UUID long类型、String类型

• 2019 年 10 月 4 日
• 筆記

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package com.test.utils;    import java.util.Random;  import java.util.UUID;     public  final class UIDUtil {      private static  final int SHORT_MAX=65536;      private static int counter=-1;      private UIDUtil(){}      /**       * Creates a unique 64 bits ID by aggregating the current time in       * milliseconds since epoch (Jan. 1, 1970) and using a 16 bits counter. The       * counter is initialized at a random number. This generator can create up       * to 65536 different id per millisecond.       *       * @return a new id.       */      public static synchronized long nextId() {          long now = System.currentTimeMillis();          if (counter == -1) {              long seed = now ^ Thread.currentThread().getId();              Random rnd = new Random(Long.hashCode(seed));              counter = rnd.nextInt(SHORT_MAX);          }          long id = (now << 16) | counter;          counter = (counter + 1) % SHORT_MAX;          return id;      }        /**       * generate uniq uuid       * @return       */      public static synchronized String getUUID(){          String s= UUID.randomUUID().toString();          return s.substring(0,8)+s.substring(9,13)+s.substring(14,18)+s.substring(19,23)+s.substring(24);      }    }