转化Date格式

        LocalDate date = LocalDate.now();//获取现在的时间
        System.out.println(date);
        final List<GraphUser> graphUsers = graphDAO.selectGraphUser(date);
        System.out.println("graphUsers:"+graphUsers);
        SimpleDateFormat sim = new SimpleDateFormat("yyyy.MM.dd");
        List<Date> dateList = graphUsers.stream().map(GraphUser::getUserDate).collect(Collectors.toList());//获取期中的UserDate列表
        List<Integer> countList = graphUsers.stream().map(GraphUser::getCount).collect(Collectors.toList());
        System.out.println(dateList);
        System.out.println(countList);
        final Iterator<Date> iterator = dateList.iterator();//迭代器
        List<String> list = new ArrayList<>();//创建一个空列表
        while (iterator.hasNext()){//如果有，则返回true
            final Date next = iterator.next();//
            list.add(sim.format(next));
        }
        System.out.println(list);