Spring Boot 3.x 自动配置详解

逃离我推掉我的手 2024-03-17 20:18 83阅读 0赞

> 基于Spring Boot 3.1.0 系列文章
> 
> 1.  [Spring Boot 源码阅读初始化环境搭建][Spring Boot]
> 2.  [Spring Boot 框架整体启动流程详解][Spring Boot 1]
> 3.  [Spring Boot 系统初始化器详解][Spring Boot 2]
> 4.  [Spring Boot 监听器详解][Spring Boot 3]
> 5.  [Spring Boot banner详解][Spring Boot banner]
> 6.  [Spring Boot 属性配置解析][Spring Boot 4]
> 7.  [Spring Boot 属性加载原理解析][Spring Boot 5]
> 8.  [Spring Boot 异常报告器解析][Spring Boot 6]
> 9.  [Spring Boot 3.x 自动配置详解][Spring Boot 3.x]

> Spring Boot ：3.1  
> Java: 17

## 前言 ##

Spring Boot 3.x 中的自动配置使用`META-INF/spring/org.springframework.boot.autoconfigure.AutoConfiguration.imports`,而不是`META-INF/spring.factories`,这个变动其实在2.7的时候已经改变

**2.6.9版本文档介绍**

![在这里插入图片描述][414be4e46be94f8f82e50afe33d485a3.png_pic_center]  
**2.7.0版本介绍**

![在这里插入图片描述][4f231e72da0b4219b5deeb9ee39f7342.png_pic_center]  
文档中有创建自己的Starter的详细介绍，[《Spring Boot 中文参考指南-创建自己的自动配置》][Spring Boot _-]

## 加载原理 ##

Spring Boot 3.x的自动配置加载入口是`META-INF/spring/org.springframework.boot.autoconfigure.AutoConfiguration.imports`,Spring Boot会读取该文件中的自动配置类，并实例化，我们以该文件为入口。

> 如果你是新手，并且没有资料可查，可以使用IDE的全局文件搜索功能，搜索关键词，如我搜索`org.springframework.boot.autoconfigure.AutoConfiguration.imports`的结果如下，再通过打断点的方式就能判断加载该文件的入口。
> 
> ![在这里插入图片描述][12be2f33a7e0441391672fe9dade53c2.png_pic_center]

可知，该文件的加载是由`AutoConfigurationImportSelector`类进行处理，但`AutoConfigurationImportSelector`类又是如何加载的。  
通过断点的堆栈可知加载使用到了Spring 框架`refresh()`中的`invokeBeanFactoryPostProcessors`，其作用是在实例化Bean之前加载额外定义的Bean到上下文中，我们从头开始梳理，能力强的可以掌握方法自行阅读。

**堆栈信息**

![在这里插入图片描述][ccfd4da7673547aa96dc2599ca52ff97.png_pic_center]

**AbstractApplicationContext-invokeBeanFactoryPostProcessors**

protected void invokeBeanFactoryPostProcessors(ConfigurableListableBeanFactory beanFactory) {
        
    		PostProcessorRegistrationDelegate.invokeBeanFactoryPostProcessors(beanFactory, getBeanFactoryPostProcessors());
    
    		// 如果beanFactory中是否包含LoadTimeWeaver，如果包含则使用临时ClassLoader进行处理，LoadTimeWeaver是一种类加载器的动态织入技术
    		if (!NativeDetector.inNativeImage() && beanFactory.getTempClassLoader() == null && beanFactory.containsBean(LOAD_TIME_WEAVER_BEAN_NAME)) {
        
    			beanFactory.addBeanPostProcessor(new LoadTimeWeaverAwareProcessor(beanFactory));
    			beanFactory.setTempClassLoader(new ContextTypeMatchClassLoader(beanFactory.getBeanClassLoader()));
    		}
    	}

该方法的作用是：实例化并调用注册的`BeanFactoryPostProcessor`

`getBeanFactoryPostProcessors()` 用来获取所有的`BeanFactoryPostProcessor`实例，`BeanFactoryPostProcessor`实例通过`ApplicationContextInitializer`来加载到上下文中，`ApplicationContextInitializer`的加载原理可以通过前面的文章了解[《Spring Boot 系统初始化器详解》][Spring Boot 2]。

`PostProcessorRegistrationDelegate.invokeBeanFactoryPostProcessors(beanFactory, getBeanFactoryPostProcessors());` 委托处理BeanFactoryPostProcessor。

