​ 在之前 讲解了springboot的启动过程,其实在面试过程中问的最多的可能是自动装配的原理,而自动装配是在启动过程中完成,只不过在刚开始的时候我们选择性的跳过了,下面详细讲解自动装配的过程。

  1. 当启动springBoot 应用程序的时候,会先创建 SpringApplication 的对象,在对象的构造方法中会进行某些参数的初始化工作 最主要的是判断当前应用程序的类型以及初始化器和监听器。在这个过程中会加载整个应用程序中的 Spring.factories 文件, 将文件的内容放到 缓存对象中,方便后续获取。

  2. SpringApplication 对象创建完成后,开始执行 run 方法,来完成整个启动,启动过程中最主要的有两个方法,第一个叫做 prepareContext , 第二个叫做 refreshContext , 在这两个关键的步骤中完成了自动装配的核心功能,前面的处理逻辑包含了上下文对象的创建,banner的打印,异常报告期的准备等各个准备工作, 方便后续来进行调用。

  3. prepareContext 方法中主要完成的是对上下文对象的初始化操作,包括了属性值的设置,比如环境对象,在整个过程中有一个非常总要的方法, 叫做 load , load 主要完成一件事, 将当前启动类作为一个 Beandefinition 注册到 registry 中,方便后续在进行 BeanFactoryProcessor 调用执行的时候, 找到对应的主类, 来完成 @SpringBootApplication, @EnableAutoConfiguration 等注解的解析工作。

  4. refreshContext 方法中会进行整个容器的刷新过程,会调用spring中的 refresh 方法,refresh中有13个非常关键的方法,来完成整个spring应用程序的启动, 在自动装配过程中,会调用 invokeBeanFactoryPostProcessor 方法,在此方法中主要是对 ConfigurationClassPostProcessor 类的处理, 这次是 BeanFactoryPostProcessor 的子类也是 BeanDefinitionRegistryPostProcessor 的子类, 在调用的时候会先调用 BeanDefinitionRegistryPostProcessor 中的postProcessBeanDefinitionRegistr 方法,3 然后调用postProcessBeanFactory 方法, 在执行postProcessBeanDefinitionRegistry 的时候会解析处理各种注解,包含 ** @PropertySource,@ComponentScan,@ComponentScans,@Bean,@Import** 等注解, 最主要的是 @Import 注解的解析。

  5. 在解析 注解的时候,会有一个 getImports 的方法,从主类开始递归解析注解,把所有包含 SCC 的注解都解析到, 然后在processImport 方法中 对Import 的类进行分类, 此处主要识别的是 AutoConfigurationImportSelect 归属的ImportSelect的子类, 在后续过程中会调用 deferredImportSelectorHandler 中的 process 方法,来完成 EnableAutoConfiguration 的加载。

  6. 上面是我对 SpringBoot 自动装配的简单理解,面试官您看一下,我回答的有没有问题,帮我指点一下

1、在springboot的启动过程中,有一个步骤是创建上下文,如果不记得可以看下面的代码:
public ConfigurableApplicationContext run(String... args) {
		StopWatch stopWatch = new StopWatch();
		stopWatch.start();
		ConfigurableApplicationContext context = null;
		Collection<SpringBootExceptionReporter> exceptionReporters = new ArrayList<>();
		configureHeadlessProperty();
		SpringApplicationRunListeners listeners = getRunListeners(args);
		listeners.starting();
		try {
			ApplicationArguments applicationArguments = new DefaultApplicationArguments(args);
			ConfigurableEnvironment environment = prepareEnvironment(listeners, applicationArguments);
			configureIgnoreBeanInfo(environment);
			Banner printedBanner = printBanner(environment);
			context = createApplicationContext();
			exceptionReporters = getSpringFactoriesInstances(SpringBootExceptionReporter.class,
					new Class[] { ConfigurableApplicationContext.class }, context);
            //此处完成自动装配的过程
			prepareContext(context, environment, listeners, applicationArguments, printedBanner);
			refreshContext(context);
			afterRefresh(context, applicationArguments);
			stopWatch.stop();
			if (this.logStartupInfo) {
				new StartupInfoLogger(this.mainApplicationClass).logStarted(getApplicationLog(), stopWatch);
			}
			listeners.started(context);
			callRunners(context, applicationArguments);
		}
		catch (Throwable ex) {
			handleRunFailure(context, ex, exceptionReporters, listeners);
			throw new IllegalStateException(ex);
		}

