【Spring源码】IOC容器实现(6)--Bean依赖注入

墨蓝 2022-05-20 06:40 152阅读 0赞

# 前言 #

Github：[https://github.com/yihonglei/thinking-in-spring][https_github.com_yihonglei_thinking-in-spring]

在前面文章中分析了容器初始化过程，建立一个可以使用的容器以及Bean对象的创建过程。

1）[BeanDefinition的Resource定位][BeanDefinition_Resource]

2）[BeanDefinition的载入和解析][BeanDefinition]

3）[BeanDefinition的注册][BeanDefinition 1]

4）[Bean对象的创建][Bean]

从上文“Bean对象的创建”中提到过，BeanFactory中getBean方法不仅是bean创建分析的入口，

也是依赖注入分析的入口，因为只有完成这两个步，才能返回给用户一个预期的Bean对象。

回顾一下上文中的**AbstractAutowireCapableBeanFactory.doCreateBean()方法源码：**

protected Object doCreateBean(final String beanName, final RootBeanDefinition mbd, final Object[] args)
          throws BeanCreationException {
     
       // Instantiate the bean.
       // 这个BeanWrapper是用来持有创建出来的Bean对象
       BeanWrapper instanceWrapper = null;
       // 如果是Singleton，先把缓存中的同名Bean清除
       if (mbd.isSingleton()) {
          instanceWrapper = this.factoryBeanInstanceCache.remove(beanName);
       }
       // 通过createBeanInstance()创建Bean
       if (instanceWrapper == null) {
          instanceWrapper = createBeanInstance(beanName, mbd, args);
       }
       final Object bean = (instanceWrapper != null ? instanceWrapper.getWrappedInstance() : null);
       Class<?> beanType = (instanceWrapper != null ? instanceWrapper.getWrappedClass() : null);
       mbd.resolvedTargetType = beanType;
     
       // Allow post-processors to modify the merged bean definition.
       synchronized (mbd.postProcessingLock) {
          if (!mbd.postProcessed) {
             try {
                applyMergedBeanDefinitionPostProcessors(mbd, beanType, beanName);
             }
             catch (Throwable ex) {
                throw new BeanCreationException(mbd.getResourceDescription(), beanName,
                      "Post-processing of merged bean definition failed", ex);
             }
             mbd.postProcessed = true;
          }
       }
     
       // 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>() {
             @Override
             public Object getObject() throws BeansException {
                return getEarlyBeanReference(beanName, mbd, bean);
             }
          });
       }
     
       // Initialize the bean instance.
       // 对Bean进行初始化，这个exposedObject在初始化以后会返回座位依赖注入完成后的Bean
       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;
    }

这个doCreateBean()中有两个方法，在上文已经从createBeanInstance()方法分析了Bean的创建过程，

还有另外一个populateBean()方法，这个是依赖注入的分析入口。

**AbstractAutowireCapableBeanFactory.populateBean()方法源码：**

protected void populateBean(String beanName, RootBeanDefinition mbd, BeanWrapper bw) {
      // 获取BeanDefinition中设置的property值
       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;
       }
       // 开始进行依赖注入过程，先处理autowire的注入
       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.
          // 根据Bean的名字，完成Bean的autowire
          if (mbd.getResolvedAutowireMode() == RootBeanDefinition.AUTOWIRE_BY_NAME) {
             autowireByName(beanName, mbd, bw, newPvs);
          }
    
          // Add property values based on autowire by type if applicable.
          // 根据Bean的类型，完成Bean的autowire
          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);
          }
       }
       // 对属性进行注入
       applyPropertyValues(beanName, mbd, bw, pvs);
    }

看这块代码有几点我们要明确：

1）后面所讲的内容全部是bean在xml中的定义的内容，我们平时用的@Resource @Autowired并不是在这里解析的，

那些属于Spring注解的内容。

2）这里的autowire跟@Autowired不一样，autowire是Spring配置文件中的一个配置，@Autowired是一个注解。

一般Spring不建议autowire的配置。

下面分析applyPropertyValues()方法实现了属性注入的解析过程。

**AbstractAutowireCapableBeanFactory.****applyPropertyValues****()方法源码：**

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;
       }
       // BeanDefinition在BeanDefinitionValueResolver中完成
       BeanDefinitionValueResolver valueResolver = new BeanDefinitionValueResolver(this, beanName, mbd, converter);
    
       // Create a deep copy, resolving any references for values.
       // 为解析值创建一个副本，副本的数据将会被注入到Bean中
       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 {
          // 这里是依赖注入放生的地方，将副本依赖注入，具体实现在BeanWrapperImpl中完成
          bw.setPropertyValues(new MutablePropertyValues(deepCopy));
       }
       catch (BeansException ex) {
          throw new BeanCreationException(
                mbd.getResourceDescription(), beanName, "Error setting property values", ex);
       }
    }

