Self injection with Spring

By the way, the more elegant solution to the self-invocation problem is to use AspectJ Load-Time Weaving for your transactional proxies (or whatever AOP-introduced proxy you're using).

For example, with annotation-driven transaction management, you can use the "aspectj" mode as follows:

<tx:annotation-driven mode="aspectj" />

Note that the default mode is "proxy" (i.e., JDK dynamic proxies).

Regards,

Sam

Update: February 2016

Self autowiring will be officially supported in Spring Framework 4.3. The implementation can be seen in this GitHub commit.

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The definitive reason that you cannot autowire yourself is that the implementation of Spring's DefaultListableBeanFactory.findAutowireCandidates(String, Class, DependencyDescriptor) method explicitly excludes the possibility. This is visible in the following code excerpt from this method:

for (String candidateName : candidateNames) {
    if (!candidateName.equals(beanName) && isAutowireCandidate(candidateName, descriptor)) {
        result.put(candidateName, getBean(candidateName));
    }
}

FYI: the name of the bean (i.e., the bean that's trying to autowire itself) is beanName. That bean is in fact an autowire candidate, but the above if-condition returns false (since candidateName in fact equals the beanName). Thus you simply cannot autowire a bean with itself (at least not as of Spring 3.1 M1).

Now as for whether or not this is intended behavior semantically speaking, that's another question. ;)

I'll ask Juergen and see what he has to say.

Regards,

Sam (Core Spring Committer)

p.s. I've opened a Spring JIRA issue to consider supporting self-autowiring by type using @Autowired. Feel free to watch or vote for this issue here: https://jira.springsource.org/browse/SPR-8450

This code works too:

@Service
public class UserService implements Service {

    @Autowired
    private ApplicationContext applicationContext;

    private Service self;

    @PostConstruct
    private void init() {
        self = applicationContext.getBean(UserService.class);
    }
}

I don't know why, but it seems that Spring can get the bean from ApplicationContext if is created, but not initialized. @Autowired works before initialization and it cannot find the same bean. So, @Resource maybe works after @Autowired and before @PostConstruct.

But I don't know, just speculating. Anyway, good question.

Given above code I don't see a cyclic dependency. You injecting some instance of Service into UserService. The implementation of the injected Service does not necessarily need to be another UserService so there is no cyclic dependency.

I do not see why you would inject a UserService into UserService but I'm hoping this is a theoretic try out or such.