Spring MVC初始化部分源码分析

首先定位到org.springframework.context.support.AbstractApplicationContext中的refresh()方法：

public void refresh() throws BeansException, IllegalStateException {
        synchronized (this.startupShutdownMonitor) {
            // Prepare this context for refreshing.
            prepareRefresh();

            // Tell the subclass to refresh the internal bean factory.
            ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory();

            // Prepare the bean factory for use in this context.
            prepareBeanFactory(beanFactory);

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

                // Invoke factory processors registered as beans in the context.
                invokeBeanFactoryPostProcessors(beanFactory);

                // Register bean processors that intercept bean creation.
                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.
                finishBeanFactoryInitialization(beanFactory);

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

            catch (BeansException ex) {
                // Destroy already created singletons to avoid dangling resources.
                destroyBeans();

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

                // Propagate exception to caller.
                throw ex;
            }
        }
    }

从这个refresh()方法入手，我们先对Spring容器启动时的大致过程有个概念：首先，Spring容器启动时会做一些初始化工作（比如注册一些默认的环境bean，添加一些必要的bean等） 。第二步会读取配置文件，并将其中定义的Bean转换成BeanDefinition。第三步的postProcessBeanFactory()相当于为上下文子类提供了一个扩展点，用于对bean factory的拦截处理（比如在AbstractRefreshableWebApplicationContext中注册了web中特有的request/session scope等）。第四步Spring容器会先实例化实现了BeanDefinitionRegistryPostProcessor接口的类，并按照一定的顺序依次调用它的回调方法postProcessBeanDefinitionRegistry(BeanDefinitionRegistry registry) 。之后是实例化BeanFactoryPostProcessor并调用它的回调方法postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory)，由于BeanDefinitionRegistryPostProcessor是BeanFactoryPostProcessor的子接口，所以BeanDefinitionRegistryPostProcessor的postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory)方法在这个阶段也会被调用，但是一般都留空。第五步，Spring容器会按照一定的顺序实例化实现了BeanPostProcessor的类，并注册到容器中。第六步，注册messageSource。其余的后续步骤就不介绍了，这里再关注一下finishBeanFactoryInitialization(ConfigurableListableBeanFactory beanFactory)，这个方法用来实例化容器中定义的所有Singleton（不包括之前已经初始化了的）。下面挑一些重要的源码分析一下：

protected void invokeBeanFactoryPostProcessors(ConfigurableListableBeanFactory beanFactory) {
        // Invoke BeanDefinitionRegistryPostProcessors first, if any.
        Set<String> processedBeans = new HashSet<String>();
        if (beanFactory instanceof BeanDefinitionRegistry) {
            // 处理BeanFactoryPostProcessor的第一阶段
            BeanDefinitionRegistry registry = (BeanDefinitionRegistry) beanFactory;
            List<BeanFactoryPostProcessor> regularPostProcessors = new LinkedList<BeanFactoryPostProcessor>();
            List<BeanDefinitionRegistryPostProcessor> registryPostProcessors =
                    new LinkedList<BeanDefinitionRegistryPostProcessor>();
            // 这里通过getBeanFactoryPostProcessors()得到的Processors是该类的成员变量值，那么应该可以注入。
            // 不过下面会直接扫描容器中的所有实现了BeanFactoryPostProcessor的类，那么这步是不是显得有点多此一举？
            for (BeanFactoryPostProcessor postProcessor : getBeanFactoryPostProcessors()) {
                if (postProcessor instanceof BeanDefinitionRegistryPostProcessor) {
                    BeanDefinitionRegistryPostProcessor registryPostProcessor =
                            (BeanDefinitionRegistryPostProcessor) postProcessor;
                    registryPostProcessor.postProcessBeanDefinitionRegistry(registry);
                    registryPostProcessors.add(registryPostProcessor);
                }
                else {
                    regularPostProcessors.add(postProcessor);
                }
            }
            // 此处是获取注册了的所有实现了BeanDefinitionRegistryPostProcessor接口的类
            Map<String, BeanDefinitionRegistryPostProcessor> beanMap =
                    beanFactory.getBeansOfType(BeanDefinitionRegistryPostProcessor.class, true, false);
            List<BeanDefinitionRegistryPostProcessor> registryPostProcessorBeans =
                    new ArrayList<BeanDefinitionRegistryPostProcessor>(beanMap.values());
            OrderComparator.sort(registryPostProcessorBeans);// 按照order排序之后依次调用
            for (BeanDefinitionRegistryPostProcessor postProcessor : registryPostProcessorBeans) {
                postProcessor.postProcessBeanDefinitionRegistry(registry);
            }
            // 这里再回调BeanFactoryPostProcessor的postProcessBeanFactory()方法
            invokeBeanFactoryPostProcessors(registryPostProcessors, beanFactory);
            invokeBeanFactoryPostProcessors(registryPostProcessorBeans, beanFactory);
            invokeBeanFactoryPostProcessors(regularPostProcessors, beanFactory);
            // 这里用processedBeans来记录处理过的Processors，以免后面再重复处理
            processedBeans.addAll(beanMap.keySet());
            // 到此，第一阶段结束
        }
        else {
            // Invoke factory processors registered with the context instance.
            invokeBeanFactoryPostProcessors(getBeanFactoryPostProcessors(), beanFactory);
        }

