Referring to @Autowired component in another component's constructor

Question

Can a Spring component's constructor refer to an @Autowired component, or does the autowiring happen too late?

I have an example that's something like this:

@Component
public class A {
    public A() { ... }
    ...
}

@Component
public class B {
    @Autowired A a;
    public B() {
        some code using a.getThisOrThat() ... // fails, a is null
    }
}

and in the config file:

<bean id="a" class="some.packagename.A" />
<bean id="b" class="some.packagename.B" depends-on="a" />

I've confirmed using System.out.println that A's constructor is called before B's; however, inside B's constructor, a is null. I'm running this as a JUnit unit test, using SpringJUnit4ClassRunner. If I defer the initialization in B until the first time another method is called, it works fine--a has been set up.

Is this the expected behavior?

Is it possible that the behavior is different when SpringJUnit4ClassRunner is being used?

Is there a way to get this to work (aside from deferring the initialization in B)?

How could `a` ever be non-null **inside** the constructor body? — Sotirios Delimanolis, Nov 19 '15 at 17:07
Your options are constructor injection and `@PostConstruct` initialization methods. — Sotirios Delimanolis, Nov 19 '15 at 17:08
`@DependsOn`/`depends-on` only sets an ordering for bean initialization, nothing else. — Sotirios Delimanolis, Nov 19 '15 at 17:09
OK, I see--Spring can't touch the object until it's been created which means the constructor has to have been completed... I missed that. Anyway, thanks for pointing me to the alternatives. — ajb, Nov 19 '15 at 17:13

Referring to @Autowired component in another component's constructor

0 Answers0