Spring源码分析之IOC的三种常见用法及源码实现（二）
- 2019 年 10 月 20 日
- 筆記
Spring源码分析之IOC的三种常见用法及源码实现（二）
回顾上文 我们研究的是
AnnotationConfigApplicationContext annotationConfigApplication = new AnnotationConfigApplicationContext (MainConfig.class); Person person2 = (Person)annotationConfigApplication.getBean("person2");这两句话的实现，其中来到了主角儿AnnotationConfigApplicationContext的构造器实现:
public AnnotationConfigApplicationContext(Class<?>... annotatedClasses) { this(); register(annotatedClasses); refresh(); }其中this()和register(annotatedClasses);看完了，我们这次来看看refresh();
一、跟进refresh()的代码
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); // Invoke factory processors registered as beans in the context. 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(); } } }讲这个之前铺垫一点前置基础知识
Spring中事件驱动开发
spring中是通过ApplicationListener及ApplicationEventMulticaster来进行事件驱动开发的，即实现观察者设计模式或发布-订阅模式。
ApplicationListener：监听容器中发布的事件，只要事件发生，就触发监听器的回调，来完成事件驱动开发。属于观察者设计模式中的Observer对象。
ApplicationEventMulticaster：用来通知所有的观察者对象，属于观察者设计模式中的Subject对象。
Spring后置处理器
BeanFactoryPostProcessor：继承这个的类它的实现方法可以在spring的bean定义好之后 而未实例化的时候做一些逻辑操作
BeanDefinitionRegistryPostProcessor：继承这个类它的实现方法可以在spring的bean未加载定义之前加些我们自己定义的bean定义
ok讲完了，回到代码。
我们铺垫了前置知识那么就对其中的
initApplicationEventMulticaster();和
registerListeners();进行讲解
二、refresh()中的initApplicationEventMulticaster
protected void initApplicationEventMulticaster() { ConfigurableListableBeanFactory beanFactory = getBeanFactory(); if (beanFactory.containsLocalBean(APPLICATION_EVENT_MULTICASTER_BEAN_NAME)) { this.applicationEventMulticaster = beanFactory.getBean(APPLICATION_EVENT_MULTICASTER_BEAN_NAME, ApplicationEventMulticaster.class); if (logger.isDebugEnabled()) { logger.debug("Using ApplicationEventMulticaster [" + this.applicationEventMulticaster + "]"); } } else { this.applicationEventMulticaster = new SimpleApplicationEventMulticaster(beanFactory); beanFactory.registerSingleton(APPLICATION_EVENT_MULTICASTER_BEAN_NAME, this.applicationEventMulticaster); if (logger.isDebugEnabled()) { logger.debug("Unable to locate ApplicationEventMulticaster with name '" + APPLICATION_EVENT_MULTICASTER_BEAN_NAME + "': using default [" + this.applicationEventMulticaster + "]"); } } }非常好懂，就一个if else，首先获取beanfactory，翻看源码知道这个beanfactory就是上篇文章讲的初始化父类时创建的DefaultListableBeanFactory，拿到这玩意。还是围绕这玩意的功能操作
接下来判断beanfactory里是不是有这个APPLICATION_EVENT_MULTICASTER_BEAN_NAME，翻看源码：
public static final String APPLICATION_EVENT_MULTICASTER_BEAN_NAME = "applicationEventMulticaster";是不是就是之前铺垫知识的listener？用来通知事件的。看看它在不在容器里面，不在的话走else创建一个，并且作为单例注册进去，在的话就从容器里面取出来赋值给当前this对象即我们的主角儿AnnotationConfigApplicationContext，而主角本身没定义这个是在主角父类AbstractApplicationContext里定义的，我们看看：
/** Helper class used in event publishing */ private ApplicationEventMulticaster applicationEventMulticaster;看看，给了注释，辅助类 ：用于事件派发的。
综上所述，这个initApplicationEventMulticaster()这行代码就是获取事件通知发布类的，没有的话就以单例创建一个放到容器并拿给主角儿，否则就直接拿到给主角儿。接下来看另一个registerListeners();
三、refresh()中的registerListeners();
源码如下：
protected void registerListeners() { // Register statically specified listeners first. for (ApplicationListener<?> listener : getApplicationListeners()) { getApplicationEventMulticaster().addApplicationListener(listener); } // Do not initialize FactoryBeans here: We need to leave all regular beans // uninitialized to let post-processors apply to them! String[] listenerBeanNames = getBeanNamesForType(ApplicationListener.class, true, false); for (String listenerBeanName : listenerBeanNames) { getApplicationEventMulticaster().addApplicationListenerBean(listenerBeanName); } // Publish early application events now that we finally have a multicaster... Set<ApplicationEvent> earlyEventsToProcess = this.earlyApplicationEvents; this.earlyApplicationEvents = null; if (earlyEventsToProcess != null) { for (ApplicationEvent earlyEvent : earlyEventsToProcess) { getApplicationEventMulticaster().multicastEvent(earlyEvent); } } } 第一个for循环是把所有listener都加到Multicaster里了（它用来通知相关事件）。其中
String[] listenerBeanNames = getBeanNamesForType(ApplicationListener.class, true, false); for (String listenerBeanName : listenerBeanNames) { getApplicationEventMulticaster().addApplicationListenerBean(listenerBeanName); }这个是从容器中拿ApplicationListener.class类型的，从名字也可以看出来getBeanForType，拿出来之后也放到Multicaster里（它用来通知相关事件），这也就是为什么我们可以自己实现ApplicationListener接口并且打上@Component注解之后能通知的原因了！它在这里加进去了。
最后一段是获取早期事件，获取了之后for循环进行触发事件。我们来看看它到底是个怎么触发的。
Set<ApplicationEvent> earlyEventsToProcess = this.earlyApplicationEvents; this.earlyApplicationEvents = null; if (earlyEventsToProcess != null) { for (ApplicationEvent earlyEvent : earlyEventsToProcess) { getApplicationEventMulticaster().multicastEvent(earlyEvent); } }打开里面的multicastEvent方法
@Override public void multicastEvent(ApplicationEvent event) { multicastEvent(event, resolveDefaultEventType(event)); } public void multicastEvent(final ApplicationEvent event, ResolvableType eventType) { ResolvableType type = (eventType != null ? eventType : resolveDefaultEventType(event)); for (final ApplicationListener<?> listener : getApplicationListeners(event, type)) { Executor executor = getTaskExecutor(); if (executor != null) { executor.execute(new Runnable() { @Override public void run() { invokeListener(listener, event); } }); } else { invokeListener(listener, event); } } }一个解析类型、一个执行invokeListener，进去再看看这个咋invokeListener调用的
protected void invokeListener(ApplicationListener listener, ApplicationEvent event) { ErrorHandler errorHandler = getErrorHandler(); if (errorHandler != null) { try { listener.onApplicationEvent(event); } catch (Throwable err) { errorHandler.handleError(err); } } else { try { listener.onApplicationEvent(event); } catch (ClassCastException ex) { String msg = ex.getMessage(); if (msg == null || msg.startsWith(event.getClass().getName())) { // Possibly a lambda-defined listener which we could not resolve the generic event type for Log logger = LogFactory.getLog(getClass()); if (logger.isDebugEnabled()) { logger.debug("Non-matching event type for listener: " + listener, ex); } } else { throw ex; } } } }仔细看下就发现重点了，其实最终就是调用listener.onApplicationEvent(event);，而这个onApplicationEvent就是ApplicationListener接口唯一的方法。换句话说，你只要实现这个接口类，并加入@Compent加入容器中，就会调用你实现类的onApplicationEvent里你自己的代码！
可能细心的同学会发现刚刚前面看到的registerListeners中最后一段里获取的是earlyApplicationEvents，这个early是什么意思？实际上是把Multicaster还没创建时就已经缓存的事件给获取播放，因为之前来了事件也不能丢掉啊。那么什么时候会有这个early事件呢？实际上是在refresh()代码里的registerListeners方法的前一句onRefresh方法中，这个方法默认是没有early事件的，会在springboot中使用.
