• Spring IoC源码：createBean（中）

    文章目录

    Spring源码系列：

    Spring IOC源码：简单易懂的Spring IOC 思路介绍
    Spring IOC源码：核心流程介绍
    Spring IOC源码：ApplicationContext刷新前准备工作
    Spring IOC源码：obtainFreshBeanFactory 详解（上）
    Spring IOC源码：obtainFreshBeanFactory 详解（中）
    Spring IOC源码：obtainFreshBeanFactory 详解（下）
    Spring IOC源码：＜context:component-scan＞源码详解
    Spring IOC源码：invokeBeanFactoryPostProcessors 后置处理器详解
    Spring IOC源码：registerBeanPostProcessors 详解
    Spring IOC源码：实例化前的准备工作
    Spring IOC源码：finishBeanFactoryInitialization详解
    Spring IoC源码：getBean 详解
    Spring IoC源码：createBean（ 上）
    Spring IoC源码：createBean（ 中）
    Spring IoC源码：createBean（ 下）
    Spring IoC源码：finishRefresh 完成刷新详解

    前言

    上篇文章讲解了Bean的实例化过程，包含构造器的选择、参数的创建等，本篇继续创建createBean的剩余流程，包括Bean实例化后的初始化属性注入工作，以及BeanPostProcessor的执行过程。

    正文

    上篇文章讲解了createBeanInstance(beanName, mbd, args)方法的流程，这节继续讲解后续内容。

    protected Object doCreateBean(final String beanName, final RootBeanDefinition mbd, final @Nullable Object[] args)
			throws BeanCreationException {

		// Instantiate the bean.
		BeanWrapper instanceWrapper = null;
		if (mbd.isSingleton()) {
		//如果是单例并且是FactoryBean则尝试移除
			instanceWrapper = this.factoryBeanInstanceCache.remove(beanName);
		}
		if (instanceWrapper == null) {
			//创建Bean实例，通过策略进行创建，如果选择有参构造或无参构造
			instanceWrapper = createBeanInstance(beanName, mbd, args);
		}
		//获取当前实例对象
		final Object bean = instanceWrapper.getWrappedInstance();
		//当前实例的Calss对象
		Class<?> beanType = instanceWrapper.getWrappedClass();
		if (beanType != NullBean.class) {
			//设置当前bean定义信息的目标类型
			mbd.resolvedTargetType = beanType;
		}

		// Allow post-processors to modify the merged bean definition.
		synchronized (mbd.postProcessingLock) {
			if (!mbd.postProcessed) {
				try {
					//执行MergedBeanDefinitionPostProcessor类型后置处理器的postProcessMergedBeanDefinition方法，
					//如@Autowire注解，就是通过该后置处理器进行解析
					applyMergedBeanDefinitionPostProcessors(mbd, beanType, beanName);
				}
				catch (Throwable ex) {
					throw new BeanCreationException(mbd.getResourceDescription(), beanName,
							"Post-processing of merged bean definition failed", ex);
				}
				mbd.postProcessed = true;
			}
		}

		// Eagerly cache singletons to be able to resolve circular references
		// even when triggered by lifecycle interfaces like BeanFactoryAware.
		//如果是单例，允许循环依赖，并且beanName正在创建中
		boolean earlySingletonExposure = (mbd.isSingleton() && this.allowCircularReferences &&
				isSingletonCurrentlyInCreation(beanName));
		if (earlySingletonExposure) {
			if (logger.isTraceEnabled()) {
				logger.trace("Eagerly caching bean '" + beanName +
						"' to allow for resolving potential circular references");
			}
			//包装成FactoryObject对象，并添加到三级缓存中
			addSingletonFactory(beanName, () -> getEarlyBeanReference(beanName, mbd, bean));
		}

		// Initialize the bean instance.
		Object exposedObject = bean;
		try {
			//初始化过程，进行属性注入。该过程递归创建其依赖的属性。如果A中有B，B中有C，则创建B跟C。
			populateBean(beanName, mbd, instanceWrapper);
			//该过程执行后置处理器的before方法，bean的init方法，后置处理器的after方法，可能会生成新的bean对象
			exposedObject = initializeBean(beanName, exposedObject, mbd);
		}
		catch (Throwable ex) {
			if (ex instanceof BeanCreationException && beanName.equals(((BeanCreationException) ex).getBeanName())) {
				throw (BeanCreationException) ex;
			}
			else {
				throw new BeanCreationException(
						mbd.getResourceDescription(), beanName, "Initialization of bean failed", ex);
			}
		}

		if (earlySingletonExposure) {
			//从缓存中获取，因为上面我们将其添加到三级缓存中，从三级缓存中获取会调用FactoryObject对象的getObject方法，可能会触发AOP代理。返回代理对象
			Object earlySingletonReference = getSingleton(beanName, false);
			if (earlySingletonReference != null) {
				//如果bean对象还是原来的，则将三级缓存中获取的对象赋值过去
				if (exposedObject == bean) {
					exposedObject = earlySingletonReference;
				}
				//如果exposedObject在initializeBean方法中被增强 && 不允许在循环引用的情况下使用注入原始bean实例
				else if (!this.allowRawInjectionDespiteWrapping && hasDependentBean(beanName)) {
					//	获取依赖当前beanName的所有bean名称
					String[] dependentBeans = getDependentBeans(beanName);
					Set<String> actualDependentBeans = new LinkedHashSet<>(dependentBeans.length);
					//尝试移除这些bean的实例，因为这些bean依赖的bean已经被增强了，他们依赖的bean相当于脏数据
					for (String dependentBean : dependentBeans) {
						if (!removeSingletonIfCreatedForTypeCheckOnly(dependentBean)) {
							actualDependentBeans.add(dependentBean);
						}
					}
					if (!actualDependentBeans.isEmpty()) {
						throw new BeanCurrentlyInCreationException(beanName,
								"Bean with name '" + beanName + "' has been injected into other beans [" +
								StringUtils.collectionToCommaDelimitedString(actualDependentBeans) +
								"] in its raw version as part of a circular reference, but has eventually been " +
								"wrapped. This means that said other beans do not use the final version of the " +
								"bean. This is often the result of over-eager type matching - consider using " +
								"'getBeanNamesOfType' with the 'allowEagerInit' flag turned off, for example.");
					}
				}
			}
		}

