Is @Autowired annotation handled by BeanPostProcessor in Spring?

Question

I claimed that:

1. Spring read bean definitions from java config
2. BeanFactory Create beans from defenitions
3. Then dependencies are injected by BeanPostProcessors

But it happened that it's not accurate:

@Configuration
@ImportResource("classpath:spring_config.xml")
public class JavaConfig {

    @Autowired
    MyBean bean;

    @Bean
    public Boolean isBeanAutowired(){
        return bean != null;
    }
}

The isBeanAutowired bean was initialized with true.

Question:

How does it happen that Autowired logic work before all beans in context were initialized?

Answer 1

Yes @Autowired is handled by a BeanPostProcessor. See org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor for more details and as an entrypoint if you try to find out more on this.

https://github.com/spring-projects/spring-framework/blob/master/spring-beans/src/main/java/org/springframework/beans/factory/annotation/AutowiredAnnotationBeanPostProcessor.java

http://docs.spring.io/spring-framework/docs/current/javadoc-api/org/springframework/beans/factory/annotation/AutowiredAnnotationBeanPostProcessor.html

In the end Spring is able to analyze the dependencies of a bean (the other beans that need to be wired) and determine an order, in which the beans will be initialized. Thereby it is possible, to autowire directly after creation of a bean. There is one exception, which occurs when Spring tries to resolve circular dependencies. Then Spring will create both beans and autowire them to each other. This works only limited though.