至此registerListeners方法也讲完了。
接下来我们来讲讲refresh()中的invokeBeanFactoryPostProcessors(beanFactory);
四、refresh()中的invokeBeanFactoryPostProcessors(beanFactory);
/** * 按照明确的顺序实例化并调用所有在BeanFactoryPostProcessor注册的bean * <p>Must be called before singleton instantiation. */ protected void invokeBeanFactoryPostProcessors(ConfigurableListableBeanFactory beanFactory) { PostProcessorRegistrationDelegate.invokeBeanFactoryPostProcessors(beanFactory, getBeanFactoryPostProcessors()); // Detect a LoadTimeWeaver and prepare for weaving, if found in the meantime // (e.g. through an @Bean method registered by ConfigurationClassPostProcessor) if (beanFactory.getTempClassLoader() == null && beanFactory.containsBean(LOAD_TIME_WEAVER_BEAN_NAME)) { beanFactory.addBeanPostProcessor(new LoadTimeWeaverAwareProcessor(beanFactory)); beanFactory.setTempClassLoader(new ContextTypeMatchClassLoader(beanFactory.getBeanClassLoader())); } }很明显继续跟进这个invokeBeanFactoryPostProcessors同名方法：
public static void invokeBeanFactoryPostProcessors( ConfigurableListableBeanFactory beanFactory, List<BeanFactoryPostProcessor> beanFactoryPostProcessors) { // Invoke BeanDefinitionRegistryPostProcessors first, if any. Set<String> processedBeans = new HashSet<String>(); if (beanFactory instanceof BeanDefinitionRegistry) { BeanDefinitionRegistry registry = (BeanDefinitionRegistry) beanFactory; List<BeanFactoryPostProcessor> regularPostProcessors = new LinkedList<BeanFactoryPostProcessor>(); List<BeanDefinitionRegistryPostProcessor> registryPostProcessors = new LinkedList<BeanDefinitionRegistryPostProcessor>(); for (BeanFactoryPostProcessor postProcessor : beanFactoryPostProcessors) { if (postProcessor instanceof BeanDefinitionRegistryPostProcessor) { BeanDefinitionRegistryPostProcessor registryPostProcessor = (BeanDefinitionRegistryPostProcessor) postProcessor; registryPostProcessor.postProcessBeanDefinitionRegistry(registry); registryPostProcessors.add(registryPostProcessor); } 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. String[] postProcessorNames = beanFactory.getBeanNamesForType(BeanDefinitionRegistryPostProcessor.class, true, false); // First, invoke the BeanDefinitionRegistryPostProcessors that implement PriorityOrdered. List<BeanDefinitionRegistryPostProcessor> priorityOrderedPostProcessors = new ArrayList<BeanDefinitionRegistryPostProcessor>(); for (String ppName : postProcessorNames) { if (beanFactory.isTypeMatch(ppName, PriorityOrdered.class)) { priorityOrderedPostProcessors.add(beanFactory.getBean(ppName, BeanDefinitionRegistryPostProcessor.class)); processedBeans.add(ppName); } } sortPostProcessors(beanFactory, priorityOrderedPostProcessors); registryPostProcessors.addAll(priorityOrderedPostProcessors); invokeBeanDefinitionRegistryPostProcessors(priorityOrderedPostProcessors, registry); // Next, invoke the BeanDefinitionRegistryPostProcessors that implement Ordered. postProcessorNames = beanFactory.getBeanNamesForType(BeanDefinitionRegistryPostProcessor.class, true, false); List<BeanDefinitionRegistryPostProcessor> orderedPostProcessors = new ArrayList<BeanDefinitionRegistryPostProcessor>(); for (String ppName : postProcessorNames) { if (!processedBeans.contains(ppName) && beanFactory.isTypeMatch(ppName, Ordered.class)) { orderedPostProcessors.add(beanFactory.getBean(ppName, BeanDefinitionRegistryPostProcessor.class)); processedBeans.add(ppName); } } sortPostProcessors(beanFactory, orderedPostProcessors); registryPostProcessors.addAll(orderedPostProcessors); invokeBeanDefinitionRegistryPostProcessors(orderedPostProcessors, registry); // 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)) { BeanDefinitionRegistryPostProcessor pp = beanFactory.getBean(ppName, BeanDefinitionRegistryPostProcessor.class); registryPostProcessors.add(pp); processedBeans.add(ppName); pp.postProcessBeanDefinitionRegistry(registry); reiterate = true; } } } // Now, invoke the postProcessBeanFactory callback of all processors handled so far. invokeBeanFactoryPostProcessors(registryPostProcessors, 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<BeanFactoryPostProcessor>(); List<String> orderedPostProcessorNames = new ArrayList<String>(); List<String> nonOrderedPostProcessorNames = new ArrayList<String>(); 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(beanFactory, priorityOrderedPostProcessors); invokeBeanFactoryPostProcessors(priorityOrderedPostProcessors, beanFactory); // Next, invoke the BeanFactoryPostProcessors that implement Ordered. List<BeanFactoryPostProcessor> orderedPostProcessors = new ArrayList<BeanFactoryPostProcessor>(); for (String postProcessorName : orderedPostProcessorNames) { orderedPostProcessors.add(beanFactory.getBean(postProcessorName, BeanFactoryPostProcessor.class)); } sortPostProcessors(beanFactory, orderedPostProcessors); invokeBeanFactoryPostProcessors(orderedPostProcessors, beanFactory); // Finally, invoke all other BeanFactoryPostProcessors. List<BeanFactoryPostProcessor> nonOrderedPostProcessors = new ArrayList<BeanFactoryPostProcessor>(); 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(); }仔细读里的逻辑会发现前半段是围绕：
List<BeanFactoryPostProcessor> regularPostProcessors = new LinkedList<BeanFactoryPostProcessor>(); List<BeanDefinitionRegistryPostProcessor> registryPostProcessors = new LinkedList<BeanDefinitionRegistryPostProcessor>();这两个list进行不断筛选分类 然后进行invokeBeanDefinitionRegistryPostProcessors方法调用
而后半段是围绕：
List<BeanFactoryPostProcessor> priorityOrderedPostProcessors = new ArrayList<BeanFactoryPostProcessor>(); List<String> orderedPostProcessorNames = new ArrayList<String>(); List<String> nonOrderedPostProcessorNames = new ArrayList<String>();三个list进行分类添加进去，然后进行invokeBeanDefinitionRegistryPostProcessors方法调用
综上核心就是这个invokeBeanDefinitionRegistryPostProcessors的逻辑，我们来看看：
private static void invokeBeanFactoryPostProcessors( Collection<? extends BeanFactoryPostProcessor> postProcessors, ConfigurableListableBeanFactory beanFactory) { for (BeanFactoryPostProcessor postProcessor : postProcessors) { postProcessor.postProcessBeanFactory(beanFactory); } }遍历集合，并调用对应方法，继续查看源码：
public void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory) { int factoryId = System.identityHashCode(beanFactory); if (this.factoriesPostProcessed.contains(factoryId)) { throw new IllegalStateException( "postProcessBeanFactory already called on this post-processor against " + beanFactory); } this.factoriesPostProcessed.add(factoryId); if (!this.registriesPostProcessed.contains(factoryId)) { // BeanDefinitionRegistryPostProcessor hook apparently not supported... // Simply call processConfigurationClasses lazily at this point then. processConfigBeanDefinitions((BeanDefinitionRegistry) beanFactory); } enhanceConfigurationClasses(beanFactory); beanFactory.addBeanPostProcessor(new ImportAwareBeanPostProcessor(beanFactory)); }设置注册id、然后这里显然主要逻辑在processConfigBeanDefinitions，继续查看：
