给定年月字符串yyyyMM，输出当月每一天

输入：yyyyMM 输出：当月每一天

==入参: ==
yyyyMM 如：202306

出参：
[yyyyMMdd,yyyyMMdd,yyyyMMdd,…] 如：[20230601,20230602,20230603, …]

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import java.util.*;

public class GetDayListOfMonth {

    public static List<String> getDayListOfMonth(String yyyyMM) {
        if (yyyyMM.length() != 6) {
            return null;
        }
        Set<String> stringSets = new HashSet<>();
        ArrayList<String> arrayList = new ArrayList<>();
        String yStr = yyyyMM.substring(0, 4);
        String mStr = yyyyMM.substring(4, 6);

        Calendar calendar = Calendar.getInstance();
        calendar.set(Calendar.YEAR, Integer.parseInt(yStr));//年份
        calendar.set(Calendar.MONTH, Integer.parseInt(mStr) - 1);
        calendar.set(Calendar.DATE, 1);
        calendar.roll(Calendar.DATE, -1);

        int maxDate = calendar.get(Calendar.DATE);
        for (int i = 0; i < maxDate; i++) {
            int d = i + 1;
            String dStr = "";
            if (d < 10) {
                dStr = "0" + String.valueOf(d);
            } else {
                dStr = String.valueOf(d);
            }
            String day = yStr + mStr + dStr;
            stringSets.add(day);
            arrayList.add(day);
        }
        return arrayList;
    }
}

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