通过使用BeanDefinitionValueResolver来对BeanDefinition进行解析，然后注入到property中。

下面分析下BeanDefinitionValueResolver中如何解析，以对Bean Reference进行解析为例。

**BeanDefinitionValueResolver.resolveValueIfNecessary()方法源码：**

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.
       // 检查每个值，看看它是否需要一个运行时引用来解析另一个bean
       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(doEvaluate(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);
       }
       // 对ManagedArray进行解析
       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);
       }
      // 对ManagedList进行解析
       else if (value instanceof ManagedList) {
          // May need to resolve contained runtime references.
          return resolveManagedList(argName, (List<?>) value);
       }
       // 对ManagedSet进行解析
       else if (value instanceof ManagedSet) {
          // May need to resolve contained runtime references.
          return resolveManagedSet(argName, (Set<?>) value);
       }
       // 对ManagedMap进行解析
       else if (value instanceof ManagedMap) {
          // May need to resolve contained runtime references.
          return resolveManagedMap(argName, (Map<?, ?>) value);
       }
       // 对ManagedProperties进行解析
       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;
       }
       // 对TypedStringValue进行解析
       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);
       }
    }

第一个if条件中的代码，表示对于RuntimeBeanReference类型的注入在resolveReference中。

**BeanDefinitionValueResolver.resolveReference()方法源码：**

private Object resolveReference(Object argName, RuntimeBeanReference ref) {
       try {
          // 从reference名字，这个refName实在载入BeanDefinition时根据配置生成的
          String refName = ref.getBeanName();
          refName = String.valueOf(doEvaluate(refName));
          // 如果ref是在双亲IOC容器中，那就到双亲IOC容器中获取
          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);
          }
          // 在当前IOC容器中获取Bean，这里会触发一个getBean的过程，如果依赖注入没有发生，
          // 这里会触发相应的依赖注入的发生
          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);
       }
    }

**BeanDefinitionValueResolver.****resolveManagedList****()方法源码：**

**对managedList的处理过程。**

private List<?> resolveManagedList(Object argName, List<?> ml) {
       List<Object> resolved = new ArrayList<Object>(ml.size());
       for (int i = 0; i < ml.size(); i++) {
          // 通过递归的方式，对List的元素进行解析
          resolved.add(
                resolveValueIfNecessary(new KeyedArgName(argName, i), ml.get(i)));
       }
       return resolved;
    }

完成这个解析过程后，也即是BeanDefinitionValueResolver的resolveValueIfNecessary()方法中的相关内容执行完成后，

这个时候未依赖注入准备好了条件，这是真正把Bean对象设置到所有依赖的因一个Bean属性中的地方，其中处理的属性

是各种各样的。

依赖注入的发生在BeanWrapperImpl中实现的。

bean属性注入通过setPropertyValues()方法完成，这是PropertyAccessor接口方法，

实现类是AbstractPropertyAccessor，看一下调用的源码。

**AbstractPropertyAccessor.setPropertyValues()方法源码：**

调用入口

@Override
    public void setPropertyValues(PropertyValues pvs) throws BeansException {
       setPropertyValues(pvs, false, false);
    }

@Override
    public void setPropertyValues(PropertyValues pvs, boolean ignoreUnknown, boolean ignoreInvalid)
          throws BeansException {
    
       List<PropertyAccessException> propertyAccessExceptions = null;
       // 得到属性列表
       List<PropertyValue> propertyValues = (pvs instanceof MutablePropertyValues ?
             ((MutablePropertyValues) pvs).getPropertyValueList() : Arrays.asList(pvs.getPropertyValues()));
       for (PropertyValue pv : propertyValues) {
          try {
             // This method may throw any BeansException, which won't be caught
             // here, if there is a critical failure such as no matching field.
             // We can attempt to deal only with less serious exceptions.
             // 属性注入
             setPropertyValue(pv);
          }
          catch (NotWritablePropertyException ex) {
             if (!ignoreUnknown) {
                throw ex;
             }
             // Otherwise, just ignore it and continue...
          }
          catch (NullValueInNestedPathException ex) {
             if (!ignoreInvalid) {
                throw ex;
             }
             // Otherwise, just ignore it and continue...
          }
          catch (PropertyAccessException ex) {
             if (propertyAccessExceptions == null) {
                propertyAccessExceptions = new LinkedList<PropertyAccessException>();
             }
             propertyAccessExceptions.add(ex);
          }
       }
    
