Spring Core — IOC源码解析

其中包括各个主要类之间的联系,以及对实现Bean解析的Refresh()、createBean()、getBean()方法的剖析。

Core包中类关系

Spring Core -- IOC源码解析

refresh方法解析

@Override
	public void refresh() throws BeansException, IllegalStateException {
		synchronized (this.startupShutdownMonitor) {
			// Prepare this context for refreshing.
			//准备所有需要初始化的资源
			// 1. 设定开始时间
			// 2. 初始化配置文件 -- 空实现,默认不作处理
			// 3. 添加环境中没有的配置
			// 4. 保存应用监听器
			// 5. 初始化earlyApplicationEvents,在multicaster可用时发布事件
			prepareRefresh();

			// Tell the subclass to refresh the internal bean factory.
			// 1. 销毁所有单例Beans,关闭当前工厂
			// 2. 新建DefaultListableBeanFactory工厂并设置
			// 3. loadBeanDefinitions方法加载BeanDefinitions到工厂
			ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory();

			// Prepare the bean factory for use in this context.
			// 1. 让工厂使用环境类的类加载器,添加Spring EL解析器,添加配置编辑器注册商(其为PropertyEditor注册器数组,它的职责是用来注册PropertyEditor,而PropertyEditor可以定义如何解析配置,比如将2019-08-18解析成java.util.date.class)
			// 2. 添加ApplicationContextAwareProcessor到工厂,主要用于在bean创建时,实例化后,初始化前,检查bean上是否实现了某个Aware接口,有的话做相应调用。
			// 3. 忽略EnvironmentAware、EmbeddedValueResolverAware、ResourceLoaderAware、ApplicationEventPublisherAware、MessageSourceAware、ApplicationContextAware接口自动注入的依赖。这里解释一下为什么要忽略这些注入:Spring自动创建Bean,但Bean是无状态的,也就是说Bean不知道Spring容器BeanFactory的任何信息,包括Bean自己的名称name,Spring这样做的目的是为了Spring容器和Bean的解耦。那么如果Bean要想定制化的做一些操作,就必须要获取BeanFactory中的信息,在Spring Bean的生命周期中我们都知道实现一些列接口去观察Bean创建过程中的一些信息。所以我们在创建Bean的过程中通过实现一些接口的方式去获取BeanDefinition信息。但这里我们需要正常实例化一个Bean并不需要去拿到这些信息,所以忽略掉这些接口。
			// 4. 建立一些没有注册到工厂中的自动装配Bean映射关联关系(BeanFactory、ResourceLoader、ApplicationEventPublisher、ApplicationContext) 即:有些对象并不在BeanFactory中,但是我们依然想让它们可以被装配。
			// 5. 添加ApplicationListenerDetector到工厂,用于探测是应用监听器的内部Bean
			// 6. 判断是否包含了类加载时期的代码织入(AspectJ)。包含则添加LoadTimeWeaverAwareProcessor(用于给LoadTimeWeaverAware Bean添加loadTimeWeaver类)到工厂
			// 7. 不存在则注册环境、系统配置、系统环境Bean到工厂
			prepareBeanFactory(beanFactory);

			try {
				// Allows post-processing of the bean factory in context subclasses.
				// 允许子类在所有的bean尚未初始化之前注册BeanPostProcessor,空实现且没有子类覆盖。
				postProcessBeanFactory(beanFactory);

				// Invoke factory processors registered as beans in the context.
				// 允许我们在bean正式初始化之前改变其值。有两种方式:
				// 通过代码的方式:context.addBeanFactoryPostProcessor
				// 通过xml配置的方式:<bean class="base.SimpleBeanFactoryPostProcessor" />
				// 具体怎么实现的这里不赘诉了,主要源码在PostProcessorRegistrationDelegate中,通过使用BeanFactory的getBeanNamesForType方法获取相应的BeanDefinition的name数组,之后逐一调用getBean方法获取到bean(初始化),这里有一个优先级的概念,如果你的BeanFactoryPostProcessor同时实现了Ordered或者是PriorityOrdered接口,那么会被首先执行。下面registerBeanPostProcessors也是一样的
				invokeBeanFactoryPostProcessors(beanFactory);

				// Register bean processors that intercept bean creation.
				// 简述一下就是在BeanDefinitions中寻找BeanPostProcessor,之后调用BeanFactory.addBeanPostProcessor方法保存在一个List中,添加的时侯有优先级的概念,优先级高的在前面。
				registerBeanPostProcessors(beanFactory);

