code: public static Date getFirstDayOfMonth(Date date) {
          Calendar calendar = Calendar.getInstance();
          calendar.setTime(date);
          int firstDay = calendar.getActualMinimum(Calendar.DAY_OF_MONTH);
          return org.apache.commons.lang.time.DateUtils.setDays(date, firstDay);
      }
docs: #func 获取当前时间当月的第一天<br>
  
  @author dongguoshuang