Spring的AbstractBeanFactory

AbstractBeanFactory

/**
 * Abstract base class for BeanFactory implementations,
 * providing the full capabilities of the ConfigurableBeanFactory SPI.
 * Does not assume a listable bean factory: can therefore(因此) also be used
 * as base class for bean factory implementations which obtain bean definitions
 * from some backend resource (where bean definition access is an expensive(昂貴的)) operation).
 *
 * This class provides a singleton cache (through its base class DefaultSingletonBeanRegistry,
 * singleton/prototype determination(決定), FactoryBean handling, aliases,
 * bean definition merging for child bean definitions,
 * and bean destruction (DisposableBean interface, custom destroy methods). Furthermore, it can manage a bean factory
 * hierarchy (delegating to the parent in case of an unknown bean), through implementing the HierarchicalBeanFactory interface
 * 
 * The main template methods to be implemented by subclasses are #getBeanDefinition and #createBean,
 * retrieving a bean definition for a given bean name and creating a bean instance for a given bean definition,respectively(各自地,獨自地).
 * Default implementations of those operations can be found in DefaultListableBeanFactory and AbstractAutowireCapableBeanFactory.
 */
public abstract class AbstractBeanFactory extends FactoryBeanRegistrySupport implements ConfigurableBeanFactory {
	/** Parent bean factory, for bean inheritance support. */
	@Nullable
	private BeanFactory parentBeanFactory; // 父類容器
	/** ClassLoader to resolve bean class names with, if necessary. */
	@Nullable
	private ClassLoader beanClassLoader = ClassUtils.getDefaultClassLoader(); // 類加載器
	/** ClassLoader to temporarily resolve bean class names with, if necessary. */
	@Nullable
	private ClassLoader tempClassLoader; // 臨時類加載器
	/** Whether to cache bean metadata or rather eobtain(寧願重新獲取) it for every access. */
    // 是用 bean元數據緩存還是每次訪問時重新獲取
	private boolean cacheBeanMetadata = true; // 是否開啓 bean元數據緩存
	/** Resolution strategy for expressions in bean definition values. */
	@Nullable
	private BeanExpressionResolver beanExpressionResolver; // bean表達式解析器
	/** Spring ConversionService to use instead of PropertyEditors. */
	@Nullable
	private ConversionService conversionService; // 類型轉換器
	/** Custom PropertyEditorRegistrars to apply to the beans of this factory. */
	private final Set<PropertyEditorRegistrar> propertyEditorRegistrars = new LinkedHashSet<>(4);//屬性編輯器
	/** Custom PropertyEditors to apply to the beans of this factory. */
	private final Map<Class<?>, Class<? extends PropertyEditor>> customEditors = new HashMap<>(4);//類的屬性編輯器
	/** A custom TypeConverter to use, overriding the default PropertyEditor mechanism. */
	@Nullable
	private TypeConverter typeConverter; // 類性轉換器
	/** String resolvers to apply e.g. to annotation attribute values. */
    // 爲嵌入值(如註釋屬性)添加字符串解析
	private final List<StringValueResolver> embeddedValueResolvers = new CopyOnWriteArrayList<>();
	/** BeanPostProcessors to apply in createBean. */ 
    // bean的後置處理 在bean的創建是應用
	private final List<BeanPostProcessor> beanPostProcessors = new CopyOnWriteArrayList<>();
	/** Indicates whether any InstantiationAwareBeanPostProcessors have been registered. */
    // InstantiationAwareBeanPostProcessors 是否已註冊
	private volatile boolean hasInstantiationAwareBeanPostProcessors;
	/** Indicates whether any DestructionAwareBeanPostProcessors have been registered. */
    // DestructionAwareBeanPostProcessors 是否已經註冊
	private volatile boolean hasDestructionAwareBeanPostProcessors;
	/** Map from scope identifier(標識符，識別) String to corresponding(相應的，一致的) Scope. */
    // 作用域
	private final Map<String, Scope> scopes = new LinkedHashMap<>(8);
	/** Security context used when running with a SecurityManager. */
	@Nullable // 提供安全作用 權限控制
	private SecurityContextProvider securityContextProvider;
	/** Map from bean name to merged RootBeanDefinition. 合併後的BeanDefinition*/ 
	private final Map<String, RootBeanDefinition> mergedBeanDefinitions = new ConcurrentHashMap<>(256);
	/** Names of beans that have already been created at least once. */
    // bean的實例是否已經創建
	private final Set<String> alreadyCreated = Collections.newSetFromMap(new ConcurrentHashMap<>(256));
	/** Names of beans that are currently in creation. */
    // 本地緩存，正在創建的原型bean。這邊用本地線程，是因爲其他線程創建bean與當前線程不衝突
	private final ThreadLocal<Object> prototypesCurrentlyInCreation =
			new NamedThreadLocal<>("Prototype beans currently in creation");
	/**
	 * Create a new AbstractBeanFactory.
	 */
	public AbstractBeanFactory() {
	}

	/**
	 * Create a new AbstractBeanFactory with the given parent.
	 */
	public AbstractBeanFactory(@Nullable BeanFactory parentBeanFactory) {
		this.parentBeanFactory = parentBeanFactory;
	}
	//---------------------------------------------------------------------
	// Implementation of BeanFactory interface 
	//---------------------------------------------------------------------

	@Override
	public Object getBean(String name) throws BeansException {
		return doGetBean(name, null, null, false);
	}
	@Override
	public <T> T getBean(String name, Class<T> requiredType) throws BeansException {
		return doGetBean(name, requiredType, null, false);
	}

	@Override
	public Object getBean(String name, Object... args) throws BeansException {
		return doGetBean(name, null, args, false);
	}

	public <T> T getBean(String name, @Nullable Class<T> requiredType, @Nullable Object... args)
			throws BeansException {
		return doGetBean(name, requiredType, args, false);
	}
	/**
	 * Return an instance, which may be shared or independent, of the specified bean.
     * 返回一個指定的bean實例，可能是 共享的或者獨立的bean-->單例或原型 bean
	 * @param name bean的名稱
	 * @param requiredType 返回的類型
	 * @param args  傳遞的構造參數
	 * @param typeCheckOnly  檢查類型
	 * @return 返回bean實例
	 * @throws BeansException if the bean could not be created
	 */
	@SuppressWarnings("unchecked")
	protected <T> T doGetBean(final String name, @Nullable final Class<T> requiredType,
			@Nullable final Object[] args, boolean typeCheckOnly) throws BeansException {
        //獲取beanName，這邊有三種形式，一個是原始的beanName，一個是加了&的，一個是別名    
		final String beanName = transformedBeanName(name);
		Object bean;
		// Eagerly(急切地，渴望) check singleton cache for manually registered singletons.
        // 是否已經創建了
		Object sharedInstance = getSingleton(beanName);
        //已經創建了，且沒有構造參數，進入這個方法，如果有構造參數，往else走，
        // 也就是說不從獲取bean，而直接創建bean
		if (sharedInstance != null && args == null) {
			if (logger.isTraceEnabled()) {
				if (isSingletonCurrentlyInCreation(beanName)) {
					logger.trace("Returning eagerly cached instance of singleton bean '" + beanName +
							"' that is not fully initialized yet - a consequence of a circular reference");
				}
				else {
					logger.trace("Returning cached instance of singleton bean '" + beanName + "'");
				}
			}
            // 如果是普通bean，直接返回，是FactoryBean，返回他的getObject
			bean = getObjectForBeanInstance(sharedInstance, name, beanName, null);
		}
		else {
			// Fail if we're already creating this bean instance:
			// We're assumably within a circular reference.
            // 沒創建過bean或者是原型bean的情況或者有參數的情況
            // 創建過Prototype的bean，會循環引用，拋出異常，單例才嘗試解決循環依賴的問題
			if (isPrototypeCurrentlyInCreation(beanName)) {
				throw new BeanCurrentlyInCreationException(beanName);
			}
			// Check if bean definition exists in this factory.
            // 父容器存在，本地沒有當前beanName，從父容器獲取
			BeanFactory parentBeanFactory = getParentBeanFactory();
			if (parentBeanFactory != null && !containsBeanDefinition(beanName)) {
				// Not found -> check parent.
                // 處理後，如果是加&,就補上&
				String nameToLookup = originalBeanName(name);
				if (parentBeanFactory instanceof AbstractBeanFactory) {
					return ((AbstractBeanFactory) parentBeanFactory).doGetBean(
							nameToLookup, requiredType, args, typeCheckOnly);
				}
				else if (args != null) {
					// Delegation to parent with explicit args.
					return (T) parentBeanFactory.getBean(nameToLookup, args);
				}
				else if (requiredType != null) {
					// No args -> delegate to standard getBean method.
					return parentBeanFactory.getBean(nameToLookup, requiredType);
				}
				else {
					return (T) parentBeanFactory.getBean(nameToLookup);
				}
			}
			if (!typeCheckOnly) { 
                // typeCheckOnly爲false，將beanName放入alreadyCreated中,並清除bean合併定義
				markBeanAsCreated(beanName);
			}
			try {
                // 獲取bean的合併定義
				final RootBeanDefinition mbd = getMergedLocalBeanDefinition(beanName);
                // 抽象類檢查
				checkMergedBeanDefinition(mbd, beanName, args);
				// Guarantee(保證) initialization of beans that the current bean depends on.
                // 如果有依賴的情況，先初始化依賴的bean
				String[] dependsOn = mbd.getDependsOn();// 獲取所有的依賴bean名稱
				if (dependsOn != null) {
					for (String dep : dependsOn) { 
                        // 檢查是否循環依賴，a依賴b，b依賴a。包括傳遞的依賴，比如a依賴b，b依賴c，c依賴a
						if (isDependent(beanName, dep)) {
							throw new BeanCreationException(mbd.getResourceDescription(), beanName,
									"Circular depends-on relationship between '" + beanName + "' and '" + dep + "'");
						}
                        // 註冊依賴關係
						registerDependentBean(dep, beanName);
						try { 
                            // 初始化依賴的bean
							getBean(dep);
						}
						catch (NoSuchBeanDefinitionException ex) {
							throw new BeanCreationException(mbd.getResourceDescription(), beanName,
									"'" + beanName + "' depends on missing bean '" + dep + "'", ex);
						}
					}
				}
				// Create bean instance.
				if (mbd.isSingleton()) { // 如果是單例
					sharedInstance = getSingleton(beanName, () -> {
						try {
							return createBean(beanName, mbd, args);// 創建bean
						}
						catch (BeansException ex) {
							// Explicitly remove instance from singleton cache: It might have been put there
							// eagerly by the creation process, to allow for circular reference resolution.
							// Also remove any beans that received a temporary reference to the bean.
							destroySingleton(beanName);
							throw ex;
						}
					});
                    // 如果是普通bean，直接返回，是FactoryBean，返回他的getObject
					bean = getObjectForBeanInstance(sharedInstance, name, beanName, mbd);
				}
				else if (mbd.isPrototype()) { // 原型bean的創建
					// It's a prototype -> create a new instance.
					Object prototypeInstance = null;
					try {
                        // 加入prototypesCurrentlyInCreation，說明正在創建
						beforePrototypeCreation(beanName);
                        // 創建bean
						prototypeInstance = createBean(beanName, mbd, args);
					}
					finally { 
                         // 移除prototypesCurrentlyInCreation，說明已經創建結束
						afterPrototypeCreation(beanName);
					}
                    // 如果是普通bean，直接返回，是FactoryBean，返回他的getObject
					bean = getObjectForBeanInstance(prototypeInstance, name, beanName, mbd);
				}
				else { // scope bean創建
					String scopeName = mbd.getScope();
					final Scope scope = this.scopes.get(scopeName);
					if (scope == null) {
						throw new IllegalStateException("No Scope registered for scope name '" + scopeName + "'");
					}
					try {
						Object scopedInstance = scope.get(beanName, () -> {
							beforePrototypeCreation(beanName);
							try {
								return createBean(beanName, mbd, args);
							}
							finally {
								afterPrototypeCreation(beanName);
							}
						});
						bean = getObjectForBeanInstance(scopedInstance, name, beanName, mbd);
					}
					catch (IllegalStateException ex) {
						throw new BeanCreationException(beanName,
								"Scope '" + scopeName + "' is not active for the current thread; consider " +
								"defining a scoped proxy for this bean if you intend to refer to it from a singleton",
								ex);
					}
				}
			}
			catch (BeansException ex) {
				cleanupAfterBeanCreationFailure(beanName);
				throw ex;
			}
		}

