Spring源码阅读（六）

    /**
     * Populate the bean instance in the given BeanWrapper with the property values
     * from the bean definition.
     * 丰富bean实例属性
     * @param beanName the name of the bean
     * @param mbd the bean definition for the bean
     * @param bw BeanWrapper with bean instance
     */
    protected void populateBean(String beanName, RootBeanDefinition mbd, @Nullable 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.
        // 属性设置前调用处理器
        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);

        // 设置bean属性
        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);
    }

    /**
     * Autowired属性注入
     * @author coshaho 
     * @param pvs
     * @param pds   注入属性配置，方法中没有使用
     * @param bean  bean实例
     * @param beanName
     * @return
     * @throws BeanCreationException
     */
    public PropertyValues postProcessPropertyValues(
            PropertyValues pvs, PropertyDescriptor[] pds, Object bean, String beanName) throws BeanCreationException {

        // 获取注入属性配置信息
        InjectionMetadata metadata = findAutowiringMetadata(beanName, bean.getClass(), pvs);
        try {
            // 属性注入
            metadata.inject(bean, beanName, pvs);
        }
        catch (BeanCreationException ex) {
            throw ex;
        }
        catch (Throwable ex) {
            throw new BeanCreationException(beanName, "Injection of autowired dependencies failed", ex);
        }
        return pvs;
    }
    public void inject(Object target, @Nullable String beanName, @Nullable PropertyValues pvs) throws Throwable {
        // 获取待注入的属性队列
        Collection<InjectedElement> checkedElements = this.checkedElements;
        Collection<InjectedElement> elementsToIterate =
                (checkedElements != null ? checkedElements : this.injectedElements);
        if (!elementsToIterate.isEmpty()) {
            boolean debug = logger.isDebugEnabled();
            for (InjectedElement element : elementsToIterate) {
                if (debug) {
                    logger.debug("Processing injected element of bean ‘" + beanName + "‘: " + element);
                }
                // 属性注入
                element.inject(target, beanName, pvs);
            }
        }
    }

    @Override
    protected void inject(Object bean, @Nullable String beanName, @Nullable PropertyValues pvs) throws Throwable {
        Field field = (Field) this.member;
        Object value;
        if (this.cached) {
            value = resolvedCachedArgument(beanName, this.cachedFieldValue);
        }
        else {
            // 获取注入属性配置：属性名称，类名称
            DependencyDescriptor desc = new DependencyDescriptor(field, this.required);
            desc.setContainingClass(bean.getClass());
            Set<String> autowiredBeanNames = new LinkedHashSet<>(1);
            Assert.state(beanFactory != null, "No BeanFactory available");
            TypeConverter typeConverter = beanFactory.getTypeConverter();
            try {
                // 获取属性值
                value = beanFactory.resolveDependency(desc, beanName, autowiredBeanNames, typeConverter);
            }
            catch (BeansException ex) {
                throw new UnsatisfiedDependencyException(null, beanName, new InjectionPoint(field), ex);
            }
            synchronized (this) {
                if (!this.cached) {
                    if (value != null || this.required) {
                        this.cachedFieldValue = desc;
                        registerDependentBeans(beanName, autowiredBeanNames);
                        if (autowiredBeanNames.size() == 1) {
                            String autowiredBeanName = autowiredBeanNames.iterator().next();
                            if (beanFactory.containsBean(autowiredBeanName)) {
                                if (beanFactory.isTypeMatch(autowiredBeanName, field.getType())) {
                                    this.cachedFieldValue = new ShortcutDependencyDescriptor(
                                            desc, autowiredBeanName, field.getType());
                                }
                            }
                        }
                    }
                    else {
                        this.cachedFieldValue = null;
                    }
                    this.cached = true;
                }
            }
        }
        if (value != null) {
            ReflectionUtils.makeAccessible(field);
            // 反射设置属性
            field.set(bean, value);
        }
    }
    
    public Object resolveDependency(DependencyDescriptor descriptor, @Nullable String requestingBeanName,
            @Nullable Set<String> autowiredBeanNames, @Nullable TypeConverter typeConverter) throws BeansException {

        descriptor.initParameterNameDiscovery(getParameterNameDiscoverer());
        if (Optional.class == descriptor.getDependencyType()) {
            return createOptionalDependency(descriptor, requestingBeanName);
        }
        else if (ObjectFactory.class == descriptor.getDependencyType() ||
                ObjectProvider.class == descriptor.getDependencyType()) {
            return new DependencyObjectProvider(descriptor, requestingBeanName);
        }
        else if (javaxInjectProviderClass == descriptor.getDependencyType()) {
            return new Jsr330ProviderFactory().createDependencyProvider(descriptor, requestingBeanName);
        }
        else {
            Object result = getAutowireCandidateResolver().getLazyResolutionProxyIfNecessary(
                    descriptor, requestingBeanName);
            if (result == null) {
                // 获取注入值
                result = doResolveDependency(descriptor, requestingBeanName, autowiredBeanNames, typeConverter);
            }
            return result;
        }
    }