public void processConfigBeanDefinitions(BeanDefinitionRegistry registry) { List<BeanDefinitionHolder> configCandidates = new ArrayList<BeanDefinitionHolder>(); String[] candidateNames = registry.getBeanDefinitionNames(); for (String beanName : candidateNames) { BeanDefinition beanDef = registry.getBeanDefinition(beanName); if (ConfigurationClassUtils.isFullConfigurationClass(beanDef) || ConfigurationClassUtils.isLiteConfigurationClass(beanDef)) { if (logger.isDebugEnabled()) { logger.debug("Bean definition has already been processed as a configuration class: " + beanDef); } } else if (ConfigurationClassUtils.checkConfigurationClassCandidate(beanDef, this.metadataReaderFactory)) { configCandidates.add(new BeanDefinitionHolder(beanDef, beanName)); } } // Return immediately if no @Configuration classes were found if (configCandidates.isEmpty()) { return; } // Sort by previously determined @Order value, if applicable Collections.sort(configCandidates, new Comparator<BeanDefinitionHolder>() { @Override public int compare(BeanDefinitionHolder bd1, BeanDefinitionHolder bd2) { int i1 = ConfigurationClassUtils.getOrder(bd1.getBeanDefinition()); int i2 = ConfigurationClassUtils.getOrder(bd2.getBeanDefinition()); return (i1 < i2) ? -1 : (i1 > i2) ? 1 : 0; } }); // Detect any custom bean name generation strategy supplied through the enclosing application context SingletonBeanRegistry sbr = null; if (registry instanceof SingletonBeanRegistry) { sbr = (SingletonBeanRegistry) registry; if (!this.localBeanNameGeneratorSet && sbr.containsSingleton(CONFIGURATION_BEAN_NAME_GENERATOR)) { BeanNameGenerator generator = (BeanNameGenerator) sbr.getSingleton(CONFIGURATION_BEAN_NAME_GENERATOR); this.componentScanBeanNameGenerator = generator; this.importBeanNameGenerator = generator; } } // Parse each @Configuration class ConfigurationClassParser parser = new ConfigurationClassParser( this.metadataReaderFactory, this.problemReporter, this.environment, this.resourceLoader, this.componentScanBeanNameGenerator, registry); Set<BeanDefinitionHolder> candidates = new LinkedHashSet<BeanDefinitionHolder>(configCandidates); Set<ConfigurationClass> alreadyParsed = new HashSet<ConfigurationClass>(configCandidates.size()); do { parser.parse(candidates); parser.validate(); Set<ConfigurationClass> configClasses = new LinkedHashSet<ConfigurationClass>(parser.getConfigurationClasses()); configClasses.removeAll(alreadyParsed); // Read the model and create bean definitions based on its content if (this.reader == null) { this.reader = new ConfigurationClassBeanDefinitionReader( registry, this.sourceExtractor, this.resourceLoader, this.environment, this.importBeanNameGenerator, parser.getImportRegistry()); } this.reader.loadBeanDefinitions(configClasses); alreadyParsed.addAll(configClasses); candidates.clear(); if (registry.getBeanDefinitionCount() > candidateNames.length) { String[] newCandidateNames = registry.getBeanDefinitionNames(); Set<String> oldCandidateNames = new HashSet<String>(Arrays.asList(candidateNames)); Set<String> alreadyParsedClasses = new HashSet<String>(); for (ConfigurationClass configurationClass : alreadyParsed) { alreadyParsedClasses.add(configurationClass.getMetadata().getClassName()); } for (String candidateName : newCandidateNames) { if (!oldCandidateNames.contains(candidateName)) { BeanDefinition bd = registry.getBeanDefinition(candidateName); if (ConfigurationClassUtils.checkConfigurationClassCandidate(bd, this.metadataReaderFactory) && !alreadyParsedClasses.contains(bd.getBeanClassName())) { candidates.add(new BeanDefinitionHolder(bd, candidateName)); } } } candidateNames = newCandidateNames; } } while (!candidates.isEmpty()); // Register the ImportRegistry as a bean in order to support ImportAware @Configuration classes if (sbr != null) { if (!sbr.containsSingleton(IMPORT_REGISTRY_BEAN_NAME)) { sbr.registerSingleton(IMPORT_REGISTRY_BEAN_NAME, parser.getImportRegistry()); } } if (this.metadataReaderFactory instanceof CachingMetadataReaderFactory) { ((CachingMetadataReaderFactory) this.metadataReaderFactory).clearCache(); } }比较长，分几部分看，第一部分刚开始是创建一个ArrayList，类型是BeanDefinitionHolder，我们看看这个：
public class BeanDefinitionHolder implements BeanMetadataElement { private final BeanDefinition beanDefinition; private final String beanName; private final String[] aliases; ....... }可以看出，这个BeanDefinitionHolder实际上就是个BeanDefinition的一个小包装。
继续看，后面的代码就是从registry容器中拿bean名字出来然后又根据名字把BeanDefinition拿出来，最后把名字和BeanDefinition本身一起装到list里面去了，再排个序。后面又创建了两bean名字生成器。
现在可以看到重点了，有一行注释：
// Parse each @Configuration class ConfigurationClassParser parser = new ConfigurationClassParser( this.metadataReaderFactory, this.problemReporter, this.environment, this.resourceLoader, this.componentScanBeanNameGenerator, registry); Set<BeanDefinitionHolder> candidates = new LinkedHashSet<BeanDefinitionHolder>(configCandidates); Set<ConfigurationClass> alreadyParsed = new HashSet<ConfigurationClass>(configCandidates.size()); do { parser.parse(candidates); parser.validate(); ...... }while(....) .....这里来到了核心重点，要解析我们的配置类了！弄了个do while循环保证这些都list里的东西都解析完，我们来看看解析方法parser.parse(candidates);吧！它是怎么解析的：
public void parse(Set<BeanDefinitionHolder> configCandidates) { this.deferredImportSelectors = new LinkedList<DeferredImportSelectorHolder>(); for (BeanDefinitionHolder holder : configCandidates) { BeanDefinition bd = holder.getBeanDefinition(); try { if (bd instanceof AnnotatedBeanDefinition) { parse(((AnnotatedBeanDefinition) bd).getMetadata(), holder.getBeanName()); } else if (bd instanceof AbstractBeanDefinition && ((AbstractBeanDefinition) bd).hasBeanClass()) { parse(((AbstractBeanDefinition) bd).getBeanClass(), holder.getBeanName()); } else { parse(bd.getBeanClassName(), holder.getBeanName()); } } catch (BeanDefinitionStoreException ex) { throw ex; } catch (Throwable ex) { throw new BeanDefinitionStoreException( "Failed to parse configuration class [" + bd.getBeanClassName() + "]", ex); } } processDeferredImportSelectors(); }这里又是分了三种情况去解析，第一种从名字可以看出来注解的那种解析，第二种是AbstractBeanDefinition这是对XML配置方式的解析，很明显我们看第一种，继续查看源码:
protected final void parse(AnnotationMetadata metadata, String beanName) throws IOException { processConfigurationClass(new ConfigurationClass(metadata, beanName)); }继续查看：
