Spring 4.x IOC介绍（六.DI — Dependency Injection 依赖注入）

Myth丶恋晨 2021-11-16 14:12 280阅读 0赞

既然说到了IoC，那么一定要说一下DI。

# DI — Dependency Injection 依赖注入 #

既然叫依赖注入了，我们要清楚几个问题：

**问题：**

*  谁依赖谁？
 *  谁注入谁？
 *  注入了什么？

**回答：**

*  应用程序依赖于IoC；
 *  IoC容器注入应用程序某个对象，应用程序依赖的对象；
 *  注入某个对象所需要的外部资源（包括对象、资源、常量数据）；

这里还是介绍两种获取Bean的方法，当然最后的代码逻辑肯定是走到一起的。

## 使用代码获取Bean ##

例子：

public class IocApplication {
        private static Logger log = LoggerFactory.getLogger(IocApplication.class);
    
        public static void main(String[] args) {
            ApplicationContext ctx = new AnnotationConfigApplicationContext(AppConfig.class);
            User user = ctx.getBean(User.class);
            log.info(user.getId() + "," + user.getUserName() + "," + user.getMessage());
        }
    }

这里使用`getBean(User.class)`获取`User`的`bean`。

### getBean ###

@Override
    	public <T> T getBean(Class<T> requiredType) throws BeansException {
    		assertBeanFactoryActive();
    		return getBeanFactory().getBean(requiredType);
    	}
    	@Override
    	public <T> T getBean(Class<T> requiredType) throws BeansException {
    		return getBean(requiredType, (Object[]) null);
    	}
    		@Override
    	public <T> T getBean(Class<T> requiredType, @Nullable Object... args) throws BeansException {
    		NamedBeanHolder<T> namedBean = resolveNamedBean(requiredType, args);
    		if (namedBean != null) {
    			return namedBean.getBeanInstance();
    		}
    		BeanFactory parent = getParentBeanFactory();
    		if (parent != null) {
    			return (args != null ? parent.getBean(requiredType, args) : parent.getBean(requiredType));
    		}
    		throw new NoSuchBeanDefinitionException(requiredType);
    	}
    	@SuppressWarnings("unchecked")
    	@Nullable
    	private <T> NamedBeanHolder<T> resolveNamedBean(Class<T> requiredType, @Nullable Object... args) throws BeansException {
    		Assert.notNull(requiredType, "Required type must not be null");
    		String[] candidateNames = getBeanNamesForType(requiredType);
    
    		if (candidateNames.length > 1) {
    			List<String> autowireCandidates = new ArrayList<>(candidateNames.length);
    			.
    			.
    			.
    		}
    		
    		// 因为只获取一个类的Bean，所以当前candidateNames.length == 1
    		if (candidateNames.length == 1) {
    			String beanName = candidateNames[0];
    			return new NamedBeanHolder<>(beanName, getBean(beanName, requiredType, args));
    		}
    		else if (candidateNames.length > 1) {
    			.
    			.
    			.
    		}
    
    		return null;
    	}
    
    	public <T> T getBean(String name, @Nullable Class<T> requiredType, @Nullable Object... args)
    			throws BeansException {
    		// ok，这便是最重要的doGetBean了。
    		return doGetBean(name, requiredType, args, false);
    	}

#### doGetBean ####

doGetBean 源码 咱们一会再看。

同样，现在使用SpringBoot 居多，那么最常见的便是`@Autowired`注解获取Bean，我们简单看下`@Autowired`获取bean的原理。

# @Autowired 源码 #

/**
     * ....
     * @see AutowiredAnnotationBeanPostProcessor
     * @see Qualifier
     * @see Value
     */
    @Target({ElementType.CONSTRUCTOR, ElementType.METHOD, ElementType.PARAMETER, ElementType.FIELD, ElementType.ANNOTATION_TYPE})
    @Retention(RetentionPolicy.RUNTIME)
    @Documented
    public @interface Autowired {
    
