SpringBoot中将@Bean方法解析为BeanDefinition详解

SpringBoot如何将@Bean方法注册为BeanDefinition

我们以MyBATisPlusAutoConfiguration为例说明sqlSessionFactory()这个方法如何解析为BeanDefinition。

@Bean
@ConditionalOnMissingBean
public SqlSessionFactory sqlSessionFactory(DataSource dataSource) throws Exception {
//...
}    

这个解析过程是在ConfigurationClassBeanDefinitionReader的loadBeanDefinitionsForBeanMethod方法。

private void loadBeanDefinitionsForBeanMethod(BeanMethod beanMethod) {
	ConfigurationClass configClass = beanMethod.getConfigurationClass();
	MethodMetadata metadata = beanMethod.getMetadata();
	//本文这里是sqlSessionFactory
	String methodName = metadata.getMethodName();
	// Do we need to mark the bean as skipped by its condition?
	//判断是否需要跳过
	if (this.conditionEvaLuator.shouldSkip(metadata, ConfigurationPhase.REGISTER_BEAN)) {
		configClass.skippedBeanMethods.add(methodName);
		return;
	}
		//判断是否需要跳过
	if (configClass.skippedBeanMethods.contains(methodName)) {
		return;
	}
//获取到@Bpythonean的注解信息
	AnnotationAttributes bean = AnnotationConfigUtils.attributesFor(metadata, Bean.class);
	Assert.state(bean != null, "No @Bean annotation attributes");
	// Consider name and any aliases
	List<String> names = new ArrayList<>(Arrays.asList(bean.getStringArray("name")));
	//尝试获取bean的名称，默认使用methodName
	String beanName = (!names.isEmpty() ? names.remove(0) : methodName);
	// Register aliases even when overridden
	//尝试注册别名
	for (String alias : names) {
		this.registry.registerAlias(beanName, alias);
	}
	// Has this effectively been overridden before (e.g. via XML)?
	//校验BeanDefinition是否存在、是否允许覆盖
	if (isOverriddenByExistingDefinition(beanMethod, beanName)) {
		if (beanName.equals(beanMethod.getConfigurationClass().getBeanName())) {
			throw new BeanDefinitionStoreException(beanMethod.getConfigurationClass().getResource().getDescription(),
					beanName, "Bean name derived from @Bean method '" + beanMethod.getMetadata().getMethodName() +
					"' clashes with bean name for containing configuration class; please make those names unique!");
		}
		return;
	}
//得到一个ConfigurationClassBeanDefinition 
	ConfigurationClassBeanDefinition beanDef = new ConfigurationClassBeanDefinition(configClass, metadata);
	beanDef.setResource(configClass.getResource());
	beanDef.setSource(this.sourceExtractor.extractSource(metadata, configClass.getResource()));
//方法是否为静态方法
	if (metadata.isStatic()) {
		// static @Bean method
		if (configClass.getMetadata() instanceof StandardAnnotationMet编程adata) {
			beanDef.setBeanClass(((StandardAnnotationMetadata) configClass.getMetadata()).getIntrospectedClass());
		}
		else {
			beanDef.setBeanClassName(configClass.getMetadata().getClassName());
		}
		beanDef.setUniqueFactoryMethodName(methodName);
	}
	elsejavascript {
	//实例方法，非静态方法
		// instance @Bean method
		//设置FactoryBeanName，本文这里是
		//com.baomidou.mybatisplus.autoconfigure.MybatisPlusAutoConf编程客栈iguration
		beanDef.setFactoryBeanName(configClass.getBeanName());
		// 设置factoryMethodName 本文这里是sqlSessionFactory
		beanDef.setUniqueFactoryMethodName(methodName);
	}
//本文这里跳过 这里是SimpleMethodMetadata
	if (metadata instanceof StandardMethodMetadata) {
		beanDef.setResolvedFactoryMethod(((StandardMethodMetadata) metadata).getIntrospectedMethod());
	}
//设置注入标识  AUTOWIRE_CONSTRUCTOR=3
	beanDef.setAutowireMode(AbstractBeanDefinition.AUTOWIRE_CONSTRUCTOR);
	//设置SKIP_REQUIRED_CHECK_ATTRIBUTE属性
	beanDef.setAttribute(org.springframework.beans.factory.annotation.RequiredAnnotationBeanPostProcessor.
			SKIP_REQUIRED_CHECK_ATTRIBUTE, Boolean.TRUE);
//BeanDefinition的通用后置处理，如Lazy、Primary、DependsOn、Role以及Description
	AnnotationConfigUtils.processCommonDefinitionAnnotations(beanDef, metadata);
//解析注解上配置的autowire
	Autowire autowire = bean.getEnum("autowire");
	if (autowire.isAutowire()) {
		beanDef.setAutowireMode(autowire.value());
	}
//解析注解上配置的autowireCandidate
	boolean autowireCandidate = bean.getBoolean("autowireCandidate");
	if (!autowireCandidate) {
		beanDef.setAutowireCandidate(false);
	}
//解析注解上配置的initMethod
	String initMethodName = bean.getString("initMethod");
	if (StringUtils.hasText(initMethodName)) {
		beanDef.setInitMethodName(initMethodName);
	}
//解析注解上配置的destroyMethod
	String destroyMethodName = bean.getString("destroyMethod");
	beanDef.setDestroyMethodName(destroyMethodName);
	// Consider scoping
	ScopedProxyMode proxyMode = ScopedProxyMode.NO;
	//获取@Scope注解信息
	AnnotationAttributes attributes = AnnotationConfigUtils.attributesFor(metadata, Scope.class);
	if (attributes != null) {
		beanDef.setScope(attributes.getString("value"));
		proxyMode = attributes.getEnum("proxyMode");
		if (proxyMode == ScopedProxyMode.DEFAULT) {
			proxyMode = ScopedProxyMode.NO;
		}
	}
	// Replace the original bean definition with the target one, if necessary
	BeanDefinition beanDefToRegister = beanDef;
	if (proxyMode != ScopedProxyMode.NO) {
	//尝试创建代理
		BeanDefinitionHolder proxyDef = ScopedProxyCreator.createScopedProxy(
				new BeanDefinitionHolder(beanDef, beanName), this.registry,
				proxyMode == ScopedProxyMode.TARGET_CLASS);
		beanDefToRegister = new ConfigurationClassBeanDefinition(
				(RootBeanDefinition) proxyDef.getBeanDefinition(), configClass, metadata);
	}
	if (logger.isTraceEnabled()) {
		logger.trace(String.format("Registering bean definition for @Bean method %s.%s()",
				configClass.getMetadata().getClassName(), beanName));
	}
	//注册BeanDefinition，beanName默认是methodName sqlSessionFactory
	this.registry.registerBeanDefinition(beanName, beanDefToRegister);
}