		// Register bean as disposable.
		try {
			//注册用于销毁的bean，执行销毁操作的有三种：自定义destroy方法、DisposableBean接口、DestructionAwareBeanPostProcessor
			registerDisposableBeanIfNecessary(beanName, bean, mbd);
		}
		catch (BeanDefinitionValidationException ex) {
			throw new BeanCreationException(
					mbd.getResourceDescription(), beanName, "Invalid destruction signature", ex);
		}

		return exposedObject;
	}

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    applyMergedBeanDefinitionPostProcessors(mbd, beanType, beanName)，见方法1详解

    addSingletonFactory(beanName, () -> getEarlyBeanReference(beanName, mbd, bean))，见方法2详解

    populateBean(beanName, mbd, instanceWrapper)，见方法3详解

    方法1：applyMergedBeanDefinitionPostProcessors

    	protected void applyMergedBeanDefinitionPostProcessors(RootBeanDefinition mbd, Class<?> beanType, String beanName) {
		for (BeanPostProcessor bp : getBeanPostProcessors()) {
			//执行类型为MergedBeanDefinitionPostProcessor的后置处理器，@Autowire注解就是在这块解析的
			if (bp instanceof MergedBeanDefinitionPostProcessor) {
				MergedBeanDefinitionPostProcessor bdp = (MergedBeanDefinitionPostProcessor) bp;
				bdp.postProcessMergedBeanDefinition(mbd, beanType, beanName);
			}
		}
	}

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    方法2：addSingletonFactory

    	protected void addSingletonFactory(String beanName, ObjectFactory<?> singletonFactory) {
		Assert.notNull(singletonFactory, "Singleton factory must not be null");
		synchronized (this.singletonObjects) {
			//如果一级缓存中不存在该对象
			if (!this.singletonObjects.containsKey(beanName)) {
				//往三级缓存中存入类型为ObjectFactory的工厂对象
				this.singletonFactories.put(beanName, singletonFactory);
				//移除二级缓存
				this.earlySingletonObjects.remove(beanName);
				//将beanName添加到注册缓存中
				this.registeredSingletons.add(beanName);
			}
		}
	}

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    三级缓存中我们存入的是工厂对象，我们知道工厂对象要获取实例是通过getObject()方法返回实例的，这里传进来是一个匿名内部类，其getObject()方法实现如代码块所示：

    	protected Object getEarlyBeanReference(String beanName, RootBeanDefinition mbd, Object bean) {
		Object exposedObject = bean;
		//判断是否有InstantiationAwareBeanPostProcessors类型的后置处理器
		if (!mbd.isSynthetic() && hasInstantiationAwareBeanPostProcessors()) {
			for (BeanPostProcessor bp : getBeanPostProcessors()) {
				//执行类型为SmartInstantiationAwareBeanPostProcessor的后置处理器
				if (bp instanceof SmartInstantiationAwareBeanPostProcessor) {
					SmartInstantiationAwareBeanPostProcessor ibp = (SmartInstantiationAwareBeanPostProcessor) bp;
					//返回实例
					exposedObject = ibp.getEarlyBeanReference(exposedObject, beanName);
				}
			}
		}
		return exposedObject;
	}

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    我们在创建完对象是往三级缓存中存入工厂对象的，以上执行后置处理器的过程返回的对象可能是代理后的对象，这样当我有被其它Bean所引用时，会执行getSingleton()方法,从三级缓存中获取对象并将其添加到二级缓存中，移除三级缓存，这样就能保证被注入的Bean是一个代理后的对象，这是解决循环依赖重要的步骤。

    方法3：populateBean

    protected void populateBean(String beanName, RootBeanDefinition mbd, @Nullable BeanWrapper bw) {
		//如果是创建的为空，则判断是否有属性需要注入，有则抛异常
		if (bw == null) {
			if (mbd.hasPropertyValues()) {
				throw new BeanCreationException(
						mbd.getResourceDescription(), beanName, "Cannot apply property values to null instance");
			}
			else {
				// Skip property population phase for null instance.
				return;
			}
		}

		// Give any InstantiationAwareBeanPostProcessors the opportunity to modify the
		// state of the bean before properties are set. This can be used, for example,
		// to support styles of field injection.
		//标识是否继续属性填充标识
		boolean continueWithPropertyPopulation = true;
		//如果不是合成的&&有注册InstantiationAwareBeanPostProcessors
		if (!mbd.isSynthetic() && hasInstantiationAwareBeanPostProcessors()) {
			//遍历执行InstantiationAwareBeanPostProcessors的postProcessAfterInstantiation方法
			for (BeanPostProcessor bp : getBeanPostProcessors()) {
				if (bp instanceof InstantiationAwareBeanPostProcessor) {
					InstantiationAwareBeanPostProcessor ibp = (InstantiationAwareBeanPostProcessor) bp;
					if (!ibp.postProcessAfterInstantiation(bw.getWrappedInstance(), beanName)) {
						continueWithPropertyPopulation = false;
						break;
					}
				}
			}
		}
		//如果经过后置处理器处理后，则跳过后续的步骤
		if (!continueWithPropertyPopulation) {
			return;
		}
		//获取bean定义信息中的属性值，如
		PropertyValues pvs = (mbd.hasPropertyValues() ? mbd.getPropertyValues() : null);
		//获取autowire属性值
		int resolvedAutowireMode = mbd.getResolvedAutowireMode();
		//如果是按name注入或按type注入
		if (resolvedAutowireMode == AUTOWIRE_BY_NAME || resolvedAutowireMode == AUTOWIRE_BY_TYPE) {
			//将户配置的属性值封装成MutablePropertyValues 
			MutablePropertyValues newPvs = new MutablePropertyValues(pvs);
			// Add property values based on autowire by name if applicable.
			//按名称进行注入
			if (resolvedAutowireMode == AUTOWIRE_BY_NAME) {
				autowireByName(beanName, mbd, bw, newPvs);
			}
			// Add property values based on autowire by type if applicable.
			//按类型进行注入
			if (resolvedAutowireMode == AUTOWIRE_BY_TYPE) {
				autowireByType(beanName, mbd, bw, newPvs);
			}
			pvs = newPvs;
		}
		//判断是否有注册InstantiationAwareBeanPostProcessors
		boolean hasInstAwareBpps = hasInstantiationAwareBeanPostProcessors();
		//判断是否有依赖项
		boolean needsDepCheck = (mbd.getDependencyCheck() != AbstractBeanDefinition.DEPENDENCY_CHECK_NONE);

