[spring源码学习]四、IOC源码——普通bean初始化

一、代码例子

　　此节开始涉及到一个bean具体生成和保存的过程，仅仅涉及到最简单的bean，代码依旧是最简单的

    public static void main(String[] args) {
        DefaultListableBeanFactory beanFacory=new DefaultListableBeanFactory();
        XmlBeanDefinitionReader reader=new XmlBeanDefinitionReader(beanFacory);
        reader.loadBeanDefinitions(new ClassPathResource("bean.xml"));
        Person person=(Person)beanFacory.getBean("person");
        person.sayHello();
    }

二、源码解析

1、通过调用getBean(String name)来进入bean的获取

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

2、经历一些列重载后，进入doGetBean，先转化beanName，如果以&开头，去掉开头，此处预留了一个factoryBean的特殊bean，到singletonObjects中获取bean，此处使用缓存，判断是否bean正在创建，控制重复创建bean，保证单例模式

        final String beanName = transformedBeanName(name);
        Object bean;

        // Eagerly check singleton cache for manually registered singletons.
        Object sharedInstance = getSingleton(beanName);
        if (sharedInstance != null && args == null) {
            if (logger.isDebugEnabled()) {
                if (isSingletonCurrentlyInCreation(beanName)) {
                    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 + "'");
                }
            }
            bean = getObjectForBeanInstance(sharedInstance, name, beanName, null);
        }

3、调用markBeanAsCreated(beanName)，判断alreadyCreated，从mergedBeanDefinitions中移除bean

4、调用getMergedLocalBeanDefinition，并调用

    protected RootBeanDefinition getMergedLocalBeanDefinition(String beanName) throws BeansException {
        // Quick check on the concurrent map first, with minimal locking.
        RootBeanDefinition mbd = this.mergedBeanDefinitions.get(beanName);
        if (mbd != null) {
            return mbd;
        }
        return getMergedBeanDefinition(beanName, getBeanDefinition(beanName));
    }

5、调用AbstractBeanFactory的getMergedBeanDefinition(String beanName, BeanDefinition bd, BeanDefinition containingBd)方法，此处会判断是否有parentBean，如果有的话，会根据parentBeanName再次调用getMergedBeanDefinition方法，我们猜测所有的bean生产都在此方法中生产的话，这里是一次递归调用，也就是要生产bean，先生成他的父bean的BeanDefinition，注意，此处如果beanName和parentBeanName相同，会判断在DefaultListableBeanFactory时候设定的ParentBeanFactory是否ConfigurableBeanFactory的实例，如果是，采用它来生产父bean的配置，产生后将子bean的BeanDefinition通过overwriteForm到父bean，也就是覆盖了父bean相同的配置

                    // Child bean definition: needs to be merged with parent.
                    BeanDefinition pbd;
                    try {
                        String parentBeanName = transformedBeanName(bd.getParentName());
                        if (!beanName.equals(parentBeanName)) {
　　　　　　　　　　　　　　　　//递归调用，生成parent的BeanDefinition
                            pbd = getMergedBeanDefinition(parentBeanName);
                        }
                        else {
　　　　　　　　　　　　　　　　//如果是ConfigurableBeanFactory,有单独的生成方法，需要有ParentBeanFactory来生成
                            if (getParentBeanFactory() instanceof ConfigurableBeanFactory) {
                                pbd = ((ConfigurableBeanFactory) getParentBeanFactory()).getMergedBeanDefinition(parentBeanName);
                            }
                            else {
                                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);
                    }
                    // Deep copy with overridden values.
                    mbd = new RootBeanDefinition(pbd);
　　　　　　　　　　　 //子bean的配置覆盖父bean
                    mbd.overrideFrom(bd);
                

6、如果自身没有设定scope，设置默认单例模式，如果containingBd有scope，则设置为它的，scope，将BeanDefinition放入mergedBeanDefinitions

7、检查bean是否为抽象，如果有抽象，直接报错，此处可以知道抽象bean不能被直接获取，那么在定义bean的时候设置abstract="true"的意义，我们结合第5步可以猜测：抽象bean的定义可以作为普通bean的parentBean来进行使用，他可以提供多个子bean的通用配置

    protected void checkMergedBeanDefinition(RootBeanDefinition mbd, String beanName, Object[] args)
            throws BeanDefinitionStoreException {