        // Do not initialize FactoryBeans here: We need to leave all regular beans
        // uninitialized to let the bean factory post-processors apply to them!
        // 这句注释暂时不是很理解
        String[] postProcessorNames =
                beanFactory.getBeanNamesForType(BeanFactoryPostProcessor.class, true, false);

        // 将BeanFactoryPostProcessors根据是否实现PriorityOrdered,Ordered,或都没实现区分成三类.
        List<BeanFactoryPostProcessor> priorityOrderedPostProcessors = new ArrayList<BeanFactoryPostProcessor>();
        List<String> orderedPostProcessorNames = new ArrayList<String>();
        List<String> nonOrderedPostProcessorNames = new ArrayList<String>();
        for (String ppName : postProcessorNames) {
            if (processedBeans.contains(ppName)) {
                // skip - already processed in first phase above
            }
            else if (isTypeMatch(ppName, PriorityOrdered.class)) {
                priorityOrderedPostProcessors.add(beanFactory.getBean(ppName, BeanFactoryPostProcessor.class));
            }
            else if (isTypeMatch(ppName, Ordered.class)) {
                orderedPostProcessorNames.add(ppName);
            }
            else {
                nonOrderedPostProcessorNames.add(ppName);
            }
        }

        // First, invoke the BeanFactoryPostProcessors that implement PriorityOrdered.
        OrderComparator.sort(priorityOrderedPostProcessors);
        invokeBeanFactoryPostProcessors(priorityOrderedPostProcessors, beanFactory);

        // Next, invoke the BeanFactoryPostProcessors that implement Ordered.
        List<BeanFactoryPostProcessor> orderedPostProcessors = new ArrayList<BeanFactoryPostProcessor>();
        for (String postProcessorName : orderedPostProcessorNames) {
            orderedPostProcessors.add(getBean(postProcessorName, BeanFactoryPostProcessor.class));
        }
        OrderComparator.sort(orderedPostProcessors);
        invokeBeanFactoryPostProcessors(orderedPostProcessors, beanFactory);

        // Finally, invoke all other BeanFactoryPostProcessors.
        List<BeanFactoryPostProcessor> nonOrderedPostProcessors = new ArrayList<BeanFactoryPostProcessor>();
        for (String postProcessorName : nonOrderedPostProcessorNames) {
            nonOrderedPostProcessors.add(getBean(postProcessorName, BeanFactoryPostProcessor.class));
        }
        invokeBeanFactoryPostProcessors(nonOrderedPostProcessors, beanFactory);
    }

