postProcessBeanDefinitionRegistry接口

实现BeanDefinitionRegistryPostProcessor接口，可以获得BeanDefinitionRegistry，BeanDefinitionRegistry可实现对BeanDefinition的增删改查操作，下面看一个对BeanDefinition的修改操作。

示例：

创建Student，定义属性username = dongsq
创建TestBeanPostProcessor 实现 BeanDefinitionRegistryPostProcessor 覆盖其两个方法，可以得到BeanDefinitionRegistry 和 DefaultListableBeanFactory 。

@Data
@Component
public class Student {
    private String username = "dongsq";
}

	...
	...
	...
@Component
public class TestBeanPostProcessor implements BeanDefinitionRegistryPostProcessor, PriorityOrdered {
    @Override
    public void postProcessBeanDefinitionRegistry(BeanDefinitionRegistry beanDefinitionRegistry) throws BeansException {
        BeanDefinition beanDefinition = beanDefinitionRegistry.getBeanDefinition("student");
        MutablePropertyValues mpv = beanDefinition.getPropertyValues();
        mpv.addPropertyValue("username", "dongsq001");
        beanDefinitionRegistry.registerBeanDefinition("student", beanDefinition);
    }

    @Override
    public void postProcessBeanFactory(ConfigurableListableBeanFactory configurableListableBeanFactory) throws BeansException {
        DefaultListableBeanFactory beanFactory = (DefaultListableBeanFactory)configurableListableBeanFactory;
        beanFactory.setAllowBeanDefinitionOverriding(true);
        beanFactory.setAllowCircularReferences(true);
    }

    @Override
    public int getOrder() {
        return 0;
    }

上述代码中的postProcessBeanDefinitionRegistry方法又是什么时候被调用的呢？

源码分析：

spring容器在启动过程中，会调用

	invokeBeanFactoryPostProcessors(beanFactory);
	...
	...
	PostProcessorRegistrationDelegate.invokeBeanFactoryPostProcessors(beanFactory, getBeanFactoryPostProcessors());

完成对BeanDefinitionRegistryPostProcessor与BeanFactoryPostProcessor两个接口的调用

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

		// Invoke BeanDefinitionRegistryPostProcessors first, if any.
		Set<String> processedBeans = new HashSet<>();

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

			//beanFactoryPostProcessors 默认为空
			for (BeanFactoryPostProcessor postProcessor : beanFactoryPostProcessors) {
				if (postProcessor instanceof BeanDefinitionRegistryPostProcessor) {
					BeanDefinitionRegistryPostProcessor registryProcessor =
							(BeanDefinitionRegistryPostProcessor) postProcessor;
					registryProcessor.postProcessBeanDefinitionRegistry(registry);
					registryProcessors.add(registryProcessor);
				}
				else {
					regularPostProcessors.add(postProcessor);
				}
			}
			List<BeanDefinitionRegistryPostProcessor> currentRegistryProcessors = new ArrayList<>();

			//获取实现了BeanDefinitionRegistryPostProcessor接口的所有类的BeanDefinition对象的beanName
			//先根据实现了PriorityOrdered进行过滤
			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);
				}
			}
			//排序
			sortPostProcessors(currentRegistryProcessors, beanFactory);
			registryProcessors.addAll(currentRegistryProcessors);
			//调用过程
			invokeBeanDefinitionRegistryPostProcessors(currentRegistryProcessors, registry);
			currentRegistryProcessors.clear();
			//再次获取获取一遍，是因为可能上述会产生新的BeanDefinitionRegistryPostProcessor实现类
			postProcessorNames = beanFactory.getBeanNamesForType(BeanDefinitionRegistryPostProcessor.class, true, false);
			for (String ppName : postProcessorNames) {
				//判断是否是实现的Ordered接口
				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);
			currentRegistryProcessors.clear();

			//没实现排序接口的调用
			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);
				currentRegistryProcessors.clear();
			}

			//调用postProcessBeanFactory方法，是因为BeanDefinitionRegistryPostProcessor 继承BeanFactoryPostProcessor
			invokeBeanFactoryPostProcessors(registryProcessors, beanFactory);
			invokeBeanFactoryPostProcessors(regularPostProcessors, beanFactory);
		}
		else {
			invokeBeanFactoryPostProcessors(beanFactoryPostProcessors, beanFactory);
		}
		//收集所有的BeanFactoryPostProcessor
		String[] postProcessorNames =
				beanFactory.getBeanNamesForType(BeanFactoryPostProcessor.class, true, false);

		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
			}
			//实现了PriorityOrdered接口的
			else if (beanFactory.isTypeMatch(ppName, PriorityOrdered.class)) {
				priorityOrderedPostProcessors.add(beanFactory.getBean(ppName, BeanFactoryPostProcessor.class));
			}
			//实现了Ordered接口的
			else if (beanFactory.isTypeMatch(ppName, Ordered.class)) {
				orderedPostProcessorNames.add(ppName);
			}
			else {
				//没实现接口的
				nonOrderedPostProcessorNames.add(ppName);
			}
		}

		//排序
		sortPostProcessors(priorityOrderedPostProcessors, beanFactory);
		//调用
		invokeBeanFactoryPostProcessors(priorityOrderedPostProcessors, beanFactory);
		List<BeanFactoryPostProcessor> orderedPostProcessors = new ArrayList<>(orderedPostProcessorNames.size());
		for (String postProcessorName : orderedPostProcessorNames) {
			orderedPostProcessors.add(beanFactory.getBean(postProcessorName, BeanFactoryPostProcessor.class));
		}
		sortPostProcessors(orderedPostProcessors, beanFactory);
		invokeBeanFactoryPostProcessors(orderedPostProcessors, beanFactory);
		List<BeanFactoryPostProcessor> nonOrderedPostProcessors = new ArrayList<>(nonOrderedPostProcessorNames.size());
		for (String postProcessorName : nonOrderedPostProcessorNames) {
			nonOrderedPostProcessors.add(beanFactory.getBean(postProcessorName, BeanFactoryPostProcessor.class));
		}
		invokeBeanFactoryPostProcessors(nonOrderedPostProcessors, beanFactory);
		beanFactory.clearMetadataCache();
	}

流程总结：

1、收集所有为BeanDefinitionRegistryPostProcessor类型的beanName数组（假设参数beanFactoryPostProcessors为空）
2、根据权重接口PriorityOrdered进行过滤
3、根据beanName数组创建postProcessor对象，并加入currentRegistryProcessors这个ArrayList集合中
4、对currentRegistryProcessors进行排序
5、调用postProcessor的postProcessBeanDefinitionRegistry方法
6、接下来获取BeanDefinitionRegistryPostProcessor和上述流程差不多，只不过根据Ordered接口进行过滤和没有实现排序接口的进行postProcessBeanDefinitionRegistry方法的调用（和PriorityOrdered接口的调用顺序不同而已）
7、调用postProcessor的postProcessBeanFactory方法，
同postProcessBeanDefinitionRegistry方法调用的过程类似。