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

8、判断是否有dependsOn,如果有判断他是否已经被实例化，如果还没有被实例化直接报错。因为如果一个bean依赖于其他bean，我们通常会使用ref标签进行注入，但是当其他bean和此bean并没有强依赖关系，只是提供一些初始化参数设定之类的话，我们在bean中看不到引用，但仍有强先后关系，那么可以使用depend-on进行配置

                String[] dependsOn = mbd.getDependsOn();
                if (dependsOn != null) {
                    for (String dependsOnBean : dependsOn) {
                        if (isDependent(beanName, dependsOnBean)) {
                            throw new BeanCreationException(mbd.getResourceDescription(), beanName,
                                    "Circular depends-on relationship between '" + beanName + "' and '" + dependsOnBean + "'");
                        }
                        registerDependentBean(dependsOnBean, beanName);
                        getBean(dependsOnBean);
                    }
                }

9、此处处理scope的设置，主要有三种：

a)单例模式，有一个getSingleton方法，如果之前已经创建，直接返回

b)prototype模式，每次都创建一个新的bean

c)自定义的scope，这个可以通过register进行注入，此处暂不考虑

同时，我们可以看到不同模式中在bean的创建前后可以添加一些参数设置和接口

　　　　if (mbd.isSingleton()) {//单例模式，会比prototype多一个getSingleton方法
                    sharedInstance = getSingleton(beanName, new ObjectFactory<Object>() {
                        @Override
                        public Object getObject() throws BeansException {
                            try {
                                return createBean(beanName, mbd, args);
                            }
                            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;
                            }
                        }
                    });
                    bean = getObjectForBeanInstance(sharedInstance, name, beanName, mbd);
                }

                else if (mbd.isPrototype()) {
                    // It's a prototype -> create a new instance.
　　　　　　　　　　　　//原型模式，直接创建新的bean
                    Object prototypeInstance = null;
                    try {
　　　　　　　　　　　　　　//创建之前处理
                        beforePrototypeCreation(beanName);
                        prototypeInstance = createBean(beanName, mbd, args);
                    }
                    finally {
　　　　　　　　　　　　　　//创建之后处理
                        afterPrototypeCreation(beanName);
                    }
                    bean = getObjectForBeanInstance(prototypeInstance, name, beanName, mbd);
                }

                else {
　　　　　　　　　　　　//自定义的scope，可以从scope中根据beanName获得他的构建方法，此处暂不深究
                    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, new ObjectFactory<Object>() {
                            @Override
                            public Object getObject() throws BeansException {
                                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);
                    }
                }

10、因为是singleton模式，我们直接进入getSingleton(String beanName, ObjectFactory<?> singletonFactory)方法，进行参数检查后，调用回调函数

public Object getSingleton(String beanName, ObjectFactory<?> singletonFactory) {
        Assert.notNull(beanName, "'beanName' must not be null");
        synchronized (this.singletonObjects) {
　　　　　　　//再次判断是否在缓存中存在，做多次检查
            Object singletonObject = this.singletonObjects.get(beanName);
            if (singletonObject == null) {
　　　　　　　　　//判断是否正在创建
                if (this.singletonsCurrentlyInDestruction) {
                    throw new BeanCreationNotAllowedException(beanName,
                            "Singleton bean creation not allowed while the singletons of this factory are in destruction " +
                            "(Do not request a bean from a BeanFactory in a destroy method implementation!)");
                }
                if (logger.isDebugEnabled()) {
                    logger.debug("Creating shared instance of singleton bean '" + beanName + "'");
                }
                beforeSingletonCreation(beanName);
                boolean newSingleton = false;
                boolean recordSuppressedExceptions = (this.suppressedExceptions == null);
                if (recordSuppressedExceptions) {
                    this.suppressedExceptions = new LinkedHashSet<Exception>();
                }
                try {
　　　　　　　　　　　　//使用回调函数，
                    singletonObject = singletonFactory.getObject();
                    newSingleton = true;
                }
                catch (IllegalStateException ex) {
                    // Has the singleton object implicitly appeared in the meantime ->
                    // if yes, proceed with it since the exception indicates that state.
                    singletonObject = this.singletonObjects.get(beanName);
                    if (singletonObject == null) {
                        throw ex;
                    }
                }
                catch (BeanCreationException ex) {
                    if (recordSuppressedExceptions) {
                        for (Exception suppressedException : this.suppressedExceptions) {
                            ex.addRelatedCause(suppressedException);
                        }
                    }
                    throw ex;
                }
                finally {
                    if (recordSuppressedExceptions) {
                        this.suppressedExceptions = null;
                    }
                    afterSingletonCreation(beanName);
                }
                if (newSingleton) {
                    addSingleton(beanName, singletonObject);
                }
            }
            return (singletonObject != NULL_OBJECT ? singletonObject : null);
        }
    }

