What is the difference between BeanFactoryPostProcessor and BeanPostProcessor in Spring, and what are their roles?

In Spring, BeanFactoryPostProcessor and BeanPostProcessor are two different interfaces that allow intervention in the process of bean creation and configuration, but at different stages.

• BeanFactoryPostProcessor executes after the bean definitions are loaded but before the beans are created. It allows modifying bean metadata (such as properties, dependencies) in the BeanFactory. This is useful for global bean configuration adjustments.

• BeanPostProcessor executes after a bean has been created and initialized, but before it is used. It allows modifying the bean instances themselves, for example, wrapping them with proxies, injecting additional dependencies, or performing validation.

Example:

@Component
public class CustomBeanFactoryPostProcessor implements BeanFactoryPostProcessor {
    @Override
    public void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory) {
        // Modify bean properties before creation
    }
}

@Component
public class CustomBeanPostProcessor implements BeanPostProcessor {
    @Override
    public Object postProcessBeforeInitialization(Object bean, String beanName) {
        // Modify bean before initialization
        return bean;
    }

    @Override
    public Object postProcessAfterInitialization(Object bean, String beanName) {
        // Modify bean after initialization
        return bean;
    }
}

Thus, BeanFactoryPostProcessor works with configuration, while BeanPostProcessor works with fully constructed objects.