下面则开始处理BeanPostProcessor：

    protected void registerBeanPostProcessors(ConfigurableListableBeanFactory beanFactory) {
        // 从容器中取得所有实现了BeanPostProcessor接口的类的名字
        String[] postProcessorNames = beanFactory.getBeanNamesForType(BeanPostProcessor.class, true, false);

        // Register BeanPostProcessorChecker that logs an info message when
        // a bean is created during BeanPostProcessor instantiation, i.e. when
        // a bean is not eligible for getting processed by all BeanPostProcessors.
        // 注册BeanPostProcessorChecker用来记录当一个bean在BeanPostProcessor初始化过程中，比如，当一个bean不能被所有BeanPostProcessors处理时
        int beanProcessorTargetCount = beanFactory.getBeanPostProcessorCount() + 1 + postProcessorNames.length;
        beanFactory.addBeanPostProcessor(new BeanPostProcessorChecker(beanFactory, beanProcessorTargetCount));

        // 和BeanFactoryPostProcessor一样，这里将BeanPostProcessors分为三种类别：实现了PriorityOrdered，实现了Ordered
        // 和两者都没有实现的
        List<BeanPostProcessor> priorityOrderedPostProcessors = new ArrayList<BeanPostProcessor>();
        List<BeanPostProcessor> internalPostProcessors = new ArrayList<BeanPostProcessor>();
        List<String> orderedPostProcessorNames = new ArrayList<String>();
        List<String> nonOrderedPostProcessorNames = new ArrayList<String>();
        for (String ppName : postProcessorNames) {
            if (isTypeMatch(ppName, PriorityOrdered.class)) {
                BeanPostProcessor pp = beanFactory.getBean(ppName, BeanPostProcessor.class);
                priorityOrderedPostProcessors.add(pp);
                if (pp instanceof MergedBeanDefinitionPostProcessor) {
                    internalPostProcessors.add(pp);
                }
            }
            else if (isTypeMatch(ppName, Ordered.class)) {
                orderedPostProcessorNames.add(ppName);
            }
            else {
                nonOrderedPostProcessorNames.add(ppName);
            }
        }

        // First, register the BeanPostProcessors that implement PriorityOrdered.
        OrderComparator.sort(priorityOrderedPostProcessors);
        registerBeanPostProcessors(beanFactory, priorityOrderedPostProcessors);

        // Next, register the BeanPostProcessors that implement Ordered.
        List<BeanPostProcessor> orderedPostProcessors = new ArrayList<BeanPostProcessor>();
        for (String ppName : orderedPostProcessorNames) {
            BeanPostProcessor pp = beanFactory.getBean(ppName, BeanPostProcessor.class);
            orderedPostProcessors.add(pp);
            if (pp instanceof MergedBeanDefinitionPostProcessor) {
                internalPostProcessors.add(pp);
            }
        }
        OrderComparator.sort(orderedPostProcessors);
        registerBeanPostProcessors(beanFactory, orderedPostProcessors);

        // Now, register all regular BeanPostProcessors.
        List<BeanPostProcessor> nonOrderedPostProcessors = new ArrayList<BeanPostProcessor>();
        for (String ppName : nonOrderedPostProcessorNames) {
            BeanPostProcessor pp = beanFactory.getBean(ppName, BeanPostProcessor.class);
            nonOrderedPostProcessors.add(pp);
            if (pp instanceof MergedBeanDefinitionPostProcessor) {
                internalPostProcessors.add(pp);
            }
        }
        registerBeanPostProcessors(beanFactory, nonOrderedPostProcessors);