		// Check if required type matches the type of the actual bean instance.
        // 檢查創建的的bean是需要的類型 類型檢查，轉換
		if (requiredType != null && !requiredType.isInstance(bean)) {
			try {
				T convertedBean = getTypeConverter().convertIfNecessary(bean, requiredType);
				if (convertedBean == null) {
					throw new BeanNotOfRequiredTypeException(name, requiredType, bean.getClass());
				}
				return convertedBean;
			}
			catch (TypeMismatchException ex) {
				if (logger.isTraceEnabled()) {
					logger.trace("Failed to convert bean '" + name + "' to required type '" +
							ClassUtils.getQualifiedName(requiredType) + "'", ex);
				}
				throw new BeanNotOfRequiredTypeException(name, requiredType, bean.getClass());
			}
		}
		return (T) bean;
	}
	@Override // 是否已經創建bean或者定義好了bean，包括當前容器以及父容器
	public boolean containsBean(String name) {
		String beanName = transformedBeanName(name);
        // 已創建單例bean或者包括bean的定義
		if (containsSingleton(beanName) || containsBeanDefinition(beanName)) {
            // 如果不是&開頭的，直接返回
            // 如果是&開頭的，判斷是否是FactoryBean，沒有找到從父類找
			return (!BeanFactoryUtils.isFactoryDereference(name) || isFactoryBean(name));
		}
		// Not found -> check parent. // 當前容器沒找到，去父類找
		BeanFactory parentBeanFactory = getParentBeanFactory();
		return (parentBeanFactory != null && parentBeanFactory.containsBean(originalBeanName(name)));
	}
	@Override // 指定beanName是否是單例，包括普通的bean和FactoryBean，包括當前容器以及父容器
	public boolean isSingleton(String name) throws NoSuchBeanDefinitionException {
		String beanName = transformedBeanName(name);
        // 如果已經實例化了
		Object beanInstance = getSingleton(beanName, false);
		if (beanInstance != null) {
			if (beanInstance instanceof FactoryBean) {
               // 是FactoryBean類型，name要&開頭或者FactoryBean中isSingleton方法返回爲true
				return (BeanFactoryUtils.isFactoryDereference(name) || ((FactoryBean<?>) beanInstance).isSingleton());
			}
			else { 
               // 如果不是FactoryBean，name就不能是&開頭
				return !BeanFactoryUtils.isFactoryDereference(name);
			}
		}
		// No singleton instance found -> check bean definition.
        // 如果當前容器還沒實例化，去父類找
		BeanFactory parentBeanFactory = getParentBeanFactory();
		if (parentBeanFactory != null && !containsBeanDefinition(beanName)) {
			// No bean definition found in this factory -> delegate to parent.
			return parentBeanFactory.isSingleton(originalBeanName(name));
		}
        // 父類也沒有，根據定義來判斷是否是單例
        // 獲取合併後的BeanDefinition
		RootBeanDefinition mbd = getMergedLocalBeanDefinition(beanName);
		// In case of FactoryBean, return singleton status of created object if not a dereference.
		if (mbd.isSingleton()) { 
            // 如果定義了是單例，判斷是否是FactoryBean，如果是FactoryBean，name就要是&開頭
			if (isFactoryBean(beanName, mbd)) {
				if (BeanFactoryUtils.isFactoryDereference(name)) {
					return true;
				}
                // 如果是單例，但是name不是&開頭，就重新獲取factoryBean，再判斷是否是單例
				FactoryBean<?> factoryBean = (FactoryBean<?>) getBean(FACTORY_BEAN_PREFIX + beanName);
				return factoryBean.isSingleton();
			}
			else {// 如果不是FactoryBean，就不能是&開頭
				return !BeanFactoryUtils.isFactoryDereference(name);
			}
		}
		else {
			return false;
		}
	}
	@Override // 指定beanName是否是原型，包括普通的bean和FactoryBean，包括當前容器以及父容器
	public boolean isPrototype(String name) throws NoSuchBeanDefinitionException {
		String beanName = transformedBeanName(name);
         // 有父容器，且沒有beanName的定義，從父容器中查找
		BeanFactory parentBeanFactory = getParentBeanFactory();
		if (parentBeanFactory != null && !containsBeanDefinition(beanName)) {
			// No bean definition found in this factory -> delegate to parent.
			return parentBeanFactory.isPrototype(originalBeanName(name));
		}
        // 沒有再從當前容器查找
		RootBeanDefinition mbd = getMergedLocalBeanDefinition(beanName);
		if (mbd.isPrototype()) {
			// In case of FactoryBean, return singleton status of created object if not a dereference.
            // 如果是普通的bean返回true，如果是&開頭的，且是FactoryBean，返回true
			return (!BeanFactoryUtils.isFactoryDereference(name) || isFactoryBean(beanName, mbd));
		}
		// Singleton or scoped - not a prototype.
		// However, FactoryBean may still produce a prototype object...
        // 如果不是Prototype，且是&開頭，&開頭就是FactoryBean，FactoryBean是單例的，所以是返回false
		if (BeanFactoryUtils.isFactoryDereference(name)) {
			return false;
		}
        // 如果是FactoryBean，判斷是否有Singleton或者Prototype
		if (isFactoryBean(beanName, mbd)) {
			final FactoryBean<?> fb = (FactoryBean<?>) getBean(FACTORY_BEAN_PREFIX + beanName);
			if (System.getSecurityManager() != null) {
				return AccessController.doPrivileged((PrivilegedAction<Boolean>) () ->
						((fb instanceof SmartFactoryBean && ((SmartFactoryBean<?>) fb).isPrototype()) || !fb.isSingleton()),
						getAccessControlContext());
			}
			else {
				return ((fb instanceof SmartFactoryBean && ((SmartFactoryBean<?>) fb).isPrototype()) ||
						!fb.isSingleton());
			}
		}
		else {
			return false;
		}
	}
	@Override // 指定的beanName是否與類型匹配
	public boolean isTypeMatch(String name, ResolvableType typeToMatch) throws NoSuchBeanDefinitionException {
		return isTypeMatch(name, typeToMatch, true);
	}
	/**
	 * Internal extended variant of isTypeMatch(String, ResolvableType)
	 * to check whether the bean with the given name matches the specified type. Allow
	 * additional constraints to be applied to ensure that beans are not created early.
	 */ // 指定的beanName是否與類型匹配
	protected boolean isTypeMatch(String name, ResolvableType typeToMatch, boolean allowFactoryBeanInit)
			throws NoSuchBeanDefinitionException {
		String beanName = transformedBeanName(name);
		boolean isFactoryDereference = BeanFactoryUtils.isFactoryDereference(name);
		// Check manually registered singletons.
        // 獲取單例
		Object beanInstance = getSingleton(beanName, false);
        // 不爲空並且不是NullBean類型
		if (beanInstance != null && beanInstance.getClass() != NullBean.class) {
			if (beanInstance instanceof FactoryBean) {
				if (!isFactoryDereference) {
                    // 不是&開頭，獲取FactoryBean的getObjectType類型，再來比較  
					Class<?> type = getTypeForFactoryBean((FactoryBean<?>) beanInstance);
					return (type != null && typeToMatch.isAssignableFrom(type));
				}
				else { 
                    // name是&開頭，直接判斷類型FactoryBean 
					return typeToMatch.isInstance(beanInstance);
				}
			}
			else if (!isFactoryDereference) {   // 普通bean，且沒有&開頭
				if (typeToMatch.isInstance(beanInstance)) {
					// Direct match for exposed instance?
					return true;
				}
                // 泛型且有beanName的定義
				else if (typeToMatch.hasGenerics() && containsBeanDefinition(beanName)) {
					// Generics potentially only match on the target class, not on the proxy...
                    // 合併定義
					RootBeanDefinition mbd = getMergedLocalBeanDefinition(beanName);
					Class<?> targetType = mbd.getTargetType();
					if (targetType != null && targetType != ClassUtils.getUserClass(beanInstance)) {
						// Check raw class match as well, making sure it's exposed on the proxy.
						Class<?> classToMatch = typeToMatch.resolve();
						if (classToMatch != null && !classToMatch.isInstance(beanInstance)) {
							return false;
						}
						if (typeToMatch.isAssignableFrom(targetType)) {
							return true;
						}
					}
					ResolvableType resolvableType = mbd.targetType;
					if (resolvableType == null) {
						resolvableType = mbd.factoryMethodReturnType;
					}
					return (resolvableType != null && typeToMatch.isAssignableFrom(resolvableType));
				}
			}
			return false;
		}
        // 已經創建了，但是沒有bean的定義，說明是空的註冊進來
		else if (containsSingleton(beanName) && !containsBeanDefinition(beanName)) {
			// null instance registered
			return false;
		}
		// No singleton instance found -> check bean definition.
        // 從父類找
		BeanFactory parentBeanFactory = getParentBeanFactory();
		if (parentBeanFactory != null && !containsBeanDefinition(beanName)) {
			// No bean definition found in this factory -> delegate to parent.
			return parentBeanFactory.isTypeMatch(originalBeanName(name), typeToMatch);
		}