		try {
			listeners.running(context);
		}
		catch (Throwable ex) {
			handleRunFailure(context, ex, exceptionReporters, null);
			throw new IllegalStateException(ex);
		}
		return context;
	}
2、在prepareContext方法中查找load方法,一层一层向内点击,找到最终的load方法
//prepareContext方法
	private void prepareContext(ConfigurableApplicationContext context, ConfigurableEnvironment environment,
			SpringApplicationRunListeners listeners, ApplicationArguments applicationArguments, Banner printedBanner) {
		context.setEnvironment(environment);
		postProcessApplicationContext(context);
		applyInitializers(context);
		listeners.contextPrepared(context);
		if (this.logStartupInfo) {
			logStartupInfo(context.getParent() == null);
			logStartupProfileInfo(context);
		}
		// Add boot specific singleton beans
		ConfigurableListableBeanFactory beanFactory = context.getBeanFactory();
		beanFactory.registerSingleton("springApplicationArguments", applicationArguments);
		if (printedBanner != null) {
			beanFactory.registerSingleton("springBootBanner", printedBanner);
		}
		if (beanFactory instanceof DefaultListableBeanFactory) {
			((DefaultListableBeanFactory) beanFactory)
					.setAllowBeanDefinitionOverriding(this.allowBeanDefinitionOverriding);
		}
		if (this.lazyInitialization) {
			context.addBeanFactoryPostProcessor(new LazyInitializationBeanFactoryPostProcessor());
		}
		// Load the sources
		Set<Object> sources = getAllSources();
		Assert.notEmpty(sources, "Sources must not be empty");
        //load方法完成该功能
		load(context, sources.toArray(new Object[0]));
		listeners.contextLoaded(context);
	}


	/**
	 * Load beans into the application context.
	 * @param context the context to load beans into
	 * @param sources the sources to load
	 * 加载bean对象到context中
	 */
	protected void load(ApplicationContext context, Object[] sources) {
		if (logger.isDebugEnabled()) {
			logger.debug("Loading source " + StringUtils.arrayToCommaDelimitedString(sources));
		}
        //获取bean对象定义的加载器
		BeanDefinitionLoader loader = createBeanDefinitionLoader(getBeanDefinitionRegistry(context), sources);
		if (this.beanNameGenerator != null) {
			loader.setBeanNameGenerator(this.beanNameGenerator);
		}
		if (this.resourceLoader != null) {
			loader.setResourceLoader(this.resourceLoader);
		}
		if (this.environment != null) {
			loader.setEnvironment(this.environment);
		}
		loader.load();
	}