    	/**
    	 * Declares whether the annotated dependency is required.
    	 * <p>Defaults to {@code true}.
    	 */
    	boolean required() default true;
    
    }

我们可以看到，@Autowired的实现于`AutowiredAnnotationBeanPostProcessor`。  
这个东西是什么时候注册进去，又是如何取得呢？在之前的文章中我们说道，SpringIoC的最后一步是执行了`AbstractApplicationContext#refresh`其中有两行代码：`registerBeanPostProcessors(beanFactory);` 和 `finishBeanFactoryInitialization(beanFactory);`注册和实例化(获取)

## registerBeanPostProcessors ##

protected void registerBeanPostProcessors(ConfigurableListableBeanFactory beanFactory) {
    		PostProcessorRegistrationDelegate.registerBeanPostProcessors(beanFactory, this);
    	}
    	public static void registerBeanPostProcessors(
    			ConfigurableListableBeanFactory beanFactory, AbstractApplicationContext applicationContext) {
    
    		String[] postProcessorNames = beanFactory.getBeanNamesForType(BeanPostProcessor.class, true, false);
    		.
    		.
    		.
    	}

通过打断点可知：postProcessorNames默认获取到Spring加载的BeanPostProcessor有：

*  **AutowiredAnnotationBeanPostProcessor**
 *  RequiredAnnotationBeanPostProcessor
 *  CommonAnnotationBeanPostProcessor

ok，我们找到什么时候注册的了。

## finishBeanFactoryInitialization ##

protected void finishBeanFactoryInitialization(ConfigurableListableBeanFactory beanFactory) {
    		// Initialize conversion service for this context.
    		if (beanFactory.containsBean(CONVERSION_SERVICE_BEAN_NAME) &&
    				beanFactory.isTypeMatch(CONVERSION_SERVICE_BEAN_NAME, ConversionService.class)) {
    			beanFactory.setConversionService(
    					beanFactory.getBean(CONVERSION_SERVICE_BEAN_NAME, ConversionService.class));
    		}
    
    		// Register a default embedded value resolver if no bean post-processor
    		// (such as a PropertyPlaceholderConfigurer bean) registered any before:
    		// at this point, primarily for resolution in annotation attribute values.
    		if (!beanFactory.hasEmbeddedValueResolver()) {
    			beanFactory.addEmbeddedValueResolver(strVal -> getEnvironment().resolvePlaceholders(strVal));
    		}
    
    		// Initialize LoadTimeWeaverAware beans early to allow for registering their transformers early.
    		String[] weaverAwareNames = beanFactory.getBeanNamesForType(LoadTimeWeaverAware.class, false, false);
    		for (String weaverAwareName : weaverAwareNames) {
    			getBean(weaverAwareName);
    		}
    
    		// Stop using the temporary ClassLoader for type matching.
    		beanFactory.setTempClassLoader(null);
    
    		// Allow for caching all bean definition metadata, not expecting further changes.
    		beanFactory.freezeConfiguration();
    
    		// Instantiate all remaining (non-lazy-init) singletons.
    		beanFactory.preInstantiateSingletons();
    	}

通过`getBean`我们很容易找到`AbstractBeanFactory#doGetBean`方法。  
这个也是通过代码获取`Bean`的`doGetBean`。来吧，看下`doGetBean`

# doGetBean #

@SuppressWarnings("unchecked")
    	protected <T> T doGetBean(final String name, @Nullable final Class<T> requiredType,
    			@Nullable final Object[] args, boolean typeCheckOnly) throws BeansException {
    		// 获取规范的bean name
    		final String beanName = transformedBeanName(name);
    		Object bean;
    
