import java.text.ParseException;
import java.text.SimpleDateFormat;
import java.util.Date;

public class CalcDays {

    public static void main(String[] args) {
        // 指定时间 - 现在时间 ms / 1000 / 3600 / 24 = day
        long currentTime = System.currentTimeMillis();

        String targetTimeStr = "2022-3-20";
        SimpleDateFormat simpleDateFormat = new SimpleDateFormat("yyyy-MM-dd");

        try {
            Date targetDate = simpleDateFormat.parse(targetTimeStr);
            long targetTime = targetDate.getTime();
            long res = (targetTime - currentTime) / 1000 / 3600 / 24;
            System.out.println(targetTimeStr + "距离今天还有：" + res + "天。");
        } catch (ParseException e) {
            e.printStackTrace();
        }
    }

}