Spring Bean Lifecycle: From Instantiation to Destruction

The Spring bean lifecycle has six main phases. First, instantiation — Spring calls the constructor or the @Bean factory method to create the raw object. Second, property population — Spring resolves and injects dependencies; @Autowired, @Value, @Resource are all handled here by the AutowiredAnnotationBeanPostProcessor. Third, Aware callbacks — if the bean implements BeanNameAware, BeanFactoryAware, ApplicationContextAware, EnvironmentAware, Spring calls the respective setter to hand the bean a reference to framework internals it needs. Fourth, BeanPostProcessor.postProcessBeforeInitialization runs across every bean — this is the hook that lets frameworks intercept. Then initialization: @PostConstruct first, then InitializingBean.afterPropertiesSet(), then a custom init-method if one is declared on the BeanDefinition. Fifth, BeanPostProcessor.postProcessAfterInitialization runs — crucially this is where AOP proxies get wrapped around the bean. AnnotationAwareAspectJAutoProxyCreator is itself a BeanPostProcessor, and when it sees a bean matching a pointcut, it wraps the original bean in a CGLIB or JDK dynamic proxy and returns the proxy to the container. From this point on, the ApplicationContext and anything that @Autowires this bean gets the proxy, not the original. Sixth, destruction on context shutdown: @PreDestroy first, then DisposableBean.destroy(), then a custom destroy-method. A key corollary: AOP being in post-init is why calling one @Transactional method from another method of the same class bypasses the transaction — the inner call is on "this" directly, not on the proxy. The fix is to get the proxy via AopContext.currentProxy() or inject the bean into itself.