    		// Eagerly check singleton cache for manually registered singletons.
    		// 1.从缓存中获取bean实例
    		Object sharedInstance = getSingleton(beanName);
    		// 能获取到
    		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.
    			// 2.从父容器中直接获取bean.
    			BeanFactory parentBeanFactory = getParentBeanFactory();
    			// 当前容器的父容器存在，且当前容器中不存在指名的Bean
    			if (parentBeanFactory != null && !containsBeanDefinition(beanName)) {
    				// Not found -> check parent.
    				// 解析Bean的原始名
    				String nameToLookup = originalBeanName(name);
    				if (parentBeanFactory instanceof AbstractBeanFactory) {
    					return ((AbstractBeanFactory) parentBeanFactory).doGetBean(
    							nameToLookup, requiredType, args, typeCheckOnly);
    				}
    				else if (args != null) {
    					// Delegation to parent with explicit args.
    					// 委派给父类容器查找，根据指定的名称和显示参数
    					return (T) parentBeanFactory.getBean(nameToLookup, args);
    				}
    				else {
    					// No args -> delegate to standard getBean method.
    					// 委派给父类容器查找，根据指定的名称和类型
    					return parentBeanFactory.getBean(nameToLookup, requiredType);
    				}
    			}
    			// 创建的Bean是否需要进行验证，一般不需要
    			if (!typeCheckOnly) {
    				// 添加进已创建set
    				markBeanAsCreated(beanName);
    			}
    
    			try {
    				// 根据Bean的名字获取BeanDefinition
    				final RootBeanDefinition mbd = getMergedLocalBeanDefinition(beanName);
    				checkMergedBeanDefinition(mbd, beanName, args);
    
    				// Guarantee initialization of beans that the current bean depends on.
    				// 初始化依赖bean
    				String[] dependsOn = mbd.getDependsOn();
    				if (dependsOn != null) {
    					for (String dep : dependsOn) {
    						if (isDependent(beanName, dep)) {
    							throw new BeanCreationException(mbd.getResourceDescription(), beanName,
    									"Circular depends-on relationship between '" + beanName + "' and '" + dep + "'");
    						}
    						registerDependentBean(dep, beanName);
    						try {
    							getBean(dep);
    						}
    						catch (NoSuchBeanDefinitionException ex) {
    							throw new BeanCreationException(mbd.getResourceDescription(), beanName,
    									"'" + beanName + "' depends on missing bean '" + dep + "'", ex);
    						}
    					}
    				}
    
    				// Create bean instance.
    				// 3.单例模式获取bean
    				if (mbd.isSingleton()) {
    					// 使用一个内部匿名类，创建Bean实例对象，并且注册对所依赖的对象
    					sharedInstance = getSingleton(beanName, () -> {
    						try {
    							// 创建一个指定Bean实例对象，如果有父级继承，则合并
    							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;
    						}
    					});
    					// 获取给定Bean实例对象FactoryBean -> bean
    					bean = getObjectForBeanInstance(sharedInstance, name, beanName, mbd);
    				}
    				// 4.原型模式获取bean
    				else if (mbd.isPrototype()) {
    					// It's a prototype -> create a new instance.
    					// 每次创建新对象实例
    					Object prototypeInstance = null;
    					try {
    						// 回调方法，注册原型对象
    						beforePrototypeCreation(beanName);
    						// 创建指定Bean对象实例
    						prototypeInstance = createBean(beanName, mbd, args);
    					}
    					finally {
    						// 回调方法，Bean无法再次创建
    						afterPrototypeCreation(beanName);
    					}
    					// 获取给定Bean实例对象FactoryBean->bean
    					bean = getObjectForBeanInstance(prototypeInstance, name, beanName, mbd);
    				}
    
    				// 5.从scope中获取bean
    				else {
    					String scopeName = mbd.getScope();
    					final Scope scope = this.scopes.get(scopeName);
    					if (scope == null) {
    						throw new IllegalStateException("No Scope registered for scope name '" + scopeName + "'");
    					}
    					try {
    						// 从scope中获取bean
    						Object scopedInstance = scope.get(beanName, () -> {
    							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.
    		// 对创建的Bean进行类型检查，如果没有问题，就返回这个新建的Bean，这个Bean已经包含了依赖关系
    		if (requiredType != null && !requiredType.isInstance(bean)) {
    			try {
    				T convertedBean = getTypeConverter().convertIfNecessary(bean, requiredType);
    				if (convertedBean == null) {
    					throw new BeanNotOfRequiredTypeException(name, requiredType, bean.getClass());
    				}
    				return convertedBean;
    			}
    			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;
    	}