	/**
	 * Load the sources into the reader.
	 * @return the number of loaded beans
	 */
	int load() {
		int count = 0;
		for (Object source : this.sources) {
			count += load(source);
		}
		return count;
	}
3、实际执行load的是BeanDefinitionLoader中的load方法,如下:
	//实际记载bean的方法
	private int load(Object source) {
		Assert.notNull(source, "Source must not be null");
        //如果是class类型,启用注解类型
		if (source instanceof Class<?>) {
			return load((Class<?>) source);
		}
        //如果是resource类型,启动xml解析
		if (source instanceof Resource) {
			return load((Resource) source);
		}
        //如果是package类型,启用扫描包,例如@ComponentScan
		if (source instanceof Package) {
			return load((Package) source);
		}
        //如果是字符串类型,直接加载
		if (source instanceof CharSequence) {
			return load((CharSequence) source);
		}
		throw new IllegalArgumentException("Invalid source type " + source.getClass());
	}
4、下面方法将用来判断是否资源的类型,是使用groovy加载还是使用注解的方式
	private int load(Class<?> source) {
        //判断使用groovy脚本
		if (isGroovyPresent() && GroovyBeanDefinitionSource.class.isAssignableFrom(source)) {
			// Any GroovyLoaders added in beans{} DSL can contribute beans here
			GroovyBeanDefinitionSource loader = BeanUtils.instantiateClass(source, GroovyBeanDefinitionSource.class);
			load(loader);
		}
        //使用注解加载
		if (isComponent(source)) {
			this.annotatedReader.register(source);
			return 1;
		}
		return 0;
	}
5、下面方法判断启动类中是否包含@Component注解,但是会神奇的发现我们的启动类中并没有该注解,继续更进发现MergedAnnotations类传入了一个参数SearchStrategy.TYPE_HIERARCHY,会查找继承关系中是否包含这个注解,@SpringBootApplication-->@SpringBootConfiguration-->@Configuration-->@Component,当找到@Component注解之后,会把该对象注册到AnnotatedBeanDefinitionReader对象中
private boolean isComponent(Class<?> type) {
   // This has to be a bit of a guess. The only way to be sure that this type is
   // eligible is to make a bean definition out of it and try to instantiate it.
   if (MergedAnnotations.from(type, SearchStrategy.TYPE_HIERARCHY).isPresent(Component.class)) {
      return true;
   }
   // Nested anonymous classes are not eligible for registration, nor are groovy
   // closures
   return !type.getName().matches(".*\\$_.*closure.*") && !type.isAnonymousClass()
         && type.getConstructors() != null && type.getConstructors().length != 0;
}

	/**
	 * Register a bean from the given bean class, deriving its metadata from
	 * class-declared annotations.
	 * 从给定的bean class中注册一个bean对象,从注解中找到相关的元数据
	 */
	private <T> void doRegisterBean(Class<T> beanClass, @Nullable String name,
			@Nullable Class<? extends Annotation>[] qualifiers, @Nullable Supplier<T> supplier,
			@Nullable BeanDefinitionCustomizer[] customizers) {

		AnnotatedGenericBeanDefinition abd = new AnnotatedGenericBeanDefinition(beanClass);
		if (this.conditionEvaluator.shouldSkip(abd.getMetadata())) {
			return;
		}

		abd.setInstanceSupplier(supplier);
		ScopeMetadata scopeMetadata = this.scopeMetadataResolver.resolveScopeMetadata(abd);
		abd.setScope(scopeMetadata.getScopeName());
		String beanName = (name != null ? name : this.beanNameGenerator.generateBeanName(abd, this.registry));

		AnnotationConfigUtils.processCommonDefinitionAnnotations(abd);
		if (qualifiers != null) {
			for (Class<? extends Annotation> qualifier : qualifiers) {
				if (Primary.class == qualifier) {
					abd.setPrimary(true);
				}
				else if (Lazy.class == qualifier) {
					abd.setLazyInit(true);
				}
				else {
					abd.addQualifier(new AutowireCandidateQualifier(qualifier));
				}
			}
		}
		if (customizers != null) {
			for (BeanDefinitionCustomizer customizer : customizers) {
				customizer.customize(abd);
			}
		}

		BeanDefinitionHolder definitionHolder = new BeanDefinitionHolder(abd, beanName);
		definitionHolder = AnnotationConfigUtils.applyScopedProxyMode(scopeMetadata, definitionHolder, this.registry);
		BeanDefinitionReaderUtils.registerBeanDefinition(definitionHolder, this.registry);
	}

	/**
	 * Register the given bean definition with the given bean factory.
	 * 注册主类,如果有别名可以设置别名
	 */
	public static void registerBeanDefinition(
			BeanDefinitionHolder definitionHolder, BeanDefinitionRegistry registry)
			throws BeanDefinitionStoreException {

		// Register bean definition under primary name.
		String beanName = definitionHolder.getBeanName();
		registry.registerBeanDefinition(beanName, definitionHolder.getBeanDefinition());

		// Register aliases for bean name, if any.
		String[] aliases = definitionHolder.getAliases();
		if (aliases != null) {
			for (String alias : aliases) {
				registry.registerAlias(beanName, alias);
			}
		}
	}

//@SpringBootApplication
@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 {}

//@SpringBootConfiguration
@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Configuration
public @interface SpringBootConfiguration {}

