日期处理 给定日期，获取是星期几

 /**
     * 获取当前日期是星期几<br>
     *
     * @param dt
     * @return 当前日期是星期几
    */
    private static String getWeekOfDate(Date dt) {
        String[] weekDays = {"周日", "周一", "周二", "周三", "周四", "周五", "周六"};
        Calendar cal = Calendar.getInstance();
        cal.setTime(dt); 
       int w = cal.get(Calendar.DAY_OF_WEEK) - 1;
        if (w < 0)
            w = 0;
       return weekDays[w];
    }