Spring IOC解析（3）---IoC容器的依赖注入

1.4 IoC容器的依赖注入

  上面对IoC容器的初始化过程进行了详细的分析，这个初始化过程完成的主要工作是在IoC容器中建立BeanDefinition数据映射。在此过程中并没有看到IoC容器对Bean依赖关系进行注入，接下来分析一下IoC容器是怎样对Bean的依赖关系进行注入的。
  假设当前IoC容器已经载入了用户定义的Bean信息，开始分析依赖注入的原理。首先， 注意到依赖注入的过程是用户第一次向IoC容器索要Bean时才触发的，当然也有例外，也就是我们可以在BeanDefinition信息中通过控制lazy-init属性来让容器完成对Bean的预实例化。这个预实例化实际上也是一个完成依赖注入的过程，但它是在初始化的过程中完成的，稍后我们会详细分析这个预实例化的处理。当用户向IoC容器索要Bean时。基本的loC容器接口BeanFactory中，有一个getBean的接口定义，这个接口的实现就是触发依赖注入发生的地方。为了进一步了解这个依赖注入过程的实现， 下面从DefaultListableBeanFactory的基类AbstractBeanFactory入手去看看getBean()的实现，如代码所示．

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);
    }

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

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);

                // Guarantee initialization of beans that the current bean depends on.
                String[] dependsOn = mbd.getDependsOn();
                if (dependsOn != null) {
                    for (String dependsOnBean : dependsOn) {
                        getBean(dependsOnBean);
                        registerDependentBean(dependsOnBean, beanName);
                    }
                }

                // Create bean instance.
                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;
                            }
                        }
                    });
                    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;
    }

  这个就是依赖注入的入口，在这里触发了依赖注入，而依赖注人的发生是在容器中的BeanDefinition数据已经建立好的前提下进行的。“程序＝数据＋算法 ”很经典的一句话，前面的BeanDefinition就是数据，下面看看这些数据是怎样为依赖注入服务的。虽然依赖注入的过程不涉及复杂的算法问题，但这个过程也不简单，因为我们都知道，对于IoC容器的使用，Spring提供了许多的参数配置，每一个参数配置实际上代表了一个IoC容器的实现特性，这些特性的实现很多都需要在依赖注入的过程中或者对Bean进行生命周期管理的过程中完成。尽管可以用最简单的方式来描述loC容器，将它视为一个hashMap ，但只能说这个hashMap是容器的最基本的数据结构，而不是IoC容器的全部。Spring IoC容器作为一个产品，其价值体现在一系列相关的产品特性上，这些产品特性以依赖反转模式的实现为核心，为用户更好地使用依赖反转提供便利，从而实现了一个完整的loC容器产品。这些产品特性的实现并不是一个简单的过程，它提供了一个成熟的IoC容器产品供用户使用．所以，尽管Spring IoC容器没有什么独特的算法， 但却可以看成是一个成功的软件工程产品。
  在下图中可以看到依赖注入的一个大致过程。

  getBean是依赖注入的起点，之后会调用createBean ，下面通过createBean代码来了解这个实现过程。在这个过程中， Bean对象会依据BeanDefinition定义的要求生成。在AbstractAutowireCapableBeanFactory中实现了这个createBean, createBean不但生成了需要的Bean ，还对Bean初始化进行了处理，比如实现了在BeanDefinition中的init-method属性定义， Bean后置处理器等。具体的过程如代码所示

@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;
    }

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) {
            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;
            }
        }

        // 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 {
            populateBean(beanName, mbd, instanceWrapper);
            if (exposedObject != null) {
                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;
    }

  在这里我们看到，与依赖注入关系特别密切的方法有createBeanlnstance和populateBean,下面分别介绍这两个方法。在createBeanlnstance中生成了Bean所包含的Java对象，这个对象的生成有很多种不同的方式，可以通过工广方法生成，也可以通过容器的autowire特性生成，
这些生成方式都是自相关的BeanDefinition来指定的。如以下代码所示，可以看到不同生成方式对应的实现。

