Java获取12个月前的月初日期

   public class FirstDayOfLastTwelveMonth {
          public static void main(String[] args){
                DateTimeFormatter formatter = DateTimeFormatter.forPattern("yyyyMMdd");
                DateTime dateTime = formatter.parseDateTime("20151231");
                
                Period period = new Period(0,11,0,0,0,0,0,0);
                DateTime theDate = dateTime.minus(period);
                DateTime firstDay = theDate.withField(DateTimeFormatter.dayOfMonth, 1)

                System.out.println(formatter.print(firstDay));
          }
   }