protected void processConfigurationClass(ConfigurationClass configClass) throws IOException { if (this.conditionEvaluator.shouldSkip(configClass.getMetadata(), ConfigurationPhase.PARSE_CONFIGURATION)) { return; } ConfigurationClass existingClass =this.configurationClasses.get(configClass); if (existingClass != null) { if (configClass.isImported()) { if (existingClass.isImported()) { existingClass.mergeImportedBy(configClass); } // Otherwise ignore new imported config class; existing non-imported class overrides it. return; } else { // Explicit bean definition found, probably replacing an import. // Let's remove the old one and go with the new one. this.configurationClasses.remove(configClass); for (Iterator<ConfigurationClass> it = this.knownSuperclasses.values().iterator(); it.hasNext();) { if (configClass.equals(it.next())) { it.remove(); } } } } // Recursively process the configuration class and its superclass hierarchy. SourceClass sourceClass = asSourceClass(configClass); do { sourceClass = doProcessConfigurationClass(configClass, sourceClass); } while (sourceClass != null); this.configurationClasses.put(configClass, configClass); }我们看Spring源码会发现，Spring源码里真正干活的都是doXXX方法，会发现这里终于也发现一个了，
前面是对配置类的一个判断处理，后面就是doProcessConfigurationClass真正处理了，处理完之后加入到configurationClasses中，也就是最后一句话。我们查看源码：
protected final SourceClass doProcessConfigurationClass(ConfigurationClass configClass, SourceClass sourceClass) throws IOException { // Recursively process any member (nested) classes first processMemberClasses(configClass, sourceClass); // Process any @PropertySource annotations for (AnnotationAttributes propertySource : AnnotationConfigUtils.attributesForRepeatable( sourceClass.getMetadata(), PropertySources.class, org.springframework.context.annotation.PropertySource.class)) { if (this.environment instanceof ConfigurableEnvironment) { processPropertySource(propertySource); } else { logger.warn("Ignoring @PropertySource annotation on [" + sourceClass.getMetadata().getClassName() + "]. Reason: Environment must implement ConfigurableEnvironment"); } } // Process any @ComponentScan annotations Set<AnnotationAttributes> componentScans = AnnotationConfigUtils.attributesForRepeatable( sourceClass.getMetadata(), ComponentScans.class, ComponentScan.class); if (!componentScans.isEmpty() && !this.conditionEvaluator.shouldSkip(sourceClass.getMetadata(), ConfigurationPhase.REGISTER_BEAN)) { for (AnnotationAttributes componentScan : componentScans) { // The config class is annotated with @ComponentScan -> perform the scan immediately Set<BeanDefinitionHolder> scannedBeanDefinitions = this.componentScanParser.parse(componentScan, sourceClass.getMetadata().getClassName()); // Check the set of scanned definitions for any further config classes and parse recursively if needed for (BeanDefinitionHolder holder : scannedBeanDefinitions) { if (ConfigurationClassUtils.checkConfigurationClassCandidate( holder.getBeanDefinition(), this.metadataReaderFactory)) { parse(holder.getBeanDefinition().getBeanClassName(), holder.getBeanName()); } } } } // Process any @Import annotations processImports(configClass, sourceClass, getImports(sourceClass), true); // Process any @ImportResource annotations if (sourceClass.getMetadata().isAnnotated(ImportResource.class.getName())) { AnnotationAttributes importResource = AnnotationConfigUtils.attributesFor(sourceClass.getMetadata(), ImportResource.class); String[] resources = importResource.getStringArray("locations"); Class<? extends BeanDefinitionReader> readerClass = importResource.getClass("reader"); for (String resource : resources) { String resolvedResource = this.environment.resolveRequiredPlaceholders(resource); configClass.addImportedResource(resolvedResource, readerClass); } } // Process individual @Bean methods Set<MethodMetadata> beanMethods = retrieveBeanMethodMetadata(sourceClass); for (MethodMetadata methodMetadata : beanMethods) { configClass.addBeanMethod(new BeanMethod(methodMetadata, configClass)); } // Process default methods on interfaces processInterfaces(configClass, sourceClass); // Process superclass, if any if (sourceClass.getMetadata().hasSuperClass()) { String superclass = sourceClass.getMetadata().getSuperClassName(); if (!superclass.startsWith("java") && !this.knownSuperclasses.containsKey(superclass)) { this.knownSuperclasses.put(superclass, configClass); // Superclass found, return its annotation metadata and recurse return sourceClass.getSuperClass(); } } // No superclass -> processing is complete return null; }到了这里有种终见神龙真身的感觉。。。终于开始对我们常用的那些注解分别进行解析了。。我们可以挑几个最常用的看看，来看看非常常用的@ComponentScan注解吧！
IOC三大常用springbean配置用法，还有个是通过@ComponentScan配置的，SpringBoot也是通过这种。
@Target({ElementType.TYPE}) @Retention(RetentionPolicy.RUNTIME) @Documented @Inherited @SpringBootConfiguration @EnableAutoConfiguration @ComponentScan( excludeFilters = {@Filter( type = FilterType.CUSTOM, classes = {TypeExcludeFilter.class} ), @Filter( type = FilterType.CUSTOM, classes = {AutoConfigurationExcludeFilter.class} )} ) public @interface SpringBootApplication { .... }@ComponentScan源码
// Process any @ComponentScan annotations Set<AnnotationAttributes> componentScans = AnnotationConfigUtils.attributesForRepeatable( sourceClass.getMetadata(), ComponentScans.class, ComponentScan.class); if (!componentScans.isEmpty() && !this.conditionEvaluator.shouldSkip(sourceClass.getMetadata(), ConfigurationPhase.REGISTER_BEAN)) { for (AnnotationAttributes componentScan : componentScans) { // The config class is annotated with @ComponentScan -> perform the scan immediately Set<BeanDefinitionHolder> scannedBeanDefinitions = this.componentScanParser.parse(componentScan, sourceClass.getMetadata().getClassName()); // Check the set of scanned definitions for any further config classes and parse recursively if needed for (BeanDefinitionHolder holder : scannedBeanDefinitions) { if (ConfigurationClassUtils.checkConfigurationClassCandidate( holder.getBeanDefinition(), this.metadataReaderFactory)) { parse(holder.getBeanDefinition().getBeanClassName(), holder.getBeanName()); } } } }这里的第一句
Set<AnnotationAttributes> componentScans = AnnotationConfigUtils.attributesForRepeatable( sourceClass.getMetadata(), ComponentScans.class, ComponentScan.class);是把我们的配置类也就是sourceClass，获取了元数据传到这个注解工具类里去了，是把配置类里面的@ComponentScan注解解析为对象了，这样方便后面拿到注解里设置的值。
然后往后看
Set<BeanDefinitionHolder> scannedBeanDefinitions = this.componentScanParser.parse(componentScan, sourceClass.getMetadata().getClassName());就是继续解析了，查看源码：
