如何得知某年某月有多少天？

Question

calendar.setTime( date );        calendar.set( calendar.YEAR, year );
        calendar.set( calendar.MONTH, month-1 );        for ( int i = 1; i < 33; i++ )
        {
            calendar.set(calendar.DAY_OF_MONTH,i);
            if ( calendar.get(calendar.DAY_OF_MONTH) == 1 && i != 1 )
            {
                i = 33;
            }
            else
            {
                String Str = changeValue(year,month,calendar.get(calendar.DAY_OF_MONTH));
                dateMap.put( dates[ (calendar.get(calendar.DAY_OF_WEEK) + 5 ) % 7 ], String.valueOf(calendar.get(calendar.DAY_OF_MONTH)) );
                dateMap.put( spans[ (calendar.get(calendar.DAY_OF_WEEK) + 5 ) % 7 ], Str );
            }
            if ( calendar.get(calendar.DAY_OF_WEEK) == 1 )
            {
                Map tempMap         = new HashMap();
                tempMap.putAll(dateMap);
                dateList.add(tempMap);
                dateMap.clear();
            }
            if ( !dateMap.isEmpty() )
            {
                if ( calendar.get(calendar.DAY_OF_MONTH) == 1 && i != 1 )
                {
                    dateList.add(dateMap);
                }
            }
        }