**PostProcessorRegistrationDelegate-invokeBeanFactoryPostProcessors**

public static void invokeBeanFactoryPostProcessors(
    			ConfigurableListableBeanFactory beanFactory, List<BeanFactoryPostProcessor> beanFactoryPostProcessors) {
        
    
    		Set<String> processedBeans = new HashSet<>();
    		//如果beanFactory 是BeanDefinitionRegistry的实现，先处理BeanDefinitionRegistryPostProcessors
    		if (beanFactory instanceof BeanDefinitionRegistry registry) {
        
    			List<BeanFactoryPostProcessor> regularPostProcessors = new ArrayList<>();
    			List<BeanDefinitionRegistryPostProcessor> registryProcessors = new ArrayList<>();
    
    			for (BeanFactoryPostProcessor postProcessor : beanFactoryPostProcessors) {
        
    				if (postProcessor instanceof BeanDefinitionRegistryPostProcessor registryProcessor) {
        
    					registryProcessor.postProcessBeanDefinitionRegistry(registry);
    					registryProcessors.add(registryProcessor);
    				}
    				else {
        
    					regularPostProcessors.add(postProcessor);
    				}
    			}
    
    			List<BeanDefinitionRegistryPostProcessor> currentRegistryProcessors = new ArrayList<>();
    
    			// 先处理 PriorityOrdered 的 BeanDefinitionRegistryPostProcessor
    			String[] postProcessorNames =
    					beanFactory.getBeanNamesForType(BeanDefinitionRegistryPostProcessor.class, true, false);
    			for (String ppName : postProcessorNames) {
        
    				if (beanFactory.isTypeMatch(ppName, PriorityOrdered.class)) {
        
    					currentRegistryProcessors.add(beanFactory.getBean(ppName, BeanDefinitionRegistryPostProcessor.class));
    					processedBeans.add(ppName);
    				}
    			}
    			sortPostProcessors(currentRegistryProcessors, beanFactory);
    			registryProcessors.addAll(currentRegistryProcessors);
    			
    //处理BeanDefinitionRegistryPostProcessors
    			invokeBeanDefinitionRegistryPostProcessors(currentRegistryProcessors, registry, beanFactory.getApplicationStartup());
    			currentRegistryProcessors.clear();
    
    			// 再处理 Ordered 的 BeanDefinitionRegistryPostProcessor
    			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, beanFactory.getApplicationStartup());
    			currentRegistryProcessors.clear();
    
    			 // 最后处理剩余的 BeanDefinitionRegistryPostProcessor，直到没有新的 BeanDefinitionRegistryPostProcessor 添加为止
    			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, beanFactory.getApplicationStartup());
    				currentRegistryProcessors.clear();
    			}
    
    			// 处理所有 BeanFactoryPostProcessor
    			invokeBeanFactoryPostProcessors(registryProcessors, beanFactory);
    			invokeBeanFactoryPostProcessors(regularPostProcessors, beanFactory);
    		}
    
    		else {
        
    			// 处理普通的上下文中的BeanFactoryPostProcessor
    	invokeBeanFactoryPostProcessors(beanFactoryPostProcessors, beanFactory);
    		}
    
    		//获取所有常规化Bean，但不初始化，保留让后期的post-processors处理
    		String[] postProcessorNames =
    				beanFactory.getBeanNamesForType(BeanFactoryPostProcessor.class, true, false);
    
    		
    		//分离实现PriorityOrdered、Ordered和其他的BeanFactoryPostProcessors
    		List<BeanFactoryPostProcessor> priorityOrderedPostProcessors = new ArrayList<>();
    		List<String> orderedPostProcessorNames = new ArrayList<>();
    		List<String> nonOrderedPostProcessorNames = new ArrayList<>();
    		for (String ppName : postProcessorNames) {
        
    			if (processedBeans.contains(ppName)) {
        
    				// 跳过已经处理的
    			}
    			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);
    			}
    		}
    
    		
    		//首先处理实现了PriorityOrdered的BeanFactoryPostProcessors
    		sortPostProcessors(priorityOrderedPostProcessors, beanFactory);
    		invokeBeanFactoryPostProcessors(priorityOrderedPostProcessors, beanFactory);
    