11、进入AbstractAutowireCapableBeanFactory的createBean方法，获取beanClass，prepareMethodOverrides

        Class<?> resolvedClass = resolveBeanClass(mbd, beanName);
        if (resolvedClass != null && !mbd.hasBeanClass() && mbd.getBeanClassName() != null) {
            mbdToUse = new RootBeanDefinition(mbd);
            mbdToUse.setBeanClass(resolvedClass);
        }

        // Prepare method overrides.
        try {
            mbdToUse.prepareMethodOverrides();
        }
        catch (BeanDefinitionValidationException ex) {
            throw new BeanDefinitionStoreException(mbdToUse.getResourceDescription(),
                    beanName, "Validation of method overrides failed", ex);
        }

12、进入resolveBeforeInstantiation方法，，如另外一篇文章中的分析，此处为另一个接口InstantiationAwareBeanPostProcessor，如果bean继承了此接口，会做一些预处理

    protected Object resolveBeforeInstantiation(String beanName, RootBeanDefinition mbd) {
        Object bean = null;
        if (!Boolean.FALSE.equals(mbd.beforeInstantiationResolved)) {
            // Make sure bean class is actually resolved at this point.
            if (!mbd.isSynthetic() && hasInstantiationAwareBeanPostProcessors()) {
                Class<?> targetType = determineTargetType(beanName, mbd);
                if (targetType != null) {
                    bean = applyBeanPostProcessorsBeforeInstantiation(targetType, beanName);
                    if (bean != null) {
                        bean = applyBeanPostProcessorsAfterInitialization(bean, beanName);
                    }
                }
            }
            mbd.beforeInstantiationResolved = (bean != null);
        }
        return bean;
    }

13、调用doCreateBean方法，先从缓存中移除bean，然后调用doCreateBean方法，再调用createBeanInstance方法

14、获取beanClass，判断是否为public，判断factoryMethodName是否为空（应该是对应factoryBean，待确认），经过各种检查，最后采用最简单的无参数构造器进行构建

protected BeanWrapper createBeanInstance(String beanName, RootBeanDefinition mbd, Object[] args) {
        // Make sure bean class is actually resolved at this point.
        Class<?> beanClass = resolveBeanClass(mbd, beanName);

        if (beanClass != null && !Modifier.isPublic(beanClass.getModifiers()) && !mbd.isNonPublicAccessAllowed()) {
            throw new BeanCreationException(mbd.getResourceDescription(), beanName,
                    "Bean class isn't public, and non-public access not allowed: " + beanClass.getName());
        }

        if (mbd.getFactoryMethodName() != null)  {
            return instantiateUsingFactoryMethod(beanName, mbd, args);
        }

        // Shortcut when re-creating the same bean...
        boolean resolved = false;
        boolean autowireNecessary = false;
        if (args == null) {
            synchronized (mbd.constructorArgumentLock) {
                if (mbd.resolvedConstructorOrFactoryMethod != null) {
                    resolved = true;
                    autowireNecessary = mbd.constructorArgumentsResolved;
                }
            }
        }
        if (resolved) {
            if (autowireNecessary) {
                return autowireConstructor(beanName, mbd, null, null);
            }
            else {
                return instantiateBean(beanName, mbd);
            }
        }

        // Need to determine the constructor...有参数构造器
        Constructor<?>[] ctors = determineConstructorsFromBeanPostProcessors(beanClass, beanName);
        if (ctors != null ||
                mbd.getResolvedAutowireMode() == RootBeanDefinition.AUTOWIRE_CONSTRUCTOR ||
                mbd.hasConstructorArgumentValues() || !ObjectUtils.isEmpty(args))  {
            return autowireConstructor(beanName, mbd, ctors, args);
        }

