protected Object doCreateBean(final String beanName, final RootBeanDefinition mbd, final @Nullable Object[] args)
      throws BeanCreationException {
    // Instantiate the bean.
    BeanWrapper instanceWrapper = null;
    if (mbd.isSingleton()) {
    //如果是单例并且是FactoryBean则尝试移除
      instanceWrapper = this.factoryBeanInstanceCache.remove(beanName);
    }
    if (instanceWrapper == null) {
      //创建Bean实例，通过策略进行创建，如果选择有参构造或无参构造
      instanceWrapper = createBeanInstance(beanName, mbd, args);
    }
    //获取当前实例对象
    final Object bean = instanceWrapper.getWrappedInstance();
    //当前实例的Calss对象
    Class<?> beanType = instanceWrapper.getWrappedClass();
    if (beanType != NullBean.class) {
      //设置当前bean定义信息的目标类型
      mbd.resolvedTargetType = beanType;
    }
    // Allow post-processors to modify the merged bean definition.
    synchronized (mbd.postProcessingLock) {
      if (!mbd.postProcessed) {
        try {
          //执行MergedBeanDefinitionPostProcessor类型后置处理器的postProcessMergedBeanDefinition方法，
          //如@Autowire注解，就是通过该后置处理器进行解析
          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.
    //如果是单例，允许循环依赖，并且beanName正在创建中
    boolean earlySingletonExposure = (mbd.isSingleton() && this.allowCircularReferences &&
        isSingletonCurrentlyInCreation(beanName));
    if (earlySingletonExposure) {
      if (logger.isTraceEnabled()) {
        logger.trace("Eagerly caching bean '" + beanName +
            "' to allow for resolving potential circular references");
      }
      //包装成FactoryObject对象，并添加到三级缓存中
      addSingletonFactory(beanName, () -> getEarlyBeanReference(beanName, mbd, bean));
    }
    // Initialize the bean instance.
    Object exposedObject = bean;
    try {
      //初始化过程，进行属性注入。该过程递归创建其依赖的属性。如果A中有B，B中有C，则创建B跟C。
      populateBean(beanName, mbd, instanceWrapper);
      //该过程执行后置处理器的before方法，bean的init方法，后置处理器的after方法，可能会生成新的bean对象
      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) {
      //从缓存中获取，因为上面我们将其添加到三级缓存中，从三级缓存中获取会调用FactoryObject对象的getObject方法，可能会触发AOP代理。返回代理对象
      Object earlySingletonReference = getSingleton(beanName, false);
      if (earlySingletonReference != null) {
        //如果bean对象还是原来的，则将三级缓存中获取的对象赋值过去
        if (exposedObject == bean) {
          exposedObject = earlySingletonReference;
        }
        //如果exposedObject在initializeBean方法中被增强 && 不允许在循环引用的情况下使用注入原始bean实例
        else if (!this.allowRawInjectionDespiteWrapping && hasDependentBean(beanName)) {
          //  获取依赖当前beanName的所有bean名称
          String[] dependentBeans = getDependentBeans(beanName);
          Set<String> actualDependentBeans = new LinkedHashSet<>(dependentBeans.length);
          //尝试移除这些bean的实例，因为这些bean依赖的bean已经被增强了，他们依赖的bean相当于脏数据
          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 {
      //注册用于销毁的bean，执行销毁操作的有三种：自定义destroy方法、DisposableBean接口、DestructionAwareBeanPostProcessor
      registerDisposableBeanIfNecessary(beanName, bean, mbd);
    }
    catch (BeanDefinitionValidationException ex) {
      throw new BeanCreationException(
          mbd.getResourceDescription(), beanName, "Invalid destruction signature", ex);
    }
    return exposedObject;
  }

  protected void applyMergedBeanDefinitionPostProcessors(RootBeanDefinition mbd, Class<?> beanType, String beanName) {
    for (BeanPostProcessor bp : getBeanPostProcessors()) {
      //执行类型为MergedBeanDefinitionPostProcessor的后置处理器，@Autowire注解就是在这块解析的
      if (bp instanceof MergedBeanDefinitionPostProcessor) {
        MergedBeanDefinitionPostProcessor bdp = (MergedBeanDefinitionPostProcessor) bp;
        bdp.postProcessMergedBeanDefinition(mbd, beanType, beanName);
      }
    }
  }

