IoC Container & Bean Lifecycle

IoC means the container controls object creation and wiring instead of your code doing it with new; ApplicationContext is the full-featured container and BeanFactory is its minimal lazy-loading parent.

Instantiate, inject dependencies, @PostConstruct, AOP proxy wrap, READY; on shutdown: @PreDestroy, destroy; the injected reference is a CGLIB proxy created in postProcessAfterInitialization, which is why self-invocation bypasses @Transactional.

Circular dependencies with constructors always fail because neither bean can be fully created first; the proper fix is to extract the shared concern into a third bean, not to use @Lazy or allow-circular-references.

Singleton means one instance for all; prototype means a new instance every time; injecting a prototype into a singleton gives you ONE prototype forever; fix with ObjectProvider.getObject() to get a fresh instance per use.