		PropertyDescriptor[] filteredPds = null;
		if (hasInstAwareBpps) {
			if (pvs == null) {
				pvs = mbd.getPropertyValues();
			}
			for (BeanPostProcessor bp : getBeanPostProcessors()) {
				if (bp instanceof InstantiationAwareBeanPostProcessor) {
					//调用InstantiationAwareBeanPostProcessor 的postProcessProperties方法
					InstantiationAwareBeanPostProcessor ibp = (InstantiationAwareBeanPostProcessor) bp;
					//通过后置处理器后，返回处理后的属性配置信息，如@Autowire注解，会在这步骤进行解析
					PropertyValues pvsToUse = ibp.postProcessProperties(pvs, bw.getWrappedInstance(), beanName);
					if (pvsToUse == null) {
						if (filteredPds == null) {
							//过滤出所有需要进行依赖检查的属性编辑器
							filteredPds = filterPropertyDescriptorsForDependencyCheck(bw, mbd.allowCaching);
						}
						pvsToUse = ibp.postProcessPropertyValues(pvs, filteredPds, bw.getWrappedInstance(), beanName);
						if (pvsToUse == null) {
							return;
						}
					}
					pvs = pvsToUse;
				}
			}
		}
		if (needsDepCheck) {
			if (filteredPds == null) {
				//	//过滤出所有需要进行依赖检查的属性编辑器
				filteredPds = filterPropertyDescriptorsForDependencyCheck(bw, mbd.allowCaching);
			}
			//依赖校验
			checkDependencies(beanName, mbd, filteredPds, pvs);
		}
		//属性值填充
		if (pvs != null) {
			applyPropertyValues(beanName, mbd, bw, pvs);
		}
	}

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    autowireByName(beanName, mbd, bw, newPvs)，见方法4详解
    autowireByType(beanName, mbd, bw, newPvs)，见方法7详解
    applyPropertyValues(beanName, mbd, bw, pvs)，见方法8详解
    applyPropertyValues(beanName, mbd, bw, pvs)，见方法16详解

    方法4：autowireByName

    protected void autowireByName(
			String beanName, AbstractBeanDefinition mbd, BeanWrapper bw, MutablePropertyValues pvs) {
		/过滤掉某些属性类型，返回需要注入的属性名称集
		String[] propertyNames = unsatisfiedNonSimpleProperties(mbd, bw);
		//遍历注入
		for (String propertyName : propertyNames) {
			//判断容器中是否存在该属性名称对应的bean
			if (containsBean(propertyName)) {
				//获取实例化Bean
				Object bean = getBean(propertyName);
				//添加到需要注入的属性值
				pvs.add(propertyName, bean);
				//注册依赖关系
				registerDependentBean(propertyName, beanName);
				if (logger.isTraceEnabled()) {
					logger.trace("Added autowiring by name from bean name '" + beanName +
							"' via property '" + propertyName + "' to bean named '" + propertyName + "'");
				}
			}
			else {
				if (logger.isTraceEnabled()) {
					logger.trace("Not autowiring property '" + propertyName + "' of bean '" + beanName +
							"' by name: no matching bean found");
				}
			}
		}
	}

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    unsatisfiedNonSimpleProperties(mbd, bw)，见方法5详解
    containsBean(propertyName)，见方法6详解

    方法5：unsatisfiedNonSimpleProperties

    protected String[] unsatisfiedNonSimpleProperties(AbstractBeanDefinition mbd, BeanWrapper bw) {
		Set<String> result = new TreeSet<>();
		//获取当前需要注入的参数值集
		PropertyValues pvs = mbd.getPropertyValues();
		//获取 bean的属性描述信息
		PropertyDescriptor[] pds = bw.getPropertyDescriptors();
		for (PropertyDescriptor pd : pds) {
			//如果有set方法&&不是排除的依赖&&不存在已解析的集合中&&不是简单的属性，如Number、DATE、基本数据类型等
			if (pd.getWriteMethod() != null && !isExcludedFromDependencyCheck(pd) && !pvs.contains(pd.getName()) &&
					!BeanUtils.isSimpleProperty(pd.getPropertyType())) {
				result.add(pd.getName());
			}
		}
		return StringUtils.toStringArray(result);
	}

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    方法6：containsBean

    	public boolean containsBean(String name) {
		//根据别名获取真正的beanName
		String beanName = transformedBeanName(name);
		//判断三级缓存中是否存在或Bean定义缓存中是否存在该定义
		if (containsSingleton(beanName) || containsBeanDefinition(beanName)) {
			//name不带&符号，并且判断是否是工厂Bean
			return (!BeanFactoryUtils.isFactoryDereference(name) || isFactoryBean(name));
		}
		// Not found -> check parent.
		//查询不到获取父类工厂，并在父工厂中进行查找
		BeanFactory parentBeanFactory = getParentBeanFactory();
		return (parentBeanFactory != null && parentBeanFactory.containsBean(originalBeanName(name)));
	}

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    方法7：autowireByType

    protected void autowireByType(
			String beanName, AbstractBeanDefinition mbd, BeanWrapper bw, MutablePropertyValues pvs) {
		//获取类型转换器
		TypeConverter converter = getCustomTypeConverter();
		if (converter == null) {
			converter = bw;
		}

