SpringBoot扩展功能之BeanFactoryPostProcessor

BeanFactoryPostProcessor作用

BeanFactoryPostProcessor作为BeanFactory的后置处理器，在bean未实例化前，修改BeanDefinition。

@FunctionalInterface
public interface BeanFactoryPostProcessor {

	void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory) throws BeansException;
}

自定义BeanFactoryPostProcessor修改bean

@Data
@Component("secondSunpyBean")
public class SecondSunpyBean {

    private String name = "马大帅";
    private Integer age = 52;
}

// 自定义BeanFactoryPostProcessor
@Slf4j
@Component
public class SunpyBeanFactoryPostProcessor implements BeanFactoryPostProcessor {

    @Override
    public void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory) throws BeansException {
        BeanDefinition beanDefinition = beanFactory.getBeanDefinition("secondSunpyBean");
        MutablePropertyValues propertyValues = beanDefinition.getPropertyValues();
        propertyValues.addPropertyValue("name", "范德彪");
        propertyValues.addPropertyValue("age", 18);
    }
}

@Slf4j
@Service
public class MenuServiceImpl {

    public Map<String, String> testMenu() {
        Map<String, String> resultMap = new HashMap<>();
        SecondSunpyBean secondSunpyBean = SpringUtils.getBean(SecondSunpyBean.class);
        resultMap.put("name", secondSunpyBean.getName());
        resultMap.put("age", secondSunpyBean.getAge().toString());
        return resultMap;
    }
}

结果：

BeanFactoryPostProcessor什么时候实例化的？

BeanFactoryPostProcessor标识了@Componennt注解，所以本身还是通过@ComponentScan扫描，自动装配进入beanDefinitionMap。

postProcessBeanFactory方法什么时候执行的？

入口：

委派给PostProcessorRegistrationDelegate.invokeBeanFactoryPostProcessors方法

public static void invokeBeanFactoryPostProcessors(
			ConfigurableListableBeanFactory beanFactory, List<BeanFactoryPostProcessor> beanFactoryPostProcessors) {

		
	Set<String> processedBeans = new HashSet<>();

	if (beanFactory instanceof BeanDefinitionRegistry) {
		BeanDefinitionRegistry registry = (BeanDefinitionRegistry) beanFactory;
		List<BeanFactoryPostProcessor> regularPostProcessors = new ArrayList<>();
		List<BeanDefinitionRegistryPostProcessor> registryProcessors = new ArrayList<>();

		for (BeanFactoryPostProcessor postProcessor : beanFactoryPostProcessors) {
			if (postProcessor instanceof BeanDefinitionRegistryPostProcessor) {
				BeanDefinitionRegistryPostProcessor registryProcessor =
						(BeanDefinitionRegistryPostProcessor) postProcessor;
				registryProcessor.postProcessBeanDefinitionRegistry(registry);
				registryProcessors.add(registryProcessor);
			}
			else {
				regularPostProcessors.add(postProcessor);
			}
		}

		// Do not initialize FactoryBeans here: We need to leave all regular beans
		// uninitialized to let the bean factory post-processors apply to them!
		// Separate between BeanDefinitionRegistryPostProcessors that implement
		// PriorityOrdered, Ordered, and the rest.
		List<BeanDefinitionRegistryPostProcessor> currentRegistryProcessors = new ArrayList<>();

		// First, invoke the BeanDefinitionRegistryPostProcessors that implement PriorityOrdered.
		String[] postProcessorNames =
				beanFactory.getBeanNamesForType(BeanDefinitionRegistryPostProcessor.class, true, false);
		for (String ppName : postProcessorNames) {
			if (beanFactory.isTypeMatch(ppName, PriorityOrdered.class)) {
				currentRegistryProcessors.add(beanFactory.getBean(ppName, BeanDefinitionRegistryPostProcessor.class));
				processedBeans.add(ppName);
			}
		}
		sortPostProcessors(currentRegistryProcessors, beanFactory);
		registryProcessors.addAll(currentRegistryProcessors);
		invokeBeanDefinitionRegistryPostProcessors(currentRegistryProcessors, registry, beanFactory.getApplicationStartup());
		currentRegistryProcessors.clear();

		// Next, invoke the BeanDefinitionRegistryPostProcessors that implement Ordered.
		postProcessorNames = beanFactory.getBeanNamesForType(BeanDefinitionRegistryPostProcessor.class, true, false);
		for (String ppName : postProcessorNames) {
			if (!processedBeans.contains(ppName) && beanFactory.isTypeMatch(ppName, Ordered.class)) {
				currentRegistryProcessors.add(beanFactory.getBean(ppName, BeanDefinitionRegistryPostProcessor.class));
				processedBeans.add(ppName);
			}
		}
		sortPostProcessors(currentRegistryProcessors, beanFactory);
		registryProcessors.addAll(currentRegistryProcessors);
		invokeBeanDefinitionRegistryPostProcessors(currentRegistryProcessors, registry, beanFactory.getApplicationStartup());
		currentRegistryProcessors.clear();