上面这一大段代码，其中最重要的一个方法：`AbstractAutowireCapableBeanFactory#createBean;`

## createBean ##

@Override
    	protected Object createBean(String beanName, RootBeanDefinition mbd, @Nullable Object[] args)
    			throws BeanCreationException {
    
    		if (logger.isDebugEnabled()) {
    			logger.debug("Creating instance of bean '" + beanName + "'");
    		}
    		RootBeanDefinition mbdToUse = mbd;
    
    		// Make sure bean class is actually resolved at this point, and
    		// clone the bean definition in case of a dynamically resolved Class
    		// which cannot be stored in the shared merged bean definition.
    		// 确保bean的类解析完毕，如果是动态解析类型，不会存储合并到bean定义中。克隆一份bean定义。
    		Class<?> resolvedClass = resolveBeanClass(mbd, beanName);
    		if (resolvedClass != null && !mbd.hasBeanClass() && mbd.getBeanClassName() != null) {
    			mbdToUse = new RootBeanDefinition(mbd);
    			mbdToUse.setBeanClass(resolvedClass);
    		}
    
    		// Prepare method overrides.
    		try {
    			mbdToUse.prepareMethodOverrides();
    		}
    		catch (BeanDefinitionValidationException ex) {
    			throw new BeanDefinitionStoreException(mbdToUse.getResourceDescription(),
    					beanName, "Validation of method overrides failed", ex);
    		}
    
    		try {
    			// Give BeanPostProcessors a chance to return a proxy instead of the target bean instance.
    			// 给BeanPostProcessors后处理器一个机会来返回代理来替代真正的实例
    			Object bean = resolveBeforeInstantiation(beanName, mbdToUse);
    			if (bean != null) {
    				return bean;
    			}
    		}
    		catch (Throwable ex) {
    			throw new BeanCreationException(mbdToUse.getResourceDescription(), beanName,
    					"BeanPostProcessor before instantiation of bean failed", ex);
    		}
    
    		try {
    			// 重要方法
    			Object beanInstance = doCreateBean(beanName, mbdToUse, args);
    			if (logger.isDebugEnabled()) {
    				logger.debug("Finished creating instance of bean '" + beanName + "'");
    			}
    			return beanInstance;
    		}
    		catch (BeanCreationException | ImplicitlyAppearedSingletonException ex) {
    			// A previously detected exception with proper bean creation context already,
    			// or illegal singleton state to be communicated up to DefaultSingletonBeanRegistry.
    			throw ex;
    		}
    		catch (Throwable ex) {
    			throw new BeanCreationException(
    					mbdToUse.getResourceDescription(), beanName, "Unexpected exception during bean creation", ex);
    		}
    	}

### doCreateBean ###

protected Object doCreateBean(final String beanName, final RootBeanDefinition mbd, final Object[] args)
                throws BeanCreationException {
    
            // Instantiate the bean.
            BeanWrapper instanceWrapper = null;
            if (mbd.isSingleton()) {// 单例模式，清除缓存bean
                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);
            mbd.resolvedTargetType = beanType;
    
            // 允许处理器修改合并bean定义
            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;
                }
            }
    
            // 如果是单例模式，且允许循环引用，且当前单列正在创建中，则返回之前的bean引用
            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);
                    }
                });
            }
    
            // 初始化（依赖注入）
            Object exposedObject = bean;
            try {
                populateBean(beanName, mbd, instanceWrapper);// 数据填充进实例
                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);
                }
            }
            // 早期已注册的单例bean生成方案，有依赖的注入依赖，无依赖的直接返回引用
            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.");
                        }
                    }
                }
            }
    
