Spring源码分析——BeanFactory体系之抽象类、类分析（二）

/*
 * Copyright 2002-2012 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.springframework.beans.factory.support;

import java.security.AccessControlContext;
import java.security.AccessController;
import java.security.PrivilegedAction;
import java.security.PrivilegedActionException;
import java.security.PrivilegedExceptionAction;
import java.util.Map;
import java.util.concurrent.ConcurrentHashMap;

import org.springframework.beans.BeansException;
import org.springframework.beans.factory.BeanCreationException;
import org.springframework.beans.factory.BeanCurrentlyInCreationException;
import org.springframework.beans.factory.FactoryBean;
import org.springframework.beans.factory.FactoryBeanNotInitializedException;

/**
 * Support base class for singleton registries which need to handle
 * {@link org.springframework.beans.factory.FactoryBean} instances,
 * integrated with {@link DefaultSingletonBeanRegistry}‘s singleton management.
 *
 * <p>Serves as base class for {@link AbstractBeanFactory}.
 *
 * @author Juergen Hoeller
 * @since 2.5.1
 */
public abstract class FactoryBeanRegistrySupport extends DefaultSingletonBeanRegistry {

    /** 工厂Bean生产的单例的集合: FactoryBean name --> object */
    private final Map<String, Object> factoryBeanObjectCache = new ConcurrentHashMap<String, Object>(16);

    //返回指定FactoryBean的类型
    protected Class getTypeForFactoryBean(final FactoryBean factoryBean) {
        try {
            if (System.getSecurityManager() != null) {//如果当前系统存在安全管理器
                return AccessController.doPrivileged(new PrivilegedAction<Class>() {//那么返回factoryBean的类型这个操作不做权限检查，直接调用
                    public Class run() {
                        return factoryBean.getObjectType();
                    }
                }, getAccessControlContext());
            }
            else {//不存在安全管理器，就直接调用！
                return factoryBean.getObjectType();
            }
        }
        catch (Throwable ex) {
            logger.warn("FactoryBean threw exception from getObjectType, despite the contract saying " +
                    "that it should return null if the type of its object cannot be determined yet", ex);
            return null;
        }
    }

    //根据FactoryBean名，返回其生产的Object，从缓存中取
    protected Object getCachedObjectForFactoryBean(String beanName) {
        Object object = this.factoryBeanObjectCache.get(beanName);
        return (object != NULL_OBJECT ? object : null);
    }

    //从工厂Bean中取实例，实际调用下面的doGetObjectFromFactoryBean方法。
    protected Object getObjectFromFactoryBean(FactoryBean factory, String beanName, boolean shouldPostProcess) {
        if (factory.isSingleton() && containsSingleton(beanName)) {//若工厂是单例，且本容器包含beanName对应的单例类
            synchronized (getSingletonMutex()) {//以所有的单例集合为锁
                Object object = this.factoryBeanObjectCache.get(beanName);//根据beanName从factoryBeanObjectCache中取
                if (object == null) {//若取不到
                    object = doGetObjectFromFactoryBean(factory, beanName, shouldPostProcess);
                    this.factoryBeanObjectCache.put(beanName, (object != null ? object : NULL_OBJECT));//放进factoryBeanObjectCache
                }
                return (object != NULL_OBJECT ? object : null);
            }
        }
        else {//否则，直接
            return doGetObjectFromFactoryBean(factory, beanName, shouldPostProcess);
        }
    }

    //从工厂Bean中取实例
    private Object doGetObjectFromFactoryBean(
            final FactoryBean factory, final String beanName, final boolean shouldPostProcess)
            throws BeanCreationException {

        Object object;
        //跟getTypeForFactoryBean的实现一样。
        try {
            if (System.getSecurityManager() != null) {//若系统存在安全管理器
                AccessControlContext acc = getAccessControlContext();//得到当前容器的安全访问上下文
                try {//返回factoryBean的类型这个操作不做权限检查，直接调用
                    object = AccessController.doPrivileged(new PrivilegedExceptionAction<Object>() {
                        public Object run() throws Exception {
                                return factory.getObject();
                            }
                        }, acc);
                }
                catch (PrivilegedActionException pae) {
                    throw pae.getException();
                }
            }
            else {//否则直接取
                object = factory.getObject();
            }
        }
        catch (FactoryBeanNotInitializedException ex) {
            throw new BeanCurrentlyInCreationException(beanName, ex.toString());
        }
        catch (Throwable ex) {
            throw new BeanCreationException(beanName, "FactoryBean threw exception on object creation", ex);
        }

        //如果从beanFactory取不到，且这个实例即将被创建，抛出异常
        if (object == null && isSingletonCurrentlyInCreation(beanName)) {
            throw new BeanCurrentlyInCreationException(
                    beanName, "FactoryBean which is currently in creation returned null from getObject");
        }
        //若取不到，且这个实例允许前处理
        if (object != null && shouldPostProcess) {
            try {
                object = postProcessObjectFromFactoryBean(object, beanName);//这里简单返回，前处理的功能留给子类重写
            }
            catch (Throwable ex) {
                throw new BeanCreationException(beanName, "Post-processing of the FactoryBean‘s object failed", ex);
            }
        }

        return object;
    }

    //这里简单返回Object，留给子类重写
    protected Object postProcessObjectFromFactoryBean(Object object, String beanName) throws BeansException {
        return object;
    }

    //如果这个Object是FactoryBean类型，就转换成FactoryBean返回
    protected FactoryBean getFactoryBean(String beanName, Object beanInstance) throws BeansException {
        if (!(beanInstance instanceof FactoryBean)) {
            throw new BeanCreationException(beanName,
                    "Bean instance of type [" + beanInstance.getClass() + "] is not a FactoryBean");
        }
        return (FactoryBean) beanInstance;
    }

    //移除单例类这个方法重写，父类的移除之外，还要移除factoryBeanObjectCache中的。
    @Override
    protected void removeSingleton(String beanName) {
        super.removeSingleton(beanName);
        this.factoryBeanObjectCache.remove(beanName);
    }

    //返回当前容器的安全访问上下文
    protected AccessControlContext getAccessControlContext() {
        return AccessController.getContext();
    }

}

public abstract class AbstractBeanFactory extends FactoryBeanRegistrySupport implements ConfigurableBeanFactory {

