code: public static int yesterday() {
          Calendar cal = Calendar.getInstance();
          cal.add(Calendar.DAY_OF_YEAR, -1);
          return cal.get(Calendar.YEAR) * 10000 + (cal.get(Calendar.MONTH) + 1) * 100 + cal.get(Calendar.DAY_OF_MONTH);
      }
docs: 获取昨天20151230格式的int值
  
  @return 20151230格式的int值