				// Initialize message source for this context.
				// 初始化国际化资源
				// 1. 如果工厂包含messageSource Bean,就调用getBean方法完成其初始化并将其保存在AbstractApplicationContext内部messageSource成员变量中,用来处理getMessage调用。此处使用了委托模式。
				// 2. 如果没有配置此bean,那么初始化一个DelegatingMessageSource对象,使用一个空实现用以处理getMessage调用请求。
				initMessageSource();

				// Initialize event multicaster for this context.
				// 1. 在BeanFactory中寻找ApplicationEventMulticaster的bean,如果找到,那么调用getBean方法将其初始化,同样这里将applicationEventMulticaster保存在变量中,并使用委托模式来处理调用publishEvent时,对委托对象的multicastEvent方法的间接调用。
				// 2. 如果找不到那么使用SimpleApplicationEventMulticaster。
				initApplicationEventMulticaster();

				// Initialize other special beans in specific context subclasses.
				// 模版方法,允许子类在进行bean初始化之前进行一些定制操作。默认空实现。
				onRefresh();

				// Check for listener beans and register them.
				// 1. 添加当前AbstractAppContext环境的应用监听器到ApplicationEventMulticaster中
				// 2. 存储所有Bean名称到AbstractApplicationEventMulticaster内部类istenerRetriever.applicationListenerBeans属性中
				// 3. 发布early application events,如果不为空
				registerListeners();

				// Instantiate all remaining (non-lazy-init) singletons.
				// 1. 如果包含conversionService Bean那么就设置ConversionService(其作用和PropertyEditor一致都是转换用)到工厂
				// 2. 如果不包含embeddedValueResolver(用于解析注解的值),设置默认值
				// 3. 初始化LoadTimeWeaverAware Bean,用以能完成转译类
				// 4. 停止使用临时类加载器,冻结且缓存工厂配置不允许修改,
				// 5. 初始化所有预加载的单例Bean
				//   1. 通过beanDefinitionNames遍历beans
				//   2. 如果当前遍历的bean不是抽象、不是懒加载、是单例的那么就判断当前bean是否是FactoryBean,如果是就给每个bean加上前缀“&”,并通过getBean初始化bean,如果此bean是FactoryBean类型还是SmartFactoryBean类型,那么需要判断是否需要eagerInit马上进行初始化。
				//   3. 如果当前bean不是FactoryBean,就直接调用getBean进行初始化
				//   4. 待遍历所有bean初始化完成后还需要遍历所有是SmartInitializingSingleton类型的bean来触发该类型接口的afterSingletonsInstantiated方法。(这里的应用场景主要是在所有单例 bean 创建完成之后,可以在该回调中做一些事情。)
				finishBeanFactoryInitialization(beanFactory);

				// Last step: publish corresponding event.
				// 1. 清理资源缓存
				// 2. 如果存在初始化生命周期处理器,则创建lifecycleProcessor bean,否则创建默认的DefaultLifecycleProcessor bean
				// 3. 委托给LifecycleProcessor去调用所有实现了SmartLifecycle bean的start方法 (这里SmartLifecycle的使用场景主要是在Spring加载和初始化所有bean后,接着执行一些任务或者启动需要的异步服务)
				// 4. 发布最后的消息
				// 5. 将环境注册到LiveBeansView:如果存在spring.liveBeansView.mbeanDomain配置则注册LiveBeansView到MBeanServer中(其实现了LiveBeansViewMBean接口的getSnapshotAsJson,主要用于将环境转换为json)
				finishRefresh();
			}

			catch (BeansException ex) {
				if (logger.isWarnEnabled()) {
					logger.warn("Exception encountered during context initialization - " +
							"cancelling refresh attempt: " + ex);
				}

				// Destroy already created singletons to avoid dangling resources.
				destroyBeans();

				// Reset 'active' flag.
				cancelRefresh(ex);

				// Propagate exception to caller.
				throw ex;
			}

			finally {
				// Reset common introspection caches in Spring's core, since we
				// might not ever need metadata for singleton beans anymore...
				resetCommonCaches();
			}
		}
	}
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CreateBean — 创建Bean实例解析

// 先说一下createBean
	// 经过resolveBeforeInstantiation方法后,如果创建了代理(即重写了InstantiationAwareBeanPostProcessor的postProcessBeforeInstantiation方法并且在方法中改变了bean)直接返回即可,否则进行常规bean的创建
	@Override
	AbstractAutowireCapableBeanFactory.createBean(String beanName, RootBeanDefinition mbd, @Nullable Object[] args){
		