        // 最后需要重新注册所有的internal BeanPostProcessors
        OrderComparator.sort(internalPostProcessors);
        registerBeanPostProcessors(beanFactory, internalPostProcessors);

        beanFactory.addBeanPostProcessor(new ApplicationListenerDetector());
    }

看到上面最后重新注册所有internal那一步可能会不解，注册过了再注册一遍是什么意思呢？我们看看源码：

    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;
        }
    }

这里会先将原来注册的BeanPostProcessor移除掉，然后再添加，这样也就保证了internal BeanPostProcessor总是在List的最后，在对Bean进行Process时总能保证internal BeanPostProcessor最后执行。（虽然不知道目的是为何，但应该确实有必要）

下面一步是初始化MessageSource。首先会在容器中寻找是否存在名为messageSource的Bean，若存在则将其初始化并作为messageSource：

    protected void initMessageSource() {
        ConfigurableListableBeanFactory beanFactory = getBeanFactory();
        if (beanFactory.containsLocalBean(MESSAGE_SOURCE_BEAN_NAME)) {
            this.messageSource = beanFactory.getBean(MESSAGE_SOURCE_BEAN_NAME, MessageSource.class);
            // Make MessageSource aware of parent MessageSource.
            if (this.parent != null && this.messageSource instanceof HierarchicalMessageSource) {
                HierarchicalMessageSource hms = (HierarchicalMessageSource) this.messageSource;
                if (hms.getParentMessageSource() == null) {
                    // Only set parent context as parent MessageSource if no parent MessageSource
                    // registered already.
                    hms.setParentMessageSource(getInternalParentMessageSource());
                }
            }
            if (logger.isDebugEnabled()) {
                logger.debug("Using MessageSource [" + this.messageSource + "]");
            }
        }
        else {
            // 如果容器中不存在messageSource，那么只能用一个空实现DelegatingMessageSource
            // 它会将所有的方法调用都委托给parentMessageSource，若parentMessageSource为null
            // 那默认的渲染策略就是将message原样返回
            DelegatingMessageSource dms = new DelegatingMessageSource();
            dms.setParentMessageSource(getInternalParentMessageSource());
            this.messageSource = dms;
            beanFactory.registerSingleton(MESSAGE_SOURCE_BEAN_NAME, this.messageSource);
            if (logger.isDebugEnabled()) {
                logger.debug("Unable to locate MessageSource with name ‘" + MESSAGE_SOURCE_BEAN_NAME +
                        "‘: using default [" + this.messageSource + "]");
            }
        }

中间省略一些略微次要的步骤，看下面这个方法：
这个方法是用来初始化容器中定义的所有Singleton（不包括之前已经初始化了的）

    protected void finishBeanFactoryInitialization(ConfigurableListableBeanFactory beanFactory) {
        // 首先初始化conversion service
        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();

        // 实例化所有剩下的非懒加载的singletons
        beanFactory.preInstantiateSingletons();
    }

可以看到，这里的最后一步才是真正做初始化工作的，其余只是做一些辅助。再跟进去看看：

public void preInstantiateSingletons() throws BeansException {
        if (this.logger.isInfoEnabled()) {
            this.logger.info("Pre-instantiating singletons in " + this);
        }
        List<String> beanNames;
        synchronized (this.beanDefinitionMap) {
            // Iterate over a copy to allow for init methods which in turn register new bean definitions.
            // While this may not be part of the regular factory bootstrap, it does otherwise work fine.
            beanNames = new ArrayList<String>(this.beanDefinitionNames);
        }
        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(new PrivilegedAction<Boolean>() {
                            public Boolean run() {
                                return ((SmartFactoryBean<?>) factory).isEagerInit();
                            }
                        }, getAccessControlContext());
                    }
                    else {
                        isEagerInit = (factory instanceof SmartFactoryBean &&
                                ((SmartFactoryBean<?>) factory).isEagerInit());
                    }
                    if (isEagerInit) {
                        getBean(beanName);
                    }
                }
                else {
                    getBean(beanName);
                }
            }
        }
    }

可以看到，这里对加载进来的BeanDefinition进行了区分，判断其是否为FactoryBean。从上面的代码可以看出，若是非FactoryBean，那么直接就调用getBean(...)方法了：

