深入理解Spring IOC之扩展篇(二)、BeanFactoryPostProcessor和BeanPostProcessor

/**
 * 1. Allows for custom modification of an application context's bean definitions,
 * adapting the bean property values of the context's underlying bean factory.
 *
 * 2. <p>Application contexts can auto-detect BeanFactoryPostProcessor beans in
 * their bean definitions and apply them before any other beans get created.
 *
 * 3. <p>Useful for custom config files targeted at system administrators that
 * override bean properties configured in the application context.
 *
 * 4. <p>See PropertyResourceConfigurer and its concrete implementations
 * for out-of-the-box solutions that address such configuration needs.
 *
 * 5. <p>A BeanFactoryPostProcessor may interact with and modify bean
 * definitions, but never bean instances. Doing so may cause premature bean
 * instantiation, violating the container and causing unintended side-effects.
 * If bean instance interaction is required, consider implementing
 * {@link BeanPostProcessor} instead.
 *
 * @author Juergen Hoeller
 * @since 06.07.2003
 * @see BeanPostProcessor
 * @see PropertyResourceConfigurer
 */
public interface BeanFactoryPostProcessor {
  /**
   * 6. Modify the application context's internal bean factory after its standard
   * initialization. All bean definitions will have been loaded, but no beans
   * will have been instantiated yet. This allows for overriding or adding
   * properties even to eager-initializing beans.
   * @param beanFactory the bean factory used by the application context
   * @throws org.springframework.beans.BeansException in case of errors
   */
  void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory) throws BeansException;
}

@Component
public class MyBeanFactoryPostProcessor implements BeanFactoryPostProcessor {
    @Override
    public void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory) {
        TestBean testBean = beanFactory.getBean(TestBean.class);
    }
}

@Component
@Data
public class TestBean {
    @Autowired
    private TestBean1 testBean1;
}

@Component
public class TestBean1 {
}

/**
 * 1. Extension to the standard {@link BeanFactoryPostProcessor} SPI, allowing for
 * the registration of further bean definitions <i>before</i> regular
 * BeanFactoryPostProcessor detection kicks in. In particular,
 * BeanDefinitionRegistryPostProcessor may register further bean definitions
 * which in turn define BeanFactoryPostProcessor instances.
 *
 * @author Juergen Hoeller
 * @since 3.0.1
 * @see org.springframework.context.annotation.ConfigurationClassPostProcessor
 */
public interface BeanDefinitionRegistryPostProcessor extends BeanFactoryPostProcessor {
  /**
   * 2. Modify the application context's internal bean definition registry after its
   * standard initialization. All regular bean definitions will have been loaded,
   * but no beans will have been instantiated yet. This allows for adding further
   * bean definitions before the next post-processing phase kicks in.
   * @param registry the bean definition registry used by the application context
   * @throws org.springframework.beans.BeansException in case of errors
   */
  void postProcessBeanDefinitionRegistry(BeanDefinitionRegistry registry) throws BeansException;
}

@Override
  public void postProcessBeanDefinitionRegistry(BeanDefinitionRegistry registry) {
    if (this.processPropertyPlaceHolders) {
      processPropertyPlaceHolders();
    }
    ClassPathMapperScanner scanner = new ClassPathMapperScanner(registry);
    scanner.setAddToConfig(this.addToConfig);
    scanner.setAnnotationClass(this.annotationClass);
    scanner.setMarkerInterface(this.markerInterface);
    scanner.setSqlSessionFactory(this.sqlSessionFactory);
    scanner.setSqlSessionTemplate(this.sqlSessionTemplate);
    scanner.setSqlSessionFactoryBeanName(this.sqlSessionFactoryBeanName);
    scanner.setSqlSessionTemplateBeanName(this.sqlSessionTemplateBeanName);
    scanner.setResourceLoader(this.applicationContext);
    scanner.setBeanNameGenerator(this.nameGenerator);
    scanner.registerFilters();
    scanner.scan(StringUtils.tokenizeToStringArray(this.basePackage, ConfigurableApplicationContext.CONFIG_LOCATION_DELIMITERS));
  }

public interface BeanPostProcessor {
  Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException;
  Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException;
}