public static String generateUUID() {
        UUID id = UUID.randomUUID();
        ByteBuffer bb = ByteBuffer.wrap(new byte[16]);
        bb.putLong(id.getMostSignificantBits());
        bb.putLong(id.getLeastSignificantBits());
        Base64 base64 = new Base64();
        return base64.encodeBase64URLSafeString(bb.array());
    }
@Test
    public void testGenerateUUID() {
        String s = HashUtil.generateUUID();
        System.out.println("s = " + s);
    }