Support loading of selected beans from external library in micronaut

[pavelfomin]

Feature description

When a micronaut library is created using io.micronaut.library plugin, all of the bean definitions are added to META-INF/services/io.micronaut.inject.BeanDefinitionReference. As the result, when such library is added to a micronaut application all of its beans are imported. While it might be a reasonable default behavior, there is frequently a need for an application to import only selected beans from a library similar to Spring Boot EnableScheduling which imports specific SchedulingConfiguration.class (i.e. different applications could choose to import different components). It's my understanding that there is currently no way to control either:

• which beans are included in META-INF/services/io.micronaut.inject.BeanDefinitionReference as part of a library jar
• or which of the beans from a library jar get imported

I've removed META-INF/services/io.micronaut.inject.BeanDefinitionReference from the library jar explicitly in my build.gradle:

jar {
    exclude('META-INF/services/io.micronaut.inject.BeanDefinitionReference')
}

and then used @Import in the application to explicitly import the desired components.

I wonder if there is a better way to do this. Thanks in advance for the consideration!

[yawkat]

You can configure which beans to load using ApplicationContextBuilder

[graemerocher]

I don't think you can actually, but it probably would be nice to allow it

[jameskleeh]

Sounds like you should break up your library into multiple artifacts. We never went down the rabbit hole that is @EnableXyz because dependencies should be broken up to allow for only the features the user wants

[alvarosanchez]

Relates to #7169

[jameskleeh]

If you want to create a jar containing multiple features then the beans can be disabled by default and could be enabled via config (equivalent to the @enable... case in boot)

[pavelfomin]

Note. My approach with removing META-INF/services/io.micronaut.inject.BeanDefinitionReference from a jar file only works for simple use cases when a component has a default constructor and does not have any dependencies. Otherwise the application fails to start since it cannot find a correctly precompiled bean reference.

If you want to create a jar containing multiple features then the beans can be disabled by default and could be enabled via config (equivalent to the @enable... case in boot)

@jameskleeh I assume your suggestion above was to use Requires with entities referencing a custom annotation

@Requirements(
    Requires(entities = [MyCustomAnnotation::class])
)

I have tried it out and it did not work for me. Micronaut seems to scan only a small subset of classes for the annotation specified. When a breakpoint is set in io.micronaut.core.beans.DefaultBeanIntrospector.findIntrospectedTypes, mostly io.micronaut components are returned by getIntrospections() with a couple of application components (I've used @MicronautTest spec to debug). Most of my application components are missing and those are the ones that would have a custom annotation added. If there is a working example of custom annotation usage with Requires(entities = [MyCustomAnnotation::class]) I would very appreciate it.

I did however make it work with the application properties:

@Requirements(
    Requires(property = "my.special.property")
)