  protected void addSingletonFactory(String beanName, ObjectFactory<?> singletonFactory) {
    Assert.notNull(singletonFactory, "Singleton factory must not be null");
    synchronized (this.singletonObjects) {
      //如果一级缓存中不存在该对象
      if (!this.singletonObjects.containsKey(beanName)) {
        //往三级缓存中存入类型为ObjectFactory的工厂对象
        this.singletonFactories.put(beanName, singletonFactory);
        //移除二级缓存
        this.earlySingletonObjects.remove(beanName);
        //将beanName添加到注册缓存中
        this.registeredSingletons.add(beanName);
      }
    }
  }

  protected Object getEarlyBeanReference(String beanName, RootBeanDefinition mbd, Object bean) {
    Object exposedObject = bean;
    //判断是否有InstantiationAwareBeanPostProcessors类型的后置处理器
    if (!mbd.isSynthetic() && hasInstantiationAwareBeanPostProcessors()) {
      for (BeanPostProcessor bp : getBeanPostProcessors()) {
        //执行类型为SmartInstantiationAwareBeanPostProcessor的后置处理器
        if (bp instanceof SmartInstantiationAwareBeanPostProcessor) {
          SmartInstantiationAwareBeanPostProcessor ibp = (SmartInstantiationAwareBeanPostProcessor) bp;
          //返回实例
          exposedObject = ibp.getEarlyBeanReference(exposedObject, beanName);
        }
      }
    }
    return exposedObject;
  }

protected void populateBean(String beanName, RootBeanDefinition mbd, @Nullable BeanWrapper bw) {
    //如果是创建的为空，则判断是否有属性需要注入，有则抛异常
    if (bw == null) {
      if (mbd.hasPropertyValues()) {
        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.
    //标识是否继续属性填充标识
    boolean continueWithPropertyPopulation = true;
    //如果不是合成的&&有注册InstantiationAwareBeanPostProcessors
    if (!mbd.isSynthetic() && hasInstantiationAwareBeanPostProcessors()) {
      //遍历执行InstantiationAwareBeanPostProcessors的postProcessAfterInstantiation方法
      for (BeanPostProcessor bp : getBeanPostProcessors()) {
        if (bp instanceof InstantiationAwareBeanPostProcessor) {
          InstantiationAwareBeanPostProcessor ibp = (InstantiationAwareBeanPostProcessor) bp;
          if (!ibp.postProcessAfterInstantiation(bw.getWrappedInstance(), beanName)) {
            continueWithPropertyPopulation = false;
            break;
          }
        }
      }
    }
    //如果经过后置处理器处理后，则跳过后续的步骤
    if (!continueWithPropertyPopulation) {
      return;
    }
    //获取bean定义信息中的属性值，如<property name="name" value="zhangsan"></property>
    PropertyValues pvs = (mbd.hasPropertyValues() ? mbd.getPropertyValues() : null);
    //获取autowire属性值
    int resolvedAutowireMode = mbd.getResolvedAutowireMode();
    //如果是按name注入或按type注入
    if (resolvedAutowireMode == AUTOWIRE_BY_NAME || resolvedAutowireMode == AUTOWIRE_BY_TYPE) {
      //将户配置的属性值封装成MutablePropertyValues 
      MutablePropertyValues newPvs = new MutablePropertyValues(pvs);
      // Add property values based on autowire by name if applicable.
      //按名称进行注入
      if (resolvedAutowireMode == AUTOWIRE_BY_NAME) {
        autowireByName(beanName, mbd, bw, newPvs);
      }
      // Add property values based on autowire by type if applicable.
      //按类型进行注入
      if (resolvedAutowireMode == AUTOWIRE_BY_TYPE) {
        autowireByType(beanName, mbd, bw, newPvs);
      }
      pvs = newPvs;
    }
    //判断是否有注册InstantiationAwareBeanPostProcessors
    boolean hasInstAwareBpps = hasInstantiationAwareBeanPostProcessors();
    //判断是否有依赖项
    boolean needsDepCheck = (mbd.getDependencyCheck() != AbstractBeanDefinition.DEPENDENCY_CHECK_NONE);
    PropertyDescriptor[] filteredPds = null;
    if (hasInstAwareBpps) {
      if (pvs == null) {
        pvs = mbd.getPropertyValues();
      }
      for (BeanPostProcessor bp : getBeanPostProcessors()) {
        if (bp instanceof InstantiationAwareBeanPostProcessor) {
          //调用InstantiationAwareBeanPostProcessor 的postProcessProperties方法
          InstantiationAwareBeanPostProcessor ibp = (InstantiationAwareBeanPostProcessor) bp;
          //通过后置处理器后，返回处理后的属性配置信息，如@Autowire注解，会在这步骤进行解析
          PropertyValues pvsToUse = ibp.postProcessProperties(pvs, bw.getWrappedInstance(), beanName);
          if (pvsToUse == null) {
            if (filteredPds == null) {
              //过滤出所有需要进行依赖检查的属性编辑器
              filteredPds = filterPropertyDescriptorsForDependencyCheck(bw, mbd.allowCaching);
            }
            pvsToUse = ibp.postProcessPropertyValues(pvs, filteredPds, bw.getWrappedInstance(), beanName);
            if (pvsToUse == null) {
              return;
            }
          }
          pvs = pvsToUse;
        }
      }
    }
    if (needsDepCheck) {
      if (filteredPds == null) {
        //  //过滤出所有需要进行依赖检查的属性编辑器
        filteredPds = filterPropertyDescriptorsForDependencyCheck(bw, mbd.allowCaching);
      }
      //依赖校验
      checkDependencies(beanName, mbd, filteredPds, pvs);
    }
    //属性值填充
    if (pvs != null) {
      applyPropertyValues(beanName, mbd, bw, pvs);
    }
  }