        // No special handling: simply use no-arg constructor.
        return instantiateBean(beanName, mbd);
    }

15、进入instantiateBean中，获取CglibSubclassingInstantiationStrategy-cglib策略，，如果没有getMethodOverrides，则直接获得无参数构造器

    public Object instantiate(RootBeanDefinition bd, String beanName, BeanFactory owner) {
        // Don't override the class with CGLIB if no overrides.
        if (bd.getMethodOverrides().isEmpty()) {
            Constructor<?> constructorToUse;
            synchronized (bd.constructorArgumentLock) {
                constructorToUse = (Constructor<?>) bd.resolvedConstructorOrFactoryMethod;
                if (constructorToUse == null) {
                    final Class<?> clazz = bd.getBeanClass();
                    if (clazz.isInterface()) {
                        throw new BeanInstantiationException(clazz, "Specified class is an interface");
                    }
                    try {
                        if (System.getSecurityManager() != null) {
                            constructorToUse = AccessController.doPrivileged(new PrivilegedExceptionAction<Constructor<?>>() {
                                @Override
                                public Constructor<?> run() throws Exception {
                                    return clazz.getDeclaredConstructor((Class[]) null);
                                }
                            });
                        }
                        else {
                            constructorToUse =    clazz.getDeclaredConstructor((Class[]) null);
                        }
                        bd.resolvedConstructorOrFactoryMethod = constructorToUse;
                    }
                    catch (Exception ex) {
                        throw new BeanInstantiationException(clazz, "No default constructor found", ex);
                    }
                }
            }
　　　　　　　//入口
            return BeanUtils.instantiateClass(constructorToUse);
        }
        else {
            // Must generate CGLIB subclass.
            return instantiateWithMethodInjection(bd, beanName, owner);
        }
    }

16、通过反射，获取class的实例

17、注册客户化解析器

BeanWrapper bw = new BeanWrapperImpl(beanInstance);
            initBeanWrapper(bw);

18、获取bean，设置psotProcessed为true，并添加到缓存

BeanWrapper instanceWrapper = null;
        if (mbd.isSingleton()) {
            instanceWrapper = this.factoryBeanInstanceCache.remove(beanName);
        }
        if (instanceWrapper == null) {
            instanceWrapper = createBeanInstance(beanName, mbd, args);
        }
        final Object bean = (instanceWrapper != null ? instanceWrapper.getWrappedInstance() : null);
        Class<?> beanType = (instanceWrapper != null ? instanceWrapper.getWrappedClass() : null);

        // Allow post-processors to modify the merged bean definition.
        synchronized (mbd.postProcessingLock) {
            if (!mbd.postProcessed) {
                applyMergedBeanDefinitionPostProcessors(mbd, beanType, beanName);
                mbd.postProcessed = true;
            }
        }

protected void addSingletonFactory(String beanName, ObjectFactory<?> singletonFactory) {
        Assert.notNull(singletonFactory, "Singleton factory must not be null");
        synchronized (this.singletonObjects) {
            if (!this.singletonObjects.containsKey(beanName)) {
                this.singletonFactories.put(beanName, singletonFactory);
                this.earlySingletonObjects.remove(beanName);
                this.registeredSingletons.add(beanName);
            }
        }
    }

19、调用populateBean，开始赋值

Object exposedObject = bean;
        try {
            populateBean(beanName, mbd, instanceWrapper);
            if (exposedObject != null) {
                exposedObject = initializeBean(beanName, exposedObject, mbd);
            }
        }

20、调用applyPropertyValues，解析参数种类为字符，对象或者数组的话，直接赋值，如果为其他，需要继续处理

protected void applyPropertyValues(String beanName, BeanDefinition mbd, BeanWrapper bw, PropertyValues pvs) {
        if (pvs == null || pvs.isEmpty()) {
            return;
        }

        MutablePropertyValues mpvs = null;
        List<PropertyValue> original;