    		//处理实现了Ordered的BeanFactoryPostProcessors
    		List<BeanFactoryPostProcessor> orderedPostProcessors = new ArrayList<>(orderedPostProcessorNames.size());
    		for (String postProcessorName : orderedPostProcessorNames) {
        
    			orderedPostProcessors.add(beanFactory.getBean(postProcessorName, BeanFactoryPostProcessor.class));
    		}
    		sortPostProcessors(orderedPostProcessors, beanFactory);
    		invokeBeanFactoryPostProcessors(orderedPostProcessors, beanFactory);
    
    		// 最后处理其他的BeanFactoryPostProcessors
    		List<BeanFactoryPostProcessor> nonOrderedPostProcessors = new ArrayList<>(nonOrderedPostProcessorNames.size());
    		for (String postProcessorName : nonOrderedPostProcessorNames) {
        
    			nonOrderedPostProcessors.add(beanFactory.getBean(postProcessorName, BeanFactoryPostProcessor.class));
    		}
    		invokeBeanFactoryPostProcessors(nonOrderedPostProcessors, beanFactory);
    
    		// 清除缓存
    		beanFactory.clearMetadataCache();
    	}

`invokeBeanDefinitionRegistryPostProcessors(currentRegistryProcessors, registry, beanFactory.getApplicationStartup());` 是处理自动配置的关键点

**PostProcessorRegistrationDelegate-invokeBeanDefinitionRegistryPostProcessors**

private static void invokeBeanDefinitionRegistryPostProcessors(
    		Collection<? extends BeanDefinitionRegistryPostProcessor> postProcessors, BeanDefinitionRegistry registry, ApplicationStartup applicationStartup) {
        
    
    //循环处理BeanDefinitionRegistryPostProcessor实现
    	for (BeanDefinitionRegistryPostProcessor postProcessor : postProcessors) {
        
    	//步骤日志记录
    		StartupStep postProcessBeanDefRegistry = applicationStartup.start("spring.context.beandef-registry.post-process")
    				.tag("postProcessor", postProcessor::toString);
    		postProcessor.postProcessBeanDefinitionRegistry(registry);
    		postProcessBeanDefRegistry.end();
    	}
    }

`BeanDefinitionRegistryPostProcessor`接口继承了BeanFactoryPostProcessor接口，允许在初始化Bean实例之前修改、添加、删除容器中注册的Bean定义信息

在该示例的SpringBoot-Demo中，只有一个BeanDefinitionRegistryPostProcessor实现，即`ConfigurationClassPostProcessor`

**ConfigurationClassPostProcessor-postProcessBeanDefinitionRegistry**

public void postProcessBeanDefinitionRegistry(BeanDefinitionRegistry registry) {
        
    //计算hashcode
    		int registryId = System.identityHashCode(registry);
    		//判断是否处理过
    		if (this.registriesPostProcessed.contains(registryId)) {
        
    			throw new IllegalStateException(
    					"postProcessBeanDefinitionRegistry already called on this post-processor against " + registry);
    		}
    		if (this.factoriesPostProcessed.contains(registryId)) {
        
    			throw new IllegalStateException(
    					"postProcessBeanFactory already called on this post-processor against " + registry);
    		}
    		this.registriesPostProcessed.add(registryId);
    
    //处理配置Bean定义信息
    		processConfigBeanDefinitions(registry);
    	}

**ConfigurationClassPostProcessor-processConfigBeanDefinitions**

public void processConfigBeanDefinitions(BeanDefinitionRegistry registry) {
        
    		List<BeanDefinitionHolder> configCandidates = new ArrayList<>();
    		//获取容器中所有的bean定义名称
    		String[] candidateNames = registry.getBeanDefinitionNames();
    
    		for (String beanName : candidateNames) {
        
    		// 获取 bean 的定义
    			BeanDefinition beanDef = registry.getBeanDefinition(beanName);
    			// 检查该 bean 是否已经被处理成配置类
    			if (beanDef.getAttribute(ConfigurationClassUtils.CONFIGURATION_CLASS_ATTRIBUTE) != null) {
        
    				if (logger.isDebugEnabled()) {
        
    					logger.debug("Bean definition has already been processed as a configuration class: " + beanDef);
    				}
    			}
    			// 检查该 bean 是否是配置类候选者
    			else if (ConfigurationClassUtils.checkConfigurationClassCandidate(beanDef, this.metadataReaderFactory)) {
        
    				configCandidates.add(new BeanDefinitionHolder(beanDef, beanName));
    			}
    		}
    
