SpringBoot Add String to CronExpression conversion support

Add String to CronExpression conversion support.

This converter use CronExpression parse () method to convert String to CronExpression.

For example, it helps us to use type-safe CronExpression in ConfigurationProperties classes.

Comment From: wilkinsona

Thanks for the suggestion. Given that CronExpression is a Spring Framework type, I wonder if the should be added to Spring Framework rather than to Spring Boot. I'll discuss it with the Framework team.

Comment From: wilkinsona

@amiriahmad72 it would also be useful to know how you're using CronExpression. There's very little, if any, API in Spring Framework that uses it. For example, CronTrigger takes a String rather than a pre-parsed CronExpression instance. It's not yet clear to me how having such conversion support would be generally useful.

Comment From: wilkinsona

No feedback received. Closing. We can reconsider if there's a compelling case for this conversion support and it can't, for some reason, be implemented in Spring Framework.