Java cron中问号的意义 [英] Significance of question mark in Java cron

问题描述

来源维基百科:

问号 (?) 代替*"用于将月中的某天或一周中的某天留空.

Question mark (?) is used instead of '*' for leaving either day-of-month or day-of-week blank.

以上说法对我来说没有多大意义.

The above statement is not making much sense to me.

那么，如果我将一些 cron 写为 0 0 0 ?* * 那么是每个月的第一天还是每天执行一次?

So if I write some cron as 0 0 0 ? * * then does it mean first of every month or it means it will execute daily?

这有点令人困惑，因为 Java cron 以秒开头，而其他 cron 以分钟开头.

It is a bit confusing as Java crons start with seconds while other crons start with minute.

推荐答案

根据Quartz CronTrigger 教程(Quartz 是 www.cronmaker.com 使用的，上面有引用)，? 通配符只用于月份的哪一天和哪一天周字段:

According to the Quartz CronTrigger tutorial (Quartz is used by www.cronmaker.com, referenced above), the ? wildcard is only used in the day of month and day of week fields:

?(无特定值") - 当您需要在允许字符的两个字段之一中指定某些内容时很有用，而另一个字段则不允许.例如，如果我希望我的触发器在一个月的某一天(比如 10 号)触发，但不关心那一天是一周中的哪一天，我会将10"放在当天-month 字段和?"在星期字段中.

? ("no specific value") - useful when you need to specify something in one of the two fields in which the character is allowed, but not the other. For example, if I want my trigger to fire on a particular day of the month (say, the 10th), but don't care what day of the week that happens to be, I would put "10" in the day-of-month field, and "?" in the day-of-week field.

我猜 * 在这里不合适，因为 * 意味着在一周中的每一天执行，这与它应该只在 10 日运行的规则相矛盾月.

I guess * isn't appropriate here because * means execute on every day of the week, which contradicts the rule saying that it should only run on the 10th of the month.

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