		// Retrieve corresponding bean definition.
        // 重新檢索相應的bean定義
		RootBeanDefinition mbd = getMergedLocalBeanDefinition(beanName);
		BeanDefinitionHolder dbd = mbd.getDecoratedDefinition();
		// Setup the types that we want to match against
		Class<?> classToMatch = typeToMatch.resolve();
		if (classToMatch == null) {
			classToMatch = FactoryBean.class;
		}
		Class<?>[] typesToMatch = (FactoryBean.class == classToMatch ?
				new Class<?>[] {classToMatch} : new Class<?>[] {FactoryBean.class, classToMatch});


		// Attempt to predict the bean type
		Class<?> predictedType = null;

		// We're looking for a regular reference but we're a factory bean that has
		// a decorated bean definition. The target bean should be the same type
		// as FactoryBean would ultimately return.
		if (!isFactoryDereference && dbd != null && isFactoryBean(beanName, mbd)) {
			// We should only attempt if the user explicitly set lazy-init to true
			// and we know the merged bean definition is for a factory bean.
			if (!mbd.isLazyInit() || allowFactoryBeanInit) {
				RootBeanDefinition tbd = getMergedBeanDefinition(dbd.getBeanName(), dbd.getBeanDefinition(), mbd);
				Class<?> targetType = predictBeanType(dbd.getBeanName(), tbd, typesToMatch);
				if (targetType != null && !FactoryBean.class.isAssignableFrom(targetType)) {
					predictedType = targetType;
				}
			}
		}

		// If we couldn't use the target type, try regular prediction.
		if (predictedType == null) {
			predictedType = predictBeanType(beanName, mbd, typesToMatch);
			if (predictedType == null) {
				return false;
			}
		}

		// Attempt to get the actual ResolvableType for the bean.
		ResolvableType beanType = null;

		// If it's a FactoryBean, we want to look at what it creates, not the factory class.
		if (FactoryBean.class.isAssignableFrom(predictedType)) {
			if (beanInstance == null && !isFactoryDereference) {
				beanType = getTypeForFactoryBean(beanName, mbd, allowFactoryBeanInit);
				predictedType = beanType.resolve();
				if (predictedType == null) {
					return false;
				}
			}
		}
		else if (isFactoryDereference) {
			// Special case: A SmartInstantiationAwareBeanPostProcessor returned a non-FactoryBean
			// type but we nevertheless are being asked to dereference a FactoryBean...
			// Let's check the original bean class and proceed with it if it is a FactoryBean.
			predictedType = predictBeanType(beanName, mbd, FactoryBean.class);
			if (predictedType == null || !FactoryBean.class.isAssignableFrom(predictedType)) {
				return false;
			}
		}

		// We don't have an exact type but if bean definition target type or the factory
		// method return type matches the predicted type then we can use that.
		if (beanType == null) {
			ResolvableType definedType = mbd.targetType;
			if (definedType == null) {
				definedType = mbd.factoryMethodReturnType;
			}
			if (definedType != null && definedType.resolve() == predictedType) {
				beanType = definedType;
			}
		}

		// If we have a bean type use it so that generics are considered
		if (beanType != null) {
			return typeToMatch.isAssignableFrom(beanType);
		}