    		// 如果没有需要处理的配置类，则直接返回
    		if (configCandidates.isEmpty()) {
        
    			return;
    		}
    
    		// 对配置类候选者进行排序，按照先前确定的 @Order 值排序
    		configCandidates.sort((bd1, bd2) -> {
        
    			int i1 = ConfigurationClassUtils.getOrder(bd1.getBeanDefinition());
    			int i2 = ConfigurationClassUtils.getOrder(bd2.getBeanDefinition());
    			return Integer.compare(i1, i2);
    		});
    
    		// 检查是否有自定义的 bean 名称生成策略
    		SingletonBeanRegistry sbr = null;
    		if (registry instanceof SingletonBeanRegistry _sbr) {
        
    			sbr = _sbr;
    			if (!this.localBeanNameGeneratorSet) {
        
    				BeanNameGenerator generator = (BeanNameGenerator) sbr.getSingleton(
    						AnnotationConfigUtils.CONFIGURATION_BEAN_NAME_GENERATOR);
    				if (generator != null) {
        
    					this.componentScanBeanNameGenerator = generator;
    					this.importBeanNameGenerator = generator;
    				}
    			}
    		}
    
    		if (this.environment == null) {
        
    			this.environment = new StandardEnvironment();
    		}
    
    		// 解析每个 @Configuration 类
    		ConfigurationClassParser parser = new ConfigurationClassParser(
    				this.metadataReaderFactory, this.problemReporter, this.environment,
    				this.resourceLoader, this.componentScanBeanNameGenerator, registry);
    
    		Set<BeanDefinitionHolder> candidates = new LinkedHashSet<>(configCandidates);
    		Set<ConfigurationClass> alreadyParsed = new HashSet<>(configCandidates.size());
    		do {
        
    			StartupStep processConfig = this.applicationStartup.start("spring.context.config-classes.parse");
    			//解析
    			parser.parse(candidates);
    			//验证
    			parser.validate();
    
    			Set<ConfigurationClass> configClasses = new LinkedHashSet<>(parser.getConfigurationClasses());
    			//去除已经解析的类
    			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);
    			processConfig.tag("classCount", () -> String.valueOf(configClasses.size())).end();
    // 检查新的 BeanDefinition 是否包含新的配置类候选者
    			candidates.clear();
    			if (registry.getBeanDefinitionCount() > candidateNames.length) {
        
    				String[] newCandidateNames = registry.getBeanDefinitionNames();
    				Set<String> oldCandidateNames = Set.of(candidateNames);
    				Set<String> alreadyParsedClasses = new HashSet<>();
    				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());
    
    		// 注册 ImportRegistry 为一个 bean，以支持 @ImportAware ConfigurationClass
    		if (sbr != null && !sbr.containsSingleton(IMPORT_REGISTRY_BEAN_NAME)) {
        
    			sbr.registerSingleton(IMPORT_REGISTRY_BEAN_NAME, parser.getImportRegistry());
    		}
    
    		// 存储 PropertySourceDescriptors，便于在AOT中使用
    		this.propertySourceDescriptors = parser.getPropertySourceDescriptors();
    
    		if (this.metadataReaderFactory instanceof CachingMetadataReaderFactory cachingMetadataReaderFactory) {
        
    			// 清除缓存，防止由于缓存无法更新导致的出错问题
    			cachingMetadataReaderFactory.clearCache();
    		}
    	}

此处代码很长，对于配置类的解析，在`parser.parse(candidates)`中完成。  
`parser`变量的实例为：`ConfigurationClassParser`

**ConfigurationClassParser-parse**

public void parse(Set<BeanDefinitionHolder> configCandidates) {
        
    		for (BeanDefinitionHolder holder : configCandidates) {
        
    			BeanDefinition bd = holder.getBeanDefinition();
    			try {
        
    			// 如果 BeanDefinition 是一个 AnnotatedBeanDefinition，则需要解析该 BeanDefinition 中的注解信息
    				if (bd instanceof AnnotatedBeanDefinition annotatedBeanDef) {
        
    					parse(annotatedBeanDef.getMetadata(), holder.getBeanName());
    				}
    				// 如果 BeanDefinition 不是 AnnotatedBeanDefinition，并且具有 beanClass 属性，则解析该 beanClass 中的注解信息
    				else if (bd instanceof AbstractBeanDefinition abstractBeanDef && abstractBeanDef.hasBeanClass()) {
        
    					parse(abstractBeanDef.getBeanClass(), holder.getBeanName());
    				}
    				else {
        