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...
        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);
    }

protected BeanWrapper instantiateBean(final String beanName, final RootBeanDefinition mbd) {
        try {
            Object beanInstance;
            final BeanFactory parent = this;
            if (System.getSecurityManager() != null) {
                beanInstance = AccessController.doPrivileged(new PrivilegedAction<Object>() {
                    public Object run() {
                        return getInstantiationStrategy().instantiate(mbd, beanName, parent);
                    }
                }, getAccessControlContext());
            }
            else {
                beanInstance = getInstantiationStrategy().instantiate(mbd, beanName, parent);
            }
            BeanWrapper bw = new BeanWrapperImpl(beanInstance);
            initBeanWrapper(bw);
            return bw;
        }
        catch (Throwable ex) {
            throw new BeanCreationException(mbd.getResourceDescription(), beanName, "Instantiation of bean failed", ex);
        }
    }

这里用CGLIB对Bean进行实例化. CGLIB是一个常用的字节码生成器的类库，它提供了一系列的API来提供生成和转换java的字节码的功能。在Spring AOP中也使用CGLIB对Java的字节码进行增强。在loC容器中，耍了解怎样使用CGLIB来生成Bean对象，需要看一下Simplelr川antiationStrategy类。这个Strategy是Spring用来生成Bean对象的默认类，它提供了两种实例化Java对象的方法，一种是通过BeanUtils ，它使用了JVM的反射功能， 一种是通过前面提到的CGLIB来生成，如代码所示。

public class SimpleInstantiationStrategy implements InstantiationStrategy {

    private static final ThreadLocal<Method> currentlyInvokedFactoryMethod = new ThreadLocal<Method>();


    /**
     * Return the factory method currently being invoked or {@code null} if none.
     * <p>Allows factory method implementations to determine whether the current
     * caller is the container itself as opposed to user code.
     */
    public static Method getCurrentlyInvokedFactoryMethod() {
        return currentlyInvokedFactoryMethod.get();
    }


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

    /**
     * Subclasses can override this method, which is implemented to throw
     * UnsupportedOperationException, if they can instantiate an object with
     * the Method Injection specified in the given RootBeanDefinition.
     * Instantiation should use a no-arg constructor.
     */
    protected Object instantiateWithMethodInjection(
            RootBeanDefinition beanDefinition, String beanName, BeanFactory owner) {

        throw new UnsupportedOperationException(
                "Method Injection not supported in SimpleInstantiationStrategy");
    }

    public Object instantiate(RootBeanDefinition beanDefinition, String beanName, BeanFactory owner,
            final Constructor<?> ctor, Object[] args) {

        if (beanDefinition.getMethodOverrides().isEmpty()) {
            if (System.getSecurityManager() != null) {
                // use own privileged to change accessibility (when security is on)
                AccessController.doPrivileged(new PrivilegedAction<Object>() {
                    public Object run() {
                        ReflectionUtils.makeAccessible(ctor);
                        return null;
                    }
                });
            }
            return BeanUtils.instantiateClass(ctor, args);
        }
        else {
            return instantiateWithMethodInjection(beanDefinition, beanName, owner, ctor, args);
        }
    }

    /**
     * Subclasses can override this method, which is implemented to throw
     * UnsupportedOperationException, if they can instantiate an object with
     * the Method Injection specified in the given RootBeanDefinition.
     * Instantiation should use the given constructor and parameters.
     */
    protected Object instantiateWithMethodInjection(RootBeanDefinition beanDefinition,
            String beanName, BeanFactory owner, Constructor<?> ctor, Object[] args) {

        throw new UnsupportedOperationException(
                "Method Injection not supported in SimpleInstantiationStrategy");
    }

    public Object instantiate(RootBeanDefinition beanDefinition, String beanName, BeanFactory owner,
            Object factoryBean, final Method factoryMethod, Object[] args) {

        try {
            if (System.getSecurityManager() != null) {
                AccessController.doPrivileged(new PrivilegedAction<Object>() {
                    public Object run() {
                        ReflectionUtils.makeAccessible(factoryMethod);
                        return null;
                    }
                });
            }
            else {
                ReflectionUtils.makeAccessible(factoryMethod);
            }