		// If we don't have a bean type, fallback to the predicted type
		return typeToMatch.isAssignableFrom(predictedType);
	}
	@Override
	public boolean isTypeMatch(String name, Class<?> typeToMatch) throws NoSuchBeanDefinitionException {
		return isTypeMatch(name, ResolvableType.forRawClass(typeToMatch));
	}
	@Override
	@Nullable // 獲取指定beanName的類型
	public Class<?> getType(String name) throws NoSuchBeanDefinitionException {
		return getType(name, true);
	}
	@Override
	@Nullable
	public Class<?> getType(String name, boolean allowFactoryBeanInit) throws NoSuchBeanDefinitionException {
		String beanName = transformedBeanName(name);
		// Check manually registered singletons.
        // 檢查手動註冊的單例 
		Object beanInstance = getSingleton(beanName, false);
        // 已經實例化並且不是NullBean
		if (beanInstance != null && beanInstance.getClass() != NullBean.class) {
            // 如果是FactoryBean，且沒有&，說明是取FactoryBean的getObjectType類型
			if (beanInstance instanceof FactoryBean && !BeanFactoryUtils.isFactoryDereference(name)) {
				return getTypeForFactoryBean((FactoryBean<?>) beanInstance);
			}
			else {
                // 直接返回類型
				return beanInstance.getClass(); 
			}
		}
		// No singleton instance found -> check bean definition.
        // 從父容器中獲取bean的類型
		BeanFactory parentBeanFactory = getParentBeanFactory();
		if (parentBeanFactory != null && !containsBeanDefinition(beanName)) {
			// No bean definition found in this factory -> delegate to parent.
			return parentBeanFactory.getType(originalBeanName(name));
		}
        // 獲取bean合併的定義
		RootBeanDefinition mbd = getMergedLocalBeanDefinition(beanName);
		// Check decorated(裝飾) bean definition, if any: We assume it'll be easier
		// to determine the decorated bean's type than the proxy's type.
        // 獲取 BeanDefinitionHolder 裝飾器
		BeanDefinitionHolder dbd = mbd.getDecoratedDefinition();
		if (dbd != null && !BeanFactoryUtils.isFactoryDereference(name)) {
			RootBeanDefinition tbd = getMergedBeanDefinition(dbd.getBeanName(), dbd.getBeanDefinition(), mbd);
			Class<?> targetClass = predictBeanType(dbd.getBeanName(), tbd);
			if (targetClass != null && !FactoryBean.class.isAssignableFrom(targetClass)) {
				return targetClass;
			}
		}
		Class<?> beanClass = predictBeanType(beanName, mbd);
		// Check bean class whether we're dealing with a FactoryBean.
		if (beanClass != null && FactoryBean.class.isAssignableFrom(beanClass)) {
			if (!BeanFactoryUtils.isFactoryDereference(name)) {
				// If it's a FactoryBean, we want to look at what it creates, not at the factory class.
				return getTypeForFactoryBean(beanName, mbd, allowFactoryBeanInit).resolve();
			}
			else {
				return beanClass;
			}
		}
		else {
			return (!BeanFactoryUtils.isFactoryDereference(name) ? beanClass : null);
		}
	}
	@Override // 獲取bean的別名
	public String[] getAliases(String name) {
		String beanName = transformedBeanName(name);
		List<String> aliases = new ArrayList<>();
		boolean factoryPrefix = name.startsWith(FACTORY_BEAN_PREFIX);
		String fullBeanName = beanName;
		if (factoryPrefix) {
			fullBeanName = FACTORY_BEAN_PREFIX + beanName;
		}
		if (!fullBeanName.equals(name)) {
			aliases.add(fullBeanName);
		}
		String[] retrievedAliases = super.getAliases(beanName);
		String prefix = factoryPrefix ? FACTORY_BEAN_PREFIX : "";
		for (String retrievedAlias : retrievedAliases) {
			String alias = prefix + retrievedAlias;
			if (!alias.equals(name)) {
				aliases.add(alias);
			}
		}
        // 沒實例化過且沒有bean的定義，從父類查找
		if (!containsSingleton(beanName) && !containsBeanDefinition(beanName)) {
			BeanFactory parentBeanFactory = getParentBeanFactory();
			if (parentBeanFactory != null) {
				aliases.addAll(Arrays.asList(parentBeanFactory.getAliases(fullBeanName)));
			}
		}
		return StringUtils.toStringArray(aliases);
	}
	//---------------------------------------------------------------------
	// Implementation of HierarchicalBeanFactory interface
	//---------------------------------------------------------------------
	@Override
	@Nullable
	public BeanFactory getParentBeanFactory() {
		return this.parentBeanFactory;
	}
	@Override // 當前容器是否有指定的bean
	public boolean containsLocalBean(String name) {
		String beanName = transformedBeanName(name);
		return ((containsSingleton(beanName) || containsBeanDefinition(beanName)) &&
				(!BeanFactoryUtils.isFactoryDereference(name) || isFactoryBean(beanName)));
	}
	//---------------------------------------------------------------------
	// Implementation of ConfigurableBeanFactory interface
	//---------------------------------------------------------------------
	@Override
	public void setParentBeanFactory(@Nullable BeanFactory parentBeanFactory) {
		if (this.parentBeanFactory != null && this.parentBeanFactory != parentBeanFactory) {
			throw new IllegalStateException("Already associated with parent BeanFactory: " + this.parentBeanFactory);
		}
		this.parentBeanFactory = parentBeanFactory;
	}
	@Override
	public void setBeanClassLoader(@Nullable ClassLoader beanClassLoader) {
		this.beanClassLoader = (beanClassLoader != null ? beanClassLoader : ClassUtils.getDefaultClassLoader());
	}
	@Override
	@Nullable
	public ClassLoader getBeanClassLoader() {
		return this.beanClassLoader;
	}
	@Override // 設置臨時加載器，如果涉及到加載時編織，通常只指定一個臨時類裝入器，以確保實際的bean類被儘可能延遲地裝入
	public void setTempClassLoader(@Nullable ClassLoader tempClassLoader) {
		this.tempClassLoader = tempClassLoader;
	}
	@Override
	@Nullable
	public ClassLoader getTempClassLoader() {
		return this.tempClassLoader;
	}
	@Override // bean的元數據緩存，默認爲true。如果爲false，每次創建bean都要從類加載器獲取信息
	public void setCacheBeanMetadata(boolean cacheBeanMetadata) {
		this.cacheBeanMetadata = cacheBeanMetadata;
	}
	@Override
	public boolean isCacheBeanMetadata() {
		return this.cacheBeanMetadata;
	}
	@Override
	public void setBeanExpressionResolver(@Nullable BeanExpressionResolver resolver) {
		this.beanExpressionResolver = resolver;
	}
	@Override
	@Nullable
	public BeanExpressionResolver getBeanExpressionResolver() {
		return this.beanExpressionResolver;
	}
	@Override
	public void setConversionService(@Nullable ConversionService conversionService) {
		this.conversionService = conversionService;
	}
	@Override
	@Nullable
	public ConversionService getConversionService() {
		return this.conversionService;
	}
	@Override
	public void addPropertyEditorRegistrar(PropertyEditorRegistrar registrar) {
		Assert.notNull(registrar, "PropertyEditorRegistrar must not be null");
		this.propertyEditorRegistrars.add(registrar);
	}
	/**
	 * Return the set of PropertyEditorRegistrars.
	 */
	public Set<PropertyEditorRegistrar> getPropertyEditorRegistrars() {
		return this.propertyEditorRegistrars;
	}
	@Override
	public void registerCustomEditor(Class<?> requiredType, Class<? extends PropertyEditor> propertyEditorClass) {
		Assert.notNull(requiredType, "Required type must not be null");
		Assert.notNull(propertyEditorClass, "PropertyEditor class must not be null");
		this.customEditors.put(requiredType, propertyEditorClass);
	}
	@Override
	public void copyRegisteredEditorsTo(PropertyEditorRegistry registry) {
		registerCustomEditors(registry);
	}
	/**
	 * Return the map of custom editors, with Classes as keys and PropertyEditor classes as values.
	 */
	public Map<Class<?>, Class<? extends PropertyEditor>> getCustomEditors() {
		return this.customEditors;
	}
	@Override
	public void setTypeConverter(TypeConverter typeConverter) {
		this.typeConverter = typeConverter;
	}
	/**
	 * Return the custom TypeConverter to use, if any.
	 * @return the custom TypeConverter, or {@code null} if none specified
	 */
	@Nullable
	protected TypeConverter getCustomTypeConverter() {
		return this.typeConverter;
	}
	@Override
	public TypeConverter getTypeConverter() {
		TypeConverter customConverter = getCustomTypeConverter();
		if (customConverter != null) {
			return customConverter;
		}
		else {
			// Build default TypeConverter, registering custom editors.
            // 沒有設值就初始化一個SimpleTypeConverter
			SimpleTypeConverter typeConverter = new SimpleTypeConverter();
			typeConverter.setConversionService(getConversionService());
			registerCustomEditors(typeConverter);
			return typeConverter;
		}
	}
	@Override
	public void addEmbeddedValueResolver(StringValueResolver valueResolver) {
		Assert.notNull(valueResolver, "StringValueResolver must not be null");
		this.embeddedValueResolvers.add(valueResolver);
	}
	@Override
	public boolean hasEmbeddedValueResolver() {
		return !this.embeddedValueResolvers.isEmpty();
	}
	@Override
	@Nullable // 解析給定的嵌入值
	public String resolveEmbeddedValue(@Nullable String value) {
		if (value == null) {
			return null;
		}
		String result = value;
		for (StringValueResolver resolver : this.embeddedValueResolvers) {
			result = resolver.resolveStringValue(result);
			if (result == null) {
				return null;
			}
		}
		return result;
	}
	@Override // 增加後置處理器
	public void addBeanPostProcessor(BeanPostProcessor beanPostProcessor) {
		Assert.notNull(beanPostProcessor, "BeanPostProcessor must not be null");
		// Remove from old position, if any 
        // 移除舊的，保證順序
		this.beanPostProcessors.remove(beanPostProcessor);
		// Track whether it is instantiation/destruction aware
        // 如果是 instantiation/destruction aware 標誌爲置true
		if (beanPostProcessor instanceof InstantiationAwareBeanPostProcessor) {
			this.hasInstantiationAwareBeanPostProcessors = true;
		}
		if (beanPostProcessor instanceof DestructionAwareBeanPostProcessor) {
			this.hasDestructionAwareBeanPostProcessors = true;
		}
		// Add to end of list
		this.beanPostProcessors.add(beanPostProcessor);
	}
	@Override // 獲取後置出處理器的個數
	public int getBeanPostProcessorCount() {
		return this.beanPostProcessors.size();
	}
	/**
	 * Return the list of BeanPostProcessors that will get applied
	 * to beans created with this factory. 
	 */
	public List<BeanPostProcessor> getBeanPostProcessors() {
		return this.beanPostProcessors;
	}
	/**
	 * Return whether this factory holds a InstantiationAwareBeanPostProcessor
	 * that will get applied to singleton beans on shutdown.
	 */
	protected boolean hasInstantiationAwareBeanPostProcessors() {
		return this.hasInstantiationAwareBeanPostProcessors;
	}
	/**
	 * Return whether this factory holds a DestructionAwareBeanPostProcessor
	 * that will get applied to singleton beans on shutdown.
	 */
	protected boolean hasDestructionAwareBeanPostProcessors() {
		return this.hasDestructionAwareBeanPostProcessors;
	}
	@Override // 註冊作用域
	public void registerScope(String scopeName, Scope scope) {
		Assert.notNull(scopeName, "Scope identifier must not be null");
		Assert.notNull(scope, "Scope must not be null");
        // 單例和原型  不允許再註冊
		if (SCOPE_SINGLETON.equals(scopeName) || SCOPE_PROTOTYPE.equals(scopeName)) {
			throw new IllegalArgumentException("Cannot replace existing scopes 'singleton' and 'prototype'");
		}
		Scope previous = this.scopes.put(scopeName, scope);
		if (previous != null && previous != scope) {
			if (logger.isDebugEnabled()) {
				logger.debug("Replacing scope '" + scopeName + "' from [" + previous + "] to [" + scope + "]");
			}
		}
		else {
			if (logger.isTraceEnabled()) {
				logger.trace("Registering scope '" + scopeName + "' with implementation [" + scope + "]");
			}
		}
	}
	@Override // 獲取作用域 名稱
	public String[] getRegisteredScopeNames() {
		return StringUtils.toStringArray(this.scopes.keySet());
	}
	@Override
	@Nullable // 通過名稱獲取作用域 
	public Scope getRegisteredScope(String scopeName) {
		Assert.notNull(scopeName, "Scope identifier must not be null");
		return this.scopes.get(scopeName);
	}
	/**
	 * Set the security context provider for this bean factory. If a security manager
	 * is set, interaction with the user code will be executed using the privileged
	 * of the provided security context.
	 */
	public void setSecurityContextProvider(SecurityContextProvider securityProvider) {
		this.securityContextProvider = securityProvider;
	}
	/**
	 * Delegate the creation of the access control context to the
	 * {@link #setSecurityContextProvider SecurityContextProvider}.
	 */
	@Override
	public AccessControlContext getAccessControlContext() {
		return (this.securityContextProvider != null ?
				this.securityContextProvider.getAccessControlContext() :
				AccessController.getContext());
	}
	@Override
	public void copyConfigurationFrom(ConfigurableBeanFactory otherFactory) {
		Assert.notNull(otherFactory, "BeanFactory must not be null");
		setBeanClassLoader(otherFactory.getBeanClassLoader());
		setCacheBeanMetadata(otherFactory.isCacheBeanMetadata());
		setBeanExpressionResolver(otherFactory.getBeanExpressionResolver());
		setConversionService(otherFactory.getConversionService());
		if (otherFactory instanceof AbstractBeanFactory) {
			AbstractBeanFactory otherAbstractFactory = (AbstractBeanFactory) otherFactory;
			this.propertyEditorRegistrars.addAll(otherAbstractFactory.propertyEditorRegistrars);
			this.customEditors.putAll(otherAbstractFactory.customEditors);
			this.typeConverter = otherAbstractFactory.typeConverter;
			this.beanPostProcessors.addAll(otherAbstractFactory.beanPostProcessors);
			this.hasInstantiationAwareBeanPostProcessors = this.hasInstantiationAwareBeanPostProcessors ||
					otherAbstractFactory.hasInstantiationAwareBeanPostProcessors;
			this.hasDestructionAwareBeanPostProcessors = this.hasDestructionAwareBeanPostProcessors ||
					otherAbstractFactory.hasDestructionAwareBeanPostProcessors;
			this.scopes.putAll(otherAbstractFactory.scopes);
			this.securityContextProvider = otherAbstractFactory.securityContextProvider;
		}
		else {
			setTypeConverter(otherFactory.getTypeConverter());
			String[] otherScopeNames = otherFactory.getRegisteredScopeNames();
			for (String scopeName : otherScopeNames) {
				this.scopes.put(scopeName, otherFactory.getRegisteredScope(scopeName));
			}
		}
	}
	/**
	 * Return a 'merged' BeanDefinition for the given bean name,
	 * merging a child bean definition with its parent if necessary.
	 * This  getMergedBeanDefinition considers bean definition
	 * in ancestors as well. 合併bean的定義，包括父類繼承下來的
	 */
	@Override
	public BeanDefinition getMergedBeanDefinition(String name) throws BeansException {
		String beanName = transformedBeanName(name);
		// Efficiently check whether bean definition exists in this factory.
        // 如果當前容器沒有，且父類是ConfigurableBeanFactory類型，去父類找
		if (!containsBeanDefinition(beanName) && getParentBeanFactory() instanceof ConfigurableBeanFactory) {
			return ((ConfigurableBeanFactory) getParentBeanFactory()).getMergedBeanDefinition(beanName);
		}
		// Resolve merged bean definition locally. 去本地找
		return getMergedLocalBeanDefinition(beanName);
	}
	@Override // 是否是FactoryBean類型
	public boolean isFactoryBean(String name) throws NoSuchBeanDefinitionException {
        // 獲取beanName
		String beanName = transformedBeanName(name);
        // 後去bean實例
		Object beanInstance = getSingleton(beanName, false);
        // 已經實例化直接判斷
		if (beanInstance != null) {
			return (beanInstance instanceof FactoryBean);
		}
		// No singleton instance found -> check bean definition.
        // 沒有實例化，從父類判斷
		if (!containsBeanDefinition(beanName) && getParentBeanFactory() instanceof ConfigurableBeanFactory) {
			// No bean definition found in this factory -> delegate to parent.
			return ((ConfigurableBeanFactory) getParentBeanFactory()).isFactoryBean(name);
		}
		return isFactoryBean(beanName, getMergedLocalBeanDefinition(beanName));
	}
	@Override// 是否正在創建的bean， 包括單例和原型
	public boolean isActuallyInCreation(String beanName) {
		return (isSingletonCurrentlyInCreation(beanName) || isPrototypeCurrentlyInCreation(beanName));
	}
	/**
	 * Return whether the specified prototype bean is currently in creation
	 * (within the current thread). 是否原型bean正在創建中
	 */
	protected boolean isPrototypeCurrentlyInCreation(String beanName) {
		Object curVal = this.prototypesCurrentlyInCreation.get(); // 當前線程有值，說明有在創建原型
        // 如果相等，或者在set中，說明創建的多例有包括指定的bean
		return (curVal != null &&
				(curVal.equals(beanName) || (curVal instanceof Set && ((Set<?>) curVal).contains(beanName))));
	}

