• Spring IoC源码：createBean（下）

    文章目录

    Spring源码系列：

    Spring IOC源码：简单易懂的Spring IOC 思路介绍
    Spring IOC源码：核心流程介绍
    Spring IOC源码：ApplicationContext刷新前准备工作
    Spring IOC源码：obtainFreshBeanFactory 详解（上）
    Spring IOC源码：obtainFreshBeanFactory 详解（中）
    Spring IOC源码：obtainFreshBeanFactory 详解（下）
    Spring IOC源码：＜context:component-scan＞源码详解
    Spring IOC源码：invokeBeanFactoryPostProcessors 后置处理器详解
    Spring IOC源码：registerBeanPostProcessors 详解
    Spring IOC源码：实例化前的准备工作
    Spring IOC源码：finishBeanFactoryInitialization详解
    Spring IoC源码：getBean 详解
    Spring IoC源码：createBean（ 上）
    Spring IoC源码：createBean（ 中）
    Spring IoC源码：createBean（ 下）
    Spring IoC源码：finishRefresh 完成刷新详解

    前言

    上篇文章讲解了实例化后，初始化属性注入过程中属性值的解析过程及其注入过程，本篇继续讲解doCreateBean流程中属性注入后的其它流程，即对bean实例进行初始化。

    正文

    populateBean方法执行完成后，开始初始化bean。

    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;
	}


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    initializeBean(beanName, exposedObject, mbd)，见方法1详解

    registerDisposableBeanIfNecessary(beanName, bean, mbd)，见方法7详解

    方法1：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 {
			//对bean的aware属性进行填充
			invokeAwareMethods(beanName, bean);
		}

		Object wrappedBean = bean;
		//执行BeanPostProcessors的postProcessBeforeInitialization方法，可能会返回新的对象值
		if (mbd == null || !mbd.isSynthetic()) {
			wrappedBean = applyBeanPostProcessorsBeforeInitialization(wrappedBean, beanName);
		}

		try {
			//调用初始化方法
			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()) {
			//执行BeanPostProcessors的postProcessAfterInitialization方法，AOP代理就是在这个步骤进行处理的
			wrappedBean = applyBeanPostProcessorsAfterInitialization(wrappedBean, beanName);
		}

		return wrappedBean;
	}


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    invokeAwareMethods(beanName, bean)，见方法2详解

    applyBeanPostProcessorsBeforeInitialization(wrappedBean, beanName)，见方法3详解

    invokeInitMethods(beanName, wrappedBean, mbd)，见方法4详解

    applyBeanPostProcessorsAfterInitialization(wrappedBean, beanName)，见方法6详解

    方法2：invokeAwareMethods

    	private void invokeAwareMethods(final String beanName, final Object bean) {
		//如果实现了Aware接口，根据实现不同接口，对属性进行填充
		if (bean instanceof Aware) {
			//填充beanName值
			if (bean instanceof BeanNameAware) {
				((BeanNameAware) bean).setBeanName(beanName);
			}
			if (bean instanceof BeanClassLoaderAware) {
				//填充ClassLoader 
				ClassLoader bcl = getBeanClassLoader();
				if (bcl != null) {
					((BeanClassLoaderAware) bean).setBeanClassLoader(bcl);
				}
			}
			if (bean instanceof BeanFactoryAware) {
				//填充当前beanFactory工厂
				((BeanFactoryAware) bean).setBeanFactory(AbstractAutowireCapableBeanFactory.this);
			}
		}
	}

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    方法3：applyBeanPostProcessorsBeforeInitialization

    	public Object applyBeanPostProcessorsBeforeInitialization(Object existingBean, String beanName)
			throws BeansException {

		Object result = existingBean;
		//执行BeanPostProcessors的postProcessBeforeInitialization方法，可能会返回新的对象值。
		for (BeanPostProcessor processor : getBeanPostProcessors()) {
			Object current = processor.postProcessBeforeInitialization(result, beanName);
			if (current == null) {
				return result;
			}
			result = current;
		}
		return result;
	}