            Method priorInvokedFactoryMethod = currentlyInvokedFactoryMethod.get();
            try {
                currentlyInvokedFactoryMethod.set(factoryMethod);
                return factoryMethod.invoke(factoryBean, args);
            }
            finally {
                if (priorInvokedFactoryMethod != null) {
                    currentlyInvokedFactoryMethod.set(priorInvokedFactoryMethod);
                }
                else {
                    currentlyInvokedFactoryMethod.remove();
                }
            }
        }
        catch (IllegalArgumentException ex) {
            throw new BeanDefinitionStoreException(
                    "Illegal arguments to factory method [" + factoryMethod + "]; " +
                    "args: " + StringUtils.arrayToCommaDelimitedString(args));
        }
        catch (IllegalAccessException ex) {
            throw new BeanDefinitionStoreException(
                    "Cannot access factory method [" + factoryMethod + "]; is it public?");
        }
        catch (InvocationTargetException ex) {
            throw new BeanDefinitionStoreException(
                    "Factory method [" + factoryMethod + "] threw exception", ex.getTargetException());
        }
    }

}

在CglibSubclassinglnstantiationStrategy 中可以看到具体的实例化过程和CG LIB的使用方法这里的Enhancer类， 是CGLIB的类，通过这个Enhancer生成Java对象，使用的是Enhancer的create方法，如代码所示。

public Object instantiate(Constructor<?> ctor, Object[] args) {
            Enhancer enhancer = new Enhancer();
            enhancer.setSuperclass(this.beanDefinition.getBeanClass());
            enhancer.setNamingPolicy(SpringNamingPolicy.INSTANCE);
            enhancer.setCallbackFilter(new CallbackFilterImpl());
            enhancer.setCallbacks(new Callback[] {
                    NoOp.INSTANCE,
                    new LookupOverrideMethodInterceptor(),
                    new ReplaceOverrideMethodInterceptor()
            });

            return (ctor != null ? enhancer.create(ctor.getParameterTypes(), args) : enhancer.create());
        }

  到这里已经分析了实例化Bean对象的整个过程。在实例化Bean对象生成的基础上，再介绍一下Spring是怎样对这些对象进行处理的，也就是Bean对象生成以后，怎样把这些Bean对象的依赖关系设置好，完成整个依赖注入过程。这个过程涉及对各种Bean对象的属性的处理过程（即依赖关系处理的过程），这些依赖关系处理的依据就是已经解析得到的BeanDefinition。要详细了解这个过程，需要回到前面的populateBean方法，这个方法在AbstractAutowireCapableBeanFactory中的实现如代码所示。

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;
        }

        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) {
                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);
            }
        }

        applyPropertyValues(beanName, mbd, bw, pvs);
    }

/**
     * Apply the given property values, resolving any runtime references
     * to other beans in this bean factory. Must use deep copy, so we
     * don't permanently modify this property.
     * @param beanName the bean name passed for better exception information
     * @param mbd the merged bean definition
     * @param bw the BeanWrapper wrapping the target object
     * @param pvs the new property values
     */
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);
        }
    }

  这里通过使用BeanDefinitionResolver来对BeanDefinition进行解析，然后注入到property中。具体的对Bean reference进行解析的过程如代码所示。

/**
     * Resolve a reference to another bean in the factory.
     */
    private Object resolveReference(Object argName, RuntimeBeanReference ref) {
        try {
            String refName = ref.getBeanName();
            refName = String.valueOf(evaluate(refName));
            if (ref.isToParent()) {
                if (this.beanFactory.getParentBeanFactory() == null) {
                    throw new BeanCreationException(
                            this.beanDefinition.getResourceDescription(), this.beanName,
                            "Can't resolve reference to bean '" + refName +
                            "' in parent factory: no parent factory available");
                }
                return this.beanFactory.getParentBeanFactory().getBean(refName);
            }
            else {
                Object bean = this.beanFactory.getBean(refName);
                this.beanFactory.registerDependentBean(refName, this.beanName);
                return bean;
            }
        }
        catch (BeansException ex) {
            throw new BeanCreationException(
                    this.beanDefinition.getResourceDescription(), this.beanName,
                    "Cannot resolve reference to bean '" + ref.getBeanName() + "' while setting " + argName, ex);
        }
    }

