用java獲得某個月份的天數

在網上找了很多例子,最後拼起來的結果,

year,month 可以是自己寫好的字符串

<%  String year = session.getAttribute("year").toString();
 String month =session.getAttribute("month").toString();
 String day = "01";
 String t = year+"-"+month+"-"+day;
    Calendar  calendar  =  Calendar.getInstance();
 int months = Integer.parseInt(month);
 int years = Integer.parseInt(year);
 int days =1;
 calendar.set(years,months-1,days);
 int dayst =calendar.getActualMaximum(calendar.DAY_OF_MONTH);
 System.out.println("-months--"+months+"days--"+dayst);
 String dd= (new Integer(dayst)).toString();  
 String lastDay = year+"-"+month+"-"+dd;
 System.out.println("-lastDay--"+lastDay);
%>