Spring源碼解析之Configuration
<!--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>
@Overridepublic 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 驗證環境屬性prepareRefresh(); // 告訴子類刷新內部bean工廠 創建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() * 創建DefaultListableBeanFactory 并設置屬性 * 加載BeanFactory； 根據不同的類型，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； 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 i18ninitMessageSource(); // 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 ，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：發布相應的事件。//完成刷新過程， 通知生命周期處現器lifecycleProcessor 刷新過程， 同時發出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 銷毀以創建的BeandestroyBeans(); //取消refresh操作，重置容器的同步標識cancelRefresh(ex); // Propagate exception to caller.throw ex;} finally {resetCommonCaches();}}}2.4 AbstractApplicationContext#invokeBeanFactoryPostProcessors
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BeanDefinitionRegistryPostProcessorList<BeanDefinitionRegistryPostProcessor> registryProcessors = new ArrayList<>(); // 遍歷所有的beanFactoryPostProcessors，將BeanDefinitionRegistryPostProcessor和普通BeanFactoryPostProcessor區分開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BeanFactoryPostProcessorregularPostProcessors.add(postProcessor);}} /**不要在這里初始化FactoryBeans: 我們需要保留所有常規bean未初始化，讓bean工廠后處理器應用到它們!BeanDefinitionRegistryPostProcessors之間的分離實現排好序，點好，等等。獲取spring配置文件中定義的所有實現BeanFactoryPostProcessor接口的bean，然后根據優先級進行排序 */List<BeanDefinitionRegistryPostProcessor> currentRegistryProcessors = new ArrayList<>(); // 首先，調用實現優先排序的BeanDefinitionRegistryPostProcessorsString[] postProcessorNames =beanFactory.getBeanNamesForType(BeanDefinitionRegistryPostProcessor.class, true, false);for (String ppName : postProcessorNames) {// PriorityOrdered.class 優先排序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Ordered的BeanDefinitionRegistryPostProcessorspostProcessorNames = beanFactory.getBeanNamesForType(BeanDefinitionRegistryPostProcessor.class, true, false);for (String ppName : postProcessorNames) {// Ordered.classif (!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BeanDefinitionnonOrderedPostProcessorNames.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();}2.6 PostProcessorRegistrationDelegate#invokeBeanFactoryPostProcessors
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 immediatelyreturn;} ConfigurationClassEnhancer enhancer = new ConfigurationClassEnhancer();// 遍歷這個mapfor (Map.Entry<String, AbstractBeanDefinition> entry : configBeanDefs.entrySet()) {AbstractBeanDefinition beanDef = entry.getValue();// If a @Configuration class gets proxied, always proxy the target classbeanDef.setAttribute(AutoProxyUtils.PRESERVE_TARGET_CLASS_ATTRIBUTE, Boolean.TRUE);try {// Set enhanced subclass of the user-specified bean classClass<?> 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);}}
1.在ConfigurationClassUtils類中的checkConfigurationClassCandidate標記是Full @Configuration還是lite @Bean mode
2.通過'full'.equals(configClassAttr)判斷是否是全類注解是全注解
3.則將beandefinition放入map中configBeanDefs.put
4.遍歷這個map
5.使用cglib技術為配置類生成一個enhancedClass
6.通過enhancer.enhance進行cglib代理，為@Configuration注解的類生成增強類
7.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
使用了@Configuration注解的類，屬于Full @Configuration。@Configuration類允許通過調用同一類中的其他@Bean方法來定義bean之間的依賴關系，保證@Bean的對象作用域受到控制，避免多例。
@Configuration類中的@Bean地方會被CGLIB進行代理。Spring會攔截該方法的執行，在默認單例情況下，容器中只有一個Bean，所以我們多次調用user()方法，獲取的都是同一個對象。
對于@Configuration注解的類中@Bean標記的方法，返回的都是一個bean，在增強的方法中，Spring會先去容器中查看一下是否有這個bean的實例了，如果有了的話，就返回已有對象，沒有的話就創建一個，然后放到容器中。
2.10 ConfigurationClassEnhancer#enhance
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) checkif (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);}}}三、總結 lite @Bean mode ：當@Bean方法在沒有使用@Configuration注解的類中聲明時稱之為lite @Bean mode Full @Configuration：如果@Bean方法在使用@Configuration注解的類中聲明時稱之為Full @Configuration
Full @Configuration中的@Bean方法會被CGLIB所代理，而 lite @Bean mode中的@Bean方法不會被CGLIB代理
@Configuration注解作用
1.告訴spring這是一個配置類，相當于spring的xml配置文件
2.被@Configuration 注解的類，會被cglib代理進行增強
3.@Configuration類允許通過調用同一類中的其他@Bean方法來定義bean之間的依賴關系，保證@Bean的對象作用域受到控制，避免多例
@Configuration注解底層是如何實現的，通過源碼咱們可以反推并總結為以下幾點：
1.Spring首先會獲取到所有的beanDefenition
2.ConfigurationClassUtils類中checkConfigurationClassCandidate方法判斷是Full @Configuration還是lite @Bean mode
3.通過ConfigurationClassPostProcessor后置處理器遍歷所有的beanDefenition
4.將標記了Full @Configuration模式的beanDefenition，會對這個類進行cglib代理，生成一個代理類，并把這個類設置到BeanDefenition的Class屬性中
5.配置類會被CGLIB增強(生成代理對象)，放進IoC容器內的是代理
6.對于內部類是沒有限制的：可以是Full模式或者Lite模式
7.配置類內部可以通過方法調用來處理依賴，并且能夠保證是同一個實例，都指向IoC內的那個單例
8.需要用這個Bean實例的時候，從這個Class屬性中拿到的Class對象進行反射，最終反射出來的是代理增強后的類
9.通過@Configuration標注類的Bean，Spring會先去容器中查看是否有這個Bean實例，如果有就返回已有的對象，沒有就創建一個，然后放到容器中
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