[FIXED] Autowiring an interface implementation from an external library

Issue

I have written a common library for future SpringBoot applications and made it into a jar. Inside, there is a service that autowires an interface:

@Service
public class MyService {
    protected @Autowired AbstractUserService abstractUserService;
}

public interface AbstractUserService {
    Optional<? extends AbstractUser> findByPrincipal(Principal principal);
}

In my main application, in build.gradle I load the library mentioned above as follows:

...
repositories {
    flatDir {
        dirs "$rootDir/libs"
    }
}
...
dependencies {
    ...
    implementation name: "my-library"
    ...
}

Then I have implemented the interface:

@Service
public class UserService implements AbstractUserService {
    @Override public Optional<? extends AbstractUser> findByPrincipal(Principal principal) {
        // do something
    }

However, it seems that the library is unable to find it and I get the following exception:

Parameter 1 of constructor in MyService required a bean of type 'AbstractUserService' that could not be found.

In my main application I have also added the following annotation in order to @Autowire the services exposed by this library:

@SpringBootApplication(scanBasePackages = {"the.root.package.of.my-library"})

Is there something that can be done? Also, is there a better way of autowiring the exposed services without the explicit scanBasePackage description?

Solution

I have managed to fix it.

First, I have removed the explicit scanBasePackage description from @SpringBootApplication.
Secondly, I have annotated the configuration file from the library with @ComponentScan and created the following file: resources/META-INF/spring.factories with the following content:

org.springframework.boot.autoconfigure.EnableAutoConfiguration=\
    my-library.package.MyLibraryConfig

This is my complete library config file:

@Configuration
@ComponentScan
public class MyConfig {
...
}

Answered By - Mihai Catalin Valentin
Answer Checked By - Marilyn (JavaFixing Volunteer)