public Set<BeanDefinitionHolder> parse(AnnotationAttributes componentScan, final String declaringClass) { Assert.state(this.environment != null, "Environment must not be null"); Assert.state(this.resourceLoader != null, "ResourceLoader must not be null"); ClassPathBeanDefinitionScanner scanner = new ClassPathBeanDefinitionScanner(this.registry, componentScan.getBoolean("useDefaultFilters"), this.environment, this.resourceLoader); Class<? extends BeanNameGenerator> generatorClass = componentScan.getClass("nameGenerator"); boolean useInheritedGenerator = (BeanNameGenerator.class == generatorClass); scanner.setBeanNameGenerator(useInheritedGenerator ? this.beanNameGenerator : BeanUtils.instantiateClass(generatorClass)); ScopedProxyMode scopedProxyMode = componentScan.getEnum("scopedProxy"); if (scopedProxyMode != ScopedProxyMode.DEFAULT) { scanner.setScopedProxyMode(scopedProxyMode); } else { Class<? extends ScopeMetadataResolver> resolverClass = componentScan.getClass("scopeResolver"); scanner.setScopeMetadataResolver(BeanUtils.instantiateClass(resolverClass)); } scanner.setResourcePattern(componentScan.getString("resourcePattern")); for (AnnotationAttributes filter : componentScan.getAnnotationArray("includeFilters")) { for (TypeFilter typeFilter : typeFiltersFor(filter)) { scanner.addIncludeFilter(typeFilter); } } for (AnnotationAttributes filter : componentScan.getAnnotationArray("excludeFilters")) { for (TypeFilter typeFilter : typeFiltersFor(filter)) { scanner.addExcludeFilter(typeFilter); } } boolean lazyInit = componentScan.getBoolean("lazyInit"); if (lazyInit) { scanner.getBeanDefinitionDefaults().setLazyInit(true); } Set<String> basePackages = new LinkedHashSet<String>(); String[] basePackagesArray = componentScan.getStringArray("basePackages"); for (String pkg : basePackagesArray) { String[] tokenized = StringUtils.tokenizeToStringArray(this.environment.resolvePlaceholders(pkg), ConfigurableApplicationContext.CONFIG_LOCATION_DELIMITERS); basePackages.addAll(Arrays.asList(tokenized)); } for (Class<?> clazz : componentScan.getClassArray("basePackageClasses")) { basePackages.add(ClassUtils.getPackageName(clazz)); } if (basePackages.isEmpty()) { basePackages.add(ClassUtils.getPackageName(declaringClass)); } scanner.addExcludeFilter(new AbstractTypeHierarchyTraversingFilter(false, false) { @Override protected boolean matchClassName(String className) { return declaringClass.equals(className); } }); return scanner.doScan(StringUtils.toStringArray(basePackages)); }又是一堆代码…总体看下来会发现，前面95%都是给下面这句话设置参数：
ClassPathBeanDefinitionScanner scanner = new ClassPathBeanDefinitionScanner(this.registry,componentScan.getBoolean("useDefaultFilters"), this.environment, this.resourceLoader);很明显ClassPathBeanDefinitionScanner是真正用来扫描类的，类注释写了“A bean definition scanner that detects bean candidates on the classpath”，后面都是给扫描器设置各种名字生成器、scope、resourcePattern、以及include和exclude和是否懒加载，直到下面这段时候才开始注意路径：
Set<String> basePackages = new LinkedHashSet<String>(); String[] basePackagesArray = componentScan.getStringArray("basePackages"); for (String pkg : basePackagesArray) { String[] tokenized = StringUtils.tokenizeToStringArray(this.environment.resolvePlaceholders(pkg), ConfigurableApplicationContext.CONFIG_LOCATION_DELIMITERS); basePackages.addAll(Arrays.asList(tokenized)); } for (Class<?> clazz : componentScan.getClassArray("basePackageClasses")) { basePackages.add(ClassUtils.getPackageName(clazz)); } if (basePackages.isEmpty()) { basePackages.add(ClassUtils.getPackageName(declaringClass)); }获取我们在注解里写的basePackages，进行环境路径设置，最后加到之前创建的hashset类型的basePackages变量里去。然后设置排除filter到扫描器。最后一句又到了核心代码了。
return scanner.doScan(StringUtils.toStringArray(basePackages));这里就是最后真正扫描了，查看源码：
protected Set<BeanDefinitionHolder> doScan(String... basePackages) { Assert.notEmpty(basePackages, "At least one base package must be specified"); Set<BeanDefinitionHolder> beanDefinitions = new LinkedHashSet<BeanDefinitionHolder>(); for (String basePackage : basePackages) { Set<BeanDefinition> candidates = findCandidateComponents(basePackage); for (BeanDefinition candidate : candidates) { ScopeMetadata scopeMetadata = this.scopeMetadataResolver.resolveScopeMetadata(candidate); candidate.setScope(scopeMetadata.getScopeName()); String beanName = this.beanNameGenerator.generateBeanName(candidate, this.registry); if (candidate instanceof AbstractBeanDefinition) { postProcessBeanDefinition((AbstractBeanDefinition) candidate, beanName); } if (candidate instanceof AnnotatedBeanDefinition) { AnnotationConfigUtils.processCommonDefinitionAnnotations((AnnotatedBeanDefinition) candidate); } if (checkCandidate(beanName, candidate)) { BeanDefinitionHolder definitionHolder = new BeanDefinitionHolder(candidate, beanName); definitionHolder = AnnotationConfigUtils.applyScopedProxyMode(scopeMetadata, definitionHolder, this.registry); beanDefinitions.add(definitionHolder); registerBeanDefinition(definitionHolder, this.registry); } } } return beanDefinitions; }for循环遍历basePackages，再通过findCandidateComponents方法拿到每个basePageage下的类BeanDefinition们，后面就是给每个BeanDefinition进行配置。
那我们就先来看看findCandidateComponents方法源码是怎么把这些BeanDefinition搞出来的：
public Set<BeanDefinition> findCandidateComponents(String basePackage) { Set<BeanDefinition> candidates = new LinkedHashSet<BeanDefinition>(); try { String packageSearchPath = ResourcePatternResolver.CLASSPATH_ALL_URL_PREFIX + resolveBasePackage(basePackage) + '/' + this.resourcePattern; Resource[] resources = this.resourcePatternResolver.getResources(packageSearchPath); boolean traceEnabled = logger.isTraceEnabled(); boolean debugEnabled = logger.isDebugEnabled(); for (Resource resource : resources) { if (traceEnabled) { logger.trace("Scanning " + resource); } if (resource.isReadable()) { try { MetadataReader metadataReader = this.metadataReaderFactory.getMetadataReader(resource); if (isCandidateComponent(metadataReader)) { ScannedGenericBeanDefinition sbd = new ScannedGenericBeanDefinition(metadataReader); sbd.setResource(resource); sbd.setSource(resource); if (isCandidateComponent(sbd)) { if (debugEnabled) { logger.debug("Identified candidate component class: " + resource); } candidates.add(sbd); } else { if (debugEnabled) { logger.debug("Ignored because not a concrete top-level class: " + resource); } } } else { if (traceEnabled) { logger.trace("Ignored because not matching any filter: " + resource); } } } catch (Throwable ex) { throw new BeanDefinitionStoreException( "Failed to read candidate component class: " + resource, ex); } } else { if (traceEnabled) { logger.trace("Ignored because not readable: " + resource); } } } } catch (IOException ex) { throw new BeanDefinitionStoreException("I/O failure during classpath scanning", ex); } return candidates; }这里的办法就比较好懂了，可能有些自己平时都写过。第一个明显拼字符串，拼最终要读取的资源文件路径，然后把文件路径交给resourcePatternResolver，获取一个Resource类（继承自InputStreamSource），这个就是个IO流读取。
这里大段都是try catch了，因为涉及到很多失败的情况，都做了处理。
里面主要还做了filter的判断，判断是不是你是不是exclude了一些 这样就不读了，然后读出来是不是打了Component注解的，最后条件都满足的话就把读出来的信息就加到 最终的一个LinkedHashSet的集合里去了，进行返回。