    //父工厂的引用
    private BeanFactory parentBeanFactory;

    //类加载器
    private ClassLoader beanClassLoader = ClassUtils.getDefaultClassLoader();

    //临时类加载器
    private ClassLoader tempClassLoader;

    /** Whether to cache bean metadata or rather reobtain it for every access */
    private boolean cacheBeanMetadata = true;

    //Bean表达式分解器，用来分解Bean定义中的表达式
    private BeanExpressionResolver beanExpressionResolver;

    //转换服务，用来替代属性编辑器的
    private ConversionService conversionService;

    //属性编辑登记员集合，容量为4的LinkedHashSet
    private final Set<PropertyEditorRegistrar> propertyEditorRegistrars =
            new LinkedHashSet<PropertyEditorRegistrar>(4);

    //通用的类型转换器，重写了默认的属相编辑器机制
    private TypeConverter typeConverter;

    //默认的属性编辑器集合
    private final Map<Class<?>, Class<? extends PropertyEditor>> customEditors =
            new HashMap<Class<?>, Class<? extends PropertyEditor>>(4);

    //嵌入值转换器集合
    private final List<StringValueResolver> embeddedValueResolvers = new LinkedList<StringValueResolver>();

    //BeanPostProcessor处理器集合
    private final List<BeanPostProcessor> beanPostProcessors = new ArrayList<BeanPostProcessor>();

    //标记是否有InstantiationAwareBeanPostProcessors实例被注册
    private boolean hasInstantiationAwareBeanPostProcessors;

    //标记是否有DestructionAwareBeanPostProcessors实例被注册
    private boolean hasDestructionAwareBeanPostProcessors;

    //范围标识符和Scope实例的对应的Map
    private final Map<String, Scope> scopes = new HashMap<String, Scope>(8);

    //安全上下文Provider，可以得到安全管理器的安全上下文
    private SecurityContextProvider securityContextProvider;

    //合并后的Bean根定义的集合
    private final Map<String, RootBeanDefinition> mergedBeanDefinitions =
            new ConcurrentHashMap<String, RootBeanDefinition>(64);

    //至少被创建过一次的Bean的集合
    private final Map<String, Boolean> alreadyCreated = new ConcurrentHashMap<String, Boolean>(64);

    //当前正在创建的原型，当前线程相关
    private final ThreadLocal<Object> prototypesCurrentlyInCreation =
            new NamedThreadLocal<Object>("Prototype beans currently in creation");


    //空构造方法
    public AbstractBeanFactory() {
    }

    //指定父Bean工厂的构造方法
    public AbstractBeanFactory(BeanFactory parentBeanFactory) {
        this.parentBeanFactory = parentBeanFactory;
    }


    //---------------------------------------------------------------------
    // 3个getBean，BeanFactory接口的实现方法，实质是在调用doGetBean
    //---------------------------------------------------------------------

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

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

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

    //    提供创建时需要参数列表的getBean
    public <T> T getBean(String name, Class<T> requiredType, Object... args) throws BeansException {
        return doGetBean(name, requiredType, args, false);
    }

    //从容器中获取bean的基本方法。
    @SuppressWarnings("unchecked")
    protected <T> T doGetBean(
            final String name, final Class<T> requiredType, final Object[] args, boolean typeCheckOnly)
            throws BeansException {

        final String beanName = transformedBeanName(name);//在aliasMap中取得的标准名
        Object bean;

        // Eagerly check singleton cache for manually registered singletons.
        Object sharedInstance = getSingleton(beanName);//首先在单例集合中取
        if (sharedInstance != null && args == null) {//如果取得到，没有指定参数
            if (logger.isDebugEnabled()) {//若Log允许调试
                if (isSingletonCurrentlyInCreation(beanName)) {//若正准备创建，输出日志
                    logger.debug("Returning eagerly cached instance of singleton bean ‘" + beanName +
                            "‘ that is not fully initialized yet - a consequence of a circular reference");
                }
                else {
                    logger.debug("Returning cached instance of singleton bean ‘" + beanName + "‘");
                }
            }
            ////根据给定的实例是否为工厂Bean，返回它自己或工厂Bean创建的实例
            bean = getObjectForBeanInstance(sharedInstance, name, beanName, null);
        }

        else {
            if (isPrototypeCurrentlyInCreation(beanName)) {//如果正在被创建，就抛出异常
                throw new BeanCurrentlyInCreationException(beanName);
            }

            BeanFactory parentBeanFactory = getParentBeanFactory();//取本容器的父容器
            if (parentBeanFactory != null && !containsBeanDefinition(beanName)) {//若存在父容器，且本容器不存在对应的Bean定义
                String nameToLookup = originalBeanName(name);//取原始的Bean名
                if (args != null) {//若参数列表存在
                    // 那么用父容器根据原始Bean名和参数列表返回
                    return (T) parentBeanFactory.getBean(nameToLookup, args);
                }
                else {
                    // 参数列表不要求，那就直接根据原始名称和要求的类型返回
                    return parentBeanFactory.getBean(nameToLookup, requiredType);
                }
            }

            //如果不需要类型检查，标记其已经被创建
            if (!typeCheckOnly) {
                markBeanAsCreated(beanName);
            }

            //根据beanName取其根Bean定义
            final RootBeanDefinition mbd = getMergedLocalBeanDefinition(beanName);
            checkMergedBeanDefinition(mbd, beanName, args);

            String[] dependsOn = mbd.getDependsOn();//得到这个根定义的所有依赖
            if (dependsOn != null) {
                for (String dependsOnBean : dependsOn) {
                    getBean(dependsOnBean);//注册这个Bean
                    //注册一个Bean和依赖于它的Bean（后参数依赖前参数）
                    registerDependentBean(dependsOnBean, beanName);
                }
            }