		Set<String> autowiredBeanNames = new LinkedHashSet<>(4);
		//过滤掉一些特定的属性类型，返回需要注入的集合
		String[] propertyNames = unsatisfiedNonSimpleProperties(mbd, bw);
		for (String propertyName : propertyNames) {
			try {
				//获取属性描述信息
				PropertyDescriptor pd = bw.getPropertyDescriptor(propertyName);
				// Don't try autowiring by type for type Object: never makes sense,
				// even if it technically is a unsatisfied, non-simple property.
				//如果不是Object类型则不处理
				if (Object.class != pd.getPropertyType()) {
					//获取该属性的set方法参数信息
					MethodParameter methodParam = BeanUtils.getWriteMethodParameter(pd);
					// Do not allow eager init for type matching in case of a prioritized post-processor.
					boolean eager = !PriorityOrdered.class.isInstance(bw.getWrappedInstance());
					//将set方法信息封装成DependencyDescriptor 对象
					DependencyDescriptor desc = new AutowireByTypeDependencyDescriptor(methodParam, eager);
					//解析当前属性所匹配的bean实例，并把解析到的bean实例的beanName存储在autowiredBeanNames中
					Object autowiredArgument = resolveDependency(desc, beanName, autowiredBeanNames, converter);
					if (autowiredArgument != null) {
						//添加到需要注入的属性值集合中
						pvs.add(propertyName, autowiredArgument);
					}
					for (String autowiredBeanName : autowiredBeanNames) {
						//注册依赖关系
						registerDependentBean(autowiredBeanName, beanName);
						if (logger.isTraceEnabled()) {
							logger.trace("Autowiring by type from bean name '" + beanName + "' via property '" +
									propertyName + "' to bean named '" + autowiredBeanName + "'");
						}
					}
					autowiredBeanNames.clear();
				}
			}
			catch (BeansException ex) {
				throw new UnsatisfiedDependencyException(mbd.getResourceDescription(), beanName, propertyName, ex);
			}
		}
	}

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    resolveDependency(desc, beanName, autowiredBeanNames, converter)，见方法8详解

    方法8：resolveDependency

    	public Object resolveDependency(DependencyDescriptor descriptor, @Nullable String requestingBeanName,
			@Nullable Set<String> autowiredBeanNames, @Nullable TypeConverter typeConverter) throws BeansException {
		//初始化参数名称查询器
		descriptor.initParameterNameDiscovery(getParameterNameDiscoverer());
		//判断依赖类型是否为Optional
		if (Optional.class == descriptor.getDependencyType()) {
			return createOptionalDependency(descriptor, requestingBeanName);
		}
		//判断依赖类型是否为ObjectFactory
		else if (ObjectFactory.class == descriptor.getDependencyType() ||
				ObjectProvider.class == descriptor.getDependencyType()) {
			return new DependencyObjectProvider(descriptor, requestingBeanName);
		}
		//判断依赖类型是否为javaxInjectProviderClass 
		else if (javaxInjectProviderClass == descriptor.getDependencyType()) {
			return new Jsr330Factory().createDependencyProvider(descriptor, requestingBeanName);
		}
		else {
		//获取懒加载代理对象
			Object result = getAutowireCandidateResolver().getLazyResolutionProxyIfNecessary(
					descriptor, requestingBeanName);
			if (result == null) {
				//解析所需依赖对象
				result = doResolveDependency(descriptor, requestingBeanName, autowiredBeanNames, typeConverter);
			}
			return result;
		}
	}

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    doResolveDependency(descriptor, requestingBeanName, autowiredBeanNames, typeConverter)，见方法9详解

    方法9：doResolveDependency

    public Object doResolveDependency(DependencyDescriptor descriptor, @Nullable String beanName,
			@Nullable Set<String> autowiredBeanNames, @Nullable TypeConverter typeConverter) throws BeansException {

		InjectionPoint previousInjectionPoint = ConstructorResolver.setCurrentInjectionPoint(descriptor);
		try {
		//获取shortcut 对象
			Object shortcut = descriptor.resolveShortcut(this);
			if (shortcut != null) {
				return shortcut;
			}
			//获取依赖类型
			Class<?> type = descriptor.getDependencyType();
			//获取指定值，如@qualifier就是在这里解析的
			Object value = getAutowireCandidateResolver().getSuggestedValue(descriptor);
			if (value != null) {
				//如果是字符串类型，则进行解析计算
				if (value instanceof String) {
					String strVal = resolveEmbeddedValue((String) value);
					BeanDefinition bd = (beanName != null && containsBean(beanName) ?
							getMergedBeanDefinition(beanName) : null);
					value = evaluateBeanDefinitionString(strVal, bd);
				}
				TypeConverter converter = (typeConverter != null ? typeConverter : getTypeConverter());
				try {
					//对值进行转换
					return converter.convertIfNecessary(value, type, descriptor.getTypeDescriptor());
				}
				catch (UnsupportedOperationException ex) {
					// A custom TypeConverter which does not support TypeDescriptor resolution...
					return (descriptor.getField() != null ?
							converter.convertIfNecessary(value, type, descriptor.getField()) :
							converter.convertIfNecessary(value, type, descriptor.getMethodParameter()));
				}
			}
			//处理类型为多个的情况，如Array、Collection、MAP
			Object multipleBeans = resolveMultipleBeans(descriptor, beanName, autowiredBeanNames, typeConverter);
			if (multipleBeans != null) {
				return multipleBeans;
			}
			//从beanFactory中解析候选类，即允许被注入的bean
			Map<String, Object> matchingBeans = findAutowireCandidates(beanName, type, descriptor);
			//查询不到时，判断是否有required标识，有则抛异常
			if (matchingBeans.isEmpty()) {
				if (isRequired(descriptor)) {
					raiseNoMatchingBeanFound(type, descriptor.getResolvableType(), descriptor);
				}
				return null;
			}