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    方法4：invokeInitMethods

    	protected void invokeInitMethods(String beanName, final Object bean, @Nullable RootBeanDefinition mbd)
			throws Throwable {
		//判断是否实现了InitializingBean接口，如果是则调用afterPropertiesSet方法
		boolean isInitializingBean = (bean instanceof InitializingBean);
		if (isInitializingBean && (mbd == null || !mbd.isExternallyManagedInitMethod("afterPropertiesSet"))) {
			if (logger.isTraceEnabled()) {
				logger.trace("Invoking afterPropertiesSet() on bean with name '" + beanName + "'");
			}
			if (System.getSecurityManager() != null) {
				try {
					AccessController.doPrivileged((PrivilegedExceptionAction<Object>) () -> {
						((InitializingBean) bean).afterPropertiesSet();
						return null;
					}, getAccessControlContext());
				}
				catch (PrivilegedActionException pae) {
					throw pae.getException();
				}
			}
			else {
				((InitializingBean) bean).afterPropertiesSet();
			}
		}
		//调用自定义初始化方法
		if (mbd != null && bean.getClass() != NullBean.class) {
			String initMethodName = mbd.getInitMethodName();
			if (StringUtils.hasLength(initMethodName) &&
					!(isInitializingBean && "afterPropertiesSet".equals(initMethodName)) &&
					!mbd.isExternallyManagedInitMethod(initMethodName)) {
				invokeCustomInitMethod(beanName, bean, mbd);
			}
		}
	}

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    invokeCustomInitMethod(beanName, bean, mbd)，见方法5详解

    方法5：invokeCustomInitMethod

    	protected void invokeCustomInitMethod(String beanName, final Object bean, RootBeanDefinition mbd)
			throws Throwable {
		//获取配置的init方法名称
		String initMethodName = mbd.getInitMethodName();
		Assert.state(initMethodName != null, "No init method set");
		//获取初始化方法
		Method initMethod = (mbd.isNonPublicAccessAllowed() ?
				BeanUtils.findMethod(bean.getClass(), initMethodName) :
				ClassUtils.getMethodIfAvailable(bean.getClass(), initMethodName));
		//如果找不到则判断是否强制执行，强制则抛异常，非强制则警告提示
		if (initMethod == null) {
			if (mbd.isEnforceInitMethod()) {
				throw new BeanDefinitionValidationException("Could not find an init method named '" +
						initMethodName + "' on bean with name '" + beanName + "'");
			}
			else {
				if (logger.isTraceEnabled()) {
					logger.trace("No default init method named '" + initMethodName +
							"' found on bean with name '" + beanName + "'");
				}
				// Ignore non-existent default lifecycle methods.
				return;
			}
		}

		if (logger.isTraceEnabled()) {
			logger.trace("Invoking init method  '" + initMethodName + "' on bean with name '" + beanName + "'");
		}
		Method methodToInvoke = ClassUtils.getInterfaceMethodIfPossible(initMethod);

		if (System.getSecurityManager() != null) {
			AccessController.doPrivileged((PrivilegedAction<Object>) () -> {
				ReflectionUtils.makeAccessible(methodToInvoke);
				return null;
			});
			try {
				AccessController.doPrivileged((PrivilegedExceptionAction<Object>) () ->
						methodToInvoke.invoke(bean), getAccessControlContext());
			}
			catch (PrivilegedActionException pae) {
				InvocationTargetException ex = (InvocationTargetException) pae.getException();
				throw ex.getTargetException();
			}
		}
		else {
			try {
			//设置权限
				ReflectionUtils.makeAccessible(methodToInvoke);
				//执行
				methodToInvoke.invoke(bean);
			}
			catch (InvocationTargetException ex) {
				throw ex.getTargetException();
			}
		}
	}

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    方法6：applyBeanPostProcessorsAfterInitialization

    	public Object applyBeanPostProcessorsAfterInitialization(Object existingBean, String beanName)
			throws BeansException {
		//执行BeanPostProcessors的postProcessAfterInitialization方法，AOP代理就是在这个步骤进行处理的
		Object result = existingBean;
		for (BeanPostProcessor processor : getBeanPostProcessors()) {
			Object current = processor.postProcessAfterInitialization(result, beanName);
			if (current == null) {
				return result;
			}
			result = current;
		}
		return result;
	}