/**
     * For each element in the managed array, resolve reference if necessary.
     */
    private Object resolveManagedArray(Object argName, List<?> ml, Class<?> elementType) {
        Object resolved = Array.newInstance(elementType, ml.size());
        for (int i = 0; i < ml.size(); i++) {
            Array.set(resolved, i,
                    resolveValueIfNecessary(new KeyedArgName(argName, i), ml.get(i)));
        }
        return resolved;
    }

    /**
     * For each element in the managed list, resolve reference if necessary.
     */
    private List<?> resolveManagedList(Object argName, List<?> ml) {
        List<Object> resolved = new ArrayList<Object>(ml.size());
        for (int i = 0; i < ml.size(); i++) {
            resolved.add(
                    resolveValueIfNecessary(new KeyedArgName(argName, i), ml.get(i)));
        }
        return resolved;
    }

  这两种属性的注入都调用了resolveValuelfNecessary ，这个方法包含了所有对注入类型的处理。下面看一下resolveValuelfNecessary的实现，如代码所示。

/**
     * Given a PropertyValue, return a value, resolving any references to other
     * beans in the factory if necessary. The value could be:
     * <li>A BeanDefinition, which leads to the creation of a corresponding
     * new bean instance. Singleton flags and names of such "inner beans"
     * are always ignored: Inner beans are anonymous prototypes.
     * <li>A RuntimeBeanReference, which must be resolved.
     * <li>A ManagedList. This is a special collection that may contain
     * RuntimeBeanReferences or Collections that will need to be resolved.
     * <li>A ManagedSet. May also contain RuntimeBeanReferences or
     * Collections that will need to be resolved.
     * <li>A ManagedMap. In this case the value may be a RuntimeBeanReference
     * or Collection that will need to be resolved.
     * <li>An ordinary object or {@code null}, in which case it's left alone.
     * @param argName the name of the argument that the value is defined for
     * @param value the value object to resolve
     * @return the resolved object
     */
    public Object resolveValueIfNecessary(Object argName, Object value) {
        // We must check each value to see whether it requires a runtime reference
        // to another bean to be resolved.
        if (value instanceof RuntimeBeanReference) {
            RuntimeBeanReference ref = (RuntimeBeanReference) value;
            return resolveReference(argName, ref);
        }
        else if (value instanceof RuntimeBeanNameReference) {
            String refName = ((RuntimeBeanNameReference) value).getBeanName();
            refName = String.valueOf(evaluate(refName));
            if (!this.beanFactory.containsBean(refName)) {
                throw new BeanDefinitionStoreException(
                        "Invalid bean name '" + refName + "' in bean reference for " + argName);
            }
            return refName;
        }
        else if (value instanceof BeanDefinitionHolder) {
            // Resolve BeanDefinitionHolder: contains BeanDefinition with name and aliases.
            BeanDefinitionHolder bdHolder = (BeanDefinitionHolder) value;
            return resolveInnerBean(argName, bdHolder.getBeanName(), bdHolder.getBeanDefinition());
        }
        else if (value instanceof BeanDefinition) {
            // Resolve plain BeanDefinition, without contained name: use dummy name.
            BeanDefinition bd = (BeanDefinition) value;
            String innerBeanName = "(inner bean)" + BeanFactoryUtils.GENERATED_BEAN_NAME_SEPARATOR +
                    ObjectUtils.getIdentityHexString(bd);
            return resolveInnerBean(argName, innerBeanName, bd);
        }
        else if (value instanceof ManagedArray) {
            // May need to resolve contained runtime references.
            ManagedArray array = (ManagedArray) value;
            Class<?> elementType = array.resolvedElementType;
            if (elementType == null) {
                String elementTypeName = array.getElementTypeName();
                if (StringUtils.hasText(elementTypeName)) {
                    try {
                        elementType = ClassUtils.forName(elementTypeName, this.beanFactory.getBeanClassLoader());
                        array.resolvedElementType = elementType;
                    }
                    catch (Throwable ex) {
                        // Improve the message by showing the context.
                        throw new BeanCreationException(
                                this.beanDefinition.getResourceDescription(), this.beanName,
                                "Error resolving array type for " + argName, ex);
                    }
                }
                else {
                    elementType = Object.class;
                }
            }
            return resolveManagedArray(argName, (List<?>) value, elementType);
        }
        else if (value instanceof ManagedList) {
            // May need to resolve contained runtime references.
            return resolveManagedList(argName, (List<?>) value);
        }
        else if (value instanceof ManagedSet) {
            // May need to resolve contained runtime references.
            return resolveManagedSet(argName, (Set<?>) value);
        }
        else if (value instanceof ManagedMap) {
            // May need to resolve contained runtime references.
            return resolveManagedMap(argName, (Map<?, ?>) value);
        }
        else if (value instanceof ManagedProperties) {
            Properties original = (Properties) value;
            Properties copy = new Properties();
            for (Map.Entry<Object, Object> propEntry : original.entrySet()) {
                Object propKey = propEntry.getKey();
                Object propValue = propEntry.getValue();
                if (propKey instanceof TypedStringValue) {
                    propKey = evaluate((TypedStringValue) propKey);
                }
                if (propValue instanceof TypedStringValue) {
                    propValue = evaluate((TypedStringValue) propValue);
                }
                copy.put(propKey, propValue);
            }
            return copy;
        }
        else if (value instanceof TypedStringValue) {
            // Convert value to target type here.
            TypedStringValue typedStringValue = (TypedStringValue) value;
            Object valueObject = evaluate(typedStringValue);
            try {
                Class<?> resolvedTargetType = resolveTargetType(typedStringValue);
                if (resolvedTargetType != null) {
                    return this.typeConverter.convertIfNecessary(valueObject, resolvedTargetType);
                }
                else {
                    return valueObject;
                }
            }
            catch (Throwable ex) {
                // Improve the message by showing the context.
                throw new BeanCreationException(
                        this.beanDefinition.getResourceDescription(), this.beanName,
                        "Error converting typed String value for " + argName, ex);
            }
        }
        else {
            return evaluate(value);
        }
    }