			String autowiredBeanName;
			Object instanceCandidate;
			//如果按类型查找出多个bean
			if (matchingBeans.size() > 1) {
				//判断是否有primary标志，并返回符合条件的beanName
				autowiredBeanName = determineAutowireCandidate(matchingBeans, descriptor);
				if (autowiredBeanName == null) {
					//有require标识，或者不是Collection等容器类型，则抛异常
					if (isRequired(descriptor) || !indicatesMultipleBeans(type)) {
						return descriptor.resolveNotUnique(descriptor.getResolvableType(), matchingBeans);
					}
					else {
						// In case of an optional Collection/Map, silently ignore a non-unique case:
						// possibly it was meant to be an empty collection of multiple regular beans
						// (before 4.3 in particular when we didn't even look for collection beans).
						return null;
					}
				}
				//获取符合条件的实例
				instanceCandidate = matchingBeans.get(autowiredBeanName);
			}
			else {
				// We have exactly one match.
				//只有一个的情况下则直接获取第一个值
				Map.Entry<String, Object> entry = matchingBeans.entrySet().iterator().next();
				autowiredBeanName = entry.getKey();
				instanceCandidate = entry.getValue();
			}
			//添加autowiredBeanName到autowiredBeanNames中
			if (autowiredBeanNames != null) {
				autowiredBeanNames.add(autowiredBeanName);
			}
			//如果类型为Class，则进行实例化
			if (instanceCandidate instanceof Class) {
				instanceCandidate = descriptor.resolveCandidate(autowiredBeanName, type, this);
			}
			Object result = instanceCandidate;
			//为空则抛异常
			if (result instanceof NullBean) {
				if (isRequired(descriptor)) {
					raiseNoMatchingBeanFound(type, descriptor.getResolvableType(), descriptor);
				}
				result = null;
			}
			//类型不一致抛异常
			if (!ClassUtils.isAssignableValue(type, result)) {
				throw new BeanNotOfRequiredTypeException(autowiredBeanName, type, instanceCandidate.getClass());
			}
			return result;
		}
		finally {
			ConstructorResolver.setCurrentInjectionPoint(previousInjectionPoint);
		}
	}


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    findAutowireCandidates(beanName, type, descriptor)，见方法10详解
    determineAutowireCandidate(matchingBeans, descriptor)，见方法13详解

    方法10：findAutowireCandidates

    protected Map<String, Object> findAutowireCandidates(
			@Nullable String beanName, Class<?> requiredType, DependencyDescriptor descriptor) {
		//从beanFactory工厂中通过类型获取对应的beanName
		String[] candidateNames = BeanFactoryUtils.beanNamesForTypeIncludingAncestors(
				this, requiredType, true, descriptor.isEager());
		Map<String, Object> result = new LinkedHashMap<>(candidateNames.length);
		//遍历依赖缓存
		for (Map.Entry<Class<?>, Object> classObjectEntry : this.resolvableDependencies.entrySet()) {
			//获取key值
			Class<?> autowiringType = classObjectEntry.getKey();
			//判断类型是否所需类型
			if (autowiringType.isAssignableFrom(requiredType)) {
				//获取依赖value
				Object autowiringValue = classObjectEntry.getValue();
				//判断需要的类型跟当前获取的值autowiringValue 不是同个类型
				//并且如果autowiringValue是工厂对象的话，则调用getObject方法获取
				autowiringValue = AutowireUtils.resolveAutowiringValue(autowiringValue, requiredType);
				//如果两个类型一致，则生成一个新的beanName，并放入map中
				if (requiredType.isInstance(autowiringValue)) {
					result.put(ObjectUtils.identityToString(autowiringValue), autowiringValue);
					break;
				}
			}
		}
		//遍历候选类集合
		for (String candidate : candidateNames) {
			//依赖所需对象不能是当前bean本身，如B中有属性B这种情况&&判断允许被其它bean注入
			if (!isSelfReference(beanName, candidate) && isAutowireCandidate(candidate, descriptor)) {
				addCandidateEntry(result, candidate, descriptor, requiredType);
			}
		}
		//如果前面获取不到合适的类型
		if (result.isEmpty()) {
			//判断是否是容器类型，如Collection
			boolean multiple = indicatesMultipleBeans(requiredType);
			// Consider fallback matches if the first pass failed to find anything...
			DependencyDescriptor fallbackDescriptor = descriptor.forFallbackMatch();
			//使用备用的依赖描述器再去获取一遍符合注入属性类型的beanName
			for (String candidate : candidateNames) {
				if (!isSelfReference(beanName, candidate) && isAutowireCandidate(candidate, fallbackDescriptor) &&
						(!multiple || getAutowireCandidateResolver().hasQualifier(descriptor))) {
					addCandidateEntry(result, candidate, descriptor, requiredType);
				}
			}
			//还是没有符合注入属性类型的beanName，又不是集合类型，考虑自引用，符合条件则将候选者添加到result中
			if (result.isEmpty() && !multiple) {
				// Consider self references as a final pass...
				// but in the case of a dependency collection, not the very same bean itself.
				for (String candidate : candidateNames) {
					if (isSelfReference(beanName, candidate) &&
							(!(descriptor instanceof MultiElementDescriptor) || !beanName.equals(candidate)) &&
							isAutowireCandidate(candidate, fallbackDescriptor)) {
						addCandidateEntry(result, candidate, descriptor, requiredType);
					}
				}
			}
		}
		return result;
	}

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    addCandidateEntry(result, candidate, descriptor, requiredType)，见方法11详解

    方法11：addCandidateEntry

    private void addCandidateEntry(Map<String, Object> candidates, String candidateName,
			DependencyDescriptor descriptor, Class<?> requiredType) {
		//如果是一个MultiElementDescriptor类型的
		if (descriptor instanceof MultiElementDescriptor) {
			//实例化
			Object beanInstance = descriptor.resolveCandidate(candidateName, requiredType, this);
			if (!(beanInstance instanceof NullBean)) {
				candidates.put(candidateName, beanInstance);
			}
		}
		else if (containsSingleton(candidateName) || (descriptor instanceof StreamDependencyDescriptor &&
				((StreamDependencyDescriptor) descriptor).isOrdered())) {
			//实例化
			Object beanInstance = descriptor.resolveCandidate(candidateName, requiredType, this);
			//加入缓存中
			candidates.put(candidateName, (beanInstance instanceof NullBean ? null : beanInstance));
		}
		else {
			//将candidateName跟candidateName的class对象存入缓存中
			candidates.put(candidateName, getType(candidateName));
		}
	}