            // 如果Bean定义是单例，就在返回单例
            if (mbd.isSingleton()) {
                sharedInstance = getSingleton(beanName, new ObjectFactory<Object>() {
                    public Object getObject() throws BeansException {
                        try {
                            return createBean(beanName, mbd, args);
                        }
                        catch (BeansException ex) {
                            destroySingleton(beanName);
                            throw ex;
                        }
                    }
                });
                //根据给定的实例是否为工厂Bean，返回它自己或工厂Bean创建的实例
                bean = getObjectForBeanInstance(sharedInstance, name, beanName, mbd);
            }
            //如果是原型
            else if (mbd.isPrototype()) {
                // It‘s a prototype -> create a new instance.
                Object prototypeInstance = null;
                try {
                    beforePrototypeCreation(beanName);//原型创建前，与当前线程绑定
                    prototypeInstance = createBean(beanName, mbd, args);
                }
                finally {
                    afterPrototypeCreation(beanName);//原型创建后，与当前线程解除绑定
                }
                bean = getObjectForBeanInstance(prototypeInstance, name, beanName, mbd);
            }

            else {//既不是单例又不是原型的情况
                String scopeName = mbd.getScope();
                final Scope scope = this.scopes.get(scopeName);//得到范围
                if (scope == null) {
                    throw new IllegalStateException("No Scope registered for scope ‘" + scopeName + "‘");
                }
                try {//根据范围创建实例
                    Object scopedInstance = scope.get(beanName, new ObjectFactory<Object>() {
                        public Object getObject() throws BeansException {
                            beforePrototypeCreation(beanName);
                            try {
                                return createBean(beanName, mbd, args);//原型创建前，与当前线程绑定
                            }
                            finally {
                                ////原型创建后，与当前线程解除绑定
                                afterPrototypeCreation(beanName);
                            }
                        }
                    });
                    //根据给定的实例是否为工厂Bean，返回它自己或工厂Bean创建的实例
                    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);
                }
            }
        }

        //判断要求的类型是否和Bean实例的类型正在匹配
        if (requiredType != null && bean != null && !requiredType.isAssignableFrom(bean.getClass())) {
            try {
                return getTypeConverter().convertIfNecessary(bean, requiredType);//转换类型，不抛出异常就说明类型匹配
            }
            catch (TypeMismatchException ex) {
                if (logger.isDebugEnabled()) {
                    logger.debug("Failed to convert bean ‘" + name + "‘ to required type [" +
                            ClassUtils.getQualifiedName(requiredType) + "]", ex);
                }
                throw new BeanNotOfRequiredTypeException(name, requiredType, bean.getClass());
            }
        }
        return (T) bean;
    }
    
    //判断本容器是否包含指定bean
    public boolean containsBean(String name) {
        String beanName = transformedBeanName(name);
        //    （如果是否包含单例 或 包含Bean定义）且 （为工厂Bean的产物 或 本身就是工厂bean），就返回true
        if (containsSingleton(beanName) || containsBeanDefinition(beanName)) {
            return (!BeanFactoryUtils.isFactoryDereference(name) || isFactoryBean(name));
        }
        // 如果不包含单例且不包含Bean定义，就从父类去查找
        BeanFactory parentBeanFactory = getParentBeanFactory();
        return (parentBeanFactory != null && parentBeanFactory.containsBean(originalBeanName(name)));
    }

    //判断指定Bean是否为单例
    public boolean isSingleton(String name) throws NoSuchBeanDefinitionException {
        String beanName = transformedBeanName(name);

        Object beanInstance = getSingleton(beanName, false);//首先从单例集合中取
        if (beanInstance != null) {//取不到，就判断它是不是FactoryBean的实例
            if (beanInstance instanceof FactoryBean) {    //    如果是，要求它是工厂Bean产生的实例或这个工厂bean是单例
                return (BeanFactoryUtils.isFactoryDereference(name) || ((FactoryBean<?>) beanInstance).isSingleton());
            }
            else {//    如果不是，要求它不是工厂Bean产生的实例
                return !BeanFactoryUtils.isFactoryDereference(name);
            }
        }//若虽然取不到，但是单例集合中包含它的名字，说明它是单例
        else if (containsSingleton(beanName)) {
            return true;
        }

        else {
            //从父工厂中去查询Bean定义
            BeanFactory parentBeanFactory = getParentBeanFactory();
            if (parentBeanFactory != null && !containsBeanDefinition(beanName)) {
                //父工厂找不到Bean定义，那就在父工厂根据原始名去查是否为单例
                return parentBeanFactory.isSingleton(originalBeanName(name));
            }
            //返回一个合并后的根Bean定义
            RootBeanDefinition mbd = getMergedLocalBeanDefinition(beanName);

            // In case of FactoryBean, return singleton status of created object if not a dereference.
            //若该根定义是单例
            if (mbd.isSingleton()) {
                if (isFactoryBean(beanName, mbd)) {    //若该根定义为工厂Bean
                    if (BeanFactoryUtils.isFactoryDereference(name)) {//判断是否为工厂产生的实例
                        return true;
                    }
                    //取对应的工厂，判断该工厂Bean是否为单例
                    FactoryBean<?> factoryBean = (FactoryBean<?>) getBean(FACTORY_BEAN_PREFIX + beanName);
                    return factoryBean.isSingleton();
                }
                else {    //    是否不为工厂Bean产生的实例（此时，即，该根定义不为工厂Bean，且不为工厂Bean产生的实例的时候，由于根定义是单例，那么它就是单例）
                    return !BeanFactoryUtils.isFactoryDereference(name);
                }
            }
            else {
                return false;
            }
        }
    }

    //判断是否为原型
    public boolean isPrototype(String name) throws NoSuchBeanDefinitionException {
        String beanName = transformedBeanName(name);

        BeanFactory parentBeanFactory = getParentBeanFactory();//得到父工厂
        //若父工厂中的定义为原型，就为原型
        if (parentBeanFactory != null && !containsBeanDefinition(beanName)) {
            return parentBeanFactory.isPrototype(originalBeanName(name));
        }

        //若合并后的根定义为原型，且不是工厂Bean产生的实例、或本身是工厂Bean，那么就为原型
        RootBeanDefinition mbd = getMergedLocalBeanDefinition(beanName);
        if (mbd.isPrototype()) {
            return (!BeanFactoryUtils.isFactoryDereference(name) || isFactoryBean(beanName, mbd));
        }
        else {
            if (BeanFactoryUtils.isFactoryDereference(name)) {//若为工厂Bean产生的实例
                return false;
            }
            if (isFactoryBean(beanName, mbd)) {//若为工厂Bean，取它产生的Bean，判断SmartFactoryBean
                final FactoryBean<?> factoryBean = (FactoryBean<?>) getBean(FACTORY_BEAN_PREFIX + beanName);
                if (System.getSecurityManager() != null) {
                    return AccessController.doPrivileged(new PrivilegedAction<Boolean>() {
                        public Boolean run() {
                            return ((factoryBean instanceof SmartFactoryBean && ((SmartFactoryBean<?>) factoryBean).isPrototype()) ||
                                    !factoryBean.isSingleton());
                        }
                    }, getAccessControlContext());
                }
                else {
                    return ((factoryBean instanceof SmartFactoryBean && ((SmartFactoryBean<?>) factoryBean).isPrototype()) ||
                            !factoryBean.isSingleton());
                }
            }
            else {
                return false;
            }
        }
    }