全读出来之后，返回上层doScan方法的这里：
Set<BeanDefinition> candidates = findCandidateComponents(basePackage); for (BeanDefinition candidate : candidates) { ScopeMetadata scopeMetadata = this.scopeMetadataResolver.resolveScopeMetadata(candidate); candidate.setScope(scopeMetadata.getScopeName()); String beanName = this.beanNameGenerator.generateBeanName(candidate, this.registry); if (candidate instanceof AbstractBeanDefinition) { postProcessBeanDefinition((AbstractBeanDefinition) candidate, beanName); } if (candidate instanceof AnnotatedBeanDefinition) { AnnotationConfigUtils.processCommonDefinitionAnnotations((AnnotatedBeanDefinition) candidate); } if (checkCandidate(beanName, candidate)) { BeanDefinitionHolder definitionHolder = new BeanDefinitionHolder(candidate, beanName); definitionHolder = AnnotationConfigUtils.applyScopedProxyMode(scopeMetadata, definitionHolder, this.registry); beanDefinitions.add(definitionHolder); registerBeanDefinition(definitionHolder, this.registry); } }给扫描出来的BeanDefinition设置scope，单例多例、搞一个名字给这个BeanDefinition，以及判断是注解形式配置的还是XML形式配置的给它设置一些默认的配置，比如默认的懒加载设置各种，spring有默认的或者读你设置的。最后把这个BeanDefinition和名字一起包装成BeanDefinitionHolder，通过：
BeanDefinitionHolder definitionHolder = new BeanDefinitionHolder(candidate, beanName); definitionHolder=AnnotationConfigUtils.applyScopedProxyMode(scopeMetadata,definitionHolder, this.registry); beanDefinitions.add(definitionHolder); registerBeanDefinition(definitionHolder, this.registry);最后registerBeanDefinition注册到容器里去。说实话我又好奇是咋注册的，不断打开源码：
public void registerBeanDefinition(String beanName, BeanDefinition beanDefinition) throws BeanDefinitionStoreException { Assert.hasText(beanName, "Bean name must not be empty"); Assert.notNull(beanDefinition, "BeanDefinition must not be null"); if (beanDefinition instanceof AbstractBeanDefinition) { try { ((AbstractBeanDefinition) beanDefinition).validate(); } catch (BeanDefinitionValidationException ex) { throw new BeanDefinitionStoreException(beanDefinition.getResourceDescription(), beanName, "Validation of bean definition failed", ex); } } BeanDefinition oldBeanDefinition; oldBeanDefinition = this.beanDefinitionMap.get(beanName); if (oldBeanDefinition != null) { if (!isAllowBeanDefinitionOverriding()) { throw new BeanDefinitionStoreException(beanDefinition.getResourceDescription(), beanName, "Cannot register bean definition [" + beanDefinition + "] for bean '" + beanName + "': There is already [" + oldBeanDefinition + "] bound."); } else if (oldBeanDefinition.getRole() < beanDefinition.getRole()) { // e.g. was ROLE_APPLICATION, now overriding with ROLE_SUPPORT or ROLE_INFRASTRUCTURE if (this.logger.isWarnEnabled()) { this.logger.warn("Overriding user-defined bean definition for bean '" + beanName + "' with a framework-generated bean definition: replacing [" + oldBeanDefinition + "] with [" + beanDefinition + "]"); } } else if (!beanDefinition.equals(oldBeanDefinition)) { if (this.logger.isInfoEnabled()) { this.logger.info("Overriding bean definition for bean '" + beanName + "' with a different definition: replacing [" + oldBeanDefinition + "] with [" + beanDefinition + "]"); } } else { if (this.logger.isDebugEnabled()) { this.logger.debug("Overriding bean definition for bean '" + beanName + "' with an equivalent definition: replacing [" + oldBeanDefinition + "] with [" + beanDefinition + "]"); } } this.beanDefinitionMap.put(beanName, beanDefinition); } else { if (hasBeanCreationStarted()) { // Cannot modify startup-time collection elements anymore (for stable iteration) synchronized (this.beanDefinitionMap) { this.beanDefinitionMap.put(beanName, beanDefinition); List<String> updatedDefinitions = new ArrayList<String>(this.beanDefinitionNames.size() + 1); updatedDefinitions.addAll(this.beanDefinitionNames); updatedDefinitions.add(beanName); this.beanDefinitionNames = updatedDefinitions; if (this.manualSingletonNames.contains(beanName)) { Set<String> updatedSingletons = new LinkedHashSet<String>(this.manualSingletonNames); updatedSingletons.remove(beanName); this.manualSingletonNames = updatedSingletons; } } } else { // Still in startup registration phase this.beanDefinitionMap.put(beanName, beanDefinition); this.beanDefinitionNames.add(beanName); this.manualSingletonNames.remove(beanName); } this.frozenBeanDefinitionNames = null; } if (oldBeanDefinition != null || containsSingleton(beanName)) { resetBeanDefinition(beanName); } }啰嗦了很长一大段，其实是一些校验、对同名BeanDefinition的处理啥的，核心就一句：
this.beanDefinitionMap.put(beanName, beanDefinition);查看这个beanDefinitionMap
private final Map<String, BeanDefinition> beanDefinitionMap = new ConcurrentHashMap<String, BeanDefinition>(256);就是个ConcurrentHashMap，在DefaultListableBeanFactory类里的一个private私有成员变量，所以也可见DefaultListableBeanFactory类的重要性，BeanDefinition都存在它这了，容器。
ok，一探到底了，开始回到上层调用吧。
回到之前的ConfigurationClassParser类的doProcessConfigurationClass方法中，是这个方法里开始的各种注解的解析：
// Process any @ComponentScan annotations Set<AnnotationAttributes> componentScans = AnnotationConfigUtils.attributesForRepeatable( sourceClass.getMetadata(), ComponentScans.class, ComponentScan.class); if (!componentScans.isEmpty() && !this.conditionEvaluator.shouldSkip(sourceClass.getMetadata(), ConfigurationPhase.REGISTER_BEAN)) { for (AnnotationAttributes componentScan : componentScans) { // The config class is annotated with @ComponentScan -> perform the scan immediately Set<BeanDefinitionHolder> scannedBeanDefinitions = this.componentScanParser.parse(componentScan, sourceClass.getMetadata().getClassName()); // Check the set of scanned definitions for any further config classes and parse recursively if needed for (BeanDefinitionHolder holder : scannedBeanDefinitions) { if (ConfigurationClassUtils.checkConfigurationClassCandidate( holder.getBeanDefinition(), this.metadataReaderFactory)) { parse(holder.getBeanDefinition().getBeanClassName(), holder.getBeanName()); } } } }我们之前是对这里的：
Set<BeanDefinitionHolder> scannedBeanDefinitions = this.componentScanParser.parse(componentScan, sourceClass.getMetadata().getClassName());进行的不断深挖，那就往下看吧:
for (BeanDefinitionHolder holder : scannedBeanDefinitions) { if (ConfigurationClassUtils.checkConfigurationClassCandidate( holder.getBeanDefinition(), this.metadataReaderFactory)) { parse(holder.getBeanDefinition().getBeanClassName(), holder.getBeanName()); } }这里是检查ComponentScan扫出来的类是不是又打了ComonentScan注解，可能就需要递归解析了。
OK，那我们就把@ComponentScan相关源码分析完了。
这个方法里还有别的注解的解析。比如我们这个系列最开始给的例子：通过Java配置类配置bean 就是用的@Bean注解。那我们来看看@Bean注解。
@Bean源码
// Process individual @Bean methods Set<MethodMetadata> beanMethods = retrieveBeanMethodMetadata(sourceClass); for (MethodMetadata methodMetadata : beanMethods) { configClass.addBeanMethod(new BeanMethod(methodMetadata, configClass)); }这里面这个addBeanMethod方法打开一看：