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    getType(candidateName)，见方法12详解

    方法12：getType

    public Class<?> getType(String name, boolean allowFactoryBeanInit) throws NoSuchBeanDefinitionException {
		String beanName = transformedBeanName(name);

		// Check manually registered singletons.
		//从一级缓存中获取对象
		Object beanInstance = getSingleton(beanName, false);
		if (beanInstance != null && beanInstance.getClass() != NullBean.class) {
			//如果是FactoryBean ,则调用其getObjectType返回真正的实例class
			if (beanInstance instanceof FactoryBean && !BeanFactoryUtils.isFactoryDereference(name)) {
				return getTypeForFactoryBean((FactoryBean<?>) beanInstance);
			}
			else {
				//返回class对象
				return beanInstance.getClass();
			}
		}

		// No singleton instance found -> check bean definition.
		//前面如果查询不到，则获取父工厂进行查询
		BeanFactory parentBeanFactory = getParentBeanFactory();
		if (parentBeanFactory != null && !containsBeanDefinition(beanName)) {
			// No bean definition found in this factory -> delegate to parent.
			return parentBeanFactory.getType(originalBeanName(name));
		}
		//获取合并的Bean定义信息
		RootBeanDefinition mbd = getMergedLocalBeanDefinition(beanName);

		// Check decorated bean definition, if any: We assume it'll be easier
		// to determine the decorated bean's type than the proxy's type.
		//获取目标代理对象
		BeanDefinitionHolder dbd = mbd.getDecoratedDefinition();
		//判断name是否带有&前缀，如果不是工厂对象
		if (dbd != null && !BeanFactoryUtils.isFactoryDereference(name)) {
			RootBeanDefinition tbd = getMergedBeanDefinition(dbd.getBeanName(), dbd.getBeanDefinition(), mbd);
			//获取beanName对应的class对象
			Class<?> targetClass = predictBeanType(dbd.getBeanName(), tbd);
			if (targetClass != null && !FactoryBean.class.isAssignableFrom(targetClass)) {
				return targetClass;
			}
		}
		//获取beanName对应的class对象
		Class<?> beanClass = predictBeanType(beanName, mbd);

		// Check bean class whether we're dealing with a FactoryBean.
		//如果不为空&&类型为FactoryBean
		if (beanClass != null && FactoryBean.class.isAssignableFrom(beanClass)) {
			//name不带&符号，即不是获取工厂对象本身
			if (!BeanFactoryUtils.isFactoryDereference(name)) {
				// If it's a FactoryBean, we want to look at what it creates, not at the factory class.
				//返回实际的对象class
				return getTypeForFactoryBean(beanName, mbd, allowFactoryBeanInit).resolve();
			}
			else {
				return beanClass;
			}
		}
		else {
			return (!BeanFactoryUtils.isFactoryDereference(name) ? beanClass : null);
		}
	}

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    方法13：determineAutowireCandidate

    	protected String determineAutowireCandidate(Map<String, Object> candidates, DependencyDescriptor descriptor) {
		//获取需要注入依赖的类型
		Class<?> requiredType = descriptor.getDependencyType();
		//解析，筛选带有primary属性的beanName
		String primaryCandidate = determinePrimaryCandidate(candidates, requiredType);
		if (primaryCandidate != null) {
			return primaryCandidate;
		}
		//如果被注入类有实现OrderComparator接口，则进行比较筛选出Priority，值越低优先级越高
		String priorityCandidate = determineHighestPriorityCandidate(candidates, requiredType);
		if (priorityCandidate != null) {
			return priorityCandidate;
		}
		// Fallback
		//遍历候选bean
		for (Map.Entry<String, Object> entry : candidates.entrySet()) {
			String candidateName = entry.getKey();
			Object beanInstance = entry.getValue();
			//如果实例不为空&&依赖集合中包含该值  或  名称是否跟需要注入的依赖类型名称一致
			if ((beanInstance != null && this.resolvableDependencies.containsValue(beanInstance)) ||
					matchesBeanName(candidateName, descriptor.getDependencyName())) {
				return candidateName;
			}
		}
		return null;
	}

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    determinePrimaryCandidate(candidates, requiredType)，见方法14详解

    determineHighestPriorityCandidate(candidates, requiredType)，见方法15详解

    方法14：determinePrimaryCandidate

    protected String determinePrimaryCandidate(Map<String, Object> candidates, Class<?> requiredType) {
		String primaryBeanName = null;
		for (Map.Entry<String, Object> entry : candidates.entrySet()) {
			String candidateBeanName = entry.getKey();
			Object beanInstance = entry.getValue();
			//判断是否有Primary标识
			if (isPrimary(candidateBeanName, beanInstance)) {
				if (primaryBeanName != null) {
					boolean candidateLocal = containsBeanDefinition(candidateBeanName);
					boolean primaryLocal = containsBeanDefinition(primaryBeanName);
					//如果存在两个依赖都有其Primary，则抛异常
					if (candidateLocal && primaryLocal) {
						throw new NoUniqueBeanDefinitionException(requiredType, candidates.size(),
								"more than one 'primary' bean found among candidates: " + candidates.keySet());
					}
					else if (candidateLocal) {
						//赋值
						primaryBeanName = candidateBeanName;
					}
				}
				else {
					//赋值
					primaryBeanName = candidateBeanName;
				}
			}
		}
		return primaryBeanName;
	}

