获取当前时间和给定时间之间相隔天数

public static void main(String[] args) throws ParseException {
/**
* 获取当前时间
*
*/
Date date = new Date();
/**转换提日期输出格式*/
SimpleDateFormat dateFormat = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");


String a = "2021-01-01"; // 时间字符串
String b = dateFormat.format(date);

Long between_dayInteger = between_days(a, b);

System.out.println(between_dayInteger);

}

public static Long between_days(String a, String b) {

SimpleDateFormat simpleDateFormat = new SimpleDateFormat("yyyy-MM-dd");// 自定义时间格式

Calendar calendar_a = Calendar.getInstance();// 获取日历对象
Calendar calendar_b = Calendar.getInstance();

Date date_a = null;
Date date_b = null;

try {
date_a = simpleDateFormat.parse(a);//字符串转Date
date_b = simpleDateFormat.parse(b);
calendar_a.setTime(date_a);// 设置日历
calendar_b.setTime(date_b);
} catch (ParseException e) {
e.printStackTrace();//格式化异常
}

long time_a = calendar_a.getTimeInMillis();
long time_b = calendar_b.getTimeInMillis();

long between_days = (time_b - time_a) / (1000 * 3600 * 24);//计算相差天数

return between_days;
}