Spring5源码解析6-ConfigurationClassParser 解析配置类

ConfigurationClassParser

在ConfigurationClassPostProcessor#processConfigBeanDefinitions方法中创建了ConfigurationClassParser对象并调用其parse方法。该方法就是在负责解析配置类、扫描包、注册BeanDefinition，源码如下：

//ConfigurationClassParser#parseSet<BeanDefinitionHolder>) 方法源码
public void parse(Set<BeanDefinitionHolder> configCandidates) {
	for (BeanDefinitionHolder holder : configCandidates) {
		BeanDefinition bd = holder.getBeanDefinition();
		try {
			// 根据不同的 BeanDefinition 实例对象 调用不同的 parse 方法
			// 底层其实都是在调用 org.springframework.context.annotation.ConfigurationClassParser.processConfigurationClass
			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DeferredImportSelector
	this.deferredImportSelectorHandler.process();
}

在该方法内部根据不同的BeanDefinition实例对象，调用了不同的parse方法，而这些parse方法底层，实际上都是调用了ConfigurationClassParser#processConfigurationClass方法。

protected void processConfigurationClass(ConfigurationClass configClass) throws IOException {
	// 是否需要跳过 @Conditional
	if (this.conditionEvaluator.shouldSkip(configClass.getMetadata(), ConfigurationPhase.PARSE_CONFIGURATION)) {
		return;
	}

	// 第一次进入的时候, configurationClasses size = 0,existingClass 肯定为 null
	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 {
		// 真正的做解析
		sourceClass = doProcessConfigurationClass(configClass, sourceClass);
	}
	while (sourceClass != null);

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

方法传入的ConfigurationClass对象是对配置类的封装。首先判断配置类上是否有@Conditional注解，是否需要跳过解析该配置类。

然后，调用doProcessConfigurationClass(configClass, sourceClass);做真正的解析。其中，configClass是程序的配置类，而sourceClass是通过configClass创建的。

protected final SourceClass doProcessConfigurationClass(ConfigurationClass configClass, SourceClass sourceClass)
		throws IOException {

	// @Configuration 继承了 @Component
	if (configClass.getMetadata().isAnnotated(Component.class.getName())) {
		// Recursively process any member (nested) classes first
		// 递归处理内部类
		processMemberClasses(configClass, sourceClass);
	}

	// Process any @PropertySource annotations
	// 处理@PropertySource
	// @PropertySource注解用来加载properties文件
	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
	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) {
				BeanDefinition bdCand = holder.getBeanDefinition().getOriginatingBeanDefinition();
				if (bdCand == null) {
					bdCand = holder.getBeanDefinition();
				}
				//判断解析获取的 BeanDefinition 中 是否有配置类
				// 这里的配置类包括FullConfigurationClass和LiteConfigurationClass
				// 也就是说只要有@Configuration、@Component、@ComponentScan、@Import、@ImportResource和@Bean中的其中一个注解
				if (ConfigurationClassUtils.checkConfigurationClassCandidate(bdCand, this.metadataReaderFactory)) {
					//如果有配置类,递归调用,解析该配置类,这个if几乎都为true，这个方法几乎都要执行
					parse(bdCand.getBeanClassName(), holder.getBeanName());
				}
			}
		}
	}

	// Process any @Import annotations
	processImports(configClass, sourceClass, getImports(sourceClass), true);

	// Process any @ImportResource annotations
	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
	//处理单个@Bean的方法
	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 != 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;
}

解析内部类

配置类上有@Configuration注解，该注解继承 @Component，if 判断为true，调用processMemberClasses方法，递归解析配置类中的内部类。

解析@PropertySource注解

如果配置类上有@PropertySource注解，则解析加载properties文件，并将属性添加到Spring上下文中。((ConfigurableEnvironment) this.environment).getPropertySources().addFirstPropertySource(newSource);。

处理@ComponentScan注解

获取配置类上的@ComponentScan注解，判断是否需要跳过。循环所有的ComponentScan，立即执行扫描。ComponentScanAnnotationParser#parse方法如下：

public Set<BeanDefinitionHolder> parse(AnnotationAttributes componentScan, final String declaringClass) {
	// 创建 ClassPathBeanDefinitionScanner
	// 在 AnnotationConfigApplicationContext 的构造器中也创建了一个ClassPathBeanDefinitionScanner
	// 这里证明了,执行扫描 scanner 不是构造器中的,而是这里创建的
	ClassPathBeanDefinitionScanner scanner = new ClassPathBeanDefinitionScanner(this.registry,
			componentScan.getBoolean("useDefaultFilters"), this.environment, this.resourceLoader);

	// @ComponentScan 中可以注册自定义的 BeanNameGenerator
	// 但是需要注意,通过源码可以明白,这里注册的自定义BeanNameGenerator 只对当前 scanner 有效
	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[] basePackagesArray = componentScan.getStringArray("basePackages");
	for (String pkg : basePackagesArray) {
		String[] tokenized = StringUtils.tokenizeToStringArray(this.environment.resolvePlaceholders(pkg),
				ConfigurableApplicationContext.CONFIG_LOCATION_DELIMITERS);
		Collections.addAll(basePackages, tokenized);
	}

	// @ComponentScan(basePackageClasses = Xx.class)
	// 可以指定basePackageClasses, 只要是与是这几个类所在包及其子包,就可以被Spring扫描
	// 经常会用一个空的类来作为basePackageClasses,默认取当前配置类所在包及其子包
	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);
		}
	});

