spring boot 加载过程分析--ConfigurationClassPostProcessor-白红宇

ConfigurationClassPostProcessor

前面说到ConfigurationClassPostProcessor是BeanDefinitionRegistryPostProcessor接口的实现，在调用invokeBeanFactoryPostProcessors时，会先被调用；而且通过之前的分析我们可以知道，它是在容器初始化置AnnotatedBeanDefinitionReader时注册到注册的（分析(二)），主要用来处理@Configuration注解。因实现还是比较复杂的，所以单独拿出来分析下。

先看一下该类实现的接口

public class ConfigurationClassPostProcessor implements BeanDefinitionRegistryPostProcessor, PriorityOrdered, ResourceLoaderAware, BeanClassLoaderAware, EnvironmentAware {        ....}复制代码

它除了是BeanDefinitionRegistryPostProcessor的实现之外，还实现了一堆的Aware接口。我们在前面有介绍ApplicationContextAwareProcessor这个bean的扩展实现的功能，注入上下文属性（在调用getBean进行实例化时调用的，关于getBean调用过程后面再介绍）。

1. postProcessBeanDefinitionRegistry

public void postProcessBeanDefinitionRegistry(BeanDefinitionRegistry registry) {		int registryId = System.identityHashCode(registry);		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);		processConfigBeanDefinitions(registry);	}复制代码

代码比较简单，取得registry的id并做判重处理或记录，直接看processConfigBeanDefinitions方法，代码如下.

public void processConfigBeanDefinitions(BeanDefinitionRegistry registry) {		List
    
      configCandidates = new ArrayList<>();		// 获取容器中注册的所有bean名字		String[] candidateNames = registry.getBeanDefinitionNames();                //遍历bean		for (String beanName : candidateNames) {			BeanDefinition beanDef = registry.getBeanDefinition(beanName);			//判断bean是否已经处理过			if (ConfigurationClassUtils.isFullConfigurationClass(beanDef) ||					ConfigurationClassUtils.isLiteConfigurationClass(beanDef)) {				if (logger.isDebugEnabled()) {					logger.debug("Bean definition has already been processed as a configuration class: " + beanDef);				}			}			// 判断是否是Configuration类, 这里其实主要是看是否有			// @Configuration, @Component, @ComponentScan, @Import, @Bean等注解			else if (ConfigurationClassUtils.checkConfigurationClassCandidate(beanDef, this.metadataReaderFactory)) {				configCandidates.add(new BeanDefinitionHolder(beanDef, beanName));			}		}		// 这里筛选完之后，符合条件的只剩启动类 @SpringBootApplication		if (configCandidates.isEmpty()) {			return;		}		// 排序		configCandidates.sort((bd1, bd2) -> {			int i1 = ConfigurationClassUtils.getOrder(bd1.getBeanDefinition());			int i2 = ConfigurationClassUtils.getOrder(bd2.getBeanDefinition());			return Integer.compare(i1, i2);		});		// 设置beanName的生成策略		SingletonBeanRegistry sbr = null;		if (registry instanceof SingletonBeanRegistry) {			sbr = (SingletonBeanRegistry) registry;			if (!this.localBeanNameGeneratorSet) {				BeanNameGenerator generator = (BeanNameGenerator) sbr.getSingleton(CONFIGURATION_BEAN_NAME_GENERATOR);				if (generator != null) {					this.componentScanBeanNameGenerator = generator;					this.importBeanNameGenerator = generator;				}			}		}		if (this.environment == null) {			this.environment = new StandardEnvironment();		}		// 配置@Configuration的解析器，这里的部分属性就是通过ApplicationContextAwareProcessor来设置注入的。		ConfigurationClassParser parser = new ConfigurationClassParser(				this.metadataReaderFactory, this.problemReporter, this.environment,				this.resourceLoader, this.componentScanBeanNameGenerator, registry);		Set
     
       candidates = new LinkedHashSet<>(configCandidates);		Set
      
        alreadyParsed = new HashSet<>(configCandidates.size());		// 解析		do {			parser.parse(candidates);			parser.validate();			Set
       