方法流程如上所示，核心步骤都加了注释。这里要特别注意的是如下几点：

• 得到的BeanDefinition是ConfigurationClassBeanDefinition类型；
• 会为BeanDefinition设置factoryMethodName，这意味着当实例化这个bean的时候将采用工厂方法；
• 会区分方法是否为静态方法来设置BeanClass或者FactoryBeanName

这里得到的configClass

这里得到的MethodMetadata

最终得到的BeanDefinition属性

annotationMetadata = {SimpleAnnotationMetadata@5352} 
factoryMethodMetadata = {SimpleMethodMetadata@5635} 
decoratedDefinition = null
qualifiedElement = null
stale = false
allowCaching = true
isFactoryMethodUnique = true
targetType = null
resolvedTargetType = null
isFactoryBean = null
factoryMethodReturnType = null
factoryMethodToIntrospect = null
constructorArgumentLock = {Object@5823} 
resolvedConstructorOrFactoryMethod = null
constructorArgumentsResolved = false
resolvedConstructorArguments = null
preparedConstructorArguments = null
postProcessingLock = {Object@5824} 
postProcessed = false
beforeInstantiationResolved = null
externallyManagedConfigMembers = null
externallyManagedInitMethods = null
externallyManagedDestroyMethods = null
beanClass = null
scope = ""
abstractFlag = false
lazyInit = null
autowireMode = 3
dependencyCheck = 0
dependsOn = null
autowireCandidate = true
primary = false
qualifiers = {LinkedHashMap@5825}  size = 0
instanceSupplier = null
nonPublicAccessAllowed = true
lenientConstructorResolution = false
factoryBeanName = "com.baomidou.mybatisplus.autoconfigure.MybatisPlusAutoConfiguration"
factoryMethodName = "sqlSessionFactory"
constructorArgumentValues = null
propertyValues = null
methodOverrides = {MethodOverrides@5826} 
iniandroidtMethodName = null
destroyMethodName = "(inferred)"
enforceInitMethod = true
enforceDestroyMethod = true
synthetic = false
role = 0
description = null
resource = {ClassPathResource@5353} "class path resource [com/baomidou/mybatisplus/autoconfigure/MybatisPlusAutoConfiguration.class]"
source = {SimpleMethodMetadata@5635} 
attributes = {LinkedHashMap@5827}  size = 1

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