       // If we encountered individual exceptions, throw the composite exception.
       if (propertyAccessExceptions != null) {
          PropertyAccessException[] paeArray =
                propertyAccessExceptions.toArray(new PropertyAccessException[propertyAccessExceptions.size()]);
          throw new PropertyBatchUpdateException(paeArray);
       }
    }

代码追溯到：

protected void setPropertyValue(PropertyTokenHolder tokens, PropertyValue pv) throws BeansException {
       if (tokens.keys != null) {
          processKeyedProperty(tokens, pv);
       }
       else {
          processLocalProperty(tokens, pv);
       }
    }

最后到在processKeyedProperty中完成依赖注入的处理：

private void processKeyedProperty(PropertyTokenHolder tokens, PropertyValue pv) {
       Object propValue = getPropertyHoldingValue(tokens);
       String lastKey = tokens.keys[tokens.keys.length - 1];
    
       if (propValue.getClass().isArray()) {
          PropertyHandler ph = getLocalPropertyHandler(tokens.actualName);
          Class<?> requiredType = propValue.getClass().getComponentType();
          int arrayIndex = Integer.parseInt(lastKey);
          Object oldValue = null;
          try {
             if (isExtractOldValueForEditor() && arrayIndex < Array.getLength(propValue)) {
                oldValue = Array.get(propValue, arrayIndex);
             }
             Object convertedValue = convertIfNecessary(tokens.canonicalName, oldValue, pv.getValue(),
                   requiredType, ph.nested(tokens.keys.length));
             int length = Array.getLength(propValue);
             if (arrayIndex >= length && arrayIndex < this.autoGrowCollectionLimit) {
                Class<?> componentType = propValue.getClass().getComponentType();
                Object newArray = Array.newInstance(componentType, arrayIndex + 1);
                System.arraycopy(propValue, 0, newArray, 0, length);
                setPropertyValue(tokens.actualName, newArray);
                propValue = getPropertyValue(tokens.actualName);
             }
             Array.set(propValue, arrayIndex, convertedValue);
          }
          catch (IndexOutOfBoundsException ex) {
             throw new InvalidPropertyException(getRootClass(), this.nestedPath + tokens.canonicalName,
                   "Invalid array index in property path '" + tokens.canonicalName + "'", ex);
          }
       }
    
       else if (propValue instanceof List) {
          PropertyHandler ph = getPropertyHandler(tokens.actualName);
          Class<?> requiredType = ph.getCollectionType(tokens.keys.length);
          List<Object> list = (List<Object>) propValue;
          int index = Integer.parseInt(lastKey);
          Object oldValue = null;
          if (isExtractOldValueForEditor() && index < list.size()) {
             oldValue = list.get(index);
          }
          Object convertedValue = convertIfNecessary(tokens.canonicalName, oldValue, pv.getValue(),
                requiredType, ph.nested(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 + tokens.canonicalName,
                         "Cannot set element with index " + index + " in List of size " +
                         size + ", accessed using property path '" + tokens.canonicalName +
                         "': 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 + tokens.canonicalName,
                      "Invalid list index in property path '" + tokens.canonicalName + "'", ex);
             }
          }
       }
    
       else if (propValue instanceof Map) {
          PropertyHandler ph = getLocalPropertyHandler(tokens.actualName);
          Class<?> mapKeyType = ph.getMapKeyType(tokens.keys.length);
          Class<?> mapValueType = ph.getMapValueType(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 = TypeDescriptor.valueOf(mapKeyType);
          Object convertedMapKey = convertIfNecessary(null, null, lastKey, 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(tokens.canonicalName, oldValue, pv.getValue(),
                mapValueType, ph.nested(tokens.keys.length));
          map.put(convertedMapKey, convertedMapValue);
       }
    
       else {
          throw new InvalidPropertyException(getRootClass(), this.nestedPath + tokens.canonicalName,
                "Property referenced in indexed property path '" + tokens.canonicalName +
                "' is neither an array nor a List nor a Map; returned value was [" + propValue + "]");
       }
    }

这个地方spring 3和Spring 4差别非常大，这里是基于spring 4的源码。

# 参考文献 #

**1、《Spring技术内幕》**

**2、《Spring实战》**

**3、Spring官网API**

**4、Spring源码**

[https_github.com_yihonglei_thinking-in-spring]: https://github.com/yihonglei/thinking-in-spring
[BeanDefinition_Resource]: https://blog.csdn.net/yhl_jxy/article/details/81019139
[BeanDefinition]: https://blog.csdn.net/yhl_jxy/article/details/81027248
[BeanDefinition 1]: https://blog.csdn.net/yhl_jxy/article/details/81035291
[Bean]: https://blog.csdn.net/yhl_jxy/article/details/81036216