protected void autowireByName(
      String beanName, AbstractBeanDefinition mbd, BeanWrapper bw, MutablePropertyValues pvs) {
    /过滤掉某些属性类型，返回需要注入的属性名称集
    String[] propertyNames = unsatisfiedNonSimpleProperties(mbd, bw);
    //遍历注入
    for (String propertyName : propertyNames) {
      //判断容器中是否存在该属性名称对应的bean
      if (containsBean(propertyName)) {
        //获取实例化Bean
        Object bean = getBean(propertyName);
        //添加到需要注入的属性值
        pvs.add(propertyName, bean);
        //注册依赖关系
        registerDependentBean(propertyName, beanName);
        if (logger.isTraceEnabled()) {
          logger.trace("Added autowiring by name from bean name '" + beanName +
              "' via property '" + propertyName + "' to bean named '" + propertyName + "'");
        }
      }
      else {
        if (logger.isTraceEnabled()) {
          logger.trace("Not autowiring property '" + propertyName + "' of bean '" + beanName +
              "' by name: no matching bean found");
        }
      }
    }
  }

protected String[] unsatisfiedNonSimpleProperties(AbstractBeanDefinition mbd, BeanWrapper bw) {
    Set<String> result = new TreeSet<>();
    //获取当前需要注入的参数值集
    PropertyValues pvs = mbd.getPropertyValues();
    //获取 bean的属性描述信息
    PropertyDescriptor[] pds = bw.getPropertyDescriptors();
    for (PropertyDescriptor pd : pds) {
      //如果有set方法&&不是排除的依赖&&不存在已解析的集合中&&不是简单的属性，如Number、DATE、基本数据类型等
      if (pd.getWriteMethod() != null && !isExcludedFromDependencyCheck(pd) && !pvs.contains(pd.getName()) &&
          !BeanUtils.isSimpleProperty(pd.getPropertyType())) {
        result.add(pd.getName());
      }
    }
    return StringUtils.toStringArray(result);
  }

  public boolean containsBean(String name) {
    //根据别名获取真正的beanName
    String beanName = transformedBeanName(name);
    //判断三级缓存中是否存在或Bean定义缓存中是否存在该定义
    if (containsSingleton(beanName) || containsBeanDefinition(beanName)) {
      //name不带&符号，并且判断是否是工厂Bean
      return (!BeanFactoryUtils.isFactoryDereference(name) || isFactoryBean(name));
    }
    // Not found -> check parent.
    //查询不到获取父类工厂，并在父工厂中进行查找
    BeanFactory parentBeanFactory = getParentBeanFactory();
    return (parentBeanFactory != null && parentBeanFactory.containsBean(originalBeanName(name)));
  }

