Bean Initialization Timeline

1. Instantiate the bean via constructor or factory method
2. Populate bean properties through dependency injection
3. If bean implements BeanNameAware, invoke setBeanName()
4. If bean implements BeanFactoryAware, invoke setBeanFactory()
5. If bean implements ApplicationContextAware, invoke setApplicationContext()
6. Execute BeanPostProcessor.postProcessBeforeInitialization() for all configured processors
7. If bean implements InitializingBean, invoke afterPropertiesSet()
8. Execute custom initialization method specified via init-method
9. Execute BeanPostProcessor.postProcessAfterInitialization() for all configured processors
10. Bean becomes ready for use
11. Container shutdown initiated
12. If bean implements DisposableBean, invoke destroy()
13. Execute custom destruction method specified via destroy-method

Initialization Method Execution Order

InstantiationAwareBeanPostProcessor → BeanPostProcessor (pre-initialization) → @PostConstruct → InitializingBean.afterPropertiesSet() → Custom init-method

Key Component Responsibilities

DeferredImportSelector: Extends bean registration capabilities by adding fully qualified bean names

AbstractAutowireCapableBeanFactory: Handles property injection for beans

AutowiredAnnotationBeanPostProcessor: Processes @Autowired and @Value annotations

AbstractBeanFactory.resolveEmbeddedValue(): Resolves embedded values in configuration

Complete Registration Process

BeanDefinitionRegistryPostProcessor enables custom bean definition registration through BeanDefinitionRegistry

ImportBeanDefinitionRegistrar works with @Import annotation to register additional beans programmatically

import org.springframework.beans.factory.support.BeanDefinitionRegistry;
import org.springframework.context.annotation.ImportBeanDefinitionRegistrar;
import org.springframework.core.type.AnnotationMetadata;

public class LoggerRegistrar implements ImportBeanDefinitionRegistrar {
    @Override
    public void registerBeanDefinitions(AnnotationMetadata metadata, BeanDefinitionRegistry registry) {
        BeanDefinition loggerDefinition = new GenericBeanDefinition();
        loggerDefinition.setBeanClassName("com.example.ApplicationLogger");
        registry.registerBeanDefinition("appLogger", loggerDefinition);
    }
}

Configuration class implementation:

import org.springframework.context.annotation.Configuration;
import org.springframework.context.annotation.Import;

@Configuration
@Import(LoggerRegistrar.class)
public class ApplicationConfiguration {
    // Additional configuration elements
}

Extension Points

InstantiationAwareBeanPostProcessor extends BeanPostProcessor with pre-instantiation capabilities for creating proxy objects:

import org.springframework.beans.BeansException;
import org.springframework.beans.factory.config.InstantiationAwareBeanPostProcessor;
import org.springframework.stereotype.Component;

@Component
public class ProxyCreationProcessor implements InstantiationAwareBeanPostProcessor {
    @Override
    public Object postProcessBeforeInstantiation(Class<?> targetClass, String beanId) throws BeansException {
        if (targetClass.isAnnotationPresent(Transactional.class)) {
            return generateProxyInstance(targetClass);
        }
        return null;
    }
}

BeanPostProcessor methods handle pre and post initialization logic for bean wrapping and processing

InitializingBean.afterPropertiesSet() executes after all properties are set, suitable for resource initializtaion like thread pools

DisposableBean.destroy() handles cleanup operations during bean destruction, such as connection pool termination