	}

	// 常规执行创建bean的逻辑
	// 这里BeanWrapper相当于一个代理器,Spring委托BeanWrapper完成Bean属性的填充工作。在Bean实例被InstantiatioonStrategy创建出来之后,容器主控程序将Bean实例通过BeanWrapper包装起来
	protected Object doCreateBean(final String beanName, final RootBeanDefinition mbd, final Object[] args){
		//Instantiate the bean
		BeanWrapper instanceWrapper = null;
		if(mbd.isSingleton()){
			// 清理缓存中的bean
			instanceWrapper = this.factoryBeanInstanceCache.remove(beanName);
		}
		if(instanceWrapper == null){
			// 使用对应的策略创建新的实例:工厂方法,构造函数自动注入,简单初始化
			instanceWrapper = createBeanInstance(beanName,mbd,args);
		}
		final Object bean = instanceWrapper.getWrappedInstance();
		Class<?> beanType = instanceWrapper.getWrappedClass();
		if (beanType != NullBean.class) {
			mbd.resolvedTargetType = beanType;
		}
		
		// Allow post-processors to modify the merged bean definition.
		synchronized (mbd.postProcessingLock) {
			if (!mbd.postProcessed) {
				try {
					// MergedBeanDefinitionPostProcessor接口是在合并处理Bean定义的时候的回调
					// 这儿方法是将MergedBeanDefinitionPostProcessor应用到这个特定的bean定义上
					applyMergedBeanDefinitionPostProcessors(mbd, beanType, beanName);
				}
				catch (Throwable ex) {
					throw new BeanCreationException(mbd.getResourceDescription(), beanName,
							"Post-processing of merged bean definition failed", ex);
				}
				mbd.postProcessed = true;
			}
		}
		
		//是否需要提前曝光:单例&允许循环依赖&bean正在创建
		boolean earlySingletonExposure = (mbd.isSingleton() && this.allowCircularReferences && isSingletonCurrentlyInCreation(beanName));
		
		if(earlySingletonExposure){
				addSingletonFactory(beanName, new ObjectFactory(){public Object getObject() throws BeansException{
				//对bean再一次依赖引用,主要引用SmartInstantiationAwareBeanPostProcessor,
				//AOP就是在这里将advice动态织入bean中,若没有直接返回bean.
				return getEarlyBeanReference(beanName,mbd,bean);
				}});
		}

		// Initialize the bean instance.
		Object exposedObject = bean;
		try {
			//对bean进行填充,将各个属性值注入,可能存在依赖于其他bean的属性,递归依赖bean
			populateBean(beanName, mbd, instanceWrapper);
			//调用初始化方法 如 init-method
			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);
			// 如果有循环依赖
			if(earlySingletonReference != null){
				//没有被代理增强
				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){
						//检测依赖
						if(!removeSingletonIfCreatedForTypeCheckOnly(dependentBean)){
							actualDependentBeans.add(dependentBean);
						}
					}
		
					//如果actualDependentBeans不为空表示当前bean创建后其依赖的bean却没有创建完,说明存在循环依赖
					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.");
				}
			}
		}
		
		try{
			//注册为一次性可销毁的bean
			registerDisposableBeanIfNecessary(beanName,bean,mbd);
		}catch (BeanDefinitionValidationException ex) {
			throw new BeanCreationException(
					mbd.getResourceDescription(), beanName, "Invalid destruction signature", ex);
		}
		return exposedObject;
	}
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GetBean — 解析Bean的初始化

// 重点解析Bean的初始化 -- getBean(name) 为例
		@Override
		public Object getBean(String name) throws BeansException {
			return doGetBean(name, null, null, false);
		}

		// 四个参数:第一个为传入的beanName,第二个为bean的Class类型,第三个表示创建bean需要的参数,最后一个表示不需要进行类型检查。
		protected <T> T doGetBean(final String name, @Nullable final Class<T> requiredType,
				@Nullable final Object[] args, boolean typeCheckOnly) throws BeansException {

			// 将是factoryBean的名称去掉 之前加的 “&” 符号
			final String beanName = transformedBeanName(name);
			Object bean;

			// 1. 检测是不是Spring手动注册的那些单例bean
			// 2. 如果是,那么再检测是不是工厂bean,如果是返回其工厂方法返回的实例,如果不是返回bean本身。
			// Eagerly check singleton cache for manually registered singletons.
			Object sharedInstance = getSingleton(beanName);
			if (sharedInstance != null && args == null) {
				if (logger.isTraceEnabled()) {
					if (isSingletonCurrentlyInCreation(beanName)) {
						logger.trace("Returning eagerly cached instance of singleton bean '" + beanName +
								"' that is not fully initialized yet - a consequence of a circular reference");
					}
					else {
						logger.trace("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);
				}