protected void autowireByType(
      String beanName, AbstractBeanDefinition mbd, BeanWrapper bw, MutablePropertyValues pvs) {
    //获取类型转换器
    TypeConverter converter = getCustomTypeConverter();
    if (converter == null) {
      converter = bw;
    }
    Set<String> autowiredBeanNames = new LinkedHashSet<>(4);
    //过滤掉一些特定的属性类型，返回需要注入的集合
    String[] propertyNames = unsatisfiedNonSimpleProperties(mbd, bw);
    for (String propertyName : propertyNames) {
      try {
        //获取属性描述信息
        PropertyDescriptor pd = bw.getPropertyDescriptor(propertyName);
        // Don't try autowiring by type for type Object: never makes sense,
        // even if it technically is a unsatisfied, non-simple property.
        //如果不是Object类型则不处理
        if (Object.class != pd.getPropertyType()) {
          //获取该属性的set方法参数信息
          MethodParameter methodParam = BeanUtils.getWriteMethodParameter(pd);
          // Do not allow eager init for type matching in case of a prioritized post-processor.
          boolean eager = !PriorityOrdered.class.isInstance(bw.getWrappedInstance());
          //将set方法信息封装成DependencyDescriptor 对象
          DependencyDescriptor desc = new AutowireByTypeDependencyDescriptor(methodParam, eager);
          //解析当前属性所匹配的bean实例，并把解析到的bean实例的beanName存储在autowiredBeanNames中
          Object autowiredArgument = resolveDependency(desc, beanName, autowiredBeanNames, converter);
          if (autowiredArgument != null) {
            //添加到需要注入的属性值集合中
            pvs.add(propertyName, autowiredArgument);
          }
          for (String autowiredBeanName : autowiredBeanNames) {
            //注册依赖关系
            registerDependentBean(autowiredBeanName, beanName);
            if (logger.isTraceEnabled()) {
              logger.trace("Autowiring by type from bean name '" + beanName + "' via property '" +
                  propertyName + "' to bean named '" + autowiredBeanName + "'");
            }
          }
          autowiredBeanNames.clear();
        }
      }
      catch (BeansException ex) {
        throw new UnsatisfiedDependencyException(mbd.getResourceDescription(), beanName, propertyName, ex);
      }
    }
  }

  public Object resolveDependency(DependencyDescriptor descriptor, @Nullable String requestingBeanName,
      @Nullable Set<String> autowiredBeanNames, @Nullable TypeConverter typeConverter) throws BeansException {
    //初始化参数名称查询器
    descriptor.initParameterNameDiscovery(getParameterNameDiscoverer());
    //判断依赖类型是否为Optional
    if (Optional.class == descriptor.getDependencyType()) {
      return createOptionalDependency(descriptor, requestingBeanName);
    }
    //判断依赖类型是否为ObjectFactory
    else if (ObjectFactory.class == descriptor.getDependencyType() ||
        ObjectProvider.class == descriptor.getDependencyType()) {
      return new DependencyObjectProvider(descriptor, requestingBeanName);
    }
    //判断依赖类型是否为javaxInjectProviderClass 
    else if (javaxInjectProviderClass == descriptor.getDependencyType()) {
      return new Jsr330Factory().createDependencyProvider(descriptor, requestingBeanName);
    }
    else {
    //获取懒加载代理对象
      Object result = getAutowireCandidateResolver().getLazyResolutionProxyIfNecessary(
          descriptor, requestingBeanName);
      if (result == null) {
        //解析所需依赖对象
        result = doResolveDependency(descriptor, requestingBeanName, autowiredBeanNames, typeConverter);
      }
      return result;
    }
  }