    				// 如果 BeanDefinition 没有 beanClass 属性，则解析该 BeanDefinition 中的 beanClassName 所指定的类中的注解信息
    					parse(bd.getBeanClassName(), holder.getBeanName());
    				}
    			}
    			catch (BeanDefinitionStoreException ex) {
        
    				throw ex;
    			}
    			catch (Throwable ex) {
        
    				throw new BeanDefinitionStoreException(
    						"Failed to parse configuration class [" + bd.getBeanClassName() + "]", ex);
    			}
    		}
    		
    		//处理所有的DeferredImportSelector实例
    		this.deferredImportSelectorHandler.process();
    	}

在开始的时候，我们已经知道实际解析自动配置类是`AutoConfigurationImportSelector`，AutoConfigurationImportSelector 实现了`DeferredImportSelector`接口，而这里正好有`deferredImportSelectorHandler`来处理所有的deferredImportSelectorHandler实例。看下`DeferredImportSelectorHandler`中的process。

**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<>();
    			}
    		}

`DeferredImportSelectorGroupingHandler` 类是在 Spring Boot 中处理 DeferredImportSelector 接口的辅助类，主要用于按照分组将DeferredImportSelector分组进行处理。

此处，我们要关注`handler.processGroupImports()`，调用到`DeferredImportSelectorGroupingHandler`类的processGroupImports方法。

**DeferredImportSelectorGroupingHandler-processGroupImports**

public void processGroupImports() {
        
    			//遍历所有分组
    			for (DeferredImportSelectorGrouping grouping : this.groupings.values()) {
        
    				//获取候选过滤器
    				Predicate<String> exclusionFilter = grouping.getCandidateFilter();
    				//遍历分组中的每个元素
    				grouping.getImports().forEach(entry -> {
        
    					ConfigurationClass configurationClass = this.configurationClasses.get(entry.getMetadata());
    					try {
        
    					//处理当前元素
    						processImports(configurationClass, asSourceClass(configurationClass, exclusionFilter),
    								Collections.singleton(asSourceClass(entry.getImportClassName(), exclusionFilter)),
    								exclusionFilter, false);
    					}
    					catch (BeanDefinitionStoreException ex) {
        
    						throw ex;
    					}
    					catch (Throwable ex) {
        
    						throw new BeanDefinitionStoreException(
    								"Failed to process import candidates for configuration class [" +
    										configurationClass.getMetadata().getClassName() + "]", ex);
    					}
    				});
    			}
    		}

这里首先要关注`grouping.getImports()`，在这里对自动配置类进行了加载

**DeferredImportSelectorGrouping-getImports**

public Iterable<Group.Entry> getImports() {
        
    	for (DeferredImportSelectorHolder deferredImport : this.deferredImports) {
        
    //处理每个分组的DeferredImportSelectorHolder
    		this.group.process(deferredImport.getConfigurationClass().getMetadata(),
    				deferredImport.getImportSelector());
    	}
    	//返回需要导入的类
    	return this.group.selectImports();
    }

`this.group.process`中进入到`AutoConfigurationImportSelector`的内部类`AutoConfigurationGroup`中

**AutoConfigurationImportSelector-AutoConfigurationGroup-process**

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()));
    					
    					//转为为AutoConfigurationImportSelector，获取AutoConfigurationEntry
    	AutoConfigurationEntry autoConfigurationEntry = ((AutoConfigurationImportSelector) deferredImportSelector)
    		.getAutoConfigurationEntry(annotationMetadata);
    	
    //添加到autoConfigurationEntries变量中，供后期使用
    this.autoConfigurationEntries.add(autoConfigurationEntry);
    //设置entries变量，导入的类名和元注解映射关系
    	for (String importClassName : autoConfigurationEntry.getConfigurations()) {
        
    		this.entries.putIfAbsent(importClassName, annotationMetadata);
    	}
    }

此处deferredImportSelector强转为AutoConfigurationImportSelector后，再次调用了getAutoConfigurationEntry方法。

