前面几篇文章中我们了解了Spring初始化过程中两种后置器postProcess的实现原理和调用过程，也明白了BeanDefinition的解析和创建，这次我们继续来分析Spring容器核心创建方法refresh（）的最后一步finishBeanFactoryInitialization(beanFactory),先看一下它在refresh（）中的位置：

public void refresh() throws BeansException, IllegalStateException {
        synchronized (this.startupShutdownMonitor) {
            // Prepare this context for refreshing.
            //设置环境变量和容器的开关标志
            prepareRefresh();

            // Tell the subclass to refresh the internal bean factory.
            //刷新beanFactory，删除旧的beanFactory，创建新的beanFactory
            ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory();

            // Prepare the bean factory for use in this context.
            // 准备beanfactory来使用这个上下文.做一些准备工作，例如classloader，beanPostProcessor等 
            prepareBeanFactory(beanFactory);

            try {
                // Allows post-processing of the bean factory in context subclasses.
                postProcessBeanFactory(beanFactory);

                // Invoke factory processors registered as beans in the context.
                //执行注册到该上下文的BeanFactoryPostProcessors  
                invokeBeanFactoryPostProcessors(beanFactory);

                // Register bean processors that intercept bean creation.
//注册BeanPostProcessors，注意只是注册，和上一行不同，没有invoke
                registerBeanPostProcessors(beanFactory);

                // Initialize message source for this context.
                initMessageSource();

                // Initialize event multicaster for this context.
                initApplicationEventMulticaster();

                // Initialize other special beans in specific context subclasses.
                onRefresh();

                // Check for listener beans and register them.
                registerListeners();

                // Instantiate all remaining (non-lazy-init) singletons.
//创建所有非懒加载的单例类（并invoke BeanPostProcessors）
                finishBeanFactoryInitialization(beanFactory);

                // Last step: publish corresponding event.
                finishRefresh();
            }

            catch (BeansException ex) {
                if (logger.isWarnEnabled()) {
                    logger.warn("Exception encountered during context initialization - " +
                            "cancelling refresh attempt: " + ex);
                }

                // Destroy already created singletons to avoid dangling resources.
                destroyBeans();

                // Reset 'active' flag.
                cancelRefresh(ex);

                // Propagate exception to caller.
                throw ex;
            }

            finally {
                // Reset common introspection caches in Spring's core, since we
                // might not ever need metadata for singleton beans anymore...
                resetCommonCaches();
            }
        }
    }

我们进入此方法：

protected void finishBeanFactoryInitialization(ConfigurableListableBeanFactory beanFactory) {
        // Initialize conversion service for this context.
        if (beanFactory.containsBean(CONVERSION_SERVICE_BEAN_NAME) &&
                beanFactory.isTypeMatch(CONVERSION_SERVICE_BEAN_NAME, ConversionService.class)) {
            beanFactory.setConversionService(
                    beanFactory.getBean(CONVERSION_SERVICE_BEAN_NAME, ConversionService.class));
        }

        // Initialize LoadTimeWeaverAware beans early to allow for registering their transformers early.
        String[] weaverAwareNames = beanFactory.getBeanNamesForType(LoadTimeWeaverAware.class, false, false);
        for (String weaverAwareName : weaverAwareNames) {
            getBean(weaverAwareName);
        }

        // Stop using the temporary ClassLoader for type matching.
        beanFactory.setTempClassLoader(null);

        // Allow for caching all bean definition metadata, not expecting further changes.
        beanFactory.freezeConfiguration();

        // Instantiate all remaining (non-lazy-init) singletons.
        beanFactory.preInstantiateSingletons();
    }

这个方法里的东西呢我们只需关注最后一行即可，也就是beanFactory.preInstantiateSingletons();

public void preInstantiateSingletons() throws BeansException {
        List<String> beanNames = new ArrayList<>(this.beanDefinitionNames);
// Trigger initialization of all non-lazy singleton beans...
for (String beanName : beanNames) {
    RootBeanDefinition bd = getMergedLocalBeanDefinition(beanName);
    if (!bd.isAbstract() && bd.isSingleton() && !bd.isLazyInit()) {
        if (isFactoryBean(beanName)) {
            final FactoryBean<?> factory = (FactoryBean<?>) getBean(FACTORY_BEAN_PREFIX + beanName);
            boolean isEagerInit;
            if (System.getSecurityManager() != null && factory instanceof SmartFactoryBean) {
                isEagerInit = AccessController.doPrivileged((PrivilegedAction<Boolean>) () ->
                        ((SmartFactoryBean<?>) factory).isEagerInit(),
                        getAccessControlContext());
            }
            else {
                isEagerInit = (factory instanceof SmartFactoryBean &&
                        ((SmartFactoryBean<?>) factory).isEagerInit());
            }
            if (isEagerInit) {
                getBean(beanName);
            }
        }
        else {
            /**
             * 核心代码
             */
            getBean(beanName);
        }
    }
}
    }

在这里我们可以看到，开头通过beanName获取bean实例，如果获取到的实例不满足条件，就会调用核心代码getBean(beanName)，这个方法也是Spring最核心的方法之一。我们把这个核心方法分为几部分来剖析：

第一段

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);
        }

这部分是通过getSingleton(beanName)方法去singleton缓存中找bean实例，应该是拿不到的，因为我们是第一次初始化，缓存中肯定不存在。

第二部分

if (isPrototypeCurrentlyInCreation(beanName)) {
                throw new BeanCurrentlyInCreationException(beanName);
            }