				// 如果父容器存在,并且存在此bean定义,那么交由其父容器初始化bean
				// Check if bean definition exists in this factory.
				BeanFactory parentBeanFactory = getParentBeanFactory();
				if (parentBeanFactory != null && !containsBeanDefinition(beanName)) {
					// Not found -> check parent.
					// 将是factoryBean的name前加上 “&” ,因为在父容器中又会再次进行这个转换操作,所以这里还需要加上 &
					String nameToLookup = originalBeanName(name);
					if (parentBeanFactory instanceof AbstractBeanFactory) {
						return ((AbstractBeanFactory) parentBeanFactory).doGetBean(
								nameToLookup, requiredType, args, typeCheckOnly);
					}
					// 下面都是交给父容器去加载
					else if (args != null) {
						// Delegation to parent with explicit args.
						return (T) parentBeanFactory.getBean(nameToLookup, args);
					}
					else if (requiredType != null) {
						// No args -> delegate to standard getBean method.
						return parentBeanFactory.getBean(nameToLookup, requiredType);
					}
					else {
						return (T) parentBeanFactory.getBean(nameToLookup);
					}
				}

				// 这里使用了synchronized的双重校验来将这个beanName加入到alreadyCreated中,用以防止有其他进程在同一时间创建
				if (!typeCheckOnly) {
					markBeanAsCreated(beanName);
				}

				try {
					// 获取到具有父子关系的bean定义的根节点
					final RootBeanDefinition mbd = getMergedLocalBeanDefinition(beanName);
					checkMergedBeanDefinition(mbd, beanName, args);

					// 拿到这个bean所依赖的所有bean定义根节点,并递归调用初始化它们
					// Guarantee initialization of beans that the current bean depends on.
					String[] dependsOn = mbd.getDependsOn();
					if (dependsOn != null) {
						for (String dep : dependsOn) {
							// registerDependentBean进行了依赖关系的注册,这么做的原因是Spring在即进行bean销毁的时候会首先销毁被依赖的bean。依赖关系的保存是通过一个ConcurrentHashMap<String, Set>完成的,key是bean名字。
							if (isDependent(beanName, dep)) {
								throw new BeanCreationException(mbd.getResourceDescription(), beanName,
										"Circular depends-on relationship between '" + beanName + "' and '" + dep + "'");
							}
							registerDependentBean(dep, beanName);
							try {
								// getBean方法是包括了所有scope的初始化的
								getBean(dep);
							}
							catch (NoSuchBeanDefinitionException ex) {
								throw new BeanCreationException(mbd.getResourceDescription(), beanName,
										"'" + beanName + "' depends on missing bean '" + dep + "'", ex);
							}
						}
					}

					// Create bean instance.
					if (mbd.isSingleton()) {
						// 
						// 1. getSingleton首先会尝试去获取这个Bean
						// 2. 然后判断是否为空,是否正在创建中,如果是则跳过,直接返回获取到的Bean
						// 3. 如果都没有,则尝试createBean去创建Bean
						// 4. 然后就是一些收尾工作,把Bean加到singletonObjects中
						sharedInstance = getSingleton(beanName, () -> {
							try {
								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;
							}
						});
						bean = getObjectForBeanInstance(sharedInstance, name, beanName, mbd);
					}

					else if (mbd.isPrototype()) {
						// It's a prototype -> create a new instance.
						Object prototypeInstance = null;
						try {
							// 确保在同一时刻只有一个Bean在初始化
							beforePrototypeCreation(beanName);
							prototypeInstance = createBean(beanName, mbd, args);
						}
						finally {
							// 标记此bean已经没有处于实例化时段了
							afterPrototypeCreation(beanName);
						}
						bean = getObjectForBeanInstance(prototypeInstance, name, beanName, mbd);
					}
					// 其余诸如:request、session这样的Scope的初始化,这里就和前面的单例初始化比较雷同,不讲了
					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 {
							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.
			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.isTraceEnabled()) {
						logger.trace("Failed to convert bean '" + name + "' to required type '" +
								ClassUtils.getQualifiedName(requiredType) + "'", ex);
					}
					throw new BeanNotOfRequiredTypeException(name, requiredType, bean.getClass());
				}
			}
			return (T) bean;
	}
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原文 

https://juejin.im/post/5d6a0387f265da0391352ca6

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