protected int getMonthNumber(String s) {
        Integer integer = monthMap.get(s);

        if (integer == null) {
            return -1;
        }

        return integer;
    }
Indicates whether the specified cron expression can be parsed into a
valid cron expression

@param cronExpression the expression to evaluate
@return a boolean indicating whether the given expression is a valid cron
        expression
server/core/src/main/java/com/ke/schedule/server/core/common/CronExpression.java