    //判断类型是否匹配
    public boolean isTypeMatch(String name, Class<?> targetType) throws NoSuchBeanDefinitionException {
        String beanName = transformedBeanName(name);
        Class<?> typeToMatch = (targetType != null ? targetType : Object.class);

        Object beanInstance = getSingleton(beanName, false);//取name对应的单例
        if (beanInstance != null) {
            if (beanInstance instanceof FactoryBean) {//若为工厂Bean
                //若不是工厂Bean产生的实例
                if (!BeanFactoryUtils.isFactoryDereference(name)) {
                    //取工厂Bean的类型与targetType进行对比
                    Class<?> type = getTypeForFactoryBean((FactoryBean<?>) beanInstance);
                    return (type != null && ClassUtils.isAssignable(typeToMatch, type));
                }
                else {
                    return ClassUtils.isAssignableValue(typeToMatch, beanInstance);
                }
            }
            //不是工厂Bean，那就直接判断
            else {
                return !BeanFactoryUtils.isFactoryDereference(name) &&
                        ClassUtils.isAssignableValue(typeToMatch, beanInstance);
            }
        }
        //单例表中，对应的Key没有值，也不包含Bean定义，说明没有注册，返回false
        else if (containsSingleton(beanName) && !containsBeanDefinition(beanName)) {
            return false;
        }
        //以下是包含Bean定义的情况
        else {
            //先查父类的Bean定义
            BeanFactory parentBeanFactory = getParentBeanFactory();
            if (parentBeanFactory != null && !containsBeanDefinition(beanName)) {
                // No bean definition found in this factory -> delegate to parent.
                return parentBeanFactory.isTypeMatch(originalBeanName(name), targetType);
            }
            
            //直接查合并后的根定义
            RootBeanDefinition mbd = getMergedLocalBeanDefinition(beanName);

            //构建类型数组
            Class[] typesToMatch = (FactoryBean.class.equals(typeToMatch) ?
                    new Class[] {typeToMatch} : new Class[] {FactoryBean.class, typeToMatch});

            // Check decorated bean definition, if any: We assume it‘ll be easier
            // to determine the decorated bean‘s type than the proxy‘s type.
            //得到Bean定义的持有者
            BeanDefinitionHolder dbd = mbd.getDecoratedDefinition();
            if (dbd != null && !BeanFactoryUtils.isFactoryDereference(name)) {//若为Bean工厂生成的实例，先得到根定义
                RootBeanDefinition tbd = getMergedBeanDefinition(dbd.getBeanName(), dbd.getBeanDefinition(), mbd);
                Class<?> targetClass = predictBeanType(dbd.getBeanName(), tbd, typesToMatch);//得到预测的根定义
                if (targetClass != null && !FactoryBean.class.isAssignableFrom(targetClass)) {
                    return typeToMatch.isAssignableFrom(targetClass);
                }
            }

            Class<?> beanType = predictBeanType(beanName, mbd, typesToMatch);//预测后的类型
            if (beanType == null) {
                return false;
            }

            if (FactoryBean.class.isAssignableFrom(beanType)) {//BeanFactory是否为其子类
                if (!BeanFactoryUtils.isFactoryDereference(name)) {//若不为工厂Bean的产物
                    // If it‘s a FactoryBean, we want to look at what it creates, not the factory class.
                    beanType = getTypeForFactoryBean(beanName, mbd);
                    if (beanType == null) {
                        return false;
                    }
                }
            }
            else if (BeanFactoryUtils.isFactoryDereference(name)) {//若为工厂类Bean的产物
                beanType = predictBeanType(beanName, mbd, FactoryBean.class);//预测类型
                if (beanType == null || !FactoryBean.class.isAssignableFrom(beanType)) {
                    return false;
                }
            }

            return typeToMatch.isAssignableFrom(beanType);
        }
    }

    //返回类型
    public Class<?> getType(String name) throws NoSuchBeanDefinitionException {
        String beanName = transformedBeanName(name);

        // Check manually registered singletons.
        Object beanInstance = getSingleton(beanName, false);
        if (beanInstance != null) {
            if (beanInstance instanceof FactoryBean && !BeanFactoryUtils.isFactoryDereference(name)) {
                return getTypeForFactoryBean((FactoryBean<?>) beanInstance);
            }
            else {
                return beanInstance.getClass();
            }
        }
        else if (containsSingleton(beanName) && !containsBeanDefinition(beanName)) {
            // null instance registered
            return null;
        }

        else {
            // No singleton instance found -> check bean definition.
            BeanFactory parentBeanFactory = getParentBeanFactory();
            if (parentBeanFactory != null && !containsBeanDefinition(beanName)) {
                // No bean definition found in this factory -> delegate to parent.
                return parentBeanFactory.getType(originalBeanName(name));
            }

            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.
            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);
                }
                else {
                    return beanClass;
                }
            }
            else {
                return (!BeanFactoryUtils.isFactoryDereference(name) ? beanClass : null);
            }
        }
    }

    //重写了，得到别名的方法。
    @Override
    public String[] getAliases(String name) {
        String beanName = transformedBeanName(name);
        List<String> aliases = new ArrayList<String>();
        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);
        for (String retrievedAlias : retrievedAliases) {
            String alias = (factoryPrefix ? FACTORY_BEAN_PREFIX : "") + retrievedAlias;
            if (!alias.equals(name)) {
                aliases.add(alias);
            }
        }
        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
    //---------------------------------------------------------------------

    //返回本Bean工厂的父Bean工厂
    public BeanFactory getParentBeanFactory() {
        return this.parentBeanFactory;
    }