**AutoConfigurationImportSelector-getAutoConfigurationEntry**

protected AutoConfigurationEntry getAutoConfigurationEntry(AnnotationMetadata annotationMetadata) {
        
        // 如果自动配置不可用，则返回 EMPTY_ENTRY
    	if (!isEnabled(annotationMetadata)) {
        
    		return EMPTY_ENTRY;
    	}
    	// 获取注解的属性
    	AnnotationAttributes attributes = getAttributes(annotationMetadata);
    	// 获取候选自动配置类，此文关键
    	List<String> configurations = getCandidateConfigurations(annotationMetadata, attributes);
    	// 去除重复的自动配置类
    	configurations = removeDuplicates(configurations);
    	// 获取需要排除的自动配置类，spring.autoconfigure.exclude配置
    	Set<String> exclusions = getExclusions(annotationMetadata, attributes);
    	// 检查是否有被排除的自动配置类
    	checkExcludedClasses(configurations, exclusions);
    	// 去除被排除的自动配置类
    	configurations.removeAll(exclusions);
    	// 使用 ConfigurationClassFilter 过滤自动配置类
    	configurations = getConfigurationClassFilter().filter(configurations);
    	// 发送自动配置事件
    	fireAutoConfigurationImportEvents(configurations, exclusions);
    	return new AutoConfigurationEntry(configurations, exclusions);
    }

该方法的作用是根据给定的注解元数据获取自动配置项，对于自动配置的加载，关键在`getCandidateConfigurations(annotationMetadata, attributes)`。

**AutoConfigurationImportSelector-getCandidateConfigurations**

protected List<String> getCandidateConfigurations(AnnotationMetadata metadata, AnnotationAttributes attributes) {
        
    //从类路径的META-INF/spring中载入名为AutoConfiguration全限定名的类
    	List<String> configurations = ImportCandidates.load(AutoConfiguration.class, getBeanClassLoader())
    		.getCandidates();
    	Assert.notEmpty(configurations,
    			"No auto configuration classes found in "
    					+ "META-INF/spring/org.springframework.boot.autoconfigure.AutoConfiguration.imports. If you "
    					+ "are using a custom packaging, make sure that file is correct.");
    	return configurations;
    }

该方法的`ImportCandidates.load(AutoConfiguration.class, getBeanClassLoader())`会拼凑出`META-INF/spring/org.springframework.boot.autoconfigure.AutoConfiguration.imports`路径，用于加载定义的AutoConfiguration类。

**ImportCandidates-ImportCandidates**

public static ImportCandidates load(Class<?> annotation, ClassLoader classLoader) {
        
    	Assert.notNull(annotation, "'annotation' must not be null");
    	ClassLoader classLoaderToUse = decideClassloader(classLoader);
    	//将META-INF/spring/%s.imports字符串格式化为指定的路径
    	String location = String.format(LOCATION, annotation.getName());
    	Enumeration<URL> urls = findUrlsInClasspath(classLoaderToUse, location);
    	List<String> importCandidates = new ArrayList<>();
    	while (urls.hasMoreElements()) {
        
    		URL url = urls.nextElement();
    		importCandidates.addAll(readCandidateConfigurations(url));
    	}
    	return new ImportCandidates(importCandidates);
    }

在`grouping.getImports()`获取到所有要导入的AutoConfigurationEntry后，通过`processImports`进行处理

**ConfigurationClassParser-processImports**

private void processImports(ConfigurationClass configClass, SourceClass currentSourceClass,
            Collection<SourceClass> importCandidates, Predicate<String> exclusionFilter,
            boolean checkForCircularImports) {
        
    
        // 如果没有可导入的类，则直接返回
        if (importCandidates.isEmpty()) {
        
            return;
        }
    
        // 检查循环导入
        if (checkForCircularImports && isChainedImportOnStack(configClass)) {
        
            this.problemReporter.error(new CircularImportProblem(configClass, this.importStack));
        }
        else {
        
            // 将当前配置类推入导入栈中
            this.importStack.push(configClass);
            try {
        
                // 处理每个导入的类
                for (SourceClass candidate : importCandidates) {
        
                    if (candidate.isAssignable(ImportSelector.class)) {
        
                        // Candidate class is an ImportSelector -> delegate to it to determine imports
                        // 如果候选类是 ImportSelector 的子类，则交由它来决定导入哪些类
                        Class<?> candidateClass = candidate.loadClass();
                        ImportSelector selector = ParserStrategyUtils.instantiateClass(candidateClass, ImportSelector.class,
                                this.environment, this.resourceLoader, this.registry);
                        Predicate<String> selectorFilter = selector.getExclusionFilter();
                        if (selectorFilter != null) {
        
