BeanFactoryPostProcessor interface

The semantics of this interface is similar to BeanPostProcessor but with one major difference : BeanFactoryPostProcessor operate on bean configuration metadata; So spring IoC container allow BeanFactoryPostProcessor to read the configuration metadata and potentially change it before the container instantiates any bean other than BeanFactoryPostProcessor .

But if you want to change the actual bean instances( the objects that are created from the configuration metadata), then use BeanPostProcessor.

Example …

import org.springframework.beans.BeansException;
import org.springframework.beans.factory.config.BeanFactoryPostProcessor;
import org.springframework.beans.factory.config.ConfigurableListableBeanFactory;

public class BeanFactoryPostProcessorImpl implements BeanFactoryPostProcessor {

    public BeanFactoryPostProcessorImpl() {
        System.out.println("BeanFactoryPostProcessorImpl class instantiated..");
    }
    
    @Override
    public void postProcessBeanFactory(ConfigurableListableBeanFactory factory)
            throws BeansException {
        System.out.println("postProcessBeanFactory method of our BeanFactoryPostProcessorImpl class called..");
        
        //dynamically registering a new bean in the context. you can try this later on.
        //similar to @Configuration and @Bean we saw in previous section.
        //factory.registerSingleton("myBean", new SampleBean());
    }    
}

Again one of the commonly used BeanFactoryPostProcessor is PropertyPlaceHolderConfigurer class. We already have seen the usage of this class before. This replaces the config of any bean containing ${}  with the actual property value so by the time the bean is instantiated, the correct values are already in the container.