What's the difference between BeanFactoryPostProcessor and BeanPostProcessor?
A BeanFactoryPostProcessor runs BEFORE any bean is instantiated, operating on bean DEFINITIONS (metadata) — PropertySourcesPlaceholderConfigurer, which resolves ${...} placeholders, is a classic example. A BeanPostProcessor runs AFTER each bean is instantiated, wrapping its initialization via postProcessBeforeInitialization()/postProcessAfterInitialization() — this is exactly how AOP proxies for @Transactional and @Cacheable get created, by replacing the raw bean instance with a proxy during this phase.
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