获取一年内的星期列表及每周起始时间

	public static function getWeeks($format="second",$year=null){
		if($year == null){
			$year=date('Y');
		}
		$second_of_day = 24*3600;
		$year_start = $year . "-01-01 00:00:00"; 
		$year_end = $year . "-12-31 23:59:59"; 
		$startday = strtotime($year_start); 
		$day_of_week = date('N', $startday);
		$first_week_start=$startday;
		$first_week_end = $startday+(7-$day_of_week)*$second_of_day+$second_of_day-1;
		$week_array[0]=array($first_week_start,$first_week_end);
		
		$endday = strtotime($year_end); 
		$day_of_week = date('N', $endday);

		$last_week_start=$endday-$day_of_week*$second_of_day+1;
		$last_week_end = $endday;
		$last_week=array($last_week_start,$last_week_end);
		
		$during = $last_week_start - $first_week_end;
		
		$during_total_week = intval($during/(7*$second_of_day));
		
		for($i=0;$i<$during_total_week;$i++){
			$week_array[$i+1]=array($first_week_end+(7*$i*$second_of_day)+1,$first_week_end+(($i+1)*$second_of_day*7));
		}
		
		$week_array[$during_total_week+1]=$last_week;
		
		if($format !="second"){
			foreach($week_array as $i => $week){
				$week_array_of_date_format[$i]=array(date($format,$week[0]),date($format,$week[1]));
			}
			return $week_array_of_date_format;
		}
		
		return $week_array;
	}