         configClasses = new LinkedHashSet<>(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());			}			// 读取配置类，加载beanDefinition			this.reader.loadBeanDefinitions(configClasses);			alreadyParsed.addAll(configClasses);			candidates.clear();			// 如果在解析过程中，有新的配置类型beanDefinition注册加入，则循环处理			if (registry.getBeanDefinitionCount() > candidateNames.length) {				String[] newCandidateNames = registry.getBeanDefinitionNames();				Set
        
          oldCandidateNames = new HashSet<>(Arrays.asList(candidateNames));				Set
         
           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()); // Register the ImportRegistry as a bean in order to support ImportAware @Configuration classes if (sbr != null && !sbr.containsSingleton(IMPORT_REGISTRY_BEAN_NAME)) { sbr.registerSingleton(IMPORT_REGISTRY_BEAN_NAME, parser.getImportRegistry()); } // 清除缓存 if (this.metadataReaderFactory instanceof CachingMetadataReaderFactory) { // Clear cache in externally provided MetadataReaderFactory; this is a no-op // for a shared cache since it'll be cleared by the ApplicationContext. ((CachingMetadataReaderFactory) this.metadataReaderFactory).clearCache(); } }复制代码

获取已经注册的bean名称,进行遍历; 判断是否已经处理过，判断是否为配置类；如果有，排下序。

如果BeanDefinitionRegistry 是SingletonBeanRegistry 子类的话,由于我们当前传入的是DefaultListableBeanFactory,是 SingletonBeanRegistry 的子类。因此会将registry强转为SingletonBeanRegistry；然后获取beanName的生成策略设置给成员变量。

实例化ConfigurationClassParser 为了解析各个配置类.实例化2个set,candidates 用于将之前加入的configCandidates 进行去重,alreadyParsed 用于判断是否处理过。

调用ConfigurationClassParser#parse进行解析将解析过的配置类加入到configClasses；实例化ConfigurationClassBeanDefinitionReader 调用ConfigurationClassBeanDefinitionReader#loadBeanDefinitions 进行加载,并加入到alreadyParsed中,用于去重将candidates进行清空,如果registry中注册的bean的数量大于之前获得的数量,则意味着在解析过程中又新加入了很多,那么就需要对其进行解析

注册一个,bean 为 ImportRegistry；清除缓存。

这里有一个判断是否为配置类的方法，其实检查的就是该类是否有@Configuration,@Component,@ComponentScan, @Import, @ImportResource, @Bean方法。

2. ConfigurationClassParser.parse

该方法的代码简单，最后调用会到processConfigurationClass方法，我们直接看该方法实现。

processConfigurationClass

protected void processConfigurationClass(ConfigurationClass configClass) throws IOException {                //是否跳过		if (this.conditionEvaluator.shouldSkip(configClass.getMetadata(), ConfigurationPhase.PARSE_CONFIGURATION)) {			return;		}		ConfigurationClass existingClass = this.configurationClasses.get(configClass);		// 处理Imported 的情况		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.				this.configurationClasses.remove(configClass);				this.knownSuperclasses.values().removeIf(configClass::equals);			}		}		// 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);}复制代码

先看ConditionEvaluator.shouldSkip判断是否跳过，根据@Condition条件来判断。

判断处理imported的情况

递归解析configClass

3. doProcessConfigurationClass

解析class配置的核心方法，代码如下:

protected final SourceClass doProcessConfigurationClass(ConfigurationClass configClass, SourceClass sourceClass)			throws IOException {		// 首先递归处理内部类		processMemberClasses(configClass, sourceClass);		// 处理 @PropertySource 注解		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");			}		}		// 处理 @ComponentScan 类		Set
    
      componentScans = AnnotationConfigUtils.attributesForRepeatable(				sourceClass.getMetadata(), ComponentScans.class, ComponentScan.class);		if (!componentScans.isEmpty() &&				!this.conditionEvaluator.shouldSkip(sourceClass.getMetadata(), ConfigurationPhase.REGISTER_BEAN)) {			for (AnnotationAttributes componentScan : componentScans) {				// 如果配置类有@ComponentScan -> 立刻运行扫描				Set
     