    //是否在本容器中（就是说，并不是工厂bean生产出来的）
    public boolean containsLocalBean(String name) {
        String beanName = transformedBeanName(name);    //    转换后的名字
        //（是否为单例或有对应的Bean定义） 且（不是工厂Bean生产出来的 或 本身就是工厂bean）
        return ((containsSingleton(beanName) || containsBeanDefinition(beanName)) &&
                (!BeanFactoryUtils.isFactoryDereference(name) || isFactoryBean(beanName)));
    }


    //---------------------------------------------------------------------
    // Implementation of ConfigurableBeanFactory interface
    //---------------------------------------------------------------------

    public void setParentBeanFactory(BeanFactory parentBeanFactory) {
        if (this.parentBeanFactory != null && this.parentBeanFactory != parentBeanFactory) {
            throw new IllegalStateException("Already associated with parent BeanFactory: " + this.parentBeanFactory);
        }
        this.parentBeanFactory = parentBeanFactory;
    }

    public void setBeanClassLoader(ClassLoader beanClassLoader) {
        this.beanClassLoader = (beanClassLoader != null ? beanClassLoader : ClassUtils.getDefaultClassLoader());
    }

    public ClassLoader getBeanClassLoader() {
        return this.beanClassLoader;
    }

    public void setTempClassLoader(ClassLoader tempClassLoader) {
        this.tempClassLoader = tempClassLoader;
    }

    public ClassLoader getTempClassLoader() {
        return this.tempClassLoader;
    }

    public void setCacheBeanMetadata(boolean cacheBeanMetadata) {
        this.cacheBeanMetadata = cacheBeanMetadata;
    }

    public boolean isCacheBeanMetadata() {
        return this.cacheBeanMetadata;
    }

    public void setBeanExpressionResolver(BeanExpressionResolver resolver) {
        this.beanExpressionResolver = resolver;
    }

    public BeanExpressionResolver getBeanExpressionResolver() {
        return this.beanExpressionResolver;
    }

    public void setConversionService(ConversionService conversionService) {
        this.conversionService = conversionService;
    }

    public ConversionService getConversionService() {
        return this.conversionService;
    }

    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;
    }

    public void registerCustomEditor(Class<?> requiredType, Class<? extends PropertyEditor> propertyEditorClass) {
        Assert.notNull(requiredType, "Required type must not be null");
        Assert.isAssignable(PropertyEditor.class, propertyEditorClass);
        this.customEditors.put(requiredType, propertyEditorClass);
    }

    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;
    }

    public void setTypeConverter(TypeConverter typeConverter) {
        this.typeConverter = typeConverter;
    }

    //得到通用的类型转换器
    protected TypeConverter getCustomTypeConverter() {
        return this.typeConverter;
    }

    //得到类型转换器
    public TypeConverter getTypeConverter() {
        TypeConverter customConverter = getCustomTypeConverter();
        if (customConverter != null) {
            return customConverter;
        }
        else {//若本容器未注册类型转换器，就创建一个简单的类型转换器
            SimpleTypeConverter typeConverter = new SimpleTypeConverter();
            typeConverter.setConversionService(getConversionService());
            registerCustomEditors(typeConverter);
            return typeConverter;
        }
    }

    public void addEmbeddedValueResolver(StringValueResolver valueResolver) {
        Assert.notNull(valueResolver, "StringValueResolver must not be null");
        this.embeddedValueResolvers.add(valueResolver);
    }

    public String resolveEmbeddedValue(String value) {
        String result = value;
        for (StringValueResolver resolver : this.embeddedValueResolvers) {
            if (result == null) {
                return null;
            }
            result = resolver.resolveStringValue(result);
        }
        return result;
    }

    public void addBeanPostProcessor(BeanPostProcessor beanPostProcessor) {
        Assert.notNull(beanPostProcessor, "BeanPostProcessor must not be null");
        this.beanPostProcessors.remove(beanPostProcessor);
        this.beanPostProcessors.add(beanPostProcessor);
        if (beanPostProcessor instanceof InstantiationAwareBeanPostProcessor) {
            this.hasInstantiationAwareBeanPostProcessors = true;
        }
        if (beanPostProcessor instanceof DestructionAwareBeanPostProcessor) {
            this.hasDestructionAwareBeanPostProcessors = true;
        }
    }

    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.
     * @see #addBeanPostProcessor
     * @see org.springframework.beans.factory.config.InstantiationAwareBeanPostProcessor
     */
    protected boolean hasInstantiationAwareBeanPostProcessors() {
        return this.hasInstantiationAwareBeanPostProcessors;
    }

    /**
     * Return whether this factory holds a DestructionAwareBeanPostProcessor
     * that will get applied to singleton beans on shutdown.
     * @see #addBeanPostProcessor
     * @see org.springframework.beans.factory.config.DestructionAwareBeanPostProcessor
     */
    protected boolean hasDestructionAwareBeanPostProcessors() {
        return this.hasDestructionAwareBeanPostProcessors;
    }

    public void registerScope(String scopeName, Scope scope) {
        Assert.notNull(scopeName, "Scope identifier must not be null");
        Assert.notNull(scope, "Scope must not be null");
        if (SCOPE_SINGLETON.equals(scopeName) || SCOPE_PROTOTYPE.equals(scopeName)) {
            throw new IllegalArgumentException("Cannot replace existing scopes ‘singleton‘ and ‘prototype‘");
        }
        this.scopes.put(scopeName, scope);
    }

    public String[] getRegisteredScopeNames() {
        return StringUtils.toStringArray(this.scopes.keySet());
    }

    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());
    }

    public void copyConfigurationFrom(ConfigurableBeanFactory otherFactory) {
        Assert.notNull(otherFactory, "BeanFactory must not be null");
        setBeanClassLoader(otherFactory.getBeanClassLoader());
        setCacheBeanMetadata(otherFactory.isCacheBeanMetadata());
        setBeanExpressionResolver(otherFactory.getBeanExpressionResolver());
        if (otherFactory instanceof AbstractBeanFactory) {
            AbstractBeanFactory otherAbstractFactory = (AbstractBeanFactory) otherFactory;
            this.customEditors.putAll(otherAbstractFactory.customEditors);
            this.propertyEditorRegistrars.addAll(otherAbstractFactory.propertyEditorRegistrars);
            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());
        }
    }