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

这里直接去调用doGetBean(...)方法：

    protected <T> T doGetBean(
            final String name, final Class<T> requiredType, final Object[] args, boolean typeCheckOnly)
            throws BeansException {

        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);
        }

        else {
            // Fail if we‘re already creating this bean instance:
            // We‘re assumably within a circular reference.
            if (isPrototypeCurrentlyInCreation(beanName)) {
                throw new BeanCurrentlyInCreationException(beanName);
            }

            // Check if bean definition exists in this factory.
            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);
                }
            }

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

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

                // 保证依赖的bean在该bean之前实例化
                String[] dependsOn = mbd.getDependsOn();
                if (dependsOn != null) {
                    for (String dependsOnBean : dependsOn) {
                        getBean(dependsOnBean);
                        registerDependentBean(dependsOnBean, beanName);
                    }
                }

                // 到这里才是真正去创建单例Bean
                if (mbd.isSingleton()) {
                    sharedInstance = getSingleton(beanName, new ObjectFactory<Object>() {
                        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;
                            }
                        }
                    });
                    // 若非FactoryBean的话，那么直接返回sharedInstance。若是FactoryBean且name不以&开头，那么则返回工厂生产的getObject()
                    bean = getObjectForBeanInstance(sharedInstance, name, beanName, mbd);
                }

                else if (mbd.isPrototype()) {
                    // It‘s a prototype -> create a new instance.
                    Object prototypeInstance = null;
                    try {
                        beforePrototypeCreation(beanName);
                        prototypeInstance = createBean(beanName, mbd, args);
                    }
                    finally {
                        afterPrototypeCreation(beanName);
                    }
                    bean = getObjectForBeanInstance(prototypeInstance, name, beanName, mbd);
                }

                else {
                    String scopeName = mbd.getScope();
                    final Scope scope = this.scopes.get(scopeName);
                    if (scope == null) {
                        throw new IllegalStateException("No Scope registered for scope ‘" + scopeName + "‘");
                    }
                    try {
                        Object scopedInstance = scope.get(beanName, new ObjectFactory<Object>() {
                            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);
                    }
                }
            }
            catch (BeansException ex) {
                cleanupAfterBeanCreationFailure(beanName);
                throw ex;
            }
        }

        // Check if required type matches the type of the actual bean instance.
        if (requiredType != null && bean != null && !requiredType.isAssignableFrom(bean.getClass())) {
            try {
                return getTypeConverter().convertIfNecessary(bean, requiredType);
            }
            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;
    }

可以看到doGetBean()中核心的方法就是createBean(...)：

    /**
     * Central method of this class: creates a bean instance,
     * populates the bean instance, applies post-processors, etc.
     * @see #doCreateBean
     */
    @Override
    protected Object createBean(final String beanName, final RootBeanDefinition mbd, final Object[] args)
            throws BeanCreationException {

        if (logger.isDebugEnabled()) {
            logger.debug("Creating instance of bean ‘" + beanName + "‘");
        }
        // Make sure bean class is actually resolved at this point.
        resolveBeanClass(mbd, beanName);

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

        try {
            // Give BeanPostProcessors a chance to return a proxy instead of the target bean instance.
            Object bean = resolveBeforeInstantiation(beanName, mbd);
            if (bean != null) {
                return bean;
            }
        }
        catch (Throwable ex) {
            throw new BeanCreationException(mbd.getResourceDescription(), beanName,
                    "BeanPostProcessor before instantiation of bean failed", ex);
        }