       scannedBeanDefinitions =						this.componentScanParser.parse(componentScan, sourceClass.getMetadata().getClassName());				// 检查扫描到的definition是否还有配置类型，有则递归解析				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 注解		processImports(configClass, sourceClass, getImports(sourceClass), true);		// 处理 @ImportResource 注解		AnnotationAttributes importResource =				AnnotationConfigUtils.attributesFor(sourceClass.getMetadata(), ImportResource.class);		if (importResource != null) {			String[] resources = importResource.getStringArray("locations");			Class
       readerClass = importResource.getClass("reader");			for (String resource : resources) {				String resolvedResource = this.environment.resolveRequiredPlaceholders(resource);				configClass.addImportedResource(resolvedResource, readerClass);			}		}		// 处理 @Bean 方法注解		Set
      
        beanMethods = retrieveBeanMethodMetadata(sourceClass);		for (MethodMetadata methodMetadata : beanMethods) {			configClass.addBeanMethod(new BeanMethod(methodMetadata, configClass));		}		// 处理接口的默认方法		processInterfaces(configClass, sourceClass);		// 处理父类		if (sourceClass.getMetadata().hasSuperClass()) {			String superclass = sourceClass.getMetadata().getSuperClassName();			if (superclass != null && !superclass.startsWith("java") &&					!this.knownSuperclasses.containsKey(superclass)) {				this.knownSuperclasses.put(superclass, configClass);				// Superclass found, return its annotation metadata and recurse				return sourceClass.getSuperClass();			}		}		// No superclass -> processing is complete		return null;}复制代码

3.1 处理内部类，不再贴代码；

遍历configClass的内部类，判断是否为配置类且类名不与configClass相同

判断是否存在循环引用

3.2 处理@PropertySource.通过遍历该类中的@PropertySource的注解,如果该类中的environment是ConfigurableEnvironment 子类的话,则调用processPropertySource进行处理.否则打印警告日志.一般都是ConfigurableEnvironment的子类

private void processPropertySource(AnnotationAttributes propertySource) throws IOException {                //获取注解上的属性name		String name = propertySource.getString("name");		if (!StringUtils.hasLength(name)) {			name = null;		}		//获取注解上的属性encoding		String encoding = propertySource.getString("encoding");		if (!StringUtils.hasLength(encoding)) {			encoding = null;		}		String[] locations = propertySource.getStringArray("value");		Assert.isTrue(locations.length > 0, "At least one @PropertySource(value) location is required");		boolean ignoreResourceNotFound = propertySource.getBoolean("ignoreResourceNotFound");		                // 获取Facotry，如果没指定使用默认的DefaultPropertySourceFactory		Class
     factoryClass = propertySource.getClass("factory");		PropertySourceFactory factory = (factoryClass == PropertySourceFactory.class ?				DEFAULT_PROPERTY_SOURCE_FACTORY : BeanUtils.instantiateClass(factoryClass));		for (String location : locations) {			try {			        // 解析点位符，多环境配置				String resolvedLocation = this.environment.resolveRequiredPlaceholders(location);				// 加载property配置文件				Resource resource = this.resourceLoader.getResource(resolvedLocation);				addPropertySource(factory.createPropertySource(name, new EncodedResource(resource, encoding)));			}			catch (IllegalArgumentException | FileNotFoundException | UnknownHostException ex) {				// Placeholders not resolvable or resource not found when trying to open it				if (ignoreResourceNotFound) {					if (logger.isInfoEnabled()) {						logger.info("Properties location [" + location + "] not resolvable: " + ex.getMessage());					}				}				else {					throw ex;				}			}		}}复制代码