    //返回合并后的bean定义（父Bean定义和子Bean定义合并）
    public BeanDefinition getMergedBeanDefinition(String name) throws BeansException {
        String beanName = transformedBeanName(name);

        // Efficiently check whether bean definition exists in this factory.
        //若Bean定义不存在，且本容器父工厂为ConfigurableBeanFactory的实例，让父工厂来调用这个方法
        if (!containsBeanDefinition(beanName) && getParentBeanFactory() instanceof ConfigurableBeanFactory) {
            return ((ConfigurableBeanFactory) getParentBeanFactory()).getMergedBeanDefinition(beanName);
        }
        //否则直接从本地合并后的Bean定义中取
        return getMergedLocalBeanDefinition(beanName);
    }

    public boolean isFactoryBean(String name) throws NoSuchBeanDefinitionException {
        String beanName = transformedBeanName(name);

        Object beanInstance = getSingleton(beanName, false);
        if (beanInstance != null) {
            return (beanInstance instanceof FactoryBean);
        }
        else if (containsSingleton(beanName)) {
            // null instance registered
            return false;
        }

        // No singleton instance found -> check bean definition.
        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
    public boolean isActuallyInCreation(String beanName) {
        return isSingletonCurrentlyInCreation(beanName) || isPrototypeCurrentlyInCreation(beanName);
    }

    //    判断指定的原型是否正在被创建
    protected boolean isPrototypeCurrentlyInCreation(String beanName) {
        Object curVal = this.prototypesCurrentlyInCreation.get();
        return (curVal != null &&
                (curVal.equals(beanName) || (curVal instanceof Set && ((Set<?>) curVal).contains(beanName))));
    }

    //原型创建前回调，需要子类重写
    @SuppressWarnings("unchecked")
    protected void beforePrototypeCreation(String beanName) {
        Object curVal = this.prototypesCurrentlyInCreation.get();
        if (curVal == null) {//原型创建状态与当前线程绑定
            this.prototypesCurrentlyInCreation.set(beanName);
        }
        else if (curVal instanceof String) {
            Set<String> beanNameSet = new HashSet<String>(2);
            beanNameSet.add((String) curVal);
            beanNameSet.add(beanName);
            this.prototypesCurrentlyInCreation.set(beanNameSet);
        }
        //这里多余了。。。
        else {
            Set<String> beanNameSet = (Set<String>) curVal;
            beanNameSet.add(beanName);
        }
    }

    //创建原型后，从当前线程解除绑定
    @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();
            }
        }
    }

    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.
     * @param beanName the name of the bean definition
     * @param beanInstance the bean instance to destroy
     * @param mbd the merged bean definition
     */
    protected void destroyBean(String beanName, Object beanInstance, RootBeanDefinition mbd) {
        new DisposableBeanAdapter(beanInstance, beanName, mbd, getBeanPostProcessors(), getAccessControlContext()).destroy();
    }

    public void destroyScopedBean(String beanName) {
        RootBeanDefinition mbd = getMergedLocalBeanDefinition(beanName);
        if (mbd.isSingleton() || mbd.isPrototype()) {
            throw new IllegalArgumentException(
                    "Bean name ‘" + beanName + "‘ does not correspond to an object in a mutable scope");
        }
        String scopeName = mbd.getScope();
        Scope scope = this.scopes.get(scopeName);
        if (scope == null) {
            throw new IllegalStateException("No Scope SPI registered for scope ‘" + scopeName + "‘");
        }
        Object bean = scope.remove(beanName);
        if (bean != null) {
            destroyBean(beanName, bean, mbd);
        }
    }


    //---------------------------------------------------------------------
    // Implementation methods
    //---------------------------------------------------------------------

    //变换后的Bean名称（先去掉BeanFactory前缀，然后在aliasMap中取标准名）
    protected String transformedBeanName(String name) {
        return canonicalName(BeanFactoryUtils.transformedBeanName(name));
    }

    //返回原始的Bean名
    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.
     * <p>The default implementation delegates to {@link #registerCustomEditors}.
     * Can be overridden in subclasses.
     * @param bw the BeanWrapper to initialize
     */
    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.
     * <p>To be called for BeanWrappers that will create and populate bean
     * instances, and for SimpleTypeConverter used for constructor argument
     * and factory method type conversion.
     * @param registry the PropertyEditorRegistry to initialize
     */
    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 {
                    registrar.registerCustomEditors(registry);
                }
                catch (BeanCreationException ex) {
                    Throwable rootCause = ex.getMostSpecificCause();
                    if (rootCause instanceof BeanCurrentlyInCreationException) {
                        BeanCreationException bce = (BeanCreationException) rootCause;
                        if (isCurrentlyInCreation(bce.getBeanName())) {
                            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()) {
            for (Map.Entry<Class<?>, Class<? extends PropertyEditor>> entry : this.customEditors.entrySet()) {
                Class<?> requiredType = entry.getKey();
                Class<? extends PropertyEditor> editorClass = entry.getValue();
                registry.registerCustomEditor(requiredType, BeanUtils.instantiateClass(editorClass));
            }
        }
    }

    //返回一个合并后的根Bean定义（父Bean定义和子Bean定义合并）（从当前容器取）
    protected RootBeanDefinition getMergedLocalBeanDefinition(String beanName) throws BeansException {
        // Quick check on the concurrent map first, with minimal locking.
        RootBeanDefinition mbd = this.mergedBeanDefinitions.get(beanName);//首先直接从合并根定义集合中取
        if (mbd != null) {
            return mbd;
        }
        //根据bean名和其对应的Bean定义，取其根Bean根定义
        return getMergedBeanDefinition(beanName, getBeanDefinition(beanName));
    }

    //根据Bean名和Bean定义取其Bean根定义
    protected RootBeanDefinition getMergedBeanDefinition(String beanName, BeanDefinition bd)
            throws BeanDefinitionStoreException {

        return getMergedBeanDefinition(beanName, bd, null);//调用重载方法
    }

    //根据Bean名称返回根定义（若给定的Bean定义为子Bean定义，那么合并它的父Bean定义）
    protected RootBeanDefinition getMergedBeanDefinition(
            String beanName, BeanDefinition bd, BeanDefinition containingBd)
            throws BeanDefinitionStoreException {

        synchronized (this.mergedBeanDefinitions) {
            RootBeanDefinition mbd = null;

