code: private static CronDefinition unixCrontab() {
          return CronDefinitionBuilder.defineCron()
                  .withMinutes().and()
                  .withHours().and()
                  .withDayOfMonth().and()
                  .withMonth().and()
                  .withDayOfWeek().withValidRange(0, 7).withMondayDoWValue(1).withIntMapping(7, 0).and()
                  .enforceStrictRanges()
                  .instance();
      }
docs: Creates CronDefinition instance matching unix crontab specification.
  
  @return CronDefinition instance, never null;