import java.text.SimpleDateFormat;
import java.util.Calendar;
import java.util.Date;

import org.apache.commons.lang.time.DateUtils;


public class t {

public static void main(String[] args) {
// TODO Auto-generated method stub
SimpleDateFormat format = new SimpleDateFormat("dd");
        Date date = new Date();
//        date.setYear(2016);
        date.setMonth(7); //表示8月
        //获取当前月最后一天
        Calendar ca = Calendar.getInstance();   
        ca.setTime(date);
        ca.set(Calendar.DAY_OF_MONTH, ca.getActualMaximum(Calendar.DAY_OF_MONTH));
        String last = format.format(ca.getTime());
        System.out.println("===============last:"+last);
        System.out.println("===============last:"+date.getMonth());
}

}

===============last:31
===============last:7