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    方法7：registerDisposableBeanIfNecessary

    	protected void registerDisposableBeanIfNecessary(String beanName, Object bean, RootBeanDefinition mbd) {
		AccessControlContext acc = (System.getSecurityManager() != null ? getAccessControlContext() : null);
		//如果不是多例&&需要销毁
		if (!mbd.isPrototype() && requiresDestruction(bean, mbd)) {
			//如果是单例
			if (mbd.isSingleton()) {
				// Register a DisposableBean implementation that performs all destruction
				// work for the given bean: DestructionAwareBeanPostProcessors,
				// DisposableBean interface, custom destroy method.
				//
				registerDisposableBean(beanName,
						new DisposableBeanAdapter(bean, beanName, mbd, getBeanPostProcessors(), acc));
			}
			else {
				// A bean with a custom scope...
				//根据自定义的Scope ，注册销毁回调方式
				Scope scope = this.scopes.get(mbd.getScope());
				if (scope == null) {
					throw new IllegalStateException("No Scope registered for scope name '" + mbd.getScope() + "'");
				}
				scope.registerDestructionCallback(beanName,
						new DisposableBeanAdapter(bean, beanName, mbd, getBeanPostProcessors(), acc));
			}
		}
	}

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    requiresDestruction(bean, mbd)，见方法8详解

    方法8：requiresDestruction

    	protected boolean requiresDestruction(Object bean, RootBeanDefinition mbd) {
		//当前bean不是null
     // 1.DisposableBeanAdapter.hasDestroyMethod(bean, mbd)：判断bean是否有destroy方法
     // 2.hasDestructionAwareBeanPostProcessors()：判断当前BeanFactory是否注册过DestructionAwareBeanPostProcessor
     // 3.DisposableBeanAdapter.hasApplicableProcessors：是否存在适用于bean的DestructionAwareBeanPostProcessor
		return (bean.getClass() != NullBean.class &&
				(DisposableBeanAdapter.hasDestroyMethod(bean, mbd) || (hasDestructionAwareBeanPostProcessors() &&
						DisposableBeanAdapter.hasApplicableProcessors(bean, getBeanPostProcessors()))));
	}

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    DisposableBeanAdapter.hasDestroyMethod(bean, mbd)，见方法9详解
    DisposableBeanAdapter.hasApplicableProcessors(bean, getBeanPostProcessors())，见方法10详解

    方法9：hasDestroyMethod

    		public static boolean hasDestroyMethod(Object bean, RootBeanDefinition beanDefinition) {
		//bean实现了DisposableBean 或AutoCloseable接口
		if (bean instanceof DisposableBean || bean instanceof AutoCloseable) {
			return true;
		}
		//获取销毁方法名称
		String destroyMethodName = beanDefinition.getDestroyMethodName();
		//如果自定销毁方法名称为 "(inferred)"
		if (AbstractBeanDefinition.INFER_METHOD.equals(destroyMethodName)) {
			//判断是否有close或shutdown方法
			return (ClassUtils.hasMethod(bean.getClass(), CLOSE_METHOD_NAME) ||
					ClassUtils.hasMethod(bean.getClass(), SHUTDOWN_METHOD_NAME));
		}
		return StringUtils.hasLength(destroyMethodName);
	}

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    方法10：hasApplicableProcessors

    	public static boolean hasApplicableProcessors(Object bean, List<BeanPostProcessor> postProcessors) {
		if (!CollectionUtils.isEmpty(postProcessors)) {
			//遍历后置处理器
			for (BeanPostProcessor processor : postProcessors) {
				//如果有类型为DestructionAwareBeanPostProcessor的后置处理器
				if (processor instanceof DestructionAwareBeanPostProcessor) {
					DestructionAwareBeanPostProcessor dabpp = (DestructionAwareBeanPostProcessor) processor;
					//判断是否需要由这个后置处理器进行销毁
					if (dabpp.requiresDestruction(bean)) {
						return true;
					}
				}
			}
		}
		return false;
	}

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    总结

    到此，整个bean的创建流程就结束了。
    1、对当前Bean实现不同的Aware接口，对不同的属性值进行填充
    2、执行BeanPostProcessors的postProcessBeforeInitialization方法，可能会返回新的对象值。
    3、调用执行自定义的初始化方法，如果当前Bean实现了InitializingBean接口，则调用afterPropertiesSet方法
    4、执行BeanPostProcessors的postProcessAfterInitialization方法，AOP代理就是在这个步骤进行处理的
    5、注册销毁相关方法，会在IOC销毁流程中进行回调。

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  • 原文地址：https://blog.csdn.net/weixin_45031612/article/details/128177069