How do I create a unique ID in Java

Question

I m looking for the best way to create a unique ID as a String in Java   Any guidance appreciated  thanks   I should mention I m using Java 5

User · Answer

There are three way to generate unique id in java.

1) the UUID class provides a simple means for generating unique ids.

 UUID id = UUID.randomUUID();
 System.out.println(id);

2) SecureRandom and MessageDigest

//initialization of the application
 SecureRandom prng = SecureRandom.getInstance("SHA1PRNG");

//generate a random number
 String randomNum = new Integer(prng.nextInt()).toString();

//get its digest
 MessageDigest sha = MessageDigest.getInstance("SHA-1");
 byte[] result =  sha.digest(randomNum.getBytes());

System.out.println("Random number: " + randomNum);
System.out.println("Message digest: " + new String(result));

3) using a java.rmi.server.UID

UID userId = new UID();
System.out.println("userId: " + userId);

User · Answer

Create a UUID   String uniqueID   UUID randomUUID   toString

User · Answer

We can create a unique ID in java by using the UUID and call the method like randomUUID   on UUID   String uniqueID   UUID randomUUID   toString      This will generate the random uniqueID whose return type will be String

User · Answer

Generate Unique ID Using Java UUID is the fastest and easiest way to generate unique ID in Java  import java util UUID   public class UniqueIDTest     public static void main String   args        UUID uniqueKey   UUID randomUUID        System out println  uniqueKey

User · Answer

String name password   public int idGen          int id   this name hashCode     this password hashCode        int length   String valueOf id  length        int Max Length   5      if String valueOf id  length   gt Max Length                 id    int   id  Math pow 10 0 length - Max Length               return  id

User · Answer

IMHO aperkins provided an an elegant solution cause is native and use less code  But if you need a shorter ID you can use this approach to reduce the generated String length      usage  GenerateShortUUID next    import java util UUID   public class GenerateShortUUID        private GenerateShortUUID          singleton    public static String next          UUID u   UUID randomUUID         return toIDString u getMostSignificantBits      toIDString u getLeastSignificantBits            private static String toIDString long i          char   buf   new char 32         int z   64     1  lt  lt  6        int cp   32        long b   z - 1        do             buf --cp    DIGITS66  int  i  amp  b              i  gt  gt  gt   6          while  i    0         return new String buf  cp   32-cp             array de 64 2 digitos   private final static char   DIGITS66          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        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        -

User · Answer

Here s my two cent s worth  I ve previously implemented an IdFactory class that created IDs in the format  host name - application start time - current time - discriminator    This largely guaranteed that IDs were unique across JVM instances whilst keeping the IDs readable  albeit quite long    Here s the code in case it s of any use   public class IdFactoryImpl implements IdFactory     private final String hostName    private final long creationTimeMillis    private long lastTimeMillis    private long discriminator     public IdFactoryImpl   throws UnknownHostException       this hostName   InetAddress getLocalHost   getHostAddress        this creationTimeMillis   System currentTimeMillis        this lastTimeMillis   creationTimeMillis         public synchronized Serializable createId         String id      long now   System currentTimeMillis         if  now    lastTimeMillis            discriminator        else         discriminator   0                creationTimeMillis used to prevent multiple instances of the JVM        running on the same host returning clashing IDs         The only way a clash could occur is if the applications started at        exactly the same time      id   String format   s- d- d- d   hostName  creationTimeMillis  now  discriminator       lastTimeMillis   now       return id         public static void main String   args  throws UnknownHostException       IdFactory fact   new IdFactoryImpl         for  int i 0  i lt 1000    i          System err println fact createId

User · Answer

This adds a bit more randomness to the UUID generation but ensures each generated id is the same length  import org apache commons codec digest DigestUtils  import java util UUID   public String createSalt         String ts   String valueOf System currentTimeMillis         String rand   UUID randomUUID   toString        return DigestUtils sha1Hex ts   rand

User · Answer

java util UUID    toString   method

User · Answer

Unique ID with count information  import java util concurrent atomic AtomicLong   public class RandomIdUtils        private static AtomicLong atomicCounter   new AtomicLong         public static String createId              String currentCounter   String valueOf atomicCounter getAndIncrement             String uniqueId   UUID randomUUID   toString             return uniqueId    -    currentCounter

User · Answer

If you want short  human-readable IDs and only need them to be unique per JVM run   private static long idCounter   0   public static synchronized String createID         return String valueOf idCounter             Edit  Alternative suggested in the comments - this relies on under-the-hood  magic  for thread safety  but is more scalable and just as safe   private static AtomicLong idCounter   new AtomicLong     public static String createID         return String valueOf idCounter getAndIncrement

[java] How do I create a unique ID in Java?

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