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

        if (pvs instanceof MutablePropertyValues) {
            mpvs = (MutablePropertyValues) pvs;
            if (mpvs.isConverted()) {
                // Shortcut: use the pre-converted values as-is.
                try {
                    bw.setPropertyValues(mpvs);
                    return;
                }
                catch (BeansException ex) {
                    throw new BeanCreationException(
                            mbd.getResourceDescription(), beanName, "Error setting property values", ex);
                }
            }
            original = mpvs.getPropertyValueList();
        }
        else {
            original = Arrays.asList(pvs.getPropertyValues());
        }

        TypeConverter converter = getCustomTypeConverter();
        if (converter == null) {
            converter = bw;
        }
        BeanDefinitionValueResolver valueResolver = new BeanDefinitionValueResolver(this, beanName, mbd, converter);

        // Create a deep copy, resolving any references for values.
        List<PropertyValue> deepCopy = new ArrayList<PropertyValue>(original.size());
        boolean resolveNecessary = false;
        for (PropertyValue pv : original) {
            if (pv.isConverted()) {
                deepCopy.add(pv);
            }
            else {
                String propertyName = pv.getName();
                Object originalValue = pv.getValue();
                Object resolvedValue = valueResolver.resolveValueIfNecessary(pv, originalValue);
                Object convertedValue = resolvedValue;
                boolean convertible = bw.isWritableProperty(propertyName) &&
                        !PropertyAccessorUtils.isNestedOrIndexedProperty(propertyName);
                if (convertible) {
                    convertedValue = convertForProperty(resolvedValue, propertyName, bw, converter);
                }
                // Possibly store converted value in merged bean definition,
                // in order to avoid re-conversion for every created bean instance.
                if (resolvedValue == originalValue) {
                    if (convertible) {
                        pv.setConvertedValue(convertedValue);
                    }
                    deepCopy.add(pv);
                }
                else if (convertible && originalValue instanceof TypedStringValue &&
                        !((TypedStringValue) originalValue).isDynamic() &&
                        !(convertedValue instanceof Collection || ObjectUtils.isArray(convertedValue))) {
                    pv.setConvertedValue(convertedValue);
                    deepCopy.add(pv);
                }
                else {
                    resolveNecessary = true;
                    deepCopy.add(new PropertyValue(pv, convertedValue));
                }
            }
        }
        if (mpvs != null && !resolveNecessary) {
            mpvs.setConverted();
        }

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

21、调用initializeBean,

    protected Object initializeBean(final String beanName, final Object bean, RootBeanDefinition mbd) {
        if (System.getSecurityManager() != null) {
            AccessController.doPrivileged(new PrivilegedAction<Object>() {
                @Override
                public Object run() {
                    invokeAwareMethods(beanName, bean);
                    return null;
                }
            }, getAccessControlContext());
        }
        else {
            invokeAwareMethods(beanName, bean);
        }

        Object wrappedBean = bean;
        if (mbd == null || !mbd.isSynthetic()) {
　　　　　　　//调用bean的预处理
            wrappedBean = applyBeanPostProcessorsBeforeInitialization(wrappedBean, beanName);
        }

        try {
　　　　　　　//调用init-method或者接口继承
            invokeInitMethods(beanName, wrappedBean, mbd);
        }
        catch (Throwable ex) {
            throw new BeanCreationException(
                    (mbd != null ? mbd.getResourceDescription() : null),
                    beanName, "Invocation of init method failed", ex);
        }

        if (mbd == null || !mbd.isSynthetic()) {
　　　　　　　//调用bean的后处理
            wrappedBean = applyBeanPostProcessorsAfterInitialization(wrappedBean, beanName);
        }
        return wrappedBean;
    }

22/

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 name '" + mbd.getScope() + "'");
                }
                scope.registerDestructionCallback(beanName,
                        new DisposableBeanAdapter(bean, beanName, mbd, getBeanPostProcessors(), acc));
            }
        }
    }

23、移除正在创建的状态

    protected void afterSingletonCreation(String beanName) {
        if (!this.inCreationCheckExclusions.contains(beanName) && !this.singletonsCurrentlyInCreation.remove(beanName)) {
            throw new IllegalStateException("Singleton '" + beanName + "' isn't currently in creation");
        }
    }

