Have you had experience writing BeanPostProcessors?

BeanPostProcessor is an interface in the Spring Framework that allows intercepting the creation of beans and modifying them before and after initialization. Writing a BeanPostProcessor is usually associated with the need to inject additional logic, such as wrapping beans with proxies, changing properties, or registering them in some services.

An example of a simple BeanPostProcessor that logs bean creation:

@Component
public class LoggingBeanPostProcessor implements BeanPostProcessor {
    @Override
    public Object postProcessBeforeInitialization(Object bean, String beanName) {
        System.out.println("Before init: " + beanName);
        return bean;
    }

    @Override
    public Object postProcessAfterInitialization(Object bean, String beanName) {
        System.out.println("After init: " + beanName);
        return bean;
    }
}

This approach is useful for cross-cutting concerns, such as injecting aspects, validation, or custom initialization logic.