随机生成指定日期区间的Date

//String startDateTime = "2019-05-06 08:00";
		//String endDateTime = "2019-05-06 18:00";
		String startDateTime = params.getStartTime();
		String endDateTime = params.getEndTime();
		String startDateStr = startDateTime.substring(0,10);
		String endDateStr = endDateTime.substring(0,10);
		String endTimeStr = endDateTime.substring(11);
		
        SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd");
		Date startDate = sdf.parse(startDateStr);
		Date endDate = sdf.parse(endDateStr);
		Long millDiff = endDate.getTime() - startDate.getTime();
		Long dayDiff = millDiff / (1000 * 60 * 60 * 24);
		System.out.println("dayDiff=" + dayDiff);
		
		Random random=new java.util.Random();//定义随机类
		Calendar cal = Calendar.getInstance();
		SimpleDateFormat sdf2 = new SimpleDateFormat("yyyy-MM-dd HH:mm");
		Date z = sdf.parse(startDateStr);//凌晨
		Date s = sdf2.parse(startDateTime);//开始时间
		Date e = sdf2.parse(startDateStr + " " + endTimeStr);//结束时间
		
		Long szMinDff = (s.getTime() - z.getTime()) / (1000 * 60);//凌晨 至 开始时间 的分钟数
		Long esMinDff = (e.getTime() - s.getTime()) / (1000 * 60);//开始时间 至 结束时间 的分钟数
		for(int i=0;i<params.getNum();i++){
			//生成随机日期
			int result = random.nextInt(dayDiff.intValue() + 1);//随机天数
			cal.setTime(startDate);
			cal.add(Calendar.DAY_OF_MONTH, result);//开始日期 + 随机天数
			Date clientInvoiceDatetime = cal.getTime();//随机日期
			
			//随机日期 + 随机分钟
			int randomMin = random.nextInt(esMinDff.intValue()) + szMinDff.intValue();
			cal.setTime(clientInvoiceDatetime);
			cal.add(Calendar.MINUTE, randomMin);
			clientInvoiceDatetime = cal.getTime(); //最终的时间
		}