Bean Post Processors
Imagine you have a factory that produces cars. Before a car is delivered, you might want to add a wax coating or install a GPS. BeanPostProcessor lets you do exactly that – intercept the bean creation process and apply custom modifications before and after initialization.
A
BeanPostProcessor is a special interface that allows you to add your own logic during the bean lifecycle. Spring itself uses many built‑in post processors (e.g., for @Autowired processing).Here's a simple example:
import org.springframework.beans.BeansException;
import org.springframework.beans.factory.config.BeanPostProcessor;
public class CustomBeanPostProcessor implements BeanPostProcessor {
@Override
public Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException {
if (bean instanceof Car) {
System.out.println("Before initialization of " + beanName);
}
return bean;
}
@Override
public Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException {
if (bean instanceof Car) {
System.out.println("After initialization of " + beanName);
}
return bean;
}
}
You then register this as a bean, and Spring will automatically apply it to all beans.
Common use cases: wrapping beans with proxies, modifying bean properties, or applying custom annotations.
Two Minute Drill
BeanPostProcessorhooks into the bean lifecycle before and after initialization.- It allows you to modify or wrap beans after they are created.
- Spring uses many built‑in post processors (e.g.,
AutowiredAnnotationBeanPostProcessor). - Implement
BeanPostProcessorand override its two methods.
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