                            exclusionFilter = exclusionFilter.or(selectorFilter);
                        }
                        if (selector instanceof DeferredImportSelector deferredImportSelector) {
        
                            this.deferredImportSelectorHandler.handle(configClass, deferredImportSelector);
                        }
                        else {
        
                            String[] importClassNames = selector.selectImports(currentSourceClass.getMetadata());
                            Collection<SourceClass> importSourceClasses = asSourceClasses(importClassNames, exclusionFilter);
                            processImports(configClass, currentSourceClass, importSourceClasses, exclusionFilter, false);
                        }
                    }
                    else if (candidate.isAssignable(ImportBeanDefinitionRegistrar.class)) {
        
                        // Candidate class is an ImportBeanDefinitionRegistrar ->
                        // delegate to it to register additional bean definitions
                        // 如果候选类是 ImportBeanDefinitionRegistrar 的子类，则交由它来注册更多的 Bean 定义
                        Class<?> candidateClass = candidate.loadClass();
                        ImportBeanDefinitionRegistrar registrar =
                                ParserStrategyUtils.instantiateClass(candidateClass, ImportBeanDefinitionRegistrar.class,
                                        this.environment, this.resourceLoader, this.registry);
                        configClass.addImportBeanDefinitionRegistrar(registrar, currentSourceClass.getMetadata());
                    }
                    else {
        
                        // Candidate class not an ImportSelector or ImportBeanDefinitionRegistrar ->
                        // process it as an @Configuration class
                        // 如果候选类不是 ImportSelector 或 ImportBeanDefinitionRegistrar 的子类，则将其作为 @Configuration 类来处理
                        this.importStack.registerImport(
                                currentSourceClass.getMetadata(), candidate.getMetadata().getClassName());
                        processConfigurationClass(candidate.asConfigClass(configClass), exclusionFilter);
                    }
                }
            }
            catch (BeanDefinitionStoreException ex) {
        
                throw ex;
            }
            catch (Throwable ex) {
        
                throw new BeanDefinitionStoreException(
                        "Failed to process import candidates for configuration class [" +
                        configClass.getMetadata().getClassName() + "]: " + ex.getMessage(), ex);
            }
            finally {
        
                this.importStack.pop();
            }
        }
    }

以`MybatisPlusLanguageDriverAutoConfiguration`自动配置为例，会通过`processConfigurationClass(candidate.asConfigClass(configClass), exclusionFilter);`进行处理。

**ConfigurationClassParser-processConfigurationClass**

protected void processConfigurationClass(ConfigurationClass configClass, Predicate<String> filter) throws IOException {
        
        // 如果该配置类被标记为跳过，则直接返回，不需要再处理
    	if (this.conditionEvaluator.shouldSkip(configClass.getMetadata(), ConfigurationPhase.PARSE_CONFIGURATION)) {
        
    		return;
    	}
    
        // 如果已经存在同名的配置类，则判断两者的导入情况并合并
    	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);
    		}
    	}
    
        // 递归地处理该配置类及其父类的继承关系，解析 Bean 定义
    	SourceClass sourceClass = asSourceClass(configClass, filter);
    	do {
        
    		sourceClass = doProcessConfigurationClass(configClass, sourceClass, filter);
    	}
    	while (sourceClass != null);
    
        // 将该配置类加入到 configurationClasses 中
    	this.configurationClasses.put(configClass, configClass);
    }

**ConfigurationClassParser-doProcessConfigurationClass**

protected final SourceClass doProcessConfigurationClass(
    			ConfigurationClass configClass, SourceClass sourceClass, Predicate<String> filter)
    			throws IOException {
        
    
    		if (configClass.getMetadata().isAnnotated(Component.class.getName())) {
        
    			// 如果该配置类被@Component注解标记，则递归处理任何嵌套类。
    			processMemberClasses(configClass, sourceClass, filter);
    		}
    