解析@PropertySource注解上的各属性值，加载配置文件，然后添加到运行环境中。

3.3 处理@ComponentScan：判断是否应该跳过，并依次通过ComponentScanAnnotationParser.parse进行解析。最终调用ClassPathBeanDefinitionScanner.doScan。代码如下:

protected Set
    
      doScan(String... basePackages) {		Assert.notEmpty(basePackages, "At least one base package must be specified");		Set
     
       beanDefinitions = new LinkedHashSet<>();		for (String basePackage : basePackages) {		        // 扫描basePackage路径下的java文件			Set
      
        candidates = findCandidateComponents(basePackage);			for (BeanDefinition candidate : candidates) {			    // 解析是否有@Scop				ScopeMetadata scopeMetadata = this.scopeMetadataResolver.resolveScopeMetadata(candidate);				candidate.setScope(scopeMetadata.getScopeName());				// 生成beanName				String beanName = this.beanNameGenerator.generateBeanName(candidate, this.registry);				// 设置默认配置				if (candidate instanceof AbstractBeanDefinition) {					postProcessBeanDefinition((AbstractBeanDefinition) candidate, beanName);				}				// 通用注解的解析设置				if (candidate instanceof AnnotatedBeanDefinition) {					AnnotationConfigUtils.processCommonDefinitionAnnotations((AnnotatedBeanDefinition) candidate);				}				// 判断beanName容器中是否存在，不存在则注册，如存在判断是否兼容，不兼容抛异常				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;	}复制代码

那么，通过上面一步后，我们自己写的@Controller, @Service等就被注册到容器中了。只是完成了beanDefinition的查找，解析并注册的工作，此时这些bean还未被实例化。ok, 回到doProcessConfigurationClass方法中对@ComponentScan的解析处接着看，因为@Controller, @Service, @Configuration等注解都是符合配置类校验的（ConfigurationClassUtils.checkConfigurationClassCandidate），所以还需要递归解析来看其他内部是否还有其他配置，比如内部类，@Bean等。

接着再往下，以次解析的是@Import, @ImportResource, 收集@Bean方法与接口的默认方法。这部分不再一一分析，流程和上面类似递归处理，最后把configClass都放到了集合中。

解析处理完之后，回到我们的ConfigurationClassPostProcessor方法继续看，实例化了reader类ConfigurationClassBeanDefinitionReader用来读取加载configClass的解析。

public void loadBeanDefinitions(Set
    
      configurationModel) {	TrackedConditionEvaluator trackedConditionEvaluator = new TrackedConditionEvaluator();	for (ConfigurationClass configClass : configurationModel) {	    loadBeanDefinitionsForConfigurationClass(configClass, trackedConditionEvaluator);	}}private void loadBeanDefinitionsForConfigurationClass(		ConfigurationClass configClass, TrackedConditionEvaluator trackedConditionEvaluator) {        //如果应该跳过，且容器中有，则移除	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;	}        // 注册@Import 	if (configClass.isImported()) {		registerBeanDefinitionForImportedConfigurationClass(configClass);	}	// @注册Bean	for (BeanMethod beanMethod : configClass.getBeanMethods()) {		loadBeanDefinitionsForBeanMethod(beanMethod);	}        // 注册@ImportResource 通过XmlBeanDefinitionReader读取配置	loadBeanDefinitionsFromImportedResources(configClass.getImportedResources());	// 注册ImportBeanDefinitionRegistrar实现	loadBeanDefinitionsFromRegistrars(configClass.getImportBeanDefinitionRegistrars());}复制代码

通过之前的分析，其实我们知道@PropertySource，@ComponentScan的解析最后会把相关注解增加到环境配置或者注册到容器中去。但对@Import, @Bean的只是收集到集合中，并未注册到容器中，所以上面的load主要处理这一部分。

registerBeanDefinitionForImportedConfigurationClass 注册@Import

loadBeanDefinitionsForBeanMethod 注册@Bean

loadBeanDefinitionsFromImportedResources 注册@ImportResource 通过XmlBeanDefinitionReader读取配置

loadBeanDefinitionsFromRegistrars 注册ImportBeanDefinitionRegistrar实现

processConfigBeanDefinitions方法再下面的处理就是判断新增的beanDefinition是否有配置类，有则递归处理，无则清除缓存。

该篇文章分析详细，建议阅读一下。

参考链接：