public Object doResolveDependency(DependencyDescriptor descriptor, @Nullable String beanName,
      @Nullable Set<String> autowiredBeanNames, @Nullable TypeConverter typeConverter) throws BeansException {
    InjectionPoint previousInjectionPoint = ConstructorResolver.setCurrentInjectionPoint(descriptor);
    try {
    //获取shortcut 对象
      Object shortcut = descriptor.resolveShortcut(this);
      if (shortcut != null) {
        return shortcut;
      }
      //获取依赖类型
      Class<?> type = descriptor.getDependencyType();
      //获取指定值，如@qualifier就是在这里解析的
      Object value = getAutowireCandidateResolver().getSuggestedValue(descriptor);
      if (value != null) {
        //如果是字符串类型，则进行解析计算
        if (value instanceof String) {
          String strVal = resolveEmbeddedValue((String) value);
          BeanDefinition bd = (beanName != null && containsBean(beanName) ?
              getMergedBeanDefinition(beanName) : null);
          value = evaluateBeanDefinitionString(strVal, bd);
        }
        TypeConverter converter = (typeConverter != null ? typeConverter : getTypeConverter());
        try {
          //对值进行转换
          return converter.convertIfNecessary(value, type, descriptor.getTypeDescriptor());
        }
        catch (UnsupportedOperationException ex) {
          // A custom TypeConverter which does not support TypeDescriptor resolution...
          return (descriptor.getField() != null ?
              converter.convertIfNecessary(value, type, descriptor.getField()) :
              converter.convertIfNecessary(value, type, descriptor.getMethodParameter()));
        }
      }
      //处理类型为多个的情况，如Array、Collection、MAP
      Object multipleBeans = resolveMultipleBeans(descriptor, beanName, autowiredBeanNames, typeConverter);
      if (multipleBeans != null) {
        return multipleBeans;
      }
      //从beanFactory中解析候选类，即允许被注入的bean
      Map<String, Object> matchingBeans = findAutowireCandidates(beanName, type, descriptor);
      //查询不到时，判断是否有required标识，有则抛异常
      if (matchingBeans.isEmpty()) {
        if (isRequired(descriptor)) {
          raiseNoMatchingBeanFound(type, descriptor.getResolvableType(), descriptor);
        }
        return null;
      }
      String autowiredBeanName;
      Object instanceCandidate;
      //如果按类型查找出多个bean
      if (matchingBeans.size() > 1) {
        //判断是否有primary标志，并返回符合条件的beanName
        autowiredBeanName = determineAutowireCandidate(matchingBeans, descriptor);
        if (autowiredBeanName == null) {
          //有require标识，或者不是Collection等容器类型，则抛异常
          if (isRequired(descriptor) || !indicatesMultipleBeans(type)) {
            return descriptor.resolveNotUnique(descriptor.getResolvableType(), matchingBeans);
          }
          else {
            // In case of an optional Collection/Map, silently ignore a non-unique case:
            // possibly it was meant to be an empty collection of multiple regular beans
            // (before 4.3 in particular when we didn't even look for collection beans).
            return null;
          }
        }
        //获取符合条件的实例
        instanceCandidate = matchingBeans.get(autowiredBeanName);
      }
      else {
        // We have exactly one match.
        //只有一个的情况下则直接获取第一个值
        Map.Entry<String, Object> entry = matchingBeans.entrySet().iterator().next();
        autowiredBeanName = entry.getKey();
        instanceCandidate = entry.getValue();
      }
      //添加autowiredBeanName到autowiredBeanNames中
      if (autowiredBeanNames != null) {
        autowiredBeanNames.add(autowiredBeanName);
      }
      //如果类型为Class，则进行实例化
      if (instanceCandidate instanceof Class) {
        instanceCandidate = descriptor.resolveCandidate(autowiredBeanName, type, this);
      }
      Object result = instanceCandidate;
      //为空则抛异常
      if (result instanceof NullBean) {
        if (isRequired(descriptor)) {
          raiseNoMatchingBeanFound(type, descriptor.getResolvableType(), descriptor);
        }
        result = null;
      }
      //类型不一致抛异常
      if (!ClassUtils.isAssignableValue(type, result)) {
        throw new BeanNotOfRequiredTypeException(autowiredBeanName, type, instanceCandidate.getClass());
      }
      return result;
    }
    finally {
      ConstructorResolver.setCurrentInjectionPoint(previousInjectionPoint);
    }
  }

protected Map<String, Object> findAutowireCandidates(
      @Nullable String beanName, Class<?> requiredType, DependencyDescriptor descriptor) {
    //从beanFactory工厂中通过类型获取对应的beanName
    String[] candidateNames = BeanFactoryUtils.beanNamesForTypeIncludingAncestors(
        this, requiredType, true, descriptor.isEager());
    Map<String, Object> result = new LinkedHashMap<>(candidateNames.length);
    //遍历依赖缓存
    for (Map.Entry<Class<?>, Object> classObjectEntry : this.resolvableDependencies.entrySet()) {
      //获取key值
      Class<?> autowiringType = classObjectEntry.getKey();
      //判断类型是否所需类型
      if (autowiringType.isAssignableFrom(requiredType)) {
        //获取依赖value
        Object autowiringValue = classObjectEntry.getValue();
        //判断需要的类型跟当前获取的值autowiringValue 不是同个类型
        //并且如果autowiringValue是工厂对象的话，则调用getObject方法获取
        autowiringValue = AutowireUtils.resolveAutowiringValue(autowiringValue, requiredType);
        //如果两个类型一致，则生成一个新的beanName，并放入map中
        if (requiredType.isInstance(autowiringValue)) {
          result.put(ObjectUtils.identityToString(autowiringValue), autowiringValue);
          break;
        }
      }
    }
    //遍历候选类集合
    for (String candidate : candidateNames) {
      //依赖所需对象不能是当前bean本身，如B中有属性B这种情况&&判断允许被其它bean注入
      if (!isSelfReference(beanName, candidate) && isAutowireCandidate(candidate, descriptor)) {
        addCandidateEntry(result, candidate, descriptor, requiredType);
      }
    }
    //如果前面获取不到合适的类型
    if (result.isEmpty()) {
      //判断是否是容器类型，如Collection
      boolean multiple = indicatesMultipleBeans(requiredType);
      // Consider fallback matches if the first pass failed to find anything...
      DependencyDescriptor fallbackDescriptor = descriptor.forFallbackMatch();
      //使用备用的依赖描述器再去获取一遍符合注入属性类型的beanName
      for (String candidate : candidateNames) {
        if (!isSelfReference(beanName, candidate) && isAutowireCandidate(candidate, fallbackDescriptor) &&
            (!multiple || getAutowireCandidateResolver().hasQualifier(descriptor))) {
          addCandidateEntry(result, candidate, descriptor, requiredType);
        }
      }
      //还是没有符合注入属性类型的beanName，又不是集合类型，考虑自引用，符合条件则将候选者添加到result中
      if (result.isEmpty() && !multiple) {
        // Consider self references as a final pass...
        // but in the case of a dependency collection, not the very same bean itself.
        for (String candidate : candidateNames) {
          if (isSelfReference(beanName, candidate) &&
              (!(descriptor instanceof MultiElementDescriptor) || !beanName.equals(candidate)) &&
              isAutowireCandidate(candidate, fallbackDescriptor)) {
            addCandidateEntry(result, candidate, descriptor, requiredType);
          }
        }
      }
    }
    return result;
  }

