public static String getUUID() {
        UUID id = UUID.randomUUID();
        ByteBuffer bb = ByteBuffer.wrap(new byte[16]);
        bb.putLong(id.getMostSignificantBits());
        bb.putLong(id.getLeastSignificantBits());
        return Base64.encodeBase64URLSafeString(bb.array());
    }
@Test
    public void testGetUUID() {
        String id1 = Util.getUUID();
        String id2 = Util.getUUID();
        System.out.println("uuid = " + id1);
        System.out.println("uuid = " + id2);
        Assert.assertNotEquals(id1, id2);
    }