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    方法15：determineHighestPriorityCandidate

    protected String determineHighestPriorityCandidate(Map<String, Object> candidates, Class<?> requiredType) {
		//最高优先级的beanName
		String highestPriorityBeanName = null;
		//最高优先级值
		Integer highestPriority = null;
		//遍历
		for (Map.Entry<String, Object> entry : candidates.entrySet()) {
			String candidateBeanName = entry.getKey();
			Object beanInstance = entry.getValue();
			if (beanInstance != null) {
				//获取优先级
				Integer candidatePriority = getPriority(beanInstance);
				if (candidatePriority != null) {
					if (highestPriorityBeanName != null) {
						//存在两个优先级一样则抛异常
						if (candidatePriority.equals(highestPriority)) {
							throw new NoUniqueBeanDefinitionException(requiredType, candidates.size(),
									"Multiple beans found with the same priority ('" + highestPriority +
									"') among candidates: " + candidates.keySet());
						}
						//比较，candidatePriority 值越低则优先级越高
						else if (candidatePriority < highestPriority) {
							highestPriorityBeanName = candidateBeanName;
							highestPriority = candidatePriority;
						}
					}
					else {
						//第一次则直接赋值
						highestPriorityBeanName = candidateBeanName;
						highestPriority = candidatePriority;
					}
				}
			}
		}
		return highestPriorityBeanName;
	}

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    方法16：applyPropertyValues

    protected void applyPropertyValues(String beanName, BeanDefinition mbd, BeanWrapper bw, PropertyValues pvs) {、
		//判断注入参数是否为空
		if (pvs.isEmpty()) {
			return;
		}

		if (System.getSecurityManager() != null && bw instanceof BeanWrapperImpl) {
			((BeanWrapperImpl) bw).setSecurityContext(getAccessControlContext());
		}

		MutablePropertyValues mpvs = null;
		//存在原始参数值
		List<PropertyValue> original;
		//如果参数MutablePropertyValues类型
		if (pvs instanceof MutablePropertyValues) {
			mpvs = (MutablePropertyValues) pvs;
			//如果已经转换过，则直接设置值
			if (mpvs.isConverted()) {
				// Shortcut: use the pre-converted values as-is.
				try {
					bw.setPropertyValues(mpvs);
					return;
				}
				catch (BeansException ex) {
					throw new BeanCreationException(
							mbd.getResourceDescription(), beanName, "Error setting property values", ex);
				}
			}
			original = mpvs.getPropertyValueList();
		}
		else {
			original = Arrays.asList(pvs.getPropertyValues());
		}
		//获取类型转换器
		TypeConverter converter = getCustomTypeConverter();
		if (converter == null) {
			converter = bw;
		}
		//创建解析器
		BeanDefinitionValueResolver valueResolver = new BeanDefinitionValueResolver(this, beanName, mbd, converter);

		// Create a deep copy, resolving any references for values.
		//存放拷贝参数值，即通知转换后的值
		List<PropertyValue> deepCopy = new ArrayList<>(original.size());
		boolean resolveNecessary = false;
		for (PropertyValue pv : original) {
			//如果已经转换过，则加入到深拷贝集合中
			if (pv.isConverted()) {
				deepCopy.add(pv);
			}
			else {
				//获取参数名称
				String propertyName = pv.getName();
				//获取参数值
				Object originalValue = pv.getValue();
				//判断值是否是AutowiredPropertyMarker类型
				if (originalValue == AutowiredPropertyMarker.INSTANCE) {
					//获取set方法
					Method writeMethod = bw.getPropertyDescriptor(propertyName).getWriteMethod();
					if (writeMethod == null) {
						throw new IllegalArgumentException("Autowire marker for property without write method: " + pv);
					}
					//将参数值封装成DependencyDescriptor
					originalValue = new DependencyDescriptor(new MethodParameter(writeMethod, 0), true);
				}
				//对值进行解析转换，如果类型是beanFactory工厂中的beanDefinition封装的信息时，则会进行实例化
				Object resolvedValue = valueResolver.resolveValueIfNecessary(pv, originalValue);
				//转换后的值
				Object convertedValue = resolvedValue;
				//判断是否有写权限&&没有嵌套属性，如不包含“.”或者“[”符号
				boolean convertible = bw.isWritableProperty(propertyName) &&
						!PropertyAccessorUtils.isNestedOrIndexedProperty(propertyName);
				if (convertible) {
					//类型转换
					convertedValue = convertForProperty(resolvedValue, propertyName, bw, converter);
				}
				// Possibly store converted value in merged bean definition,
				// in order to avoid re-conversion for every created bean instance.
				//如果解析值跟转换后的值一直
				if (resolvedValue == originalValue) {
					//转换标志
					if (convertible) {
						//设置转换后的值
						pv.setConvertedValue(convertedValue);
					}
					//加入解析后的集合中
					deepCopy.add(pv);
				}
				else if (convertible && originalValue instanceof TypedStringValue &&
						!((TypedStringValue) originalValue).isDynamic() &&
						!(convertedValue instanceof Collection || ObjectUtils.isArray(convertedValue))) {
					pv.setConvertedValue(convertedValue);
					deepCopy.add(pv);
				}
				else {
					resolveNecessary = true;
					deepCopy.add(new PropertyValue(pv, convertedValue));
				}
			}
		}
		if (mpvs != null && !resolveNecessary) {
			mpvs.setConverted();
		}

		// Set our (possibly massaged) deep copy.
		try {
			//属性值注入
			bw.setPropertyValues(new MutablePropertyValues(deepCopy));
		}
		catch (BeansException ex) {
			throw new BeanCreationException(
					mbd.getResourceDescription(), beanName, "Error setting property values", ex);
		}
	}

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    valueResolver.resolveValueIfNecessary(pv, originalValue)，见方法17详解