            //若给定的Bean定义并没有包含子Bean定义，那么直接根据Bean名取根定义
            if (containingBd == null) {
                mbd = this.mergedBeanDefinitions.get(beanName);
            }

            if (mbd == null) {//若取不到
                if (bd.getParentName() == null) {//若Bean定义没有父类，就很简单了
                    if (bd instanceof RootBeanDefinition) {//若Bean定义是RootBeanDefinition的实例，克隆、强转后返回
                        mbd = ((RootBeanDefinition) bd).cloneBeanDefinition();
                    }
                    else {//否则，根据Bean定义，来构造一个根Bean定义
                        mbd = new RootBeanDefinition(bd);
                    }
                }
                else {//若Bean定义有父类
                    // Child bean definition: needs to be merged with parent.
                    BeanDefinition pbd;
                    try {
                        String parentBeanName = transformedBeanName(bd.getParentName());//取其父Bean定义的名字
                        if (!beanName.equals(parentBeanName)) {//若Bean名字并不是bd的父Bean的名字
                            pbd = getMergedBeanDefinition(parentBeanName);//根据父Bean定义名称来返回合并后的bean定义
                        }
                        else {//如果beanName对应的Bean就是bd的父Bean
                            if (getParentBeanFactory() instanceof ConfigurableBeanFactory) {//若父Bean工厂为ConfigurableBeanFactory的实例
                                //    那么强转成ConfigurableBeanFactory后再调用合并方法
                                pbd = ((ConfigurableBeanFactory) getParentBeanFactory()).getMergedBeanDefinition(parentBeanName);
                            }
                            else {//若父Bean工厂不是ConfigurableBeanFactory的实例，就抛出异常
                                throw new NoSuchBeanDefinitionException(bd.getParentName(),
                                        "Parent name ‘" + bd.getParentName() + "‘ 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);
                    }
                    // 深度复制
                    mbd = new RootBeanDefinition(pbd);//根据Bean定义生成一个根Bean定义
                    mbd.overrideFrom(bd);//将Bean定义的属性复制进自己的定义（根Bean定义）中
                }

                if (!StringUtils.hasLength(mbd.getScope())) {//如果根Bean定义未设置范围
                    mbd.setScope(RootBeanDefinition.SCOPE_SINGLETON);//那么设置其范围为单例
                }

                //    若本根Bean定义包含Bean定义、本根Bean定义为单例且包含的Bean定义并不是单例
                if (containingBd != null && !containingBd.isSingleton() && mbd.isSingleton()) {
                    mbd.setScope(containingBd.getScope());//    那么将本根Bean定义的范围设置为包含的Bean定义的范围
                }

                //若本根Bean定义不包含Bean定义，且是缓存Bean元数据（重写前均为true）且Bean定义是否有资格缓存（默认实现是，这个Bean已经创建便有资格）
                if (containingBd == null && isCacheBeanMetadata() && isBeanEligibleForMetadataCaching(beanName)) {
                    this.mergedBeanDefinitions.put(beanName, mbd);//放进mergedBeanDefinitions中
                }
            }

            return mbd;
        }
    }

    //检查Bean定义，抛出异常
    protected void checkMergedBeanDefinition(RootBeanDefinition mbd, String beanName, Object[] args)
            throws BeanDefinitionStoreException {

        if (mbd.isAbstract()) {
            throw new BeanIsAbstractException(beanName);
        }

        if (args != null && !mbd.isPrototype()) {
            throw new BeanDefinitionStoreException(
                    "Can only specify arguments for the getBean method when referring to a prototype bean definition");
        }
    }

    /**
     * Remove the merged bean definition for the specified bean,
     * recreating it on next access.
     * @param beanName the bean name to clear the merged definition for
     */
    protected void clearMergedBeanDefinition(String beanName) {
        this.mergedBeanDefinitions.remove(beanName);
    }

    //解析类型，处理异常
    protected Class<?> resolveBeanClass(final RootBeanDefinition mbd, String beanName, final Class<?>... typesToMatch)
            throws CannotLoadBeanClassException {
        try {
            if (mbd.hasBeanClass()) {
                return mbd.getBeanClass();
            }
            if (System.getSecurityManager() != null) {
                return AccessController.doPrivileged(new PrivilegedExceptionAction<Class<?>>() {
                    public Class<?> run() throws Exception {
                        return 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);
        }
    }

    // 真正的解析类型
    private Class<?> doResolveBeanClass(RootBeanDefinition mbd, Class<?>... typesToMatch) throws ClassNotFoundException {
        if (!ObjectUtils.isEmpty(typesToMatch)) {
            ClassLoader tempClassLoader = getTempClassLoader();//找到临时的类加载器
            if (tempClassLoader != null) {
                if (tempClassLoader instanceof DecoratingClassLoader) {//若为装饰类加载器
                    DecoratingClassLoader dcl = (DecoratingClassLoader) tempClassLoader;
                    for (Class<?> typeToMatch : typesToMatch) {
                        dcl.excludeClass(typeToMatch.getName());
                    }
                }
                String className = mbd.getBeanClassName();
                return (className != null ? ClassUtils.forName(className, tempClassLoader) : null);
            }
        }
        return mbd.resolveBeanClass(getBeanClassLoader());
    }

    /**
     * Evaluate the given String as contained in a bean definition,
     * potentially resolving it as an expression.
     * @param value the value to check
     * @param beanDefinition the bean definition that the value comes from
     * @return the resolved value
     * @see #setBeanExpressionResolver
     */
    protected Object evaluateBeanDefinitionString(String value, BeanDefinition beanDefinition) {
        if (this.beanExpressionResolver == null) {
            return value;
        }
        Scope scope = (beanDefinition != null ? getRegisteredScope(beanDefinition.getScope()) : null);
        return this.beanExpressionResolver.evaluate(value, new BeanExpressionContext(this, scope));
    }

    //预测类型
    protected Class<?> predictBeanType(String beanName, RootBeanDefinition mbd, Class<?>... typesToMatch) {
        //若根Bena定义的工厂方法名存在，说明它是工厂Bean创建的，无法预测类型？
        if (mbd.getFactoryMethodName() != null) {
            return null;
        }
        //否则，解析Bean的Class
        return resolveBeanClass(mbd, beanName, typesToMatch);
    }

