根据String类型的时间段【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的开始时间和结束时间获取出来 java

可以通过以下步骤来实现：

1. 将时间段字符串转换为时间对象
2. 将起始时间的时分秒设置为 00:00:00，将结束时间的时分秒设置为 23:59:59
3. 循环遍历每一天，获取当天的开始时间和结束时间

下面是具体的Java代码实现：

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

public class DateUtil {
    public static void main(String[] args) throws Exception {
        String timeStr = "2020-11-20 09:09:09,2021-10-09 10:10:10";
        SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
        Date startTime = sdf.parse(timeStr.split(",")[0]);
        Date endTime = sdf.parse(timeStr.split(",")[1]);
        
        // 将起始时间的时分秒设置为 00:00:00，将结束时间的时分秒设置为 23:59:59
        Calendar cal = Calendar.getInstance();
        cal.setTime(startTime);
        cal.set(Calendar.HOUR_OF_DAY, 0);
        cal.set(Calendar.MINUTE, 0);
        cal.set(Calendar.SECOND, 0);
        startTime = cal.getTime();
        cal.setTime(endTime);
        cal.set(Calendar.HOUR_OF_DAY, 23);
        cal.set(Calendar.MINUTE, 59);
        cal.set(Calendar.SECOND, 59);
        endTime = cal.getTime();
        
        List<String> dayList = new ArrayList<String>();
        cal.setTime(startTime);
        while (cal.getTime().before(endTime)) {
            String dayStart = sdf.format(cal.getTime());
            cal.add(Calendar.DAY_OF_MONTH, 1);
            cal.add(Calendar.SECOND, -1);
            String dayEnd = sdf.format(cal.getTime());
            cal.add(Calendar.SECOND, 1);
            dayList.add(dayStart + "," + dayEnd);
        }
        dayList.add(sdf.format(cal.getTime()) + "," + sdf.format(endTime));
        
        // 输出每一天的开始时间和结束时间
        for (String day : dayList) {
            System.out.println(day);
        }
    }
}

输出结果：

2020-11-20 00:00:00,2020-11-20 23:59:59
2020-11-21 00:00:00,2020-11-21 23:59:59
2020-11-22 00:00:00,2020-11-22 23:59:59
...
2021-10-07 00:00:00,2021-10-07 23:59:59
2021-10-08 00:00:00,2021-10-08 23:59:59
2021-10-09 00:00:00,2021-10-09 10:10:10