/**
     * Resolve a reference to another bean in the factory.
     */
    private Object resolveReference(Object argName, RuntimeBeanReference ref) {
        try {
            String refName = ref.getBeanName();
            refName = String.valueOf(evaluate(refName));
            if (ref.isToParent()) {
                if (this.beanFactory.getParentBeanFactory() == null) {
                    throw new BeanCreationException(
                            this.beanDefinition.getResourceDescription(), this.beanName,
                            "Can't resolve reference to bean '" + refName +
                            "' in parent factory: no parent factory available");
                }
                return this.beanFactory.getParentBeanFactory().getBean(refName);
            }
            else {
                Object bean = this.beanFactory.getBean(refName);
                this.beanFactory.registerDependentBean(refName, this.beanName);
                return bean;
            }
        }
        catch (BeansException ex) {
            throw new BeanCreationException(
                    this.beanDefinition.getResourceDescription(), this.beanName,
                    "Cannot resolve reference to bean '" + ref.getBeanName() + "' while setting " + argName, ex);
        }
    }

/**
     * For each element in the managed list, resolve reference if necessary.
     */
    private List<?> resolveManagedList(Object argName, List<?> ml) {
        List<Object> resolved = new ArrayList<Object>(ml.size());
        for (int i = 0; i < ml.size(); i++) {
            resolved.add(
                    resolveValueIfNecessary(new KeyedArgName(argName, i), ml.get(i)));
        }
        return resolved;
    }