//@Configuration
@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Component
public @interface Configuration {}

当看完上述代码之后,只是完成了启动对象的注入,自动装配还没有开始,下面开始进入到自动装配。

6、自动装配入口,从刷新容器开始
@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);

				// Invoke factory processors registered as beans in the context.
                // 此处是自动装配的入口
				invokeBeanFactoryPostProcessors(beanFactory);
            }
7、在invokeBeanFactoryPostProcessors方法中完成bean的实例化和执行
/**
	 * Instantiate and invoke all registered BeanFactoryPostProcessor beans,
	 * respecting explicit order if given.
	 * <p>Must be called before singleton instantiation.
	 */
	protected void invokeBeanFactoryPostProcessors(ConfigurableListableBeanFactory beanFactory) {
        //开始执行beanFactoryPostProcessor对应实现类,需要知道的是beanFactoryPostProcessor是spring的扩展接口,在刷新容器之前,该接口可以用来修改bean元数据信息
		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()));
		}
	}
8、查看invokeBeanFactoryPostProcessors的具体执行方法
	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<>();
			//开始遍历三个内部类,如果属于BeanDefinitionRegistryPostProcessor子类,加入到bean注册的集合,否则加入到regularPostProcessors
			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<>();

			// First, invoke the BeanDefinitionRegistryPostProcessors that implement PriorityOrdered.
            //通过BeanDefinitionRegistryPostProcessor获取到对应的处理类“org.springframework.context.annotation.internalConfigurationAnnotationProcessor”,但是需要注意的是这个类在springboot中搜索不到,这个类的完全限定名在AnnotationConfigEmbeddedWebApplicationContext中,在进行初始化的时候会装配几个类,在创建AnnotatedBeanDefinitionReader对象的时候会将该类注册到bean对象中,此处可以看到internalConfigurationAnnotationProcessor为bean名称,容器中真正的类是ConfigurationClassPostProcessor
			String[] postProcessorNames =
					beanFactory.getBeanNamesForType(BeanDefinitionRegistryPostProcessor.class, true, false);
            //首先执行类型为PriorityOrdered的BeanDefinitionRegistryPostProcessor
            //PriorityOrdered类型表明为优先执行
			for (String ppName : postProcessorNames) {
				if (beanFactory.isTypeMatch(ppName, PriorityOrdered.class)) {
                    //获取对应的bean
					currentRegistryProcessors.add(beanFactory.getBean(ppName, BeanDefinitionRegistryPostProcessor.class));
                    //用来存储已经执行过的BeanDefinitionRegistryPostProcessor
					processedBeans.add(ppName);
				}
			}
			sortPostProcessors(currentRegistryProcessors, beanFactory);
			registryProcessors.addAll(currentRegistryProcessors);
            //开始执行装配逻辑
			invokeBeanDefinitionRegistryPostProcessors(currentRegistryProcessors, registry);
			currentRegistryProcessors.clear();

			// Next, invoke the BeanDefinitionRegistryPostProcessors that implement Ordered.
            //其次执行类型为Ordered的BeanDefinitionRegistryPostProcessor
            //Ordered表明按顺序执行
			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();

			// Finally, invoke all other BeanDefinitionRegistryPostProcessors until no further ones appear.
            //循环中执行类型不为PriorityOrdered,Ordered类型的BeanDefinitionRegistryPostProcessor
			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.	
            //执行父类方法,优先执行注册处理类
			invokeBeanFactoryPostProcessors(registryProcessors, beanFactory);
            //执行有规则处理类
			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<>();
		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();
	}

9、开始执行自动配置逻辑(启动类指定的配置,非默认配置),可以通过debug的方式一层层向里进行查找,会发现最终会在ConfigurationClassParser类中,此类是所有配置类的解析类,所有的解析逻辑在parser.parse(candidates)中

public void parse(Set<BeanDefinitionHolder> configCandidates) {
		for (BeanDefinitionHolder holder : configCandidates) {
			BeanDefinition bd = holder.getBeanDefinition();
			try {
                //是否是注解类
				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);
			}
		}
    	//执行配置类
		this.deferredImportSelectorHandler.process();
	}
-------------------
    	protected final void parse(AnnotationMetadata metadata, String beanName) throws IOException {
		processConfigurationClass(new ConfigurationClass(metadata, beanName));
	}
-------------------
    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);
				this.knownSuperclasses.values().removeIf(configClass::equals);
			}
		}

