Spring注解之@Configuration的作用和使用 詳細源碼解析

<!--logback-test.xml，配置不打印日志-->
<?xml version="1.0" encoding="UTF-8"?>
<configuration>
    <include resource="org/springframework/boot/logging/logback/base.xml" />
    <logger name="org.springframework" level="OFF"/>
</configuration>

@Override
	public void refresh() throws BeansException, IllegalStateException {
		// 同步，線程安全； 防止 fresh還沒結束  就又進入改方法 導致容器初始化錯亂
		synchronized (this.startupShutdownMonitor) {
			// 準備刷新 記錄開始時間  設置幾個標志位  驗證環(huán)境屬性
			prepareRefresh();
 
			// 告訴子類刷新內部bean工廠  創(chuàng)建BeanFactory  并且獲取BeanDefinition的定義信息
			/**
			 *	obtainFreshBeanFactory();方法
			 *		解析為一個個beanDefinition 放在我們beanDefinitionMap中管理起來
			 *  1. refreshBeanFactory(); 核心方法
			 * 		AbstractRefreshableApplicationContext#refreshBeanFactory()
			 * 		創(chuàng)建DefaultListableBeanFactory 并設置屬性
			 * 		加載BeanFactory； 根據(jù)不同的類型，調用不同的方法
			 * 			org.springframework.context.support.AbstractXmlApplicationContext#loadBeanDefinitions(org.springframework.beans.factory.support.DefaultListableBeanFactory)
			 */
			ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory();
 
			// 準備在這種情況下使用的bean工廠  向beanFactory中設置一些屬性  。對BeanFactory 進行各種功能填充
			prepareBeanFactory(beanFactory);
 
			try {
				// 允許在上下文 的子類中對bean工廠進行后處理  由子類去實現(xiàn)； 主要是自定義去使用
				postProcessBeanFactory(beanFactory);
 
				// 第5步 【BeanFactoryPostProcessors ;bean工廠后置處理器】調用我們的bean工廠后置處理器 (所有實現(xiàn)接口BeanFactoryPostProcessor接口的)
				//		主要是
				// 		會在此將class掃描成BeanDefinition 并注冊bean 到一個BeanDefinitionMap中 這個過程使用到代理
				//BeanFactoryPostProcessor 可以 用于容器完成初始化()
				// 此處可以 還沒有實例化Bean之前讀取Bean的信息，并作出一些修改。
				// 例如修改Bean的屬性，修改Bean的scope等
				invokeBeanFactoryPostProcessors(beanFactory);
 
				//https://blog.csdn.net/caihaijiang/article/details/35552859
				// 【BeanPostProcessors ;bean后置處理器】 注冊BeanPostProcessor
				// BeanPostProcessor是Bean的后置處理器，
				// 在Bean的初始化方法[InitializingBean 以及init-method]前，后執(zhí)行。
				registerBeanPostProcessors(beanFactory);
 
				// 為上下文初始化Message 源， 即不同語言的消息體， 國際化處理 i18n
				initMessageSource();
 
				// 初始化事件傳播器
				//初始化應用消息廣播器， 并放入"applicationEventMulticaster" bean 中
				initApplicationEventMulticaster();
 
				// 擴展的一個實現(xiàn) ，留給子類來初始化其它的Bean。如springboot內嵌的tomcat在這個階段完成
				onRefresh();
 
				// 注冊監(jiān)聽器
				// 在所有注冊的bean 中查找Listener bean ， 注冊到消息廣播報中
				registerListeners();
 
				/**第11步
					對于非抽象類、非延遲初始化的單例bean，
					在spring容器啟動的時候調用getBean方法來實例化bean， 并進行相關初始化工作，
					getBean方法最終調用AbstractAutowireCapableBeanFactory.doCreateBean方法
				 */
				// 在創(chuàng)建BeanFactory的過程中，BeanDefinition注冊到了BeanFactory中的一個ConCurretHashMap對象中
				// 以BeanName為key，BeanDefinition為value ； 實例化所有剩余的（非延遲初始化）單例。
				finishBeanFactoryInitialization(beanFactory);
 
				// 第12步 最后一步：發(fā)布相應的事件。
				//完成刷新過程， 通知生命周期處現(xiàn)器lifecycleProcessor 刷新過程， 同時發(fā)出ContextRefreshEvent 通知別人
				finishRefresh();
			}
 
			catch (BeansException ex) {
				if (logger.isWarnEnabled()) {
					logger.warn("Exception encountered during context initialization - " +
							"cancelling refresh attempt: " + ex);
				}
 
				// 第13步 銷毀以創(chuàng)建的Bean
				destroyBeans();
 
				//取消refresh操作，重置容器的同步標識
				cancelRefresh(ex);
 
				// Propagate exception to caller.
				throw ex;
			}
 
			finally {
				resetCommonCaches();
			}
		}
	}

public static void invokeBeanFactoryPostProcessors(
			ConfigurableListableBeanFactory beanFactory, List<BeanFactoryPostProcessor> beanFactoryPostProcessors) {
 
		Set<String> processedBeans = new HashSet<>();
 
