JAVA如何产生uuid

直接通过java.util.randomUUID() 产生，源码如下：

  public static UUID randomUUID() {
        SecureRandom ng = numberGenerator;
        if (ng == null) {
            numberGenerator = ng = new SecureRandom();
        }

        byte[] randomBytes = new byte[16];
        ng.nextBytes(randomBytes);
        randomBytes[6]  &= 0x0f;  /* clear version        */
        randomBytes[6]  |= 0x40;  /* set to version 4     */
        randomBytes[8]  &= 0x3f;  /* clear variant        */
        randomBytes[8]  |= 0x80;  /* set to IETF variant  */
        return new UUID(randomBytes);
    }

 注意

 1.numberGenerator = ng = new SecureRandom();
 2.private static volatile SecureRandom numberGenerator = null;

 1.是连续赋值，引用相同

 2.volatile 标识某变量在内存中仅存在一份不存在copy，如果变量比较简单那么可以认为是线程同步的另外一种机制