private void addCandidateEntry(Map<String, Object> candidates, String candidateName,
      DependencyDescriptor descriptor, Class<?> requiredType) {
    //如果是一个MultiElementDescriptor类型的
    if (descriptor instanceof MultiElementDescriptor) {
      //实例化
      Object beanInstance = descriptor.resolveCandidate(candidateName, requiredType, this);
      if (!(beanInstance instanceof NullBean)) {
        candidates.put(candidateName, beanInstance);
      }
    }
    else if (containsSingleton(candidateName) || (descriptor instanceof StreamDependencyDescriptor &&
        ((StreamDependencyDescriptor) descriptor).isOrdered())) {
      //实例化
      Object beanInstance = descriptor.resolveCandidate(candidateName, requiredType, this);
      //加入缓存中
      candidates.put(candidateName, (beanInstance instanceof NullBean ? null : beanInstance));
    }
    else {
      //将candidateName跟candidateName的class对象存入缓存中
      candidates.put(candidateName, getType(candidateName));
    }
  }

public Class<?> getType(String name, boolean allowFactoryBeanInit) throws NoSuchBeanDefinitionException {
    String beanName = transformedBeanName(name);
    // Check manually registered singletons.
    //从一级缓存中获取对象
    Object beanInstance = getSingleton(beanName, false);
    if (beanInstance != null && beanInstance.getClass() != NullBean.class) {
      //如果是FactoryBean ,则调用其getObjectType返回真正的实例class
      if (beanInstance instanceof FactoryBean && !BeanFactoryUtils.isFactoryDereference(name)) {
        return getTypeForFactoryBean((FactoryBean<?>) beanInstance);
      }
      else {
        //返回class对象
        return beanInstance.getClass();
      }
    }
    // No singleton instance found -> check bean definition.
    //前面如果查询不到，则获取父工厂进行查询
    BeanFactory parentBeanFactory = getParentBeanFactory();
    if (parentBeanFactory != null && !containsBeanDefinition(beanName)) {
      // No bean definition found in this factory -> delegate to parent.
      return parentBeanFactory.getType(originalBeanName(name));
    }
    //获取合并的Bean定义信息
    RootBeanDefinition mbd = getMergedLocalBeanDefinition(beanName);
    // Check decorated bean definition, if any: We assume it'll be easier
    // to determine the decorated bean's type than the proxy's type.
    //获取目标代理对象
    BeanDefinitionHolder dbd = mbd.getDecoratedDefinition();
    //判断name是否带有&前缀，如果不是工厂对象
    if (dbd != null && !BeanFactoryUtils.isFactoryDereference(name)) {
      RootBeanDefinition tbd = getMergedBeanDefinition(dbd.getBeanName(), dbd.getBeanDefinition(), mbd);
      //获取beanName对应的class对象
      Class<?> targetClass = predictBeanType(dbd.getBeanName(), tbd);
      if (targetClass != null && !FactoryBean.class.isAssignableFrom(targetClass)) {
        return targetClass;
      }
    }
    //获取beanName对应的class对象
    Class<?> beanClass = predictBeanType(beanName, mbd);
    // Check bean class whether we're dealing with a FactoryBean.
    //如果不为空&&类型为FactoryBean
    if (beanClass != null && FactoryBean.class.isAssignableFrom(beanClass)) {
      //name不带&符号，即不是获取工厂对象本身
      if (!BeanFactoryUtils.isFactoryDereference(name)) {
        // If it's a FactoryBean, we want to look at what it creates, not at the factory class.
        //返回实际的对象class
        return getTypeForFactoryBean(beanName, mbd, allowFactoryBeanInit).resolve();
      }
      else {
        return beanClass;
      }
    }
    else {
      return (!BeanFactoryUtils.isFactoryDereference(name) ? beanClass : null);
    }
  }