	/**
	 * Callback before prototype creation.
	 * The default implementation register the prototype as currently in creation.
     * 原型創建前，把beanName加入到prototypesCurrentlyInCreation，如果是string，說明已加入一個，轉換爲set
	 */
	@SuppressWarnings("unchecked")
	protected void beforePrototypeCreation(String beanName) {
		Object curVal = this.prototypesCurrentlyInCreation.get();
		if (curVal == null) {
			this.prototypesCurrentlyInCreation.set(beanName);
		}
		else if (curVal instanceof String) {
			Set<String> beanNameSet = new HashSet<>(2);
			beanNameSet.add((String) curVal);
			beanNameSet.add(beanName);
			this.prototypesCurrentlyInCreation.set(beanNameSet);
		}
		else {
			Set<String> beanNameSet = (Set<String>) curVal;
			beanNameSet.add(beanName);
		}
	}
	/**
	 * Callback after prototype creation.
	 * The default implementation marks the prototype as not in creation anymore.
     * 原型創建完了，從prototypesCurrentlyInCreation移除
	 */
	@SuppressWarnings("unchecked")
	protected void afterPrototypeCreation(String beanName) {
		Object curVal = this.prototypesCurrentlyInCreation.get();
		if (curVal instanceof String) {
			this.prototypesCurrentlyInCreation.remove();
		}
		else if (curVal instanceof Set) {
			Set<String> beanNameSet = (Set<String>) curVal;
			beanNameSet.remove(beanName);
			if (beanNameSet.isEmpty()) {
				this.prototypesCurrentlyInCreation.remove();
			}
		}
	}
	@Override// 銷燬bean
	public void destroyBean(String beanName, Object beanInstance) {
		destroyBean(beanName, beanInstance, getMergedLocalBeanDefinition(beanName));
	}
	/**
	 * Destroy the given bean instance (usually a prototype instance
	 * obtained from this factory) according to the given bean definition.
	 */
	protected void destroyBean(String beanName, Object bean, RootBeanDefinition mbd) {
		new DisposableBeanAdapter(bean, beanName, mbd, getBeanPostProcessors(), getAccessControlContext()).destroy();
	}
	@Override // scope的bean 銷燬
	public void destroyScopedBean(String beanName) {
		RootBeanDefinition mbd = getMergedLocalBeanDefinition(beanName);
		if (mbd.isSingleton() || mbd.isPrototype()) { // 單例和原型不能銷燬 
			throw new IllegalArgumentException(
					"Bean name '" + beanName + "' does not correspond to an object in a mutable scope");
		}
		String scopeName = mbd.getScope();
        // 沒有對應的scope，不能刪除
		Scope scope = this.scopes.get(scopeName);
		if (scope == null) {
			throw new IllegalStateException("No Scope SPI registered for scope name '" + scopeName + "'");
		}
		Object bean = scope.remove(beanName);
		if (bean != null) {
			destroyBean(beanName, bean, mbd);
		}
	}

