Spring Bean的加载流程

MyTestBean bean=(MyTestBean)bf.getBean("MyTestBean")；

/**
*这个方法中蕴含了解决循环依赖的原理
*/
protected Object getSingleton(String beanName, boolean allowEarlyReference) {
		//尝试从缓存中拿该bean
		Object singletonObject = this.singletonObjects.get(beanName);
		if (singletonObject == null && isSingletonCurrentlyInCreation(beanName)) {
			//如果缓存中没有该bean，且该bean正在创建中