            // 注册完成依赖注入的Bean.（如果有销毁方法添加销毁方法等待回调）
            try {
                registerDisposableBeanIfNecessary(beanName, bean, mbd);
            }
            catch (BeanDefinitionValidationException ex) {
                throw new BeanCreationException(
                        mbd.getResourceDescription(), beanName, "Invalid destruction signature", ex);
            }
    
            return exposedObject;
        }

所以doCreateBean 重要方法为：

1.  createBeanInstance ：创建bean实例对象instanceWrapper
2.  populateBean ：定义中配置的属性注入实例对象instanceWrapper
3.  initializeBean ：初始化bean
4.  applyMergedBeanDefinitionPostProcessors ： 加载PostProcessors(这里面其实就是加载了@Autowired)

#### createBeanInstance ####

protected BeanWrapper createBeanInstance(String beanName, RootBeanDefinition mbd, @Nullable 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());
    		}
    
    		Supplier<?> instanceSupplier = mbd.getInstanceSupplier();
    		if (instanceSupplier != null) {
    			return obtainFromSupplier(instanceSupplier, beanName);
    		}
    		// 使用工厂方法进行实例化
    		if (mbd.getFactoryMethodName() != null)  {
    			return instantiateUsingFactoryMethod(beanName, mbd, args);
    		}
    
    		// 使用容器自动装配方法进行实例化
    		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);
    			}
    		}
    
    		// 使用构造函数进行实例化
    		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);
    	}

##### instantiateBean #####

最终调用：`org.springframework.beans.factory.support.SimpleInstantiationStrategy#instantiate(org.springframework.beans.factory.support.RootBeanDefinition, java.lang.String, org.springframework.beans.factory.BeanFactory)`

@Override
    	public Object instantiate(RootBeanDefinition bd, @Nullable String beanName, BeanFactory owner) {
    		// Don't override the class with CGLIB if no overrides.
    		if (!bd.hasMethodOverrides()) {
    			Constructor<?> constructorToUse;
    			synchronized (bd.constructorArgumentLock) {
    				constructorToUse = (Constructor<?>) bd.resolvedConstructorOrFactoryMethod;
    				if (constructorToUse == null) {
    					final Class<?> clazz = bd.getBeanClass();
    					if (clazz.isInterface()) {
    						throw new BeanInstantiationException(clazz, "Specified class is an interface");
    					}
    					try {
    						if (System.getSecurityManager() != null) {
    							constructorToUse = AccessController.doPrivileged(
    									(PrivilegedExceptionAction<Constructor<?>>) clazz::getDeclaredConstructor);
    						}
    						else {
    							constructorToUse =	clazz.getDeclaredConstructor();
    						}
    						bd.resolvedConstructorOrFactoryMethod = constructorToUse;
    					}
    					catch (Throwable ex) {
    						throw new BeanInstantiationException(clazz, "No default constructor found", ex);
    					}
    				}
    			}
    			// 通过BeanUtils进行实例化，利用反射机制获取：java.lang.reflect.Constructor
    			return BeanUtils.instantiateClass(constructorToUse);
    		}
    		else {
    			// 使用Cglib代理
    			return instantiateWithMethodInjection(bd, beanName, owner);
    		}
    	}

#### populateBean ####

protected void populateBean(String beanName, RootBeanDefinition mbd, @Nullable BeanWrapper bw) {
    		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.
    		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;
    		}
    
    		PropertyValues pvs = (mbd.hasPropertyValues() ? mbd.getPropertyValues() : null);
    
    		// 开始进行依赖注入过程，先处理autowire的注入：名字+类型注入
    		if (mbd.getResolvedAutowireMode() == RootBeanDefinition.AUTOWIRE_BY_NAME ||
    				mbd.getResolvedAutowireMode() == RootBeanDefinition.AUTOWIRE_BY_TYPE) {
    			MutablePropertyValues newPvs = new MutablePropertyValues(pvs);
    
