해당 날짜가 포함된 주의 월요일 구하기

Calendar가 젤 어렵드라 난

public static String getMondayFromDay(String yyyymmdd) {

int yyyy = Integer.parseInt(yyyymmdd.substring(0, 4));

int mm = Integer.parseInt(yyyymmdd.substring(4, 6)) - 1;

int dd = Integer.parseInt(yyyymmdd.substring(6, 8));

SimpleDateFormat formatter = new SimpleDateFormat("yyyy-MM-dd");

String setDate = ""; 

Calendar calendar = Calendar.getInstance();

calendar.set(yyyy, mm, dd);

setDate = formatter.format(calendar.getTime());

int yoil = calendar.get(Calendar.DAY_OF_WEEK);

System.out.println("입력날짜:"+setDate + ", 요일:"+yoil);

int gap = 0;

int[] idx = {1, 2, 3, 4, 5, 6, 7};

for(int i = 0; i < idx.length; i++) {

if( yoil != 2 && yoil == idx[i] ) {

gap = i*2-yoil;

gap = 0-gap;

}

}

calendar.add(Calendar.DATE, gap);

setDate = formatter.format(calendar.getTime());

yoil = calendar.get(Calendar.DAY_OF_WEEK);

System.out.println("입력날짜:"+setDate + ", 요일:"+yoil);

return "";

}