public static String next() {
		return next(false);
	}
@Test
	public void distinctTest() {
		//生成10000个id测试是否重复
		HashSet<String> set = new HashSet<>();
		for(int i = 0; i < 10000; i++) {
			set.add(ObjectId.next());
		}

		assertEquals(10000, set.size());
	}