    		// 处理 @PropertySource
    		for (AnnotationAttributes propertySource : AnnotationConfigUtils.attributesForRepeatable(
    				sourceClass.getMetadata(), PropertySources.class,
    				org.springframework.context.annotation.PropertySource.class)) {
        
    			if (this.propertySourceRegistry != null) {
        
    				this.propertySourceRegistry.processPropertySource(propertySource);
    			}
    			else {
        
    				logger.info("Ignoring @PropertySource annotation on [" + sourceClass.getMetadata().getClassName() +
    						"]. Reason: Environment must implement ConfigurableEnvironment");
    			}
    		}
    
    		// 处理@ComponentScan注解
    		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());
    				// 检查扫描的定义集是否有任何进一步的配置类，并在需要时递归解析
    
    				for (BeanDefinitionHolder holder : scannedBeanDefinitions) {
        
    					BeanDefinition bdCand = holder.getBeanDefinition().getOriginatingBeanDefinition();
    					if (bdCand == null) {
        
    						bdCand = holder.getBeanDefinition();
    					}
    					if (ConfigurationClassUtils.checkConfigurationClassCandidate(bdCand, this.metadataReaderFactory)) {
        
    						parse(bdCand.getBeanClassName(), holder.getBeanName());
    					}
    				}
    			}
    		}
    
    		// 处理@Import
    		processImports(configClass, sourceClass, getImports(sourceClass), filter, true);
    
    		// 处理@ImportResource
    		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);
    			}
    		}
    
    		// 处理单个的@Bean方法
    		Set<MethodMetadata> beanMethods = retrieveBeanMethodMetadata(sourceClass);
    		for (MethodMetadata methodMetadata : beanMethods) {
        
    			configClass.addBeanMethod(new BeanMethod(methodMetadata, configClass));
    		}
    
    		// 处理接口上的默认方法
    		processInterfaces(configClass, sourceClass);
    
    		// 处理超类
    		if (sourceClass.getMetadata().hasSuperClass()) {
        
    			String superclass = sourceClass.getMetadata().getSuperClassName();
    			if (superclass != null && !superclass.startsWith("java") &&
    					!this.knownSuperclasses.containsKey(superclass)) {
        
    				this.knownSuperclasses.put(superclass, configClass);
    				// 找到超类，返回其注释元数据并递归
    				return sourceClass.getSuperClass();
    			}
    		}
    
    		// 没有超类，完成
    		return null;
    	}

## 总结 ##

一张图说明整个自动配置加载解析流程  
![在这里插入图片描述][8c67002a29204eeea515b64efa9b3295.jpeg]

[Spring Boot]: https://itsaysay.blog.csdn.net/article/details/129665897
[Spring Boot 1]: https://itsaysay.blog.csdn.net/article/details/130981611
[Spring Boot 2]: https://itsaysay.blog.csdn.net/article/details/131034991
[Spring Boot 3]: https://itsaysay.blog.csdn.net/article/details/131073017
[Spring Boot banner]: https://itsaysay.blog.csdn.net/article/details/131116036
[Spring Boot 4]: https://itsaysay.blog.csdn.net/article/details/131178566
[Spring Boot 5]: https://itsaysay.blog.csdn.net/article/details/131205549
[Spring Boot 6]: https://itsaysay.blog.csdn.net/article/details/131242002
[Spring Boot 3.x]: https://itsaysay.blog.csdn.net/article/details/131736129
[414be4e46be94f8f82e50afe33d485a3.png_pic_center]: https://image.dandelioncloud.cn/pgy_files/images/2024/03/14/08a5d3b392324e0497bf71943a147eaa.png
[4f231e72da0b4219b5deeb9ee39f7342.png_pic_center]: https://image.dandelioncloud.cn/pgy_files/images/2024/03/14/5f89a555065441c382e8cc83f195edf4.png
[Spring Boot _-]: https://itsaysay.blog.csdn.net/article/details/128922165
[12be2f33a7e0441391672fe9dade53c2.png_pic_center]: https://image.dandelioncloud.cn/pgy_files/images/2024/03/14/cbf2e44ee71a41a6a093ca723e96521b.png
[ccfd4da7673547aa96dc2599ca52ff97.png_pic_center]: https://image.dandelioncloud.cn/pgy_files/images/2024/03/14/75ccb013dc504523a764047b6ec2d577.png
[8c67002a29204eeea515b64efa9b3295.jpeg]: https://image.dandelioncloud.cn/pgy_files/images/2024/03/14/25a3309bb42f42f388989fc41ff9890b.png