How to make a configuration conditional on another configuration?

Question

I want to make my spring-boot configuration class A dependent on another configuration class B, i.e. A configuration is evaluated only if B configuration is evaluated.

In the real context, I have hundreds of Ai configurations and only one B, and I want to implement a way to exclude all the Ai configs by excluding only B during tests.

I tried the following:

@Configuration
@ConditionalOnBean(type = "org.my.B")
public class A1AutoConfiguration {
// ...
}

Where B is a unconditioned configuration class.

But when I run mvn spring-boot:run -Ddebug=true I see that A is never evaluated because B is missing. While the beans created inside B are in the application context, B itself is not.

I though I can make the Ai configuration classes dependent on beans created inside B but I don't like so much this solution.

Is there a cleaner (and working) way to implement such a dependency mechanism?

Answer 1

The key is to make sure that things are ordered correctly. It does not make any sense to request A to only apply if B is present if you can't make sure that B is evaluated first.

The hundreds part frightens me a bit. If As and B are auto-configuration, you can use the following

@AutoconfigureAfter(B.class)
@ConditionalOnBean(B.class)
public class A123AutoConfiguration { ...}

If As and B are not auto-configuration, you need to make sure B is processed first so you can't rely on regular classpath scanning for those.