    方法17：resolveValueIfNecessary

    public Object resolveValueIfNecessary(Object argName, @Nullable Object value) {
		// We must check each value to see whether it requires a runtime reference
		// to another bean to be resolved.
		if (value instanceof RuntimeBeanReference) {
			//如果参数值为RuntimeBeanReference类型，则调用getBean方法获取创建实例
			RuntimeBeanReference ref = (RuntimeBeanReference) value;
			return resolveReference(argName, ref);
		}
		else if (value instanceof RuntimeBeanNameReference) {
			//获取依赖的beanName
			String refName = ((RuntimeBeanNameReference) value).getBeanName();
			refName = String.valueOf(doEvaluate(refName));
			if (!this.beanFactory.containsBean(refName)) {
				throw new BeanDefinitionStoreException(
						"Invalid bean name '" + refName + "' in bean reference for " + argName);
			}
			return refName;
		}
		else if (value instanceof BeanDefinitionHolder) {
			// Resolve BeanDefinitionHolder: contains BeanDefinition with name and aliases.
			//解析BeanDefinitionHolder:包含带有名称和别名的BeanDefinition。
			BeanDefinitionHolder bdHolder = (BeanDefinitionHolder) value;
			return resolveInnerBean(argName, bdHolder.getBeanName(), bdHolder.getBeanDefinition());
		}
		else if (value instanceof BeanDefinition) {
			// Resolve plain BeanDefinition, without contained name: use dummy name.
			//解析普通的BeanDefinition，不包含名称:使用虚拟名称
			BeanDefinition bd = (BeanDefinition) value;
			String innerBeanName = "(inner bean)" + BeanFactoryUtils.GENERATED_BEAN_NAME_SEPARATOR +
					ObjectUtils.getIdentityHexString(bd);
			return resolveInnerBean(argName, innerBeanName, bd);
		}
		else if (value instanceof DependencyDescriptor) {
			Set<String> autowiredBeanNames = new LinkedHashSet<>(4);
			//创建实例，并解析出候选的bean信息
			Object result = this.beanFactory.resolveDependency(
					(DependencyDescriptor) value, this.beanName, autowiredBeanNames, this.typeConverter);
			//实例化，并注册依赖关系
			for (String autowiredBeanName : autowiredBeanNames) {
				if (this.beanFactory.containsBean(autowiredBeanName)) {
					this.beanFactory.registerDependentBean(autowiredBeanName, this.beanName);
				}
			}
			return result;
		}
		else if (value instanceof ManagedArray) {
			// May need to resolve contained runtime references.
			ManagedArray array = (ManagedArray) value;
			Class<?> elementType = array.resolvedElementType;
			if (elementType == null) {
				String elementTypeName = array.getElementTypeName();
				if (StringUtils.hasText(elementTypeName)) {
					try {
						elementType = ClassUtils.forName(elementTypeName, this.beanFactory.getBeanClassLoader());
						array.resolvedElementType = elementType;
					}
					catch (Throwable ex) {
						// Improve the message by showing the context.
						throw new BeanCreationException(
								this.beanDefinition.getResourceDescription(), this.beanName,
								"Error resolving array type for " + argName, ex);
					}
				}
				else {
					elementType = Object.class;
				}
			}
			return resolveManagedArray(argName, (List<?>) value, elementType);
		}

		else if (value instanceof ManagedList) {
			// May need to resolve contained runtime references.
			return resolveManagedList(argName, (List<?>) value);
		}
		else if (value instanceof ManagedSet) {
			// May need to resolve contained runtime references.
			return resolveManagedSet(argName, (Set<?>) value);
		}
		else if (value instanceof ManagedMap) {
			// May need to resolve contained runtime references.
			return resolveManagedMap(argName, (Map<?, ?>) value);
		}
		else if (value instanceof ManagedProperties) {
			Properties original = (Properties) value;
			Properties copy = new Properties();
			original.forEach((propKey, propValue) -> {
				if (propKey instanceof TypedStringValue) {
					propKey = evaluate((TypedStringValue) propKey);
				}
				if (propValue instanceof TypedStringValue) {
					propValue = evaluate((TypedStringValue) propValue);
				}
				if (propKey == null || propValue == null) {
					throw new BeanCreationException(
							this.beanDefinition.getResourceDescription(), this.beanName,
							"Error converting Properties key/value pair for " + argName + ": resolved to null");
				}
				copy.put(propKey, propValue);
			});
			return copy;
		}
		//如果是字符串
		else if (value instanceof TypedStringValue) {
			// Convert value to target type here.
			//进行类型解析
			TypedStringValue typedStringValue = (TypedStringValue) value;
			Object valueObject = evaluate(typedStringValue);
			try {
				//获取目标类型
				Class<?> resolvedTargetType = resolveTargetType(typedStringValue);
				if (resolvedTargetType != null) {
					return this.typeConverter.convertIfNecessary(valueObject, resolvedTargetType);
				}
				else {
					return valueObject;
				}
			}
			catch (Throwable ex) {
				// Improve the message by showing the context.
				throw new BeanCreationException(
						this.beanDefinition.getResourceDescription(), this.beanName,
						"Error converting typed String value for " + argName, ex);
			}
		}
		else if (value instanceof NullBean) {
			return null;
		}
		else {
			return evaluate(value);
		}
	}

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    限于篇幅，本篇文章讲解到这，后续文章继续讲解populateBean及其createBean后续流程。

    总结

    本篇文章讲解了属性注入过程中所需参数的解析工作，一般我们可以在xml配置文件中指定其参数值，或通知设置autowire属性指定byType或byName，从beanFactory查找出所需注入对象，梳理一下流程。

    1、获取BeanDefinition中已经解析的参数信息
    2、判断是否有autowire属性，如果其指定值为byName，则通过其属性名称去缓存中获取实例，并封装到参数集合中。
    3、如果autowire属性值为byType，则尝试通过需要注入的beanName从依赖缓存resolvableDependencies中获取，及从beanFactory工厂中获取类型为注入Bean类型的定义信息，返回beanName:class集合
    4、如果候选的依赖有多个值，则遍历查询是否有primary属性，有则筛选对应的bean。如果都没有primary属性，则判断是否有实现OrderComparator接口，则进行比较筛选出Priority，值越低优先级越高。前面两者都不满足时，判断是否有候选的beanName值与要注入的属性的依赖名称一致，有则返回。没有筛选出则抛出异常
    5、对筛选出来的候选类进行实例化，并封装到属性参数中
    6、对所有的参数类型进行转换创建，如参数类型RuntimeBeanReference时，会调用getBean进行获取创建，最后通过反射的返回注入到Bean中。

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  • 原文地址：https://blog.csdn.net/weixin_45031612/article/details/128139272