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

可以看到，上面的方法返回的beanInstance是通过doCreateBean(...)方法得到的，跟踪进去：

protected Object doCreateBean(final String beanName, final RootBeanDefinition mbd, final Object[] args) {
        // Instantiate the bean.
        BeanWrapper instanceWrapper = null;
        if (mbd.isSingleton()) {
            instanceWrapper = this.factoryBeanInstanceCache.remove(beanName);
        }
        if (instanceWrapper == null) {
            // 这里包含几个步骤：1、实例化bean 2、创建BeanWrapper来包装bean 3、并给BeanWrapper设置conversionService和propertyEditor
            instanceWrapper = createBeanInstance(beanName, mbd, args);
        }
        final Object bean = (instanceWrapper != null ? instanceWrapper.getWrappedInstance() : null);
        Class<?> beanType = (instanceWrapper != null ? instanceWrapper.getWrappedClass() : null);

        synchronized (mbd.postProcessingLock) {
            if (!mbd.postProcessed) {
                // 调用BeanFactory上注册的MergedBeanDefinitionPostProcessor的回调方法，用来修改BeanDefinition
                // 这里包括对一些注解的解析支持（比如@Resource，@PostConstruct——CommonAnnotationBeanPostProcessor
                // @Value，@Autowired——AutowiredAnnotationBeanPostProcessor
                // @Required——RequiredAnnotationBeanPostProcessor）
                applyMergedBeanDefinitionPostProcessors(mbd, beanType, beanName);
                mbd.postProcessed = true;
            }
        }

        // Eagerly cache singletons to be able to resolve circular references
        // even when triggered by lifecycle interfaces like BeanFactoryAware.
        boolean earlySingletonExposure = (mbd.isSingleton() && this.allowCircularReferences &&
                isSingletonCurrentlyInCreation(beanName));
        if (earlySingletonExposure) {
            if (logger.isDebugEnabled()) {
                logger.debug("Eagerly caching bean ‘" + beanName +
                        "‘ to allow for resolving potential circular references");
            }

            addSingletonFactory(beanName, new ObjectFactory<Object>() {
                public Object getObject() throws BeansException {
                    return getEarlyBeanReference(beanName, mbd, bean);
                }
            });
        }

        // Initialize the bean instance.
        Object exposedObject = bean;
        try {
            // 给bean注入依赖 这个方法下面会分析一下
            populateBean(beanName, mbd, instanceWrapper);
            if (exposedObject != null) {
                // 这里调用init方法，并用BeanPostProcessor来拦截Bean
                exposedObject = initializeBean(beanName, exposedObject, mbd);
            }
        }
        catch (Throwable ex) {
            if (ex instanceof BeanCreationException && beanName.equals(((BeanCreationException) ex).getBeanName())) {
                throw (BeanCreationException) ex;
            }
            else {
                throw new BeanCreationException(mbd.getResourceDescription(), beanName, "Initialization of bean failed", ex);
            }
        }

        if (earlySingletonExposure) {
            Object earlySingletonReference = getSingleton(beanName, false);
            if (earlySingletonReference != null) {
                if (exposedObject == bean) {
                    exposedObject = earlySingletonReference;
                }
                else if (!this.allowRawInjectionDespiteWrapping && hasDependentBean(beanName)) {
                    String[] dependentBeans = getDependentBeans(beanName);
                    Set<String> actualDependentBeans = new LinkedHashSet<String>(dependentBeans.length);
                    for (String dependentBean : dependentBeans) {
                        if (!removeSingletonIfCreatedForTypeCheckOnly(dependentBean)) {
                            actualDependentBeans.add(dependentBean);
                        }
                    }
                    if (!actualDependentBeans.isEmpty()) {
                        throw new BeanCurrentlyInCreationException(beanName,
                                "Bean with name ‘" + beanName + "‘ has been injected into other beans [" +
                                StringUtils.collectionToCommaDelimitedString(actualDependentBeans) +
                                "] in its raw version as part of a circular reference, but has eventually been " +
                                "wrapped. This means that said other beans do not use the final version of the " +
                                "bean. This is often the result of over-eager type matching - consider using " +
                                "‘getBeanNamesOfType‘ with the ‘allowEagerInit‘ flag turned off, for example.");
                    }
                }
            }
        }