	//---------------------------------------------------------------------
	// Implementation methods
	//---------------------------------------------------------------------
	/**
	 * Return the bean name, stripping out the factory dereference prefix if necessary,
	 * and resolving aliases to canonical names.
     * 獲取beanName，有可能傳過來的是原始的beanName，有可能是加了&的，有可能是別名。
     * 如果是加了&的，先去除，再獲取。如果是別名，先遞歸到最原始的別名，再獲取beanName
	 */
	protected String transformedBeanName(String name) {
		return canonicalName(BeanFactoryUtils.transformedBeanName(name));
	}
	/**
	 * Determine the original bean name, resolving locally defined aliases to canonical names.
	 * 獲取原始的beanName，如果有&，要加上&
	 */
	protected String originalBeanName(String name) {
		String beanName = transformedBeanName(name);
		if (name.startsWith(FACTORY_BEAN_PREFIX)) {
			beanName = FACTORY_BEAN_PREFIX + beanName;
		}
		return beanName;
	}
	/**
	 * Initialize the given BeanWrapper with the custom editors registered
	 * with this factory. To be called for BeanWrappers that will create
	 * and populate bean instances.
	 * 初始化BeanWrapper
	 */
	protected void initBeanWrapper(BeanWrapper bw) {
		bw.setConversionService(getConversionService());
		registerCustomEditors(bw);
	}
	/**
	 * Initialize the given PropertyEditorRegistry with the custom editors
	 * that have been registered with this BeanFactory.
	 * To be called for BeanWrappers that will create and populate bean
	 * instances, and for SimpleTypeConverter used for constructor argument
	 * and factory method type conversion.
	 * 批量註冊屬性編輯器
	 */
	protected void registerCustomEditors(PropertyEditorRegistry registry) {
		PropertyEditorRegistrySupport registrySupport =
				(registry instanceof PropertyEditorRegistrySupport ? (PropertyEditorRegistrySupport) registry : null);
		if (registrySupport != null) {
			registrySupport.useConfigValueEditors();
		}
		if (!this.propertyEditorRegistrars.isEmpty()) {
			for (PropertyEditorRegistrar registrar : this.propertyEditorRegistrars) {
				try {  // 批量註冊到propertyEditorRegistrars
					registrar.registerCustomEditors(registry);
				}
				catch (BeanCreationException ex) {
					Throwable rootCause = ex.getMostSpecificCause();
					if (rootCause instanceof BeanCurrentlyInCreationException) {
						BeanCreationException bce = (BeanCreationException) rootCause;
						String bceBeanName = bce.getBeanName();
						if (bceBeanName != null && isCurrentlyInCreation(bceBeanName)) {
							if (logger.isDebugEnabled()) {
								logger.debug("PropertyEditorRegistrar [" + registrar.getClass().getName() +
										"] failed because it tried to obtain currently created bean '" +
										ex.getBeanName() + "': " + ex.getMessage());
							}
							onSuppressedException(ex);
							continue;
						}
					}
					throw ex;
				}
			}
		}
		if (!this.customEditors.isEmpty()) {
			this.customEditors.forEach((requiredType, editorClass) ->
					registry.registerCustomEditor(requiredType, BeanUtils.instantiateClass(editorClass)));
		}
	}


	/**
	 * Return a merged RootBeanDefinition, traversing(穿越) the parent bean definition
	 * if the specified bean corresponds(相應地) to a child bean definition.
     *
	 */
	protected RootBeanDefinition getMergedLocalBeanDefinition(String beanName) throws BeansException {
		// Quick check on the concurrent map first, with minimal locking.
		RootBeanDefinition mbd = this.mergedBeanDefinitions.get(beanName);
        // 緩存
		if (mbd != null && !mbd.stale) {
			return mbd;
		}
		return getMergedBeanDefinition(beanName, getBeanDefinition(beanName));
	}
	/**
	 * Return a RootBeanDefinition for the given top-level bean, by merging with
	 * the parent if the given bean's definition is a child bean definition.
	 */
	protected RootBeanDefinition getMergedBeanDefinition(String beanName, BeanDefinition bd)
			throws BeanDefinitionStoreException {
		return getMergedBeanDefinition(beanName, bd, null);
	}

	/**
	 * Return a RootBeanDefinition for the given bean, by merging with the
	 * parent if the given bean's definition is a child bean definition.
	 */
	protected RootBeanDefinition getMergedBeanDefinition(
			String beanName, BeanDefinition bd, @Nullable BeanDefinition containingBd)
			throws BeanDefinitionStoreException {

		synchronized (this.mergedBeanDefinitions) {
			RootBeanDefinition mbd = null;
			RootBeanDefinition previous = null;
			// Check with full lock now in order to enforce the same merged instance.
			if (containingBd == null) {
				mbd = this.mergedBeanDefinitions.get(beanName);
			}
			if (mbd == null || mbd.stale) {
				previous = mbd;
                 // 沒有父類，根據bd類型直接創建或者克隆返回
				if (bd.getParentName() == null) {
					// Use copy of given root bean definition.
					if (bd instanceof RootBeanDefinition) {
						mbd = ((RootBeanDefinition) bd).cloneBeanDefinition();
					}
					else {
						mbd = new RootBeanDefinition(bd);
					}
				}
				else {
					// Child bean definition: needs to be merged with parent.
					BeanDefinition pbd;
					try {
						String parentBeanName = transformedBeanName(bd.getParentName());
						if (!beanName.equals(parentBeanName)) {
							pbd = getMergedBeanDefinition(parentBeanName);
						}
						else {
							BeanFactory parent = getParentBeanFactory();
							if (parent instanceof ConfigurableBeanFactory) {
								pbd = ((ConfigurableBeanFactory) parent).getMergedBeanDefinition(parentBeanName);
							}
							else {
								throw new NoSuchBeanDefinitionException(parentBeanName,
										"Parent name '" + parentBeanName + "' is equal to bean name '" + beanName +
										"': cannot be resolved without an AbstractBeanFactory parent");
							}
						}
					}
					catch (NoSuchBeanDefinitionException ex) {
						throw new BeanDefinitionStoreException(bd.getResourceDescription(), beanName,
								"Could not resolve parent bean definition '" + bd.getParentName() + "'", ex);
					}
					// Deep copy with overridden values.
					mbd = new RootBeanDefinition(pbd);
					mbd.overrideFrom(bd);
				}
				// Set default singleton scope, if not configured before.
                // 默認單例
				if (!StringUtils.hasLength(mbd.getScope())) {
					mbd.setScope(SCOPE_SINGLETON);
				}
				// A bean contained in a non-singleton bean cannot be a singleton itself.
				// Let's correct this on the fly here, since this might be the result of
				// parent-child merging for the outer bean, in which case the original inner bean
				// definition will not have inherited the merged outer bean's singleton status.
				if (containingBd != null && !containingBd.isSingleton() && mbd.isSingleton()) {
					mbd.setScope(containingBd.getScope());
				}
				// Cache the merged bean definition for the time being
				// (it might still get re-merged later on in order to pick up metadata changes)
                // 緩存bean的定義定義
				if (containingBd == null && isCacheBeanMetadata()) {
					this.mergedBeanDefinitions.put(beanName, mbd);
				}
			}
			if (previous != null) {
				copyRelevantMergedBeanDefinitionCaches(previous, mbd);
			}
			return mbd;
		}
	}
	private void copyRelevantMergedBeanDefinitionCaches(RootBeanDefinition previous, RootBeanDefinition mbd) {
		if (ObjectUtils.nullSafeEquals(mbd.getBeanClassName(), previous.getBeanClassName()) &&
				ObjectUtils.nullSafeEquals(mbd.getFactoryBeanName(), previous.getFactoryBeanName()) &&
				ObjectUtils.nullSafeEquals(mbd.getFactoryMethodName(), previous.getFactoryMethodName())) {
			ResolvableType targetType = mbd.targetType;
			ResolvableType previousTargetType = previous.targetType;
			if (targetType == null || targetType.equals(previousTargetType)) {
				mbd.targetType = previousTargetType;
				mbd.isFactoryBean = previous.isFactoryBean;
				mbd.resolvedTargetType = previous.resolvedTargetType;
				mbd.factoryMethodReturnType = previous.factoryMethodReturnType;
				mbd.factoryMethodToIntrospect = previous.factoryMethodToIntrospect;
			}
		}
	}
	/**
	 * Check the given merged bean definition,
	 * potentially throwing validation exceptions.
	 * 如果是抽象的，就拋異常
	 */
	protected void checkMergedBeanDefinition(RootBeanDefinition mbd, String beanName, @Nullable Object[] args)
			throws BeanDefinitionStoreException {
		if (mbd.isAbstract()) {
			throw new BeanIsAbstractException(beanName);
		}
	}
	/**
	 * Remove the merged bean definition for the specified bean,
	 * recreating it on next access.
	 * 移除bean的定義
	 */
	protected void clearMergedBeanDefinition(String beanName) {
		RootBeanDefinition bd = this.mergedBeanDefinitions.get(beanName);
		if (bd != null) {
			bd.stale = true;
		}
	}
	/**
	 * Clear the merged bean definition cache, removing entries for beans
	 * which are not considered eligible for full metadata caching yet.
	 * Typically triggered after changes to the original bean definitions,
	 * e.g. after applying a {@code BeanFactoryPostProcessor}. Note that metadata
	 * for beans which have already been created at this point will be kept around.
	 * 移除還沒創建的bean對應的bean定義
	 */
	public void clearMetadataCache() {
		this.mergedBeanDefinitions.forEach((beanName, bd) -> {
			if (!isBeanEligibleForMetadataCaching(beanName)) {
				bd.stale = true;
			}
		});
	}
	/**
	 * Resolve the bean class for the specified bean definition,
	 * resolving a bean class name into a Class reference (if necessary)
	 * and storing the resolved Class in the bean definition for further use.
	 */
	@Nullable
	protected Class<?> resolveBeanClass(final RootBeanDefinition mbd, String beanName, final Class<?>... typesToMatch)
			throws CannotLoadBeanClassException {

