【死磕源码系列】BeanDefinitionRegistryPostProcessor作用及源码分析

浅浅的花香味﹌ 2022-12-07 15:26 240阅读 0赞

> BeanDefinitionRegistryPostProcessor接口实现了BeanFactoryPostProcessor接口，BeanFactoryPostProcessor接口的作用是在bean已经注册完成为BeanDefinition，但是还未实例化之前修改BeanDefinition属性；BeanDefinitionRegistryPostProcessor接口提供了一个通过代码形式来注册bean到IOC容器的钩子方法；

##### 1.先看下源码 #####

/** * 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 { 
    
    	/** * 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;
    
    }

> BeanDefinitionRegistryPostProcessor接口会在bean实例化之前调用postProcessBeanDefinitionRegistry、postProcessBeanFactory方法对指定的bean进行实例化及修改BeanDefinition；

##### 2.org.springframework.context.support.PostProcessorRegistrationDelegate\#invokeBeanFactoryPostProcessors方法是调用处理器方法的入口 #####

首先看下refresh方法：

@Override
    	public void refresh() throws BeansException, IllegalStateException { 
    		synchronized (this.startupShutdownMonitor) { 
    			// Prepare this context for refreshing.
    			prepareRefresh();
    
    			// Tell the subclass to refresh the internal bean factory.
    			ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory();
    
    			// Prepare the bean factory for use in this context.
    			prepareBeanFactory(beanFactory);
    
    			try { 
    				// Allows post-processing of the bean factory in context subclasses.
    				postProcessBeanFactory(beanFactory);
    
    				// 调用BeanFactoryPostProcessor接口实现类及BeanDefinitionRegistryPostProcessor实现类的入口方法
    				invokeBeanFactoryPostProcessors(beanFactory);
    
    				// Register bean processors that intercept bean creation.
    				registerBeanPostProcessors(beanFactory);
    
    				// Initialize message source for this context.
    				initMessageSource();
    
    				// Initialize event multicaster for this context.
    				initApplicationEventMulticaster();
    
    				// Initialize other special beans in specific context subclasses.
    				onRefresh();
    
    				// Check for listener beans and register them.
    				registerListeners();
    
    				// Instantiate all remaining (non-lazy-init) singletons.
    				finishBeanFactoryInitialization(beanFactory);
    
    				// Last step: publish corresponding event.
    				finishRefresh();
    			}
    
    			catch (BeansException ex) { 
    				if (logger.isWarnEnabled()) { 
    					logger.warn("Exception encountered during context initialization - " +
    							"cancelling refresh attempt: " + ex);
    				}
    
    				// Destroy already created singletons to avoid dangling resources.
    				destroyBeans();
    
    				// Reset 'active' flag.
    				cancelRefresh(ex);
    
    				// Propagate exception to caller.
    				throw ex;
    			}
    
    			finally { 
    				// Reset common introspection caches in Spring's core, since we
    				// might not ever need metadata for singleton beans anymore...
    				resetCommonCaches();
    			}
    		}
    	}

上述源码中invokeBeanFactoryPostProcessors是调用BeanDefinitionRegistryPostProcessor的入口，接下来看下具体的方法调用PostProcessorRegistrationDelegate\#invokeBeanFactoryPostProcessors：

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<>();
    
    			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<>();
    			//首先，所有实现了PriorityOrdered接口BeanDefinitionRegistryPostProcessors实现类实例化并调用后置处理方法
    			// 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);
    			currentRegistryProcessors.clear();
    			//接着，对所有实现了Ordered接口的BeanDefinitionRegistryPostProcessors实现类进行实例化并调用后置处理方法
    			// 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);
    			currentRegistryProcessors.clear();
    			//最后，调用所有其它的BeanDefinitionRegistryPostProcessors实现类，自定义的BeanDefinitionRegistryPostProcessors实现类就是在这里被实例化并调用后置处理器方法的
    			// 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);
            //调用处理方法，注册相关bean到IOC容器之中
    				invokeBeanDefinitionRegistryPostProcessors(currentRegistryProcessors, registry);
    				currentRegistryProcessors.clear();
    			}
    			//现在，调用所有的postProcessBeanFactory方法对BeanDefinition进行修改
    			// Now, invoke the postProcessBeanFactory callback of all processors handled so far.
    			invokeBeanFactoryPostProcessors(registryProcessors, beanFactory);
    			invokeBeanFactoryPostProcessors(regularPostProcessors, beanFactory);
    		}
    
    		else { 
          //调用BeanFactoryPostProcessor的后置处理方法
    			// 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();
    	}

上述源码中文注解部分是BeanDefinitionRegistryPostProcessor实现类的实例化及方法调用的入口，会在BeanFactoryPostProcessors实现类方法实例化及方法调用之前执行；

##### 3.示例代码 #####

public class TestBeanDefinitionRegistryPostProcessor implements BeanDefinitionRegistryPostProcessor { 
        @Override
        public void postProcessBeanDefinitionRegistry(BeanDefinitionRegistry registry) throws BeansException { 
            RootBeanDefinition beanDefinition = new RootBeanDefinition(AsyncLogHttpClientServiceImpl.class);
          	//将指定的bean注册到IOC容器之中
            registry.registerBeanDefinition(AsyncLogHttpClientServiceImpl.class.getName(), beanDefinition);
        }
    
        @Override
        public void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory) throws BeansException { 
    			//在这里可以对已经注册到容器之中的BeanDefinition的属性进行修改
        }
    }

GitHub地址：[https://github.com/mingyang66/spring-parent/tree/master/doc/base][https_github.com_mingyang66_spring-parent_tree_master_doc_base]

[https_github.com_mingyang66_spring-parent_tree_master_doc_base]: https://github.com/mingyang66/spring-parent/tree/master/doc/base