java 某一个月的最后一天

private String  getInvoiceMonth(String invoiceMonth){//invoiceMonth 的格式为 201108
  String year = invoiceMonth.substring(0, 4);
  String month = invoiceMonth.substring(4, invoiceMonth.length());
  
  Calendar   date   =   Calendar.getInstance();
  int   yeari   =  Integer.parseInt(year);
  int   monthi   =  Integer.parseInt(month);
  if(monthi==1){
   monthi=12;
  }
  date.set(yeari,monthi-1,1);
  int   maxDayOfMonth   =   date.getActualMaximum(Calendar.DAY_OF_MONTH);
  logger.info("-----------------------"+year+"-"+monthi+"-"+maxDayOfMonth);
  return year+"-"+monthi+"-"+maxDayOfMonth;
 }