Long toHexString MSB   ng nextLong      Long toHexString MSB   ng nextLong                      Usage  RandomUtil unique     Tests  Some of the inputs I ve tested to make sure it s working   public static void main String   args        System out println UUID randomUUID   toString         System out println RandomUtil unique          System out println        System out println Long toHexString 0x8000000000000000L  21        System out println Long toBinaryString 0x8000000000000000L  21        System out println Long toHexString Long MAX VALUE   1

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I use org apache commons codec binary Base64 to convert a UUID into a url-safe unique string that is 22 characters in length and has the same uniqueness as UUID    I posted my code on Storing UUID as base64 String

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I used JUG  Java UUID Generator  to generate unique ID   It is unique across JVMs  Pretty good to use  Here is the code for your reference   private static final SecureRandom secureRandom   new SecureRandom    private static final UUIDGenerator generator   UUIDGenerator getInstance     public synchronized static String generateUniqueId       UUID uuid   generator generateRandomBasedUUID secureRandom      return uuid toString   replaceAll  -       toUpperCase        You could download the library from  https   github com cowtowncoder java-uuid-generator

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I just implemented this utility class that creates UUIDs as String with or without dashes  Fell free to use and share  I hope that it helps  package your package name   import java security SecureRandom  import java util Random          Utility class that creates random-based UUIDs          public abstract class RandomUuidStringCreator        private static final int RANDOM VERSION   4                  Returns a random-based UUID as String                 It uses a thread local   link SecureRandom                   return a random-based UUID string             public static String getRandomUuid             return getRandomUuid SecureRandomLazyHolder SECURE RANDOM                         Returns a random-based UUID as String WITH dashes                 It uses a thread local   link SecureRandom                   return a random-based UUID string             public static String getRandomUuidWithDashes             return format getRandomUuid                           Returns a random-based UUID String                 It uses any instance of   link Random                   return a random-based UUID string             public static String getRandomUuid Random random             long msb   0          long lsb   0               3  set all bit randomly         if  random instanceof SecureRandom                   Faster for instances of SecureRandom             final byte   bytes   new byte 16               random nextBytes bytes               msb   toNumber bytes  0  8      first 8 bytes for MSB             lsb   toNumber bytes  8  16      last 8 bytes for LSB           else               msb   random nextLong       first 8 bytes for MSB             lsb   random nextLong       last 8 bytes for LSB                       Apply version and variant bits  required for RFC-4122 compliance          msb    msb  amp  0xffffffffffff0fffL     RANDOM VERSION  amp  0x0f   lt  lt  12     apply version bits         lsb    lsb  amp  0x3fffffffffffffffL    0x8000000000000000L     apply variant bits             Convert MSB and LSB to hexadecimal         String msbHex   zerofill Long toHexString msb   16           String lsbHex   zerofill Long toHexString lsb   16               Return the UUID         return msbHex   lsbHex                        Returns a random-based UUID as String WITH dashes                 It uses a thread local   link SecureRandom                   return a random-based UUID string             public static String getRandomUuidWithDashes Random random            return format getRandomUuid random               private static long toNumber final byte   bytes  final int start  final int length            long result   0          for  int i   start  i  lt  length  i                  result    result  lt  lt  8     bytes i   amp  0xff                     return result             private static String zerofill String string  int length            return new String lpad string toCharArray    length   0                private static char   lpad char   chars  int length  char fill             int delta   0          int limit   0           if  length  gt  chars length                delta   length - chars length              limit   length            else               delta   0              limit   chars length                     char   output   new char chars length   delta           for  int i   0  i  lt  limit  i                  if  i  lt  delta                    output i    fill                else                   output i    chars i - delta                                   return output             private static String format String string            char   input   string toCharArray            char   output   new char 36            System arraycopy input  0  output  0  8           System arraycopy input  8  output  9  4           System arraycopy input  12  output  14  4           System arraycopy input  16  output  19  4           System arraycopy input  20  output  24  12            output 8     -           output 13     -           output 18     -           output 23     -            return new String output                 Holds lazy secure random     private static class SecureRandomLazyHolder           static final Random SECURE RANDOM   new SecureRandom                          For tests              public static void main String   args             System out println  quot    Using  java security SecureRandom   DEFAULT  quot            System out println  quot RandomUuidCreator getRandomUuid   quot            System out println            for  int i   0  i  lt  5  i                  System out println RandomUuidStringCreator getRandomUuid                        System out println            System out println  quot    Using  java util Random   FASTER  quot            System out println  quot RandomUuidCreator getRandomUuid new Random    quot            System out println            Random random   new Random            for  int i   0  i  lt  5  i                  System out println RandomUuidStringCreator getRandomUuid random                        This is the output     Using  java security SecureRandom   DEFAULT  RandomUuidStringCreator getRandomUuid     f553ca75657b4b5d85bedf1082785a0b   525ecc389e934f209b97d0f0db09d9c6   93ec6425bb04499ab47b790fd013ab0d   c2d438c620ea4cd5baafd448f9fe945b   fb4bc5734931415e94e78da62cb5fe0d      Using  java util Random   FASTER  RandomUuidStringCreator getRandomUuid new Random      051360b5c92d40fbbb89b40842adbacc   a993896538aa43faacbcfd83f913f38b   720684d22c584d5299cb03cdbc1912d2   82cf94ea296a4a138a92825a0068d4a1   a7eda46a215c4e55be3aa957ba74ca9c   There s a codec in uuid-creator that can do it more efficiently  Base16Codec  Example     Returns a base-16 string    It is much faster than doing  uuid toString   replaceAll  quot - quot    quot  quot     UuidCodec lt String gt  codec   new Base16Codec    String string   codec encode UUID randomUUID

[java] Efficient method to generate UUID String in JAVA (UUID.randomUUID().toString() without the dashes)

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