        // Register bean as disposable.
        try {
            registerDisposableBeanIfNecessary(beanName, bean, mbd);
        }
        catch (BeanDefinitionValidationException ex) {
            throw new BeanCreationException(mbd.getResourceDescription(), beanName, "Invalid destruction signature", ex);
        }

        return exposedObject;
    }

最后再看下populateBean(...)这个注入依赖的方法：

    protected void populateBean(String beanName, RootBeanDefinition mbd, BeanWrapper bw) {
        PropertyValues pvs = mbd.getPropertyValues();

        if (bw == null) {
            if (!pvs.isEmpty()) {
                throw new BeanCreationException(
                        mbd.getResourceDescription(), beanName, "Cannot apply property values to null instance");
            }
            else {
                // Skip property population phase for null instance.
                return;
            }
        }

        // Give any InstantiationAwareBeanPostProcessors the opportunity to modify the
        // state of the bean before properties are set. This can be used, for example,
        // to support styles of field injection.
        boolean continueWithPropertyPopulation = true;

        if (!mbd.isSynthetic() && hasInstantiationAwareBeanPostProcessors()) {
            for (BeanPostProcessor bp : getBeanPostProcessors()) {
                if (bp instanceof InstantiationAwareBeanPostProcessor) {
                    InstantiationAwareBeanPostProcessor ibp = (InstantiationAwareBeanPostProcessor) bp;
                    if (!ibp.postProcessAfterInstantiation(bw.getWrappedInstance(), beanName)) {
                        continueWithPropertyPopulation = false;
                        break;
                    }
                }
            }
        }

        if (!continueWithPropertyPopulation) {
            return;
        }

        // 处理autowire byname和bytype的情况
        if (mbd.getResolvedAutowireMode() == RootBeanDefinition.AUTOWIRE_BY_NAME ||
                mbd.getResolvedAutowireMode() == RootBeanDefinition.AUTOWIRE_BY_TYPE) {
            MutablePropertyValues newPvs = new MutablePropertyValues(pvs);

            // Add property values based on autowire by name if applicable.
            if (mbd.getResolvedAutowireMode() == RootBeanDefinition.AUTOWIRE_BY_NAME) {
                autowireByName(beanName, mbd, bw, newPvs);
            }

            // Add property values based on autowire by type if applicable.
            if (mbd.getResolvedAutowireMode() == RootBeanDefinition.AUTOWIRE_BY_TYPE) {
                autowireByType(beanName, mbd, bw, newPvs);
            }

            pvs = newPvs;
        }

        boolean hasInstAwareBpps = hasInstantiationAwareBeanPostProcessors();
        boolean needsDepCheck = (mbd.getDependencyCheck() != RootBeanDefinition.DEPENDENCY_CHECK_NONE);

        if (hasInstAwareBpps || needsDepCheck) {
            PropertyDescriptor[] filteredPds = filterPropertyDescriptorsForDependencyCheck(bw, mbd.allowCaching);
            if (hasInstAwareBpps) {
                // 而这里则是处理@Resource、@Autowire等自动装配的依赖
                for (BeanPostProcessor bp : getBeanPostProcessors()) {
                    if (bp instanceof InstantiationAwareBeanPostProcessor) {
                        InstantiationAwareBeanPostProcessor ibp = (InstantiationAwareBeanPostProcessor) bp;
                        pvs = ibp.postProcessPropertyValues(pvs, filteredPds, bw.getWrappedInstance(), beanName);
                        if (pvs == null) {
                            return;
                        }
                    }
                }
            }
            if (needsDepCheck) {
                checkDependencies(beanName, mbd, filteredPds, pvs);
            }
        }

        // 将pvs转换成相应类型的属性值并设置到对应字段中去
        applyPropertyValues(beanName, mbd, bw, pvs);
    }

差不多分析完了，也就是自己对Spring源码的一个学习，希望对大家也可以有帮助。