	//执行扫描
	return scanner.doScan(StringUtils.toStringArray(basePackages));
}

挑一些我觉得是重点的地方记录一下：

1. parse方法中新创建了一个ClassPathBeanDefinitionScanner对象，而在 AnnotationConfigApplicationContext 的构造器中也创建了一个ClassPathBeanDefinitionScanner对象，这里证实了在Spring内部，真正执行扫描的不是AnnotationConfigApplicationContext中的scanner。
2. 通过源码可以了解到，在@ComponentScan中是可以注册自定义的 BeanNameGenerator的，而这个BeanNameGenerator只对当前scanner有效。也就是说，这个BeanNameGenerator只能影响通过该scanner扫描的路径下的bean的BeanName生成规则。
3. 最后调用scanner.doScan(StringUtils.toStringArray(basePackages));方法执行真正的扫描，方法返回扫描获取到的BeanDefinition。

检验获得的BeanDefinition中是否有配置类

检验扫描获得的BeanDefinition中是否有配置类，如果有配置类，这里的配置类包括FullConfigurationClass和LiteConfigurationClass。（也就是说只要有@Configuration、@Component、@ComponentScan、@Import、@ImportResource和@Bean中的其中一个注解），则递归调用parse方法，进行解析。

解析 @Import 注解

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

processImports方法负责对@Import注解进行解析。configClass是配置类，sourceClass又是通过configClass创建的，getImports(sourceClass)从sourceClass获取所有的@Import注解信息，然后调用ConfigurationClassParser#processImports。

// ConfigurationClassParser#processImports 源码
private void processImports(ConfigurationClass configClass, SourceClass currentSourceClass,
							Collection<SourceClass> importCandidates, boolean checkForCircularImports) {

	if (importCandidates.isEmpty()) {
		return;
	}

	if (checkForCircularImports && isChainedImportOnStack(configClass)) {
		this.problemReporter.error(new CircularImportProblem(configClass, this.importStack));
	} else {
		this.importStack.push(configClass);
		try {
			// importCandidates是@Import的封装
			// 循环importCandidates对import的内容进行分类
			for (SourceClass candidate : importCandidates) {
				// import导入实现ImportSelector接口的类
				if (candidate.isAssignable(ImportSelector.class)) {
					// Candidate class is an ImportSelector -> delegate to it to determine imports
					Class<?> candidateClass = candidate.loadClass();
					// 反射创建这个类的实例对象
					ImportSelector selector = BeanUtils.instantiateClass(candidateClass, ImportSelector.class);
					//是否有实现相关Aware接口,如果有,这调用相关方法
					ParserStrategyUtils.invokeAwareMethods(
							selector, this.environment, this.resourceLoader, this.registry);
					// 延迟加载的ImportSelector
					if (selector instanceof DeferredImportSelector) {
						//  延迟加载的ImportSelector先放到List中,延迟加载
						this.deferredImportSelectorHandler.handle(configClass, (DeferredImportSelector) selector);
					} else {
						// 普通的ImportSelector ,执行其selectImports方法,获取需要导入的类的全限定类名数组
						String[] importClassNames = selector.selectImports(currentSourceClass.getMetadata());
						Collection<SourceClass> importSourceClasses = asSourceClasses(importClassNames);
						// 递归调用
						processImports(configClass, currentSourceClass, importSourceClasses, false);
					}
					// 是否为ImportBeanDefinitionRegistrar
				} else if (candidate.isAssignable(ImportBeanDefinitionRegistrar.class)) {
					// Candidate class is an ImportBeanDefinitionRegistrar ->
					// delegate to it to register additional bean definitions
					Class<?> candidateClass = candidate.loadClass();
					ImportBeanDefinitionRegistrar registrar =
							BeanUtils.instantiateClass(candidateClass, ImportBeanDefinitionRegistrar.class);
					ParserStrategyUtils.invokeAwareMethods(
							registrar, this.environment, this.resourceLoader, this.registry);
					// 添加到成员变量 org.springframework.context.annotation.ConfigurationClass.importBeanDefinitionRegistrars 中
					configClass.addImportBeanDefinitionRegistrar(registrar, currentSourceClass.getMetadata());
				} else {
					// Candidate class not an ImportSelector or ImportBeanDefinitionRegistrar ->
					// process it as an @Configuration class
					// 普通 @Configuration class
					this.importStack.registerImport(
							currentSourceClass.getMetadata(), candidate.getMetadata().getClassName());
					// 解析导入的@Configuration class
					processConfigurationClass(candidate.asConfigClass(configClass));
				}
			}
		} catch (BeanDefinitionStoreException ex) {
			throw ex;
		} catch (Throwable ex) {
			throw new BeanDefinitionStoreException(
					"Failed to process import candidates for configuration class [" +
							configClass.getMetadata().getClassName() + "]", ex);
		} finally {
			this.importStack.pop();
		}
	}
}

解析 @ImportResource 注解

@ImportResource注解可以导入xml配置文件。

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);
	}
}

解析@Bean方法

Set<MethodMetadata> beanMethods = retrieveBeanMethodMetadata(sourceClass);
for (MethodMetadata methodMetadata : beanMethods) {
	configClass.addBeanMethod(new BeanMethod(methodMetadata, configClass));
}

将@Bean方法转化为BeanMethod对象，添加到ConfigurationClass#beanMethods集合中。

如果有父类，则解析父类

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();
	}
}

如果有父类则返回父类Class对象，继续调用该方法。直到返回null，外层循环结束。

do {
    // 真正的做解析
    sourceClass = doProcessConfigurationClass(configClass, sourceClass);
}
while (sourceClass != null);

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