		// 對BeanDefinitionRegistry 類型的處理
		if (beanFactory instanceof BeanDefinitionRegistry) {
			BeanDefinitionRegistry registry = (BeanDefinitionRegistry) beanFactory;
			List<BeanFactoryPostProcessor> regularPostProcessors = new ArrayList<>();
			// 用于存放BeanDefinitionRegistryPostProcessor
			List<BeanDefinitionRegistryPostProcessor> registryProcessors = new ArrayList<>();
 
			// 遍歷所有的beanFactoryPostProcessors，將BeanDefinitionRegistryPostProcessor和普通BeanFactoryPostProcessor區(qū)分開
			for (BeanFactoryPostProcessor postProcessor : beanFactoryPostProcessors) {
				if (postProcessor instanceof BeanDefinitionRegistryPostProcessor) {
					BeanDefinitionRegistryPostProcessor registryProcessor =
							(BeanDefinitionRegistryPostProcessor) postProcessor;
					/**
						對于BeanDefinitionRegistryPostProcessor 類型， 在BeanFactoryPostProcessor 的
						基礎上還有自己定義的方法，需要先調用
					 */
					registryProcessor.postProcessBeanDefinitionRegistry(registry);
					registryProcessors.add(registryProcessor);
				}
				else {
					// 記錄常規(guī)BeanFactoryPostProcessor
					regularPostProcessors.add(postProcessor);
				}
			}
 
			/**
				不要在這里初始化FactoryBeans: 我們需要保留所有常規(guī)bean未初始化，讓bean工廠后處理器應用到它們!
				BeanDefinitionRegistryPostProcessors之間的分離實現(xiàn)排好序，點好，等等。
				獲取spring配置文件中定義的所有實現(xiàn)BeanFactoryPostProcessor接口的bean，然后根據(jù)優(yōu)先級進行排序
			 */
			List<BeanDefinitionRegistryPostProcessor> currentRegistryProcessors = new ArrayList<>();
 
			// 首先，調用實現(xiàn)優(yōu)先排序的BeanDefinitionRegistryPostProcessors
			String[] postProcessorNames =
					beanFactory.getBeanNamesForType(BeanDefinitionRegistryPostProcessor.class, true, false);
			for (String ppName : postProcessorNames) {
				// PriorityOrdered.class 優(yōu)先排序
				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();
 
			// 接下來，調用實現(xiàn)Ordered的BeanDefinitionRegistryPostProcessors
			postProcessorNames = beanFactory.getBeanNamesForType(BeanDefinitionRegistryPostProcessor.class, true, false);
			for (String ppName : postProcessorNames) {
				// Ordered.class
				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();
 
			// 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);
				currentRegistryProcessors.clear();
			}
 
			// Now, invoke the postProcessBeanFactory callback of all processors handled so far.
			// 調用ConfigurationClassPostProcessor#postProcessBeanFactory增強配置類
			// 通過cglib生成增強類
			// 設置beanDefinition的beanClass為增強類，讓@Bean生成的bean是單例
			invokeBeanFactoryPostProcessors(registryProcessors, beanFactory);
			invokeBeanFactoryPostProcessors(regularPostProcessors, beanFactory);
		}
 
		else {
			// Invoke factory processors registered with the context instance.
			invokeBeanFactoryPostProcessors(beanFactoryPostProcessors, beanFactory);
		}
 
		// BeanFactoryPostProcessor.class類型
		// 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);
		// 篩選出bean工程中存在的所有實現(xiàn)BeanFactoryPostProcessor類的類名稱
 
		// 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
				// 已經(jīng)存在了，不再處理
			}
			else if (beanFactory.isTypeMatch(ppName, PriorityOrdered.class)) {
				// 為PriorityOrdered類型
				priorityOrderedPostProcessors.add(beanFactory.getBean(ppName, BeanFactoryPostProcessor.class));
			}
			else if (beanFactory.isTypeMatch(ppName, Ordered.class)) {
				// 為Ordered類型
				orderedPostProcessorNames.add(ppName);
			}
			else {
				// 這個就是我們當前需要關心的PostProcessors
				//nonOrderedPostProcessors添加的不是bean實例，而是BeanDefinition
				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<>();
		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<>();
		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();
	}

public void enhanceConfigurationClasses(ConfigurableListableBeanFactory beanFactory) {
		Map<String, AbstractBeanDefinition> configBeanDefs = new LinkedHashMap<>();
		for (String beanName : beanFactory.getBeanDefinitionNames()) {
			BeanDefinition beanDef = beanFactory.getBeanDefinition(beanName);
			// 判斷是否是一個全注解類
			// 掃描是全注解類？full和lite的關系
			if (ConfigurationClassUtils.isFullConfigurationClass(beanDef)) {
				if (!(beanDef instanceof AbstractBeanDefinition)) {
					throw new BeanDefinitionStoreException("Cannot enhance @Configuration bean definition '" +
							beanName + "' since it is not stored in an AbstractBeanDefinition subclass");
				}
				else if (logger.isInfoEnabled() && beanFactory.containsSingleton(beanName)) {
					logger.info("Cannot enhance @Configuration bean definition '" + beanName +
							"' since its singleton instance has been created too early. The typical cause " +
							"is a non-static @Bean method with a BeanDefinitionRegistryPostProcessor " +
							"return type: Consider declaring such methods as 'static'.");
				}
				// 是全注解，需要代理，添加到configBeanDefs中
				configBeanDefs.put(beanName, (AbstractBeanDefinition) beanDef);
			}
		}
		if (configBeanDefs.isEmpty()) {
			// nothing to enhance -> return immediately
			return;
		}
 
