Spring - @Autowired bean from @Configuration is null

Question

I define a bean in a configuration class. I would like to autowire this bean in a component. However, the property stays null. E.g.:

Appconfiguration.java

@Configuration
public class AppConfiguration {

    @Bean
    public SomeType someObject() {
        return new SomeType();
    }
}

AppComponent.java

@Component
public class AppComponent {

    @Autowired
    private SomeType someObject;  // TODO why null?

    public AppComponent() {  // note: passing a SomeType constructor argument works
        System.out.println(someObject);
    }
}

How can I autowire a bean defined in a configuration class?

Answer 1

Are you missing a fundamental detail that properties are injected after a bean is created? Have you tried access your property after a bean is fully initialized?

Update: I've reworked your example a little to demonstrate you the difference:

@Test
public void initializationTest() {
    try (AnnotationConfigApplicationContext context =
                 new AnnotationConfigApplicationContext()) {
        context.register(AppConfiguration.class, AppComponent.class);
        context.refresh();
    }
}

@Configuration
public class AppConfiguration {

    @Bean
    public SomeType someObject() {
        return new SomeType();
    }
}


@Component
public class AppComponent {

    @Autowired
    private SomeType someObject;

    public AppComponent() {
        // Here properties are not yet injected by Spring IoC container
        System.out.println(someObject); // Obviously prints null
    }

    /**
     * Method is invoked after a bean is initialized and all its properties are being set.
     */
    @PostConstruct
    private void init() {
        System.out.println(someObject); // Prints SomeType@6b419da
    }
}

public class SomeType {
}

So basically bean lifecycle consists of the following steps:

1. Bean instance is created
2. Bean properties are set
3. In case bean implements Aware interfaces - those implemented methods are invoked
4. BeanPostProcessor#postProcessBeforeInitialization methods of custom bean post-processors are invoked
5. Initialization callbacks are invoked in the following order:
5.1. @PostConstruct method is invoked
5.2. InitializingBean#afterPropertiesSet() method is invoked
5.3. @Bean#initMethod() method is invoked
Bean is fully initialized now.
6. BeanPostProcessor#postProcessAfterInitialization methods of custom post-processors are invoked are invoked.
7. Destruction callbacks are invoked in the following order:
7.1. @PreDestroy method is invoked
7.2. DisposableBean#destroy() method is invoked
7.3. @Bean#destroyMethod method is invoked