  在完成这个解析过程后，已经为依赖注入准备好了条件，这是真正把Bean对象设置到它所依赖的另一个Bean的属性中去的地方，其中处理的属性是各种各样的。依赖注入的发生是在BeanWrapper的setPropertyValues 中实现的，具体的完成却是在BeanWrapper的子类Bean Wrapperlmpl中实现的，如代码所示。

@SuppressWarnings("unchecked")
    private void setPropertyValue(PropertyTokenHolder tokens, PropertyValue pv) throws BeansException {
        String propertyName = tokens.canonicalName;
        String actualName = tokens.actualName;

        if (tokens.keys != null) {
            // Apply indexes and map keys: fetch value for all keys but the last one.
            PropertyTokenHolder getterTokens = new PropertyTokenHolder();
            getterTokens.canonicalName = tokens.canonicalName;
            getterTokens.actualName = tokens.actualName;
            getterTokens.keys = new String[tokens.keys.length - 1];
            System.arraycopy(tokens.keys, 0, getterTokens.keys, 0, tokens.keys.length - 1);
            Object propValue;
            try {
                propValue = getPropertyValue(getterTokens);
            }
            catch (NotReadablePropertyException ex) {
                throw new NotWritablePropertyException(getRootClass(), this.nestedPath + propertyName,
                        "Cannot access indexed value in property referenced " +
                        "in indexed property path '" + propertyName + "'", ex);
            }
            // Set value for last key.
            String key = tokens.keys[tokens.keys.length - 1];
            if (propValue == null) {
                // null map value case
                if (this.autoGrowNestedPaths) {
                    // TODO: cleanup, this is pretty hacky
                    int lastKeyIndex = tokens.canonicalName.lastIndexOf('[');
                    getterTokens.canonicalName = tokens.canonicalName.substring(0, lastKeyIndex);
                    propValue = setDefaultValue(getterTokens);
                }
                else {
                    throw new NullValueInNestedPathException(getRootClass(), this.nestedPath + propertyName,
                            "Cannot access indexed value in property referenced " +
                            "in indexed property path '" + propertyName + "': returned null");
                }
            }
            if (propValue.getClass().isArray()) {
                PropertyDescriptor pd = getCachedIntrospectionResults().getPropertyDescriptor(actualName);
                Class<?> requiredType = propValue.getClass().getComponentType();
                int arrayIndex = Integer.parseInt(key);
                Object oldValue = null;
                try {
                    if (isExtractOldValueForEditor() && arrayIndex < Array.getLength(propValue)) {
                        oldValue = Array.get(propValue, arrayIndex);
                    }
                    Object convertedValue = convertIfNecessary(propertyName, oldValue, pv.getValue(),
                            requiredType, TypeDescriptor.nested(property(pd), tokens.keys.length));
                    Array.set(propValue, arrayIndex, convertedValue);
                }
                catch (IndexOutOfBoundsException ex) {
                    throw new InvalidPropertyException(getRootClass(), this.nestedPath + propertyName,
                            "Invalid array index in property path '" + propertyName + "'", ex);
                }
            }
            else if (propValue instanceof List) {
                PropertyDescriptor pd = getCachedIntrospectionResults().getPropertyDescriptor(actualName);
                Class<?> requiredType = GenericCollectionTypeResolver.getCollectionReturnType(
                        pd.getReadMethod(), tokens.keys.length);