		try {
			if (mbd.hasBeanClass()) { // 已經解析過，直接返回
				return mbd.getBeanClass();
			}
			if (System.getSecurityManager() != null) {
				return AccessController.doPrivileged((PrivilegedExceptionAction<Class<?>>) () ->
					doResolveBeanClass(mbd, typesToMatch), getAccessControlContext());
			}
			else {
				return doResolveBeanClass(mbd, typesToMatch);
			}
		}
		catch (PrivilegedActionException pae) {
			ClassNotFoundException ex = (ClassNotFoundException) pae.getException();
			throw new CannotLoadBeanClassException(mbd.getResourceDescription(), beanName, mbd.getBeanClassName(), ex);
		}
		catch (ClassNotFoundException ex) {
			throw new CannotLoadBeanClassException(mbd.getResourceDescription(), beanName, mbd.getBeanClassName(), ex);
		}
		catch (LinkageError err) {
			throw new CannotLoadBeanClassException(mbd.getResourceDescription(), beanName, mbd.getBeanClassName(), err);
		}
	}
	@Nullable // 根據bean定義 解析 bean的類型class
	private Class<?> doResolveBeanClass(RootBeanDefinition mbd, Class<?>... typesToMatch)
			throws ClassNotFoundException {
		ClassLoader beanClassLoader = getBeanClassLoader();
		ClassLoader dynamicLoader = beanClassLoader;
		boolean freshResolve = false;
		if (!ObjectUtils.isEmpty(typesToMatch)) {
			// When just doing type checks (i.e. not creating an actual instance yet),
			// use the specified temporary class loader (e.g. in a weaving scenario).
			ClassLoader tempClassLoader = getTempClassLoader();
			if (tempClassLoader != null) {
				dynamicLoader = tempClassLoader;
				freshResolve = true;
				if (tempClassLoader instanceof DecoratingClassLoader) {
					DecoratingClassLoader dcl = (DecoratingClassLoader) tempClassLoader;
					for (Class<?> typeToMatch : typesToMatch) {
                        // 臨時加載器排序這些類型
						dcl.excludeClass(typeToMatch.getName());
					}
				}
			}
		}
		String className = mbd.getBeanClassName();
		if (className != null) {
            // bean的表達式解析器解析
			Object evaluated = evaluateBeanDefinitionString(className, mbd);
            // 類名不一樣
			if (!className.equals(evaluated)) {
				// A dynamically resolved expression, supported as of 4.2...
                // 是class直接返回
				if (evaluated instanceof Class) {
					return (Class<?>) evaluated;
				}
				else if (evaluated instanceof String) { // 字符串freshResolve爲true
					className = (String) evaluated;
					freshResolve = true;
				}
				else {
					throw new IllegalStateException("Invalid class name expression result: " + evaluated);
				}
			}
			if (freshResolve) {
				// When resolving against a temporary class loader, exit early in order
				// to avoid storing the resolved Class in the bean definition.
                //  類命一樣，且是字符串
				if (dynamicLoader != null) {
					try { // 類加載器加載
						return dynamicLoader.loadClass(className);
					}
					catch (ClassNotFoundException ex) {
						if (logger.isTraceEnabled()) {
							logger.trace("Could not load class [" + className + "] from " + dynamicLoader + ": " + ex);
						}
					}
				}  // 沒有類加載器
				return ClassUtils.forName(className, dynamicLoader);
			}
		}
		// Resolve regularly, caching the result in the BeanDefinition...
        // 解析並緩存在bean的定義中
		return mbd.resolveBeanClass(beanClassLoader);
	}
	/**
	 * Evaluate the given String as contained in a bean definition,
	 * potentially resolving it as an expression.
	 */
	@Nullable
	protected Object evaluateBeanDefinitionString(@Nullable String value, @Nullable BeanDefinition beanDefinition) {
         // bean的表達式解析器爲空直接返回value
		if (this.beanExpressionResolver == null) {
			return value;
		}
		Scope scope = null;   // 不爲空，取scope，去解析
		if (beanDefinition != null) {
			String scopeName = beanDefinition.getScope();
			if (scopeName != null) {
				scope = getRegisteredScope(scopeName);
			}
		}
		return this.beanExpressionResolver.evaluate(value, new BeanExpressionContext(this, scope));
	}


	/**
	 * Predict the eventual bean type (of the processed bean instance) for the
	 * specified bean. Called by #getType and  #isTypeMatch.
	 * Does not need to handle FactoryBeans specifically, since it is only
	 * supposed to operate on the raw bean type.
	 * This implementation is simplistic in that it is not able to
	 * handle factory methods and InstantiationAwareBeanPostProcessors.
	 * It only predicts the bean type correctly for a standard bean.
	 * To be overridden in subclasses, applying more sophisticated type detection.
	 * 預測bean的類型
	 */
	@Nullable
	protected Class<?> predictBeanType(String beanName, RootBeanDefinition mbd, Class<?>... typesToMatch) {
        // 如果targetType不爲空，直接返回
		Class<?> targetType = mbd.getTargetType();
		if (targetType != null) {
			return targetType;
		}
		if (mbd.getFactoryMethodName() != null) {
			return null;
		}
		return resolveBeanClass(mbd, beanName, typesToMatch);
	}
	/**
	 * Check whether the given bean is defined as a {@link FactoryBean}.
	 */
	protected boolean isFactoryBean(String beanName, RootBeanDefinition mbd) {
		Boolean result = mbd.isFactoryBean;
		if (result == null) { 
            // 獲取解析後的類型
			Class<?> beanType = predictBeanType(beanName, mbd, FactoryBean.class);
            // 如果解析的類型不爲空，且是FactoryBean，返回true
			result = (beanType != null && FactoryBean.class.isAssignableFrom(beanType));
			mbd.isFactoryBean = result;
		}
		return result;
	}