		// Recursively process the configuration class and its superclass hierarchy.
		SourceClass sourceClass = asSourceClass(configClass);
		do {
            //循环处理bean,如果有父类,则处理父类,直至结束
			sourceClass = doProcessConfigurationClass(configClass, sourceClass);
		}
		while (sourceClass != null);

		this.configurationClasses.put(configClass, configClass);
	}

10、继续跟进doProcessConfigurationClass方法,此方式是支持注解配置的核心逻辑

/**
	 * Apply processing and build a complete {@link ConfigurationClass} by reading the
	 * annotations, members and methods from the source class. This method can be called
	 * multiple times as relevant sources are discovered.
	 * @param configClass the configuration class being build
	 * @param sourceClass a source class
	 * @return the superclass, or {@code null} if none found or previously processed
	 */
	@Nullable
	protected final SourceClass doProcessConfigurationClass(ConfigurationClass configClass, SourceClass sourceClass)
			throws IOException {

        //处理内部类逻辑,由于传来的参数是启动类,并不包含内部类,所以跳过
		if (configClass.getMetadata().isAnnotated(Component.class.getName())) {
			// Recursively process any member (nested) classes first
			processMemberClasses(configClass, sourceClass);
		}

		// Process any @PropertySource annotations
        //针对属性配置的解析
		for (AnnotationAttributes propertySource : AnnotationConfigUtils.attributesForRepeatable(
				sourceClass.getMetadata(), PropertySources.class,
				org.springframework.context.annotation.PropertySource.class)) {
			if (this.environment instanceof ConfigurableEnvironment) {
				processPropertySource(propertySource);
			}
			else {
				logger.info("Ignoring @PropertySource annotation on [" + sourceClass.getMetadata().getClassName() +
						"]. Reason: Environment must implement ConfigurableEnvironment");
			}
		}

		// Process any @ComponentScan annotations
        // 这里是根据启动类@ComponentScan注解来扫描项目中的bean
		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
                //遍历项目中的bean,如果是注解定义的bean,则进一步解析
				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) {
					BeanDefinition bdCand = holder.getBeanDefinition().getOriginatingBeanDefinition();
					if (bdCand == null) {
						bdCand = holder.getBeanDefinition();
					}
					if (ConfigurationClassUtils.checkConfigurationClassCandidate(bdCand, this.metadataReaderFactory)) {
                        //递归解析,所有的bean,如果有注解,会进一步解析注解中包含的bean
						parse(bdCand.getBeanClassName(), holder.getBeanName());
					}
				}
			}
		}

		// Process any @Import annotations
        //递归解析,获取导入的配置类,很多情况下,导入的配置类中会同样包含导入类注解
		processImports(configClass, sourceClass, getImports(sourceClass), true);

		// Process any @ImportResource annotations
        //解析@ImportResource配置类
		AnnotationAttributes importResource =
				AnnotationConfigUtils.attributesFor(sourceClass.getMetadata(), ImportResource.class);
		if (importResource != null) {
			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
        //处理@Bean注解修饰的类
		Set<MethodMetadata> beanMethods = retrieveBeanMethodMetadata(sourceClass);
		for (MethodMetadata methodMetadata : beanMethods) {
			configClass.addBeanMethod(new BeanMethod(methodMetadata, configClass));
		}

		// Process default methods on interfaces
        // 处理接口中的默认方法
		processInterfaces(configClass, sourceClass);

		// Process superclass, if any
        //如果该类有父类,则继续返回,上层方法判断不为空,则继续递归执行
		if (sourceClass.getMetadata().hasSuperClass()) {
			String superclass = sourceClass.getMetadata().getSuperClassName();
			if (superclass != null && !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;
	}

11、查看获取配置类的逻辑

processImports(configClass, sourceClass, getImports(sourceClass), true);