		// Finally, invoke all other BeanDefinitionRegistryPostProcessors until no further ones appear.
		boolean reiterate = true;
		while (reiterate) {
			reiterate = false;
			postProcessorNames = beanFactory.getBeanNamesForType(BeanDefinitionRegistryPostProcessor.class, true, false);
			for (String ppName : postProcessorNames) {
				if (!processedBeans.contains(ppName)) {
					currentRegistryProcessors.add(beanFactory.getBean(ppName, BeanDefinitionRegistryPostProcessor.class));
					processedBeans.add(ppName);
					reiterate = true;
				}
			}
			sortPostProcessors(currentRegistryProcessors, beanFactory);
			registryProcessors.addAll(currentRegistryProcessors);
			invokeBeanDefinitionRegistryPostProcessors(currentRegistryProcessors, registry, beanFactory.getApplicationStartup());
			currentRegistryProcessors.clear();
		}

		// Now, invoke the postProcessBeanFactory callback of all processors handled so far.
		invokeBeanFactoryPostProcessors(registryProcessors, beanFactory);
		invokeBeanFactoryPostProcessors(regularPostProcessors, beanFactory);
	}

	else {
		// Invoke factory processors registered with the context instance.
		invokeBeanFactoryPostProcessors(beanFactoryPostProcessors, beanFactory);
	}

	// Do not initialize FactoryBeans here: We need to leave all regular beans
	// uninitialized to let the bean factory post-processors apply to them!
	String[] postProcessorNames =
			beanFactory.getBeanNamesForType(BeanFactoryPostProcessor.class, true, false);

	// Separate between BeanFactoryPostProcessors that implement PriorityOrdered,
	// Ordered, and the rest.
	List<BeanFactoryPostProcessor> priorityOrderedPostProcessors = new ArrayList<>();
	List<String> orderedPostProcessorNames = new ArrayList<>();
	List<String> nonOrderedPostProcessorNames = new ArrayList<>();
	for (String ppName : postProcessorNames) {
		if (processedBeans.contains(ppName)) {
			// skip - already processed in first phase above
		}
		else if (beanFactory.isTypeMatch(ppName, PriorityOrdered.class)) {
			priorityOrderedPostProcessors.add(beanFactory.getBean(ppName, BeanFactoryPostProcessor.class));
		}
		else if (beanFactory.isTypeMatch(ppName, Ordered.class)) {
			orderedPostProcessorNames.add(ppName);
		}
		else {
			nonOrderedPostProcessorNames.add(ppName);
		}
	}

	// First, invoke the BeanFactoryPostProcessors that implement PriorityOrdered.
	sortPostProcessors(priorityOrderedPostProcessors, beanFactory);
	invokeBeanFactoryPostProcessors(priorityOrderedPostProcessors, beanFactory);

	// Next, invoke the BeanFactoryPostProcessors that implement Ordered.
	List<BeanFactoryPostProcessor> orderedPostProcessors = new ArrayList<>(orderedPostProcessorNames.size());
	for (String postProcessorName : orderedPostProcessorNames) {
		orderedPostProcessors.add(beanFactory.getBean(postProcessorName, BeanFactoryPostProcessor.class));
	}
	sortPostProcessors(orderedPostProcessors, beanFactory);
	invokeBeanFactoryPostProcessors(orderedPostProcessors, beanFactory);

	// Finally, invoke all other BeanFactoryPostProcessors.
	List<BeanFactoryPostProcessor> nonOrderedPostProcessors = new ArrayList<>(nonOrderedPostProcessorNames.size());
	for (String postProcessorName : nonOrderedPostProcessorNames) {
		nonOrderedPostProcessors.add(beanFactory.getBean(postProcessorName, BeanFactoryPostProcessor.class));
	}
	invokeBeanFactoryPostProcessors(nonOrderedPostProcessors, beanFactory);

	// Clear cached merged bean definitions since the post-processors might have
	// modified the original metadata, e.g. replacing placeholders in values...
	beanFactory.clearMetadataCache();
}

委派给PostProcessorRegistrationDelegate.invokeBeanFactoryPostProcessors方法：

上面可以看出来，就是遍历实现了BeanFactoryPostProcessor接口的bean，然后直接调用postProcessBeanFactory方法。

注意

• BeanFactoryPostProcessor.postProcessBeanFactory方法中不要对bean实例化，无论是new还是@Autowired注入。

与BeanDefinitionRegistryPostProcessor区别

BeanDefinitionRegistryPostProcessor用来添加额外的beanDefinition，而BeanFactoryPostProcessor用来修改beanDefinition。

• BeanDefinitionRegistryPostProcessor什么时候执行？
  PostProcessorRegistrationDelegate.invokeBeanFactoryPostProcessors方法中执行：