	/**
	 * Determine the bean type for the given FactoryBean definition, as far as possible.
	 * Only called if there is no singleton instance registered for the target bean
	 * already. Implementations are only allowed to instantiate the factory bean if
	 * allowInit is true, otherwise they should try to determine the
	 * result through other means.
	 * If no FactoryBean#OBJECT_TYPE_ATTRIBUTE if set on the bean definition
	 * and allowInit is  true, the default implementation will create
	 * the FactoryBean via  getBean to call its  getObjectType method.
	 * Subclasses are encouraged to optimize this, typically by inspecting the generic
	 * signature of the factory bean class or the factory method that creates it. If
	 * subclasses do instantiate the FactoryBean, they should consider trying the
	 * getObjectType method without fully populating the bean. If this fails, a
	 * full FactoryBean creation as performed by this implementation should be used as
	 * fallback.
	 * 通過beanName和定義獲取FactoryBean的類型
	 */
	protected ResolvableType getTypeForFactoryBean(String beanName, RootBeanDefinition mbd, boolean allowInit) {
		ResolvableType result = getTypeForFactoryBeanFromAttributes(mbd);
		if (result != ResolvableType.NONE) {
			return result;
		}
		if (allowInit && mbd.isSingleton()) {
			try {
				FactoryBean<?> factoryBean = doGetBean(FACTORY_BEAN_PREFIX + beanName, FactoryBean.class, null, true);
				Class<?> objectType = getTypeForFactoryBean(factoryBean);
				return (objectType != null) ? ResolvableType.forClass(objectType) : ResolvableType.NONE;
			}
			catch (BeanCreationException ex) {
				if (ex.contains(BeanCurrentlyInCreationException.class)) {
					logger.trace(LogMessage.format("Bean currently in creation on FactoryBean type check: %s", ex));
				}
				else if (mbd.isLazyInit()) {
					logger.trace(LogMessage.format("Bean creation exception on lazy FactoryBean type check: %s", ex));
				}
				else {
					logger.debug(LogMessage.format("Bean creation exception on non-lazy FactoryBean type check: %s", ex));
				}
				onSuppressedException(ex);
			}
		}
		return ResolvableType.NONE;
	}
	/**
	 * Determine the bean type for a FactoryBean by inspecting its attributes for a
	 * FactoryBean#OBJECT_TYPE_ATTRIBUTE value.
	 */
	ResolvableType getTypeForFactoryBeanFromAttributes(AttributeAccessor attributes) {
		Object attribute = attributes.getAttribute(FactoryBean.OBJECT_TYPE_ATTRIBUTE);
		if (attribute instanceof ResolvableType) {
			return (ResolvableType) attribute;
		}
		if (attribute instanceof Class) {
			return ResolvableType.forClass((Class<?>) attribute);
		}
		return ResolvableType.NONE;
	}
	/**
	 * Determine the bean type for the given FactoryBean definition, as far as possible.
	 * Only called if there is no singleton instance registered for the target bean already.
	 * <p>The default implementation creates the FactoryBean via getBean
	 * to call its  getObjectType method. Subclasses are encouraged to optimize
	 * this, typically by just instantiating the FactoryBean but not populating it yet,
	 * trying whether its  getObjectType method already returns a type.
	 * If no type found, a full FactoryBean creation as performed by this implementation
	 * should be used as fallback.
	 */
	@Nullable
	@Deprecated
	protected Class<?> getTypeForFactoryBean(String beanName, RootBeanDefinition mbd) {
		return getTypeForFactoryBean(beanName, mbd, true).resolve();
	}
	/**
	 * Mark the specified bean as already created (or about to be created).
     * 如果沒有加入到alreadyCreated，就清除當前bean的定義，並加入到alreadyCreated
	 */
	protected void markBeanAsCreated(String beanName) {
		if (!this.alreadyCreated.contains(beanName)) {
			synchronized (this.mergedBeanDefinitions) {
				if (!this.alreadyCreated.contains(beanName)) {
					// Let the bean definition get re-merged now that we're actually creating
					// the bean... just in case some of its metadata changed in the meantime.
					clearMergedBeanDefinition(beanName);
					this.alreadyCreated.add(beanName);
				}
			}
		}
	}
	/**
	 * Perform appropriate cleanup of cached metadata after bean creation failed.
	 * 創建失敗後，從alreadyCreated移除
	 */
	protected void cleanupAfterBeanCreationFailure(String beanName) {
		synchronized (this.mergedBeanDefinitions) {
			this.alreadyCreated.remove(beanName);
		}
	}
	/**
	 * Determine whether the specified bean is eligible for having
	 * its bean definition metadata cached.
	 * 是否已創建
	 */
	protected boolean isBeanEligibleForMetadataCaching(String beanName) {
		return this.alreadyCreated.contains(beanName);
	}
	/**
	 * Remove the singleton instance (if any) for the given bean name,
	 * but only if it hasn't been used for other purposes than type checking.
	 * 移除沒有在alreadyCreated中的單例
	 */
	protected boolean removeSingletonIfCreatedForTypeCheckOnly(String beanName) {
		if (!this.alreadyCreated.contains(beanName)) {
			removeSingleton(beanName);
			return true;
		}
		else {
			return false;
		}
	}
	/**
	 * Check whether this factory's bean creation phase already started,
	 * i.e. whether any bean has been marked as created in the meantime.
	 * 是否已經有bean開始創建了，alreadyCreated爲空，說明還沒創建，不爲空，已經創建
	 */
	protected boolean hasBeanCreationStarted() {
		return !this.alreadyCreated.isEmpty();
	}
	/**
	 * Get the object for the given bean instance, either the bean
	 * instance itself or its created object in case of a FactoryBean.
	 * 如果是非FactoryBean的直接返回，如果是FactoryBean的則處理
	 */
	protected Object getObjectForBeanInstance(
			Object beanInstance, String name, String beanName, @Nullable RootBeanDefinition mbd) {
		// Don't let calling code try to dereference the factory if the bean isn't a factory.
        // 如果beanname是&開頭的，這個bean必須是FactoryBean類型
		if (BeanFactoryUtils.isFactoryDereference(name)) {
			if (beanInstance instanceof NullBean) {
				return beanInstance;
			}
			if (!(beanInstance instanceof FactoryBean)) {
				throw new BeanIsNotAFactoryException(beanName, beanInstance.getClass());
			}
			if (mbd != null) {
				mbd.isFactoryBean = true;
			}
			return beanInstance;
		}

		// Now we have the bean instance, which may be a normal bean or a FactoryBean.
		// If it's a FactoryBean, we use it to create a bean instance, unless the
		// caller actually wants a reference to the factory.
        // 普通bean或者beanname是&開頭的，返回beanInstance
		if (!(beanInstance instanceof FactoryBean)) {
			return beanInstance;
		}
        // 是FactoryBean但是沒有&開頭的
		Object object = null;
		if (mbd != null) {
			mbd.isFactoryBean = true;
		}
		else { 
            // bean的定義信息是空的，從緩存中拿
			object = getCachedObjectForFactoryBean(beanName);
		}
		if (object == null) {  //緩存不存在
			// Return bean instance from factory.
			FactoryBean<?> factory = (FactoryBean<?>) beanInstance;
			// Caches object obtained from FactoryBean if it is a singleton.
            // mdb爲空，並且已經實例化過
			if (mbd == null && containsBeanDefinition(beanName)) {
				mbd = getMergedLocalBeanDefinition(beanName);
			}
            // 是否是用戶定義的，而不是程序本身定義的
			boolean synthetic = (mbd != null && mbd.isSynthetic());
			object = getObjectFromFactoryBean(factory, beanName, !synthetic);
		}
		return object;
	}
	/**
	 * Determine whether the given bean name is already in use within this factory,
	 * i.e. whether there is a local bean or alias registered under this name or
	 * an inner bean created with this name.
	 * 從別名、bean的定義、依賴判斷beanName是否已使用
	 */
	public boolean isBeanNameInUse(String beanName) {
		return isAlias(beanName) || containsLocalBean(beanName) || hasDependentBean(beanName);
	}
	/**
	 * Determine whether the given bean requires destruction on shutdown.
	 * <p>The default implementation checks the DisposableBean interface as well as
	 * a specified destroy method and registered DestructionAwareBeanPostProcessors.
	 * 確定給定的bean在關閉時是否需要銷燬
	 */
	protected boolean requiresDestruction(Object bean, RootBeanDefinition mbd) {
		return (bean.getClass() != NullBean.class &&
				(DisposableBeanAdapter.hasDestroyMethod(bean, mbd) || (hasDestructionAwareBeanPostProcessors() &&
						DisposableBeanAdapter.hasApplicableProcessors(bean, getBeanPostProcessors()))));
	}
	/**
	 * Add the given bean to the list of disposable beans in this factory,
	 * registering its DisposableBean interface and/or the given destroy method
	 * to be called on factory shutdown (if applicable). Only applies to singletons.
	 * 根據scope註冊需要銷燬的bean
	 */
	protected void registerDisposableBeanIfNecessary(String beanName, Object bean, RootBeanDefinition mbd) {
		AccessControlContext acc = (System.getSecurityManager() != null ? getAccessControlContext() : null);
        // 不是原型且需要銷燬
		if (!mbd.isPrototype() && requiresDestruction(bean, mbd)) {
			if (mbd.isSingleton()) {
				// Register a DisposableBean implementation that performs all destruction
				// work for the given bean: DestructionAwareBeanPostProcessors,
				// DisposableBean interface, custom destroy method.
                // 單例模式下需要銷燬的bean
				registerDisposableBean(beanName,
						new DisposableBeanAdapter(bean, beanName, mbd, getBeanPostProcessors(), acc));
			}
			else {
				// A bean with a custom scope... 
                // 自定義scope的處理
				Scope scope = this.scopes.get(mbd.getScope());
				if (scope == null) {
					throw new IllegalStateException("No Scope registered for scope name '" + mbd.getScope() + "'");
				}
				scope.registerDestructionCallback(beanName,
						new DisposableBeanAdapter(bean, beanName, mbd, getBeanPostProcessors(), acc));
			}
		}
	}
	//---------------------------------------------------------------------
	// Abstract methods to be implemented by subclasses 抽象的模板方法
	//---------------------------------------------------------------------

	/**
	 * Check if this bean factory contains a bean definition with the given name.
	 * Does not consider any hierarchy this factory may participate in.
	 * Invoked by {@code containsBean} when no cached singleton instance is found.
	 * <p>Depending on the nature of the concrete bean factory implementation,
	 * this operation might be expensive (for example, because of directory lookups
	 * in external registries). However, for listable bean factories, this usually
	 * just amounts to a local hash lookup: The operation is therefore part of the
	 * public interface there. The same implementation can serve for both this
	 * template method and the public interface method in that case.
	 */
	protected abstract boolean containsBeanDefinition(String beanName);

	/**
	 * Return the bean definition for the given bean name.
	 * Subclasses should normally implement caching, as this method is invoked
	 * by this class every time bean definition metadata is needed.
	 * <p>Depending on the nature of the concrete bean factory implementation,
	 * this operation might be expensive (for example, because of directory lookups
	 * in external registries). However, for listable bean factories, this usually
	 * just amounts to a local hash lookup: The operation is therefore part of the
	 * public interface there. The same implementation can serve for both this
	 * template method and the public interface method in that case.
	 */
	protected abstract BeanDefinition getBeanDefinition(String beanName) throws BeansException;

	/**
	 * Create a bean instance for the given merged bean definition (and arguments).
	 * The bean definition will already have been merged with the parent definition
	 * in case of a child definition.
	 * <p>All bean retrieval methods delegate to this method for actual bean creation.
	 */
	protected abstract Object createBean(String beanName, RootBeanDefinition mbd, @Nullable Object[] args)
			throws BeanCreationException;

}