Java Development _ UUID (universally unique identifier, globally unique identifier) and guid (globally unique identifier, globally unique identifier)

Guid: that is, globally unique identifier (globally unique identifier) is also called UUID (universally unique identifier ).

Therefore, the guid is the UUID.

GUID is a 128-bit long number, which is generally expressed in hexadecimal notation.AlgorithmThe core idea is to combine the machine's Nic, local time, and a random number to generate a guid.

Theoretically, if a machine generates 10000000 guids per second, it can ensure (in probability) that there will be no duplicates in 3240.

The following is a demo:

PackageCom. mytest;ImportJava. util. UUID;/*** Jdk1.5 or later **/Public ClassUuidtest {Public Static VoidMain (string [] ARGs) {UUID=UUID. randomuuid (); system. Out. println (UUID );}}
 

Output result:

 
1Fd61384b-05a5-4030-885e-a6bd3b60ef1a
 

The following is how to remove "-" From UUID "-"

 

 1   /**  2   *  3    */  4   Package  Com. b510;  5   6   Import  Java. util. UUID;  7   8   /** 9   * @ Date 2012-11-7  10   *  @ Author  Xhw  11   *  12    */  13   Public   Class  Uuidtest {  14       /**  15  * Obtain a uuid that removes the "-" symbol.  16   *  17   *  @ Return  String UUID  18        */  19       Public   Static  String getuuid (){  20 String S = UUID. randomuuid (). tostring ();  21          //  Remove the "-" symbol  22           Return S. substring (0, 8) + S. substring (9, 13) + S. substring (14, 18) + S. substring (19, 23) + S. substring (24 );  23   }  24   25       /**  26   * Obtain a uuid that removes the "-" symbol.  27   *  28  *  @ Return  29        */  30       Public   Static  String getuuid (){  31 String S = UUID. randomuuid (). tostring ();  32           //  Remove the "-" symbol  33           Return S. Replace ("-","" ); 34   }  35   36       /**  37   * Obtain the specified UUID.  38   *  39   *  @ Param  Number  40   * Number of UUID to be obtained for int  41   * @ Return  String [] UUID Array  42        */  43       Public   Static String [] getuuid ( Int  Number ){  44           If (Number <1 ){  45               Return   Null  ; 46   }  47 String [] Ss = New  String [number];  48           For ( Int I = 0; I <number; I ++ ){  49               If (I % 2 = 0 ){  50 Ss [I] = Getuuid ();  51 } Else  {  52 Ss [I] = Getuuid ();  53   }  54   }  55           Return  SS;  56   }  57   58       Public  Static   Void  Main (string [] ARGs ){  59 String [] Ss = getuuid (10 );  60           For ( Int I = 0; I <ss. length; I ++ ){  61   System. Out. println (ss [I]);  62   }  63   } 64   65 }

Output result:

 1   /**  2   Ca31b9c6bff04ecfb5dfd1675905338d  3   78af094061c04fc6b578a0f62aa09373  4   51f228083c6e4dcb855a8e733efded7c  5   Fceca14fdc194d889c05c1dcf8ccaf3b  6   4c7695ed08494b978fa9737dfe36f6a5 7   B7573dbadfe84ba2b3659d1e49f8bf08  8   F4391ba40f114ad19711a507971a994b  9   6e1d576301c749bcb7b7943c1782a920  10   Fb60bd4fe28d47cda-bb0eb6834e84e  11   5238ba7d27c7452698e075f64472fadf  12   */ 

The preceding two methods are provided to remove "-" From UUID "-"

 

 1   /** 2   * Obtain a uuid that removes the "-" symbol.  3   *  4   *  @ Return  String UUID  5        */  6       Public   Static  String getuuid (){  7 String S = UUID. randomuuid (). tostring (); 8           //  Remove the "-" symbol  9           Return S. substring (0, 8) + S. substring (9, 13) + S. substring (14, 18) + S. substring (19, 23) + S. substring (24 );  10   }  11   12       /**  13   * Obtain a uuid that removes the "-" symbol.  14   * 15   *  @ Return  16        */  17       Public   Static  String getuuid (){  18 String S = UUID. randomuuid (). tostring ();  19           //  Remove the "-" symbol  20           Return S. Replace ("-","");  21 }

 

UUID consists of the following parts:

(1) The current date and time. The first part of UUID is related to the time. If you generate a uuid after several seconds and then generate a uuid, the first part is different, others are the same

(2) Clock Sequence

(3) Globally Unique IEEE machine identification number. If there is a nic, it is obtained from the nic mac address, and no Nic is obtained in other ways.

Disadvantage: the unique defect of UUID is that the generated result string is long.