@Primary with Cyclic DI

[daodefengshang]

Version: spring-boot-2.5.6

Code:

public interface LoopService {

	void testLoop();
	
	void testInnerLoop();
}

@Service
public class DefaultLoopService implements LoopService {

	private static final Logger log = LoggerFactory.getLogger(DefaultLoopService.class);
	
	@Autowired
	private LoopService loopService;

	@Override
	public void testLoop() {
		log.info("DefaultLoopService");
	}

	@Override
	public void testInnerLoop() {
		log.info("DefaultLoopService--testInnerLoop");
	}

}

@Service
@Primary
public class UsingLoopService implements LoopService {

	private static final Logger log = LoggerFactory.getLogger(UsingLoopService.class);
	
	@Autowired
	private LoopService loopService;
	
	@Override
	public void testLoop() {
		log.info("UsingLoopService");
		loopService.testInnerLoop();
	}

	@Override
	public void testInnerLoop() {
		log.info("UsingLoopService--testInnerLoop");
	}
}

@RestController
public class LoopController {
	
	@Autowired
	private LoopService loopService;

	@GetMapping("/testLoop")
	public void testLoop() {
		loopService.testLoop();
	}
}

Expect Print:

service.impl.UsingLoopService : UsingLoopService
service.impl.UsingLoopService : UsingLoopService--testInnerLoop

But Actual Print:

service.impl.UsingLoopService : UsingLoopService
service.impl.DefaultLoopService : DefaultLoopService--testInnerLoop

[philwebb]

I think that this is working as expected. You can't inject a bean into itself so UsingLoopService is injected with a DefaultLoopService

[mdeinum]

You can't inject a bean into itself

Well actually you can (as of Spring 4.3) so you can call a method on yourself so AOP is applied (instead of using this). See #13096.

[philwebb]

Thanks @mdeinum, I wasn't aware of that. It looks like that will only work if there's not another candidate to inject. I'll re-open this issue and transfer it to the Framework team to check if the behavior is expected.

[JintaoXIAO]

the logic locates in org.springframework.beans.factory.support.DefaultListableBeanFactory@L1533
@daodefengshang

[snicoll]

I don't think you should be doing that at all for a start. Cycles are highly discouraged and the self-injection for AOP purpose is actually a design smell. We'll share more details in #28299