		ConfigurationClassEnhancer enhancer = new ConfigurationClassEnhancer();
		// 遍歷這個map
		for (Map.Entry<String, AbstractBeanDefinition> entry : configBeanDefs.entrySet()) {
			AbstractBeanDefinition beanDef = entry.getValue();
			// If a @Configuration class gets proxied, always proxy the target class
			beanDef.setAttribute(AutoProxyUtils.PRESERVE_TARGET_CLASS_ATTRIBUTE, Boolean.TRUE);
			try {
				// Set enhanced subclass of the user-specified bean class
				Class<?> configClass = beanDef.resolveBeanClass(this.beanClassLoader);
				if (configClass != null) {
					// 進行cglib代理，為@Configuration注解的類生成增強類
					Class<?> enhancedClass = enhancer.enhance(configClass, this.beanClassLoader);
					if (configClass != enhancedClass) {
						if (logger.isTraceEnabled()) {
							logger.trace(String.format("Replacing bean definition '%s' existing class '%s' with " +
									"enhanced class '%s'", entry.getKey(), configClass.getName(), enhancedClass.getName()));
						}
						// 再通過beanDef.setBeanClass(enhancedClass)修改beanDefinition的BeanClass屬性，
						// 在bean實例化階段，會利用反射技術將beanClass屬性對應的類實例化出來
						// 所以最終實例化出來的@Configuration bean是一個代理類的實例
						beanDef.setBeanClass(enhancedClass);
					}
				}
			}
			catch (Throwable ex) {
				throw new IllegalStateException("Cannot load configuration class: " + beanDef.getBeanClassName(), ex);
			}
		}

	private Object resolveBeanReference(Method beanMethod, Object[] beanMethodArgs,
				ConfigurableBeanFactory beanFactory, String beanName) {
 
			// The user (i.e. not the factory) is requesting this bean through a call to
			// the bean method, direct or indirect. The bean may have already been marked
			// as 'in creation' in certain autowiring scenarios; if so, temporarily set
			// the in-creation status to false in order to avoid an exception.
			// 判斷他是否正在創(chuàng)建
			boolean alreadyInCreation = beanFactory.isCurrentlyInCreation(beanName);
			try {
				if (alreadyInCreation) {
					beanFactory.setCurrentlyInCreation(beanName, false);
				}
				boolean useArgs = !ObjectUtils.isEmpty(beanMethodArgs);
				if (useArgs && beanFactory.isSingleton(beanName)) {
					// Stubbed null arguments just for reference purposes,
					// expecting them to be autowired for regular singleton references?
					// A safe assumption since @Bean singleton arguments cannot be optional...
					for (Object arg : beanMethodArgs) {
						if (arg == null) {
							useArgs = false;
							break;
						}
					}
				}
				Object beanInstance = (useArgs ? beanFactory.getBean(beanName, beanMethodArgs) :
						beanFactory.getBean(beanName));
				if (!ClassUtils.isAssignableValue(beanMethod.getReturnType(), beanInstance)) {
					// Detect package-protected NullBean instance through equals(null) check
					if (beanInstance.equals(null)) {
						if (logger.isDebugEnabled()) {
							logger.debug(String.format("@Bean method %s.%s called as bean reference " +
									"for type [%s] returned null bean; resolving to null value.",
									beanMethod.getDeclaringClass().getSimpleName(), beanMethod.getName(),
									beanMethod.getReturnType().getName()));
						}
						beanInstance = null;
					}
					else {
						String msg = String.format("@Bean method %s.%s called as bean reference " +
								"for type [%s] but overridden by non-compatible bean instance of type [%s].",
								beanMethod.getDeclaringClass().getSimpleName(), beanMethod.getName(),
								beanMethod.getReturnType().getName(), beanInstance.getClass().getName());
						try {
							BeanDefinition beanDefinition = beanFactory.getMergedBeanDefinition(beanName);
							msg += " Overriding bean of same name declared in: " + beanDefinition.getResourceDescription();
						}
						catch (NoSuchBeanDefinitionException ex) {
							// Ignore - simply no detailed message then.
						}
						throw new IllegalStateException(msg);
					}
				}
				Method currentlyInvoked = SimpleInstantiationStrategy.getCurrentlyInvokedFactoryMethod();
				if (currentlyInvoked != null) {
					String outerBeanName = BeanAnnotationHelper.determineBeanNameFor(currentlyInvoked);
					beanFactory.registerDependentBean(beanName, outerBeanName);
				}
				return beanInstance;
			}
			finally {
				if (alreadyInCreation) {
					beanFactory.setCurrentlyInCreation(beanName, true);
				}
			}
		}