  protected String determineAutowireCandidate(Map<String, Object> candidates, DependencyDescriptor descriptor) {
    //获取需要注入依赖的类型
    Class<?> requiredType = descriptor.getDependencyType();
    //解析，筛选带有primary属性的beanName
    String primaryCandidate = determinePrimaryCandidate(candidates, requiredType);
    if (primaryCandidate != null) {
      return primaryCandidate;
    }
    //如果被注入类有实现OrderComparator接口，则进行比较筛选出Priority，值越低优先级越高
    String priorityCandidate = determineHighestPriorityCandidate(candidates, requiredType);
    if (priorityCandidate != null) {
      return priorityCandidate;
    }
    // Fallback
    //遍历候选bean
    for (Map.Entry<String, Object> entry : candidates.entrySet()) {
      String candidateName = entry.getKey();
      Object beanInstance = entry.getValue();
      //如果实例不为空&&依赖集合中包含该值  或  名称是否跟需要注入的依赖类型名称一致
      if ((beanInstance != null && this.resolvableDependencies.containsValue(beanInstance)) ||
          matchesBeanName(candidateName, descriptor.getDependencyName())) {
        return candidateName;
      }
    }
    return null;
  }

protected String determinePrimaryCandidate(Map<String, Object> candidates, Class<?> requiredType) {
    String primaryBeanName = null;
    for (Map.Entry<String, Object> entry : candidates.entrySet()) {
      String candidateBeanName = entry.getKey();
      Object beanInstance = entry.getValue();
      //判断是否有Primary标识
      if (isPrimary(candidateBeanName, beanInstance)) {
        if (primaryBeanName != null) {
          boolean candidateLocal = containsBeanDefinition(candidateBeanName);
          boolean primaryLocal = containsBeanDefinition(primaryBeanName);
          //如果存在两个依赖都有其Primary，则抛异常
          if (candidateLocal && primaryLocal) {
            throw new NoUniqueBeanDefinitionException(requiredType, candidates.size(),
                "more than one 'primary' bean found among candidates: " + candidates.keySet());
          }
          else if (candidateLocal) {
            //赋值
            primaryBeanName = candidateBeanName;
          }
        }
        else {
          //赋值
          primaryBeanName = candidateBeanName;
        }
      }
    }
    return primaryBeanName;
  }

protected String determineHighestPriorityCandidate(Map<String, Object> candidates, Class<?> requiredType) {
    //最高优先级的beanName
    String highestPriorityBeanName = null;
    //最高优先级值
    Integer highestPriority = null;
    //遍历
    for (Map.Entry<String, Object> entry : candidates.entrySet()) {
      String candidateBeanName = entry.getKey();
      Object beanInstance = entry.getValue();
      if (beanInstance != null) {
        //获取优先级
        Integer candidatePriority = getPriority(beanInstance);
        if (candidatePriority != null) {
          if (highestPriorityBeanName != null) {
            //存在两个优先级一样则抛异常
            if (candidatePriority.equals(highestPriority)) {
              throw new NoUniqueBeanDefinitionException(requiredType, candidates.size(),
                  "Multiple beans found with the same priority ('" + highestPriority +
                  "') among candidates: " + candidates.keySet());
            }
            //比较，candidatePriority 值越低则优先级越高
            else if (candidatePriority < highestPriority) {
              highestPriorityBeanName = candidateBeanName;
              highestPriority = candidatePriority;
            }
          }
          else {
            //第一次则直接赋值
            highestPriorityBeanName = candidateBeanName;
            highestPriority = candidatePriority;
          }
        }
      }
    }
    return highestPriorityBeanName;
  }

