根据时间段【2020-11-20 09:09:09,2021-10-09 10:10:10】先转换为【2020-11-20 00:00:00,2021-10-09 59:59:59】 再根据转换时间把里面的每一天获取出来 java

可以使用 Java 中的 Date 类和 Calendar 类来完成该任务。具体的实现步骤如下：

1. 将时间字符串转换为 Date 对象，并设置时间为 00:00:00。

DateFormat dateFormat = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
Date startDate = dateFormat.parse("2020-11-20 09:09:09");
Date endDate = dateFormat.parse("2021-10-09 10:10:10");

Calendar calendar = Calendar.getInstance();
calendar.setTime(startDate);
calendar.set(Calendar.HOUR_OF_DAY, 0);
calendar.set(Calendar.MINUTE, 0);
calendar.set(Calendar.SECOND, 0);
startDate = calendar.getTime();

calendar.setTime(endDate);
calendar.set(Calendar.HOUR_OF_DAY, 23);
calendar.set(Calendar.MINUTE, 59);
calendar.set(Calendar.SECOND, 59);
endDate = calendar.getTime();

2. 计算两个日期之间的天数，并将每一天的日期加入到 List 中。

List<Date> dateList = new ArrayList<>();
calendar.setTime(startDate);
while (calendar.getTimeInMillis() <= endDate.getTime()) {
    dateList.add(calendar.getTime());
    calendar.add(Calendar.DATE, 1);
}

完整代码如下：

import java.text.DateFormat;
import java.text.SimpleDateFormat;
import java.util.ArrayList;
import java.util.Calendar;
import java.util.Date;
import java.util.List;

public class DateUtils {
    public static void main(String[] args) throws Exception {
        DateFormat dateFormat = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
        Date startDate = dateFormat.parse("2020-11-20 09:09:09");
        Date endDate = dateFormat.parse("2021-10-09 10:10:10");

        Calendar calendar = Calendar.getInstance();
        calendar.setTime(startDate);
        calendar.set(Calendar.HOUR_OF_DAY, 0);
        calendar.set(Calendar.MINUTE, 0);
        calendar.set(Calendar.SECOND, 0);
        startDate = calendar.getTime();

        calendar.setTime(endDate);
        calendar.set(Calendar.HOUR_OF_DAY, 23);
        calendar.set(Calendar.MINUTE, 59);
        calendar.set(Calendar.SECOND, 59);
        endDate = calendar.getTime();

        List<Date> dateList = new ArrayList<>();
        calendar.setTime(startDate);
        while (calendar.getTimeInMillis() <= endDate.getTime()) {
            dateList.add(calendar.getTime());
            calendar.add(Calendar.DATE, 1);
        }

        for (Date date : dateList) {
            System.out.println(dateFormat.format(date));
        }
    }
}