PROBLEM

Let’s assume we have the following Spring Data JPA repository…

public interface ProjectRepository extends JpaRepository<Project, Long>, ProjectRepositoryCustom {
    Project findByName(String name);
}

… this repository has some custom implementation…

public interface ProjectRepositoryCustom {
    Project doCustom(String name);
}

… this custom implementation depends on the original repository to reuse existing APIs…

public final class ProjectRepositoryImpl implements ProjectRepositoryCustom {
    private final ProjectRepository projectRepository;

    @Autowired
    public ProjectRepositoryImpl(final ProjectRepository projectRepository) {
        this.projectRepository = projectRepository;
    }

    @Override
    public Project doCustom(final String name) {
        final Project project = projectRepository.findByName(name);
        return ...
    }
}

When we run the code, we get the following exception:-

Caused by: org.springframework.beans.factory.BeanCurrentlyInCreationException: 
Error creating bean with name 'projectRepositoryImpl': Requested bean 
is currently in creation: Is there an unresolvable circular reference?
	at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.beforeSingletonCreation(DefaultSingletonBeanRegistry.java:347)
	at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:223)
	at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:299)
	at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:194)
	at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:293)

SOLUTION

To fix the circular reference problem, instead of auto-wiring ProjectRepository using the constructor, auto-wire using the field or setter method:-

public final class ProjectRepositoryImpl implements ProjectRepositoryCustom {
    // this field cannot be `final` anymore
    private ProjectRepository projectRepository;

    @Autowired
    public void setProjectRepository(final ProjectRepository projectRepository) {
        this.projectRepository = projectRepository;
    }

    @Override
    public Project doCustom(final String name) {
        final Project project = projectRepository.findByName(name);
        return ...
    }
}