	/**
	 * Returns {@code @Import} class, considering all meta-annotations.
	 */
	private Set<SourceClass> getImports(SourceClass sourceClass) throws IOException {
		Set<SourceClass> imports = new LinkedHashSet<>();
		Set<SourceClass> visited = new LinkedHashSet<>();
		collectImports(sourceClass, imports, visited);
		return imports;
	}
------------------
    	/**
	 * Recursively collect all declared {@code @Import} values. Unlike most
	 * meta-annotations it is valid to have several {@code @Import}s declared with
	 * different values; the usual process of returning values from the first
	 * meta-annotation on a class is not sufficient.
	 * <p>For example, it is common for a {@code @Configuration} class to declare direct
	 * {@code @Import}s in addition to meta-imports originating from an {@code @Enable}
	 * annotation.
	 * 看到所有的bean都以导入的方式被加载进去
	 */
	private void collectImports(SourceClass sourceClass, Set<SourceClass> imports, Set<SourceClass> visited)
			throws IOException {

		if (visited.add(sourceClass)) {
			for (SourceClass annotation : sourceClass.getAnnotations()) {
				String annName = annotation.getMetadata().getClassName();
				if (!annName.equals(Import.class.getName())) {
					collectImports(annotation, imports, visited);
				}
			}
			imports.addAll(sourceClass.getAnnotationAttributes(Import.class.getName(), "value"));
		}
	}
12、继续回到ConfigurationClassParser中的parse方法中的最后一行,继续跟进该方法:
this.deferredImportSelectorHandler.process()
-------------
public void process() {
			List<DeferredImportSelectorHolder> deferredImports = this.deferredImportSelectors;
			this.deferredImportSelectors = null;
			try {
				if (deferredImports != null) {
					DeferredImportSelectorGroupingHandler handler = new DeferredImportSelectorGroupingHandler();
					deferredImports.sort(DEFERRED_IMPORT_COMPARATOR);
					deferredImports.forEach(handler::register);
					handler.processGroupImports();
				}
			}
			finally {
				this.deferredImportSelectors = new ArrayList<>();
			}
		}
---------------
  public void processGroupImports() {
			for (DeferredImportSelectorGrouping grouping : this.groupings.values()) {
				grouping.getImports().forEach(entry -> {
					ConfigurationClass configurationClass = this.configurationClasses.get(
							entry.getMetadata());
					try {
						processImports(configurationClass, asSourceClass(configurationClass),
								asSourceClasses(entry.getImportClassName()), false);
					}
					catch (BeanDefinitionStoreException ex) {
						throw ex;
					}
					catch (Throwable ex) {
						throw new BeanDefinitionStoreException(
								"Failed to process import candidates for configuration class [" +
										configurationClass.getMetadata().getClassName() + "]", ex);
					}
				});
			}
		}
------------
    /**
		 * Return the imports defined by the group.
		 * @return each import with its associated configuration class
		 */
		public Iterable<Group.Entry> getImports() {
			for (DeferredImportSelectorHolder deferredImport : this.deferredImports) {
				this.group.process(deferredImport.getConfigurationClass().getMetadata(),
						deferredImport.getImportSelector());
			}
			return this.group.selectImports();
		}
	}
------------
    public DeferredImportSelector getImportSelector() {
			return this.importSelector;
		}
------------
    @Override
		public void process(AnnotationMetadata annotationMetadata, DeferredImportSelector deferredImportSelector) {
			Assert.state(deferredImportSelector instanceof AutoConfigurationImportSelector,
					() -> String.format("Only %s implementations are supported, got %s",
							AutoConfigurationImportSelector.class.getSimpleName(),
							deferredImportSelector.getClass().getName()));
			AutoConfigurationEntry autoConfigurationEntry = ((AutoConfigurationImportSelector) deferredImportSelector)
					.getAutoConfigurationEntry(getAutoConfigurationMetadata(), annotationMetadata);
			this.autoConfigurationEntries.add(autoConfigurationEntry);
			for (String importClassName : autoConfigurationEntry.getConfigurations()) {
				this.entries.putIfAbsent(importClassName, annotationMetadata);
			}
		}