public void addBeanMethod(BeanMethod method) { this.beanMethods.add(method); }而beanMehtods是个private final Set
感觉是啥也没干，就是加进去了而已。只能看看retrieveBeanMethodMetadata是在干嘛了，打开：
private Set<MethodMetadata> retrieveBeanMethodMetadata(SourceClass sourceClass) { AnnotationMetadata original = sourceClass.getMetadata(); Set<MethodMetadata> beanMethods = original.getAnnotatedMethods(Bean.class.getName()); if (beanMethods.size() > 1 && original instanceof StandardAnnotationMetadata) { // Try reading the class file via ASM for deterministic declaration order... // Unfortunately, the JVM's standard reflection returns methods in arbitrary // order, even between different runs of the same application on the same JVM. try { AnnotationMetadata asm = this.metadataReaderFactory.getMetadataReader(original.getClassName()).getAnnotationMetadata(); Set<MethodMetadata> asmMethods = asm.getAnnotatedMethods(Bean.class.getName()); if (asmMethods.size() >= beanMethods.size()) { Set<MethodMetadata> selectedMethods = new LinkedHashSet<MethodMetadata>(asmMethods.size()); for (MethodMetadata asmMethod : asmMethods) { for (MethodMetadata beanMethod : beanMethods) { if (beanMethod.getMethodName().equals(asmMethod.getMethodName())) { selectedMethods.add(beanMethod); break; } } } if (selectedMethods.size() == beanMethods.size()) { // All reflection-detected methods found in ASM method set -> proceed beanMethods = selectedMethods; } } } catch (IOException ex) { logger.debug("Failed to read class file via ASM for determining @Bean method order", ex); // No worries, let's continue with the reflection metadata we started with... } } return beanMethods; }这里貌似也没干啥，就是把配置类里面的打了bean注解的方法返回拿出来了，啥也没干。那么这个@Bean注解标注里的创建对象到底在哪里创建并加到容器呢？
这里明显就是个预操作，那么真正的操作在上层调用后面（实际上这个parse解析方法里也就只有@ComponentScan的真正处理了），我们返回上层直到有parse方法的地方：来到ConfigurationClassPostProcessor的processConfigBeanDefinitions方法:
public void processConfigBeanDefinitions(BeanDefinitionRegistry registry) { List<BeanDefinitionHolder> configCandidates = new ArrayList<BeanDefinitionHolder>(); String[] candidateNames = registry.getBeanDefinitionNames(); for (String beanName : candidateNames) { BeanDefinition beanDef = registry.getBeanDefinition(beanName); if (ConfigurationClassUtils.isFullConfigurationClass(beanDef) || ConfigurationClassUtils.isLiteConfigurationClass(beanDef)) { if (logger.isDebugEnabled()) { logger.debug("Bean definition has already been processed as a configuration class: " + beanDef); } } else if (ConfigurationClassUtils.checkConfigurationClassCandidate(beanDef, this.metadataReaderFactory)) { configCandidates.add(new BeanDefinitionHolder(beanDef, beanName)); } } // Return immediately if no @Configuration classes were found if (configCandidates.isEmpty()) { return; } // Sort by previously determined @Order value, if applicable Collections.sort(configCandidates, new Comparator<BeanDefinitionHolder>() { @Override public int compare(BeanDefinitionHolder bd1, BeanDefinitionHolder bd2) { int i1 = ConfigurationClassUtils.getOrder(bd1.getBeanDefinition()); int i2 = ConfigurationClassUtils.getOrder(bd2.getBeanDefinition()); return (i1 < i2) ? -1 : (i1 > i2) ? 1 : 0; } }); // Detect any custom bean name generation strategy supplied through the enclosing application context SingletonBeanRegistry sbr = null; if (registry instanceof SingletonBeanRegistry) { sbr = (SingletonBeanRegistry) registry; if (!this.localBeanNameGeneratorSet && sbr.containsSingleton(CONFIGURATION_BEAN_NAME_GENERATOR)) { BeanNameGenerator generator = (BeanNameGenerator) sbr.getSingleton(CONFIGURATION_BEAN_NAME_GENERATOR); this.componentScanBeanNameGenerator = generator; this.importBeanNameGenerator = generator; } } // Parse each @Configuration class ConfigurationClassParser parser = new ConfigurationClassParser( this.metadataReaderFactory, this.problemReporter, this.environment, this.resourceLoader, this.componentScanBeanNameGenerator, registry); Set<BeanDefinitionHolder> candidates = new LinkedHashSet<BeanDefinitionHolder>(configCandidates); Set<ConfigurationClass> alreadyParsed = new HashSet<ConfigurationClass>(configCandidates.size()); do { parser.parse(candidates); parser.validate(); Set<ConfigurationClass> configClasses = new LinkedHashSet<ConfigurationClass>(parser.getConfigurationClasses()); configClasses.removeAll(alreadyParsed); // Read the model and create bean definitions based on its content if (this.reader == null) { this.reader = new ConfigurationClassBeanDefinitionReader( registry, this.sourceExtractor, this.resourceLoader, this.environment, this.importBeanNameGenerator, parser.getImportRegistry()); } this.reader.loadBeanDefinitions(configClasses); alreadyParsed.addAll(configClasses); candidates.clear(); if (registry.getBeanDefinitionCount() > candidateNames.length) { String[] newCandidateNames = registry.getBeanDefinitionNames(); Set<String> oldCandidateNames = new HashSet<String>(Arrays.asList(candidateNames)); Set<String> alreadyParsedClasses = new HashSet<String>(); for (ConfigurationClass configurationClass : alreadyParsed) { alreadyParsedClasses.add(configurationClass.getMetadata().getClassName()); } for (String candidateName : newCandidateNames) { if (!oldCandidateNames.contains(candidateName)) { BeanDefinition bd = registry.getBeanDefinition(candidateName); if (ConfigurationClassUtils.checkConfigurationClassCandidate(bd, this.metadataReaderFactory) && !alreadyParsedClasses.contains(bd.getBeanClassName())) { candidates.add(new BeanDefinitionHolder(bd, candidateName)); } } } candidateNames = newCandidateNames; } } while (!candidates.isEmpty()); // Register the ImportRegistry as a bean in order to support ImportAware @Configuration classes if (sbr != null) { if (!sbr.containsSingleton(IMPORT_REGISTRY_BEAN_NAME)) { sbr.registerSingleton(IMPORT_REGISTRY_BEAN_NAME, parser.getImportRegistry()); } } if (this.metadataReaderFactory instanceof CachingMetadataReaderFactory) { ((CachingMetadataReaderFactory) this.metadataReaderFactory).clearCache(); } }我们只看我们之前查看源代码的parse方法那附近和后面就行了，有个do while循环解析那：
