Assign String in @Scheduled(cron ="Some String")

Question

We have a properties file in which we mention to take the properties to be taken from JSON/Zookeeper.

Example:

AppName : SampleApp

Inside SampleApp.properties we will specify

configmode=json
jsonfile=/config.json

There are many examples how to assign the properties inside the @Scheduled annotation using properties file.

But in this scenario ,

we have to read the property using some Java class (say Name is Config) String cronExp=Config.get("CRONEXPRESSION") ; and put that cron inside @Scheduled(cron = cronExp) ..Is this possible?

Note we cannot move the CRONEXPRESSION propepty to property file directly..Inside properties file we mention json..inside code we read that json and pick the property from there..

Answer 1

Short answer:

saddly, you cannot do that.

In Java, annotation attributes are resolved at compile time. Which means that you can only provide an immediate value or a constant.

Use case specific answer:

Spring let's you use SpEL in a number of places. In this case, the value of the annotation's attribute is still resolved at compile time, but this value is evaluated by Spring at runtime. @RC provided a good link to a discussion of the details.

Somewhat longer answer:

It is possible to modify annotations at runtime by using reflection, but that's a tricky path, and the code processing the annotation need to handle the case where annotations change at runtime (this is very rarely the case).