                List<Object> list = (List<Object>) propValue;
                int index = Integer.parseInt(key);
                Object oldValue = null;
                if (isExtractOldValueForEditor() && index < list.size()) {
                    oldValue = list.get(index);
                }
                Object convertedValue = convertIfNecessary(propertyName, oldValue, pv.getValue(),
                        requiredType, TypeDescriptor.nested(property(pd), tokens.keys.length));
                int size = list.size();
                if (index >= size && index < this.autoGrowCollectionLimit) {
                    for (int i = size; i < index; i++) {
                        try {
                            list.add(null);
                        }
                        catch (NullPointerException ex) {
                            throw new InvalidPropertyException(getRootClass(), this.nestedPath + propertyName,
                                    "Cannot set element with index " + index + " in List of size " +
                                    size + ", accessed using property path '" + propertyName +
                                    "': List does not support filling up gaps with null elements");
                        }
                    }
                    list.add(convertedValue);
                }
                else {
                    try {
                        list.set(index, convertedValue);
                    }
                    catch (IndexOutOfBoundsException ex) {
                        throw new InvalidPropertyException(getRootClass(), this.nestedPath + propertyName,
                                "Invalid list index in property path '" + propertyName + "'", ex);
                    }
                }
            }
            else if (propValue instanceof Map) {
                PropertyDescriptor pd = getCachedIntrospectionResults().getPropertyDescriptor(actualName);
                Class<?> mapKeyType = GenericCollectionTypeResolver.getMapKeyReturnType(
                        pd.getReadMethod(), tokens.keys.length);
                Class<?> mapValueType = GenericCollectionTypeResolver.getMapValueReturnType(
                        pd.getReadMethod(), tokens.keys.length);
                Map<Object, Object> map = (Map<Object, Object>) propValue;
                // IMPORTANT: Do not pass full property name in here - property editors
                // must not kick in for map keys but rather only for map values.
                TypeDescriptor typeDescriptor = (mapKeyType != null ?
                        TypeDescriptor.valueOf(mapKeyType) : TypeDescriptor.valueOf(Object.class));
                Object convertedMapKey = convertIfNecessary(null, null, key, mapKeyType, typeDescriptor);
                Object oldValue = null;
                if (isExtractOldValueForEditor()) {
                    oldValue = map.get(convertedMapKey);
                }
                // Pass full property name and old value in here, since we want full
                // conversion ability for map values.
                Object convertedMapValue = convertIfNecessary(propertyName, oldValue, pv.getValue(),
                        mapValueType, TypeDescriptor.nested(property(pd), tokens.keys.length));
                map.put(convertedMapKey, convertedMapValue);
            }
            else {
                throw new InvalidPropertyException(getRootClass(), this.nestedPath + propertyName,
                        "Property referenced in indexed property path '" + propertyName +
                        "' is neither an array nor a List nor a Map; returned value was [" + propValue + "]");
            }
        }