    /**
     * Check whether the given bean is defined as a {@link FactoryBean}.
     * @param beanName the name of the bean
     * @param mbd the corresponding bean definition
     */
    protected boolean isFactoryBean(String beanName, RootBeanDefinition mbd) {
        Class<?> beanType = predictBeanType(beanName, mbd, FactoryBean.class);
        return (beanType != null && FactoryBean.class.isAssignableFrom(beanType));
    }

    //返回工厂Bean的类型
    protected Class<?> getTypeForFactoryBean(String beanName, RootBeanDefinition mbd) {
        if (!mbd.isSingleton()) {
            return null;
        }
        try {
            FactoryBean<?> factoryBean = doGetBean(FACTORY_BEAN_PREFIX + beanName, FactoryBean.class, null, true);
            return getTypeForFactoryBean(factoryBean);
        }
        catch (BeanCreationException ex) {
            // Can only happen when getting a FactoryBean.
            if (logger.isDebugEnabled()) {
                logger.debug("Ignoring bean creation exception on FactoryBean type check: " + ex);
            }
            onSuppressedException(ex);
            return null;
        }
    }

    //标记这个Bean已经被创建
    protected void markBeanAsCreated(String beanName) {
        this.alreadyCreated.put(beanName, Boolean.TRUE);
    }

    /**
     * Determine whether the specified bean is eligible for having
     * its bean definition metadata cached.
     * @param beanName the name of the bean
     * @return {@code true} if the bean‘s metadata may be cached
     * at this point already
     */
    //若本根Bean定义包含Bean元定义作为缓存，这个方法应被之类覆盖，这里仅判断Bean是否已经被创建
    protected boolean isBeanEligibleForMetadataCaching(String beanName) {
        return this.alreadyCreated.containsKey(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.
     * @param beanName the name of the bean
     * @return {@code true} if actually removed, {@code false} otherwise
     */
    protected boolean removeSingletonIfCreatedForTypeCheckOnly(String beanName) {
        if (!this.alreadyCreated.containsKey(beanName)) {
            removeSingleton(beanName);
            return true;
        }
        else {
            return false;
        }
    }

    //根据给定的实例是否为工厂Bean，返回它自己或工厂Bean创建的实例
    protected Object getObjectForBeanInstance(
            Object beanInstance, String name, String beanName, RootBeanDefinition mbd) {

        //如果这个Bean是工厂Bean创建的 且 这个Bean实例并不是FactoryBean实例，抛异常
        if (BeanFactoryUtils.isFactoryDereference(name) && !(beanInstance instanceof FactoryBean)) {
            throw new BeanIsNotAFactoryException(transformedBeanName(name), beanInstance.getClass());
        }

        //如果这个Bean实例并不是FactoryBean实例 或 这个Bean是工厂Bean创建的，直接返回
        if (!(beanInstance instanceof FactoryBean) || BeanFactoryUtils.isFactoryDereference(name)) {
            return beanInstance;
        }

        //——————————以下都是 这个Bean实例是FactoryBean实例的情况
        Object object = null;
        if (mbd == null) {//若根Bean定义为空，取这个BeanFactory所生产的实例
            object = getCachedObjectForFactoryBean(beanName);
        }
        if (object == null) {//若取不到，那么手动取
            FactoryBean<?> factory = (FactoryBean<?>) beanInstance;//把这个实例转化成一个FactoryBean
            // Caches object obtained from FactoryBean if it is a singleton.
            if (mbd == null && containsBeanDefinition(beanName)) {//若根Bean定义为空，但是容器内有Bean定义
                mbd = getMergedLocalBeanDefinition(beanName);//返回合并后的Bean定义
            }
            boolean synthetic = (mbd != null && mbd.isSynthetic());//标记这个Bean定义是合并的
            object = getObjectFromFactoryBean(factory, beanName, !synthetic);//从工厂Bean中取
        }
        return object;
    }

    //判断给定的Bean是否被使用过
    public boolean isBeanNameInUse(String beanName) {
        //若是别名 或 并非工厂bean生产出来的 或 被其他某个bean所依赖，那么判断其被使用过
        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.
     * @param bean the bean instance to check
     * @param mbd the corresponding bean definition
     * @see org.springframework.beans.factory.DisposableBean
     * @see AbstractBeanDefinition#getDestroyMethodName()
     * @see org.springframework.beans.factory.config.DestructionAwareBeanPostProcessor
     */
    protected boolean requiresDestruction(Object bean, RootBeanDefinition mbd) {
        return (bean != null &&
                (DisposableBeanAdapter.hasDestroyMethod(bean, mbd) || hasDestructionAwareBeanPostProcessors()));
    }

    /**
     * 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.
     * @param beanName the name of the bean
     * @param bean the bean instance
     * @param mbd the bean definition for the bean
     * @see RootBeanDefinition#isSingleton
     * @see RootBeanDefinition#getDependsOn
     * @see #registerDisposableBean
     * @see #registerDependentBean
     */
    protected void registerDisposableBeanIfNecessary(String beanName, Object bean, RootBeanDefinition mbd) {
        AccessControlContext acc = (System.getSecurityManager() != null ? getAccessControlContext() : null);
        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.
                registerDisposableBean(beanName,
                        new DisposableBeanAdapter(bean, beanName, mbd, getBeanPostProcessors(), acc));
            }
            else {
                // A bean with a custom scope...
                Scope scope = this.scopes.get(mbd.getScope());
                if (scope == null) {
                    throw new IllegalStateException("No Scope registered for scope ‘" + mbd.getScope() + "‘");
                }
                scope.registerDestructionCallback(beanName,
                        new DisposableBeanAdapter(bean, beanName, mbd, getBeanPostProcessors(), acc));
            }
        }
    }


    //---------------------------------------------------------------------
    // Abstract methods to be implemented by subclasses
    //---------------------------------------------------------------------

    //标记是否包含Bean定义的方法
    protected abstract boolean containsBeanDefinition(String beanName);

    //根据Bean名返回其BeanDefinition
    protected abstract BeanDefinition getBeanDefinition(String beanName) throws BeansException;

    //根据指定的bean定义和bean名、参数，创建对象
    protected abstract Object createBean(String beanName, RootBeanDefinition mbd, Object[] args)
            throws BeanCreationException;

}