public static void main(String[] args) throws Exception{
        Date now = new Date();
        System.out.println("now:"+now);
		SimpleDateFormat format = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
		Calendar calendar = Calendar.getInstance();
		calendar.setTime(now);
		//获取前24小时的时间
		calendar.add(Calendar.HOUR, -24);
		//获取后十分钟的时间
		//calendar.add(Calendar.MINUTE, +10);
		//获取前30秒的时间
		//calendar.add(Calendar.SECOND,-30); 
		now = calendar.getTime();
		String time = format.format(now);
		System.out.println("time:"+time);
    }