        else {
            PropertyDescriptor pd = pv.resolvedDescriptor;
            if (pd == null || !pd.getWriteMethod().getDeclaringClass().isInstance(this.object)) {
                pd = getCachedIntrospectionResults().getPropertyDescriptor(actualName);
                if (pd == null || pd.getWriteMethod() == null) {
                    if (pv.isOptional()) {
                        logger.debug("Ignoring optional value for property '" + actualName +
                                "' - property not found on bean class [" + getRootClass().getName() + "]");
                        return;
                    }
                    else {
                        PropertyMatches matches = PropertyMatches.forProperty(propertyName, getRootClass());
                        throw new NotWritablePropertyException(
                                getRootClass(), this.nestedPath + propertyName,
                                matches.buildErrorMessage(), matches.getPossibleMatches());
                    }
                }
                pv.getOriginalPropertyValue().resolvedDescriptor = pd;
            }

            Object oldValue = null;
            try {
                Object originalValue = pv.getValue();
                Object valueToApply = originalValue;
                if (!Boolean.FALSE.equals(pv.conversionNecessary)) {
                    if (pv.isConverted()) {
                        valueToApply = pv.getConvertedValue();
                    }
                    else {
                        if (isExtractOldValueForEditor() && pd.getReadMethod() != null) {
                            final Method readMethod = pd.getReadMethod();
                            if (!Modifier.isPublic(readMethod.getDeclaringClass().getModifiers()) &&
                                    !readMethod.isAccessible()) {
                                if (System.getSecurityManager()!= null) {
                                    AccessController.doPrivileged(new PrivilegedAction<Object>() {
                                        public Object run() {
                                            readMethod.setAccessible(true);
                                            return null;
                                        }
                                    });
                                }
                                else {
                                    readMethod.setAccessible(true);
                                }
                            }
                            try {
                                if (System.getSecurityManager() != null) {
                                    oldValue = AccessController.doPrivileged(new PrivilegedExceptionAction<Object>() {
                                        public Object run() throws Exception {
                                            return readMethod.invoke(object);
                                        }
                                    }, acc);
                                }
                                else {
                                    oldValue = readMethod.invoke(object);
                                }
                            }
                            catch (Exception ex) {
                                if (ex instanceof PrivilegedActionException) {
                                    ex = ((PrivilegedActionException) ex).getException();
                                }
                                if (logger.isDebugEnabled()) {
                                    logger.debug("Could not read previous value of property '" +
                                            this.nestedPath + propertyName + "'", ex);
                                }
                            }
                        }
                        valueToApply = convertForProperty(
                                propertyName, oldValue, originalValue, new TypeDescriptor(property(pd)));
                    }
                    pv.getOriginalPropertyValue().conversionNecessary = (valueToApply != originalValue);
                }
                final Method writeMethod = (pd instanceof GenericTypeAwarePropertyDescriptor ?
                        ((GenericTypeAwarePropertyDescriptor) pd).getWriteMethodForActualAccess() :
                        pd.getWriteMethod());
                if (!Modifier.isPublic(writeMethod.getDeclaringClass().getModifiers()) && !writeMethod.isAccessible()) {
                    if (System.getSecurityManager()!= null) {
                        AccessController.doPrivileged(new PrivilegedAction<Object>() {
                            public Object run() {
                                writeMethod.setAccessible(true);
                                return null;
                            }
                        });
                    }
                    else {
                        writeMethod.setAccessible(true);
                    }
                }
                final Object value = valueToApply;
                if (System.getSecurityManager() != null) {
                    try {
                        AccessController.doPrivileged(new PrivilegedExceptionAction<Object>() {
                            public Object run() throws Exception {
                                writeMethod.invoke(object, value);
                                return null;
                            }
                        }, acc);
                    }
                    catch (PrivilegedActionException ex) {
                        throw ex.getException();
                    }
                }
                else {
                    writeMethod.invoke(this.object, value);
                }
            }
            catch (TypeMismatchException ex) {
                throw ex;
            }
            catch (InvocationTargetException ex) {
                PropertyChangeEvent propertyChangeEvent =
                        new PropertyChangeEvent(this.rootObject, this.nestedPath + propertyName, oldValue, pv.getValue());
                if (ex.getTargetException() instanceof ClassCastException) {
                    throw new TypeMismatchException(propertyChangeEvent, pd.getPropertyType(), ex.getTargetException());
                }
                else {
                    throw new MethodInvocationException(propertyChangeEvent, ex.getTargetException());
                }
            }
            catch (Exception ex) {
                PropertyChangeEvent pce =
                        new PropertyChangeEvent(this.rootObject, this.nestedPath + propertyName, oldValue, pv.getValue());
                throw new MethodInvocationException(pce, ex);
            }
        }
    }

这样就完成于对各种Bean属性的依赖注入过程。
  在Bean的创建和对象依赖注入的过程中，需要依据BeanDefinition中的信息来递归地完成依赖注入。从上面的几个递归过程中可以看到，这些递归都是以getBean为入口的。一个递归是在上下文体系中查找需要的Bean和创建Bean的递归调用，另一个递归是在依赖注入时，通过递归调用容器的getBean方法，得到当前Bean的依赖Bean ，同时也触发对依赖Bean的创建和注入。在对Bean的属性进行依赖注入时，解析的过程也是一个递归的过程。这样，根据依赖关系， 一层一层地完成Bean的创建和注入，直到最后完成当前Bean的创建。有了这个顶层Bean的创建和对它的属性依赖注入的完成，意味着和当前Bean相关的整个依赖链的注入也完成了。
  在Bean创建和依赖注入完成以后，在IoC容器中建立起一系列依集依赖关系联系起来的Bean ，这个Bean 已经不是简单的Java对象了。该Bean系列以及Bean之间的依赖关系建立完成以后，通过IoC容器的相关接口方法，就可以非常方便地供上层应用使用了。