protected void applyPropertyValues(String beanName, BeanDefinition mbd, BeanWrapper bw, PropertyValues pvs) {、
    //判断注入参数是否为空
    if (pvs.isEmpty()) {
      return;
    }
    if (System.getSecurityManager() != null && bw instanceof BeanWrapperImpl) {
      ((BeanWrapperImpl) bw).setSecurityContext(getAccessControlContext());
    }
    MutablePropertyValues mpvs = null;
    //存在原始参数值
    List<PropertyValue> original;
    //如果参数MutablePropertyValues类型
    if (pvs instanceof MutablePropertyValues) {
      mpvs = (MutablePropertyValues) pvs;
      //如果已经转换过，则直接设置值
      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());
    }
    //获取类型转换器
    TypeConverter converter = getCustomTypeConverter();
    if (converter == null) {
      converter = bw;
    }
    //创建解析器
    BeanDefinitionValueResolver valueResolver = new BeanDefinitionValueResolver(this, beanName, mbd, converter);
    // Create a deep copy, resolving any references for values.
    //存放拷贝参数值，即通知转换后的值
    List<PropertyValue> deepCopy = new ArrayList<>(original.size());
    boolean resolveNecessary = false;
    for (PropertyValue pv : original) {
      //如果已经转换过，则加入到深拷贝集合中
      if (pv.isConverted()) {
        deepCopy.add(pv);
      }
      else {
        //获取参数名称
        String propertyName = pv.getName();
        //获取参数值
        Object originalValue = pv.getValue();
        //判断值是否是AutowiredPropertyMarker类型
        if (originalValue == AutowiredPropertyMarker.INSTANCE) {
          //获取set方法
          Method writeMethod = bw.getPropertyDescriptor(propertyName).getWriteMethod();
          if (writeMethod == null) {
            throw new IllegalArgumentException("Autowire marker for property without write method: " + pv);
          }
          //将参数值封装成DependencyDescriptor
          originalValue = new DependencyDescriptor(new MethodParameter(writeMethod, 0), true);
        }
        //对值进行解析转换，如果类型是beanFactory工厂中的beanDefinition封装的信息时，则会进行实例化
        Object resolvedValue = valueResolver.resolveValueIfNecessary(pv, originalValue);
        //转换后的值
        Object convertedValue = resolvedValue;
        //判断是否有写权限&&没有嵌套属性，如不包含“.”或者“[”符号
        boolean convertible = bw.isWritableProperty(propertyName) &&
            !PropertyAccessorUtils.isNestedOrIndexedProperty(propertyName);
        if (convertible) {
          //类型转换
          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.
        //如果解析值跟转换后的值一直
        if (resolvedValue == originalValue) {
          //转换标志
          if (convertible) {
            //设置转换后的值
            pv.setConvertedValue(convertedValue);
          }
          //加入解析后的集合中
          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 {
      //属性值注入
      bw.setPropertyValues(new MutablePropertyValues(deepCopy));
    }
    catch (BeansException ex) {
      throw new BeanCreationException(
          mbd.getResourceDescription(), beanName, "Error setting property values", ex);
    }
  }

public Object resolveValueIfNecessary(Object argName, @Nullable 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) {
      //如果参数值为RuntimeBeanReference类型，则调用getBean方法获取创建实例
      RuntimeBeanReference ref = (RuntimeBeanReference) value;
      return resolveReference(argName, ref);
    }
    else if (value instanceof RuntimeBeanNameReference) {
      //获取依赖的beanName
      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.
      //解析BeanDefinitionHolder:包含带有名称和别名的BeanDefinition。
      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.
      //解析普通的BeanDefinition，不包含名称:使用虚拟名称
      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 DependencyDescriptor) {
      Set<String> autowiredBeanNames = new LinkedHashSet<>(4);
      //创建实例，并解析出候选的bean信息
      Object result = this.beanFactory.resolveDependency(
          (DependencyDescriptor) value, this.beanName, autowiredBeanNames, this.typeConverter);
      //实例化，并注册依赖关系
      for (String autowiredBeanName : autowiredBeanNames) {
        if (this.beanFactory.containsBean(autowiredBeanName)) {
          this.beanFactory.registerDependentBean(autowiredBeanName, this.beanName);
        }
      }
      return result;
    }
    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();
      original.forEach((propKey, propValue) -> {
        if (propKey instanceof TypedStringValue) {
          propKey = evaluate((TypedStringValue) propKey);
        }
        if (propValue instanceof TypedStringValue) {
          propValue = evaluate((TypedStringValue) propValue);
        }
        if (propKey == null || propValue == null) {
          throw new BeanCreationException(
              this.beanDefinition.getResourceDescription(), this.beanName,
              "Error converting Properties key/value pair for " + argName + ": resolved to null");
        }
        copy.put(propKey, propValue);
      });
      return copy;
    }
    //如果是字符串
    else if (value instanceof TypedStringValue) {
      // Convert value to target type here.
      //进行类型解析
      TypedStringValue typedStringValue = (TypedStringValue) value;
      Object valueObject = evaluate(typedStringValue);
      try {
        //获取目标类型
        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 if (value instanceof NullBean) {
      return null;
    }
    else {
      return evaluate(value);
    }
  }