    			// 根据Bean的名字自动装配注入
    			if (mbd.getResolvedAutowireMode() == RootBeanDefinition.AUTOWIRE_BY_NAME) {
    				autowireByName(beanName, mbd, bw, newPvs);
    			}
    
    			// 根据Bean的类型自动装配注入
    			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);
    
    		// 有实例化bean处理器/需要依赖检查
    		if (hasInstAwareBpps || needsDepCheck) {
    			if (pvs == null) {
    				pvs = mbd.getPropertyValues();
    			}
    			PropertyDescriptor[] filteredPds = filterPropertyDescriptorsForDependencyCheck(bw, mbd.allowCaching);
    			
    			// 实例化bean处理器
    			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;
    						}
    					}
    				}
    			}
    
    			// 依赖检查
    			if (needsDepCheck) {
    				checkDependencies(beanName, mbd, filteredPds, pvs);
    			}
    		}
    
    		if (pvs != null) {
    			// 对属性进行依赖注入
    			applyPropertyValues(beanName, mbd, bw, pvs);
    		}
    	}

#### initializeBean ####

protected Object initializeBean(final String beanName, final Object bean, @Nullable RootBeanDefinition mbd) {
    		if (System.getSecurityManager() != null) {
    			AccessController.doPrivileged((PrivilegedAction<Object>) () -> {
    				invokeAwareMethods(beanName, bean);
    				return null;
    			}, getAccessControlContext());
    		}
    		else {
    		    // Aware接口 设置bean name、factory、classloader13         }
    			invokeAwareMethods(beanName, bean);
    		}
    
    		Object wrappedBean = bean;
    		if (mbd == null || !mbd.isSynthetic()) {
    		
    			// bea后处理器-初始化之前
    			wrappedBean = applyBeanPostProcessorsBeforeInitialization(wrappedBean, beanName);
    		}
    
    		try {
    
    			// 执行初始化方法（InitializingBean）
    			invokeInitMethods(beanName, wrappedBean, mbd);
    		}
    		catch (Throwable ex) {
    			throw new BeanCreationException(
    					(mbd != null ? mbd.getResourceDescription() : null),
    					beanName, "Invocation of init method failed", ex);
    		}
    		if (mbd == null || !mbd.isSynthetic()) {
    			// bea后处理器-初始化之后
    			wrappedBean = applyBeanPostProcessorsAfterInitialization(wrappedBean, beanName);
    		}
    
    		return wrappedBean;
    	}
    
        private void invokeAwareMethods(final String beanName, final Object bean) {
            if (bean instanceof Aware) {
                if (bean instanceof BeanNameAware) {
                	// 设置bean 名称
                    ((BeanNameAware) bean).setBeanName(beanName);
                }
                if (bean instanceof BeanClassLoaderAware) {
               		 // 设置bean类加载器	
                    ((BeanClassLoaderAware) bean).setBeanClassLoader(getBeanClassLoader());
                }
                if (bean instanceof BeanFactoryAware) {
    				
    				// 设置bean 工厂
                    ((BeanFactoryAware) bean).setBeanFactory(AbstractAutowireCapableBeanFactory.this);
                }
            }
        }

#### applyMergedBeanDefinitionPostProcessors ####

protected void applyMergedBeanDefinitionPostProcessors(RootBeanDefinition mbd, Class<?> beanType, String beanName) {
    		for (BeanPostProcessor bp : getBeanPostProcessors()) {
    			if (bp instanceof MergedBeanDefinitionPostProcessor) {
    				MergedBeanDefinitionPostProcessor bdp = (MergedBeanDefinitionPostProcessor) bp;
    				bdp.postProcessMergedBeanDefinition(mbd, beanType, beanName);
    			}
    		}
    	}

参考文章：[https://www.cnblogs.com/dennyzhangdd/p/7694250.html][https_www.cnblogs.com_dennyzhangdd_p_7694250.html]

[https_www.cnblogs.com_dennyzhangdd_p_7694250.html]: https://www.cnblogs.com/dennyzhangdd/p/7694250.html