24、单例模式需要再次添加到缓存

    protected void addSingleton(String beanName, Object singletonObject) {
        synchronized (this.singletonObjects) {
            this.singletonObjects.put(beanName, (singletonObject != null ? singletonObject : NULL_OBJECT));
            this.singletonFactories.remove(beanName);
            this.earlySingletonObjects.remove(beanName);
            this.registeredSingletons.add(beanName);
        }
    }

25、检查beanName是否为&开通并且继承FactoryBean，表示是一个工厂bean，如果不是，直接返回，如果是从getCachedObjectForFactoryBean中获取

protected Object getObjectForBeanInstance(
            Object beanInstance, String name, String beanName, RootBeanDefinition mbd) {

        // Don't let calling code try to dereference the factory if the bean isn't a factory.
        if (BeanFactoryUtils.isFactoryDereference(name) && !(beanInstance instanceof FactoryBean)) {
            throw new BeanIsNotAFactoryException(transformedBeanName(name), beanInstance.getClass());
        }

        // 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.
        if (!(beanInstance instanceof FactoryBean) || BeanFactoryUtils.isFactoryDereference(name)) {
            return beanInstance;
        }

        Object object = null;
        if (mbd == null) {
            object = getCachedObjectForFactoryBean(beanName);
        }
        if (object == null) {
            // Return bean instance from factory.
            FactoryBean<?> factory = (FactoryBean<?>) beanInstance;
            // Caches object obtained from FactoryBean if it is a singleton.
            if (mbd == null && containsBeanDefinition(beanName)) {
                mbd = getMergedLocalBeanDefinition(beanName);
            }
            boolean synthetic = (mbd != null && mbd.isSynthetic());
            object = getObjectFromFactoryBean(factory, beanName, !synthetic);
        }
        return object;
    }

26、根据工厂bean，获取真实的bean，此处结合第二步我们可以看到：

spring提供了一种特殊的bean，他继承接口FactoryBean，它无法使用getBean（beanName）获取实例，必须使用getBean(&beanName)获取，

spring在处理完成后，首先获得FactoryBean的实例，然后使用实例中的getObject()来获取真正的bean

protected Object getObjectFromFactoryBean(FactoryBean<?> factory, String beanName, boolean shouldPostProcess) {
        if (factory.isSingleton() && containsSingleton(beanName)) {
            synchronized (getSingletonMutex()) {
                Object object = this.factoryBeanObjectCache.get(beanName);
                if (object == null) {
                    object = doGetObjectFromFactoryBean(factory, beanName);
                    // Only post-process and store if not put there already during getObject() call above
                    // (e.g. because of circular reference processing triggered by custom getBean calls)
                    Object alreadyThere = this.factoryBeanObjectCache.get(beanName);
                    if (alreadyThere != null) {
                        object = alreadyThere;
                    }
                    else {
                        if (object != null && shouldPostProcess) {
                            try {
                                object = postProcessObjectFromFactoryBean(object, beanName);
                            }
                            catch (Throwable ex) {
                                throw new BeanCreationException(beanName,
                                        "Post-processing of FactoryBean's singleton object failed", ex);
                            }
                        }
                        this.factoryBeanObjectCache.put(beanName, (object != null ? object : NULL_OBJECT));
                    }
                }
                return (object != NULL_OBJECT ? object : null);
            }
        }
        else {
            Object object = doGetObjectFromFactoryBean(factory, beanName);
            if (object != null && shouldPostProcess) {
                try {
                    object = postProcessObjectFromFactoryBean(object, beanName);
                }
                catch (Throwable ex) {
                    throw new BeanCreationException(beanName, "Post-processing of FactoryBean's object failed", ex);
                }
            }
            return object;
        }
    }

到此之后，一路返回，我们就可以获得到希望的bean

三、总结

1、最简单的spring的bean生成流程基本按照我们之前预想的那样，从容器中获取BeanDefinition，然后根据class生成对象，并且注入参数

2、spring的bean的产生过程非常的复杂，因为他根据客户配置不同，预留了很多变化，如单例的生成一次进行缓存，原型的每次生成，预留了自定义的scope等

3、对bean的生成前后，spring均预留了一些接口，可以对bean进行额外的参数注入和设置

4、FactoryBean的出现，我们bean配置的class并不一定是最终生成的bean的class，需要额外处理

5、整个过程采用了各种缓存和多次检查防止重复