            // Check if bean definition exists in this factory.
//获取父类的beanfactory
            BeanFactory parentBeanFactory = getParentBeanFactory();
            if (parentBeanFactory != null && !containsBeanDefinition(beanName)) {
                // Not found -> check parent.
                String nameToLookup = originalBeanName(name);
                if (args != null) {
                    // Delegation to parent with explicit args.
                    return (T) parentBeanFactory.getBean(nameToLookup, args);
                }
                else {
                    // No args -> delegate to standard getBean method.
                    return parentBeanFactory.getBean(nameToLookup, requiredType);
                }
            }

这段是根据当前的beanfactory获取父一级的beanfactory，然后逐级递归的查找我们需要的bean，很显然在这里依然获取不到我们的bean，原因同第一部分。

第三部分

            if (!typeCheckOnly) {
                markBeanAsCreated(beanName);
            }

            try {
                final RootBeanDefinition mbd = getMergedLocalBeanDefinition(beanName);
                checkMergedBeanDefinition(mbd, beanName, args);

                // Guarantee initialization of beans that the current bean depends on.
                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);
                    }
                }

第三部分先判断并把需要创建的bean打上正在创建标记，也就是开头的if判断加markBeanAsCreated(beanName)方法（这样做的目的是在我创建这个bean之前就先打上创建标记，告诉其它来创建的线程，避免了重复创建，那么这个方法内部肯定是同步的），然后获取到该bean对应的BeanDefinition，在Spring创建初期把bean的初始化信息通过配置文件（xml）和反射等预先存在了BeanDefinition中，当然也包括bean依赖等，所以在这里把BeanDefinition里存储的依赖bean挨个取出来进行实例化

第四部分

// Create bean instance.
                if (mbd.isSingleton()) {
                    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);
                }

这部分我们通过单例的代码来进行分析，如果当前bean是Singleton，则调用createBean(beanName, mbd, args)方法，并返回。我们继续看这个方法

第五部分

protected Object createBean(String beanName, RootBeanDefinition mbd, Object[] args) throws BeanCreationException {
        if (logger.isDebugEnabled()) {
            logger.debug("Creating instance of bean '" + beanName + "'");
        }
        RootBeanDefinition mbdToUse = mbd;
//注释一
        // Make sure bean class is actually resolved at this point, and
        // clone the bean definition in case of a dynamically resolved Class
        // which cannot be stored in the shared merged bean definition.
        Class<?> resolvedClass = resolveBeanClass(mbd, beanName);
        if (resolvedClass != null && !mbd.hasBeanClass() && mbd.getBeanClassName() != null) {
            mbdToUse = new RootBeanDefinition(mbd);
            mbdToUse.setBeanClass(resolvedClass);
        }
//注释二
        // Prepare method overrides.
        try {
            mbdToUse.prepareMethodOverrides();
        }
        catch (BeanDefinitionValidationException ex) {
            throw new BeanDefinitionStoreException(mbdToUse.getResourceDescription(),
                    beanName, "Validation of method overrides failed", ex);
        }
//注释三
        try {
            // Give BeanPostProcessors a chance to return a proxy instead of the target bean instance.
            Object bean = resolveBeforeInstantiation(beanName, mbdToUse);
            if (bean != null) {
                return bean;
            }
        }
        catch (Throwable ex) {
            throw new BeanCreationException(mbdToUse.getResourceDescription(), beanName,
                    "BeanPostProcessor before instantiation of bean failed", ex);
        }

        Object beanInstance = doCreateBean(beanName, mbdToUse, args);
        if (logger.isDebugEnabled()) {
            logger.debug("Finished creating instance of bean '" + beanName + "'");
        }
        return beanInstance;
    }

这部分标注了三个注释

注释一:判断该bean的class是否存在，也就是该bean是可以通过class创建的
注释二：准备方法重写
注释三：这边有个return，也就是说这边有可能提前返回bean，看注释：Give BeanPostProcessors a chance to return a proxy instead of the target bean instance.我们以前在beanPostProcessor时说过，beanPostProcessor是可以临时修改bean的，它的优先级高于正常实例化bean的（也就是后续实例化该bean的过程），如果beanPostProcessor能返回，则直接返回了

最后doCreateBean

BeanWrapper instanceWrapper = null;
        if (mbd.isSingleton()) {
            instanceWrapper = this.factoryBeanInstanceCache.remove(beanName);
        }
        if (instanceWrapper == null) {
            //在这里进行了bean的构造方法等的执行，并创建bean
            instanceWrapper = createBeanInstance(beanName, mbd, args);
        }
        final Object bean = (instanceWrapper != null ? instanceWrapper.getWrappedInstance() : null);
        Class<?> beanType = (instanceWrapper != null ? instanceWrapper.getWrappedClass() : null);
        mbd.resolvedTargetType = beanType;

        if (beanType != null) {
            // Allow post-processors to modify the merged bean definition.
            synchronized (mbd.postProcessingLock) {
                if (!mbd.postProcessed) {
                    try {
                        applyMergedBeanDefinitionPostProcessors(mbd, beanType, beanName);
                    }
                    catch (Throwable ex) {
                        throw new BeanCreationException(mbd.getResourceDescription(), beanName,
                                "Post-processing of merged bean definition failed", ex);
                    }
                    mbd.postProcessed = true;
                }
            }
        }