do { parser.parse(candidates); parser.validate(); Set<ConfigurationClass> configClasses = new LinkedHashSet<ConfigurationClass>(parser.getConfigurationClasses()); configClasses.removeAll(alreadyParsed); // Read the model and create bean definitions based on its content if (this.reader == null) { this.reader = new ConfigurationClassBeanDefinitionReader( registry, this.sourceExtractor, this.resourceLoader, this.environment, this.importBeanNameGenerator, parser.getImportRegistry()); } this.reader.loadBeanDefinitions(configClasses); alreadyParsed.addAll(configClasses); candidates.clear(); if (registry.getBeanDefinitionCount() > candidateNames.length) { String[] newCandidateNames = registry.getBeanDefinitionNames(); Set<String> oldCandidateNames = new HashSet<String>(Arrays.asList(candidateNames)); Set<String> alreadyParsedClasses = new HashSet<String>(); for (ConfigurationClass configurationClass : alreadyParsed) { alreadyParsedClasses.add(configurationClass.getMetadata().getClassName()); } for (String candidateName : newCandidateNames) { if (!oldCandidateNames.contains(candidateName)) { BeanDefinition bd = registry.getBeanDefinition(candidateName); if (ConfigurationClassUtils.checkConfigurationClassCandidate(bd, this.metadataReaderFactory) && !alreadyParsedClasses.contains(bd.getBeanClassName())) { candidates.add(new BeanDefinitionHolder(bd, candidateName)); } } } candidateNames = newCandidateNames; } } while (!candidates.isEmpty());parser.parse(candidates);后面是校验和创建配置类的Set。注意到有一个方法：
this.reader.loadBeanDefinitions(configClasses);这个操作reader的loadBeanDefinitions比较贴近意思了，点进去看看：
/** * 读取 {@code configurationModel}, 根据其内容在registry中注册bean定义. */ public void loadBeanDefinitions(Set<ConfigurationClass> configurationModel) { TrackedConditionEvaluator trackedConditionEvaluator = new TrackedConditionEvaluator(); for (ConfigurationClass configClass : configurationModel) { loadBeanDefinitionsForConfigurationClass(configClass, trackedConditionEvaluator); } }这个注释提示得非常明显，继续跟进loadBeanDefinitionsForConfigurationClass：
/** * Read a particular {@link ConfigurationClass}, registering bean definitions * for the class itself and all of its {@link Bean} methods. */ private void loadBeanDefinitionsForConfigurationClass(ConfigurationClass configClass, TrackedConditionEvaluator trackedConditionEvaluator) { if (trackedConditionEvaluator.shouldSkip(configClass)) { String beanName = configClass.getBeanName(); if (StringUtils.hasLength(beanName) && this.registry.containsBeanDefinition(beanName)) { this.registry.removeBeanDefinition(beanName); } this.importRegistry.removeImportingClass(configClass.getMetadata().getClassName()); return; } if (configClass.isImported()) { registerBeanDefinitionForImportedConfigurationClass(configClass); } for (BeanMethod beanMethod : configClass.getBeanMethods()) { loadBeanDefinitionsForBeanMethod(beanMethod); } loadBeanDefinitionsFromImportedResources(configClass.getImportedResources()); loadBeanDefinitionsFromRegistrars(configClass.getImportBeanDefinitionRegistrars()); }注意到里面有个重点啊：
for (BeanMethod beanMethod : configClass.getBeanMethods()) { loadBeanDefinitionsForBeanMethod(beanMethod); }这也太明显了哈，把配置的bean方法拿出来，一个个去加载，继续跟进：
/** * Read the given {@link BeanMethod}, registering bean definitions * with the BeanDefinitionRegistry based on its contents. */ private void loadBeanDefinitionsForBeanMethod(BeanMethod beanMethod) { ConfigurationClass configClass = beanMethod.getConfigurationClass(); MethodMetadata metadata = beanMethod.getMetadata(); String methodName = metadata.getMethodName(); // Do we need to mark the bean as skipped by its condition? if (this.conditionEvaluator.shouldSkip(metadata, ConfigurationPhase.REGISTER_BEAN)) { configClass.skippedBeanMethods.add(methodName); return; } if (configClass.skippedBeanMethods.contains(methodName)) { return; } // Consider name and any aliases AnnotationAttributes bean = AnnotationConfigUtils.attributesFor(metadata, Bean.class); List<String> names = new ArrayList<String>(Arrays.asList(bean.getStringArray("name"))); String beanName = (!names.isEmpty() ? names.remove(0) : methodName); // Register aliases even when overridden for (String alias : names) { this.registry.registerAlias(beanName, alias); } // Has this effectively been overridden before (e.g. via XML)? if (isOverriddenByExistingDefinition(beanMethod, beanName)) { return; } ConfigurationClassBeanDefinition beanDef = new ConfigurationClassBeanDefinition(configClass, metadata); beanDef.setResource(configClass.getResource()); beanDef.setSource(this.sourceExtractor.extractSource(metadata, configClass.getResource())); if (metadata.isStatic()) { // static @Bean method beanDef.setBeanClassName(configClass.getMetadata().getClassName()); beanDef.setFactoryMethodName(methodName); } else { // instance @Bean method beanDef.setFactoryBeanName(configClass.getBeanName()); beanDef.setUniqueFactoryMethodName(methodName); } beanDef.setAutowireMode(RootBeanDefinition.AUTOWIRE_CONSTRUCTOR); beanDef.setAttribute(RequiredAnnotationBeanPostProcessor.SKIP_REQUIRED_CHECK_ATTRIBUTE, Boolean.TRUE); AnnotationConfigUtils.processCommonDefinitionAnnotations(beanDef, metadata); Autowire autowire = bean.getEnum("autowire"); if (autowire.isAutowire()) { beanDef.setAutowireMode(autowire.value()); } String initMethodName = bean.getString("initMethod"); if (StringUtils.hasText(initMethodName)) { beanDef.setInitMethodName(initMethodName); } String destroyMethodName = bean.getString("destroyMethod"); if (destroyMethodName != null) { beanDef.setDestroyMethodName(destroyMethodName); } // Consider scoping ScopedProxyMode proxyMode = ScopedProxyMode.NO; AnnotationAttributes attributes = AnnotationConfigUtils.attributesFor(metadata, Scope.class); if (attributes != null) { beanDef.setScope(attributes.getString("value")); proxyMode = attributes.getEnum("proxyMode"); if (proxyMode == ScopedProxyMode.DEFAULT) { proxyMode = ScopedProxyMode.NO; } } // Replace the original bean definition with the target one, if necessary BeanDefinition beanDefToRegister = beanDef; if (proxyMode != ScopedProxyMode.NO) { BeanDefinitionHolder proxyDef = ScopedProxyCreator.createScopedProxy( new BeanDefinitionHolder(beanDef, beanName), this.registry, proxyMode == ScopedProxyMode.TARGET_CLASS); beanDefToRegister = new ConfigurationClassBeanDefinition( (RootBeanDefinition) proxyDef.getBeanDefinition(), configClass, metadata); } if (logger.isDebugEnabled()) { logger.debug(String.format("Registering bean definition for @Bean method %s.%s()", configClass.getMetadata().getClassName(), beanName)); } this.registry.registerBeanDefinition(beanName, beanDefToRegister); }通过方法注释更加确定了，最后一句代码正是容器注册代码。
我们大致来看看，前三句是把配置类拿出来、拿方法数据、方法名。后面两个判断是要看看要不要跳过，跳过就直接return了，不注册。再往后是把@Bean注解里的name对应的值拿出来，也就是别名拿出来并注册，后面也是各种把@Bean注解里的东西取出来操作，autowire模型（通过id还是name?）、initMethod、destroyMethod，各种细节配置就不多说了。最后通过this.registry.registerBeanDefinition就注册进去了。
值得注意的是beanName来自里面的：
List<String> names = new ArrayList<String(Arrays.asList(bean.getStringArray("name"))); String beanName = (!names.isEmpty() ? names.remove(0) : methodName);也就是你的@Bean注解里面没有写name的时候，实际上默认就是拿方法名做beanName了!
至此，@Bean注解也分析完毕.
至此ioc构造器的三大方法中的refresh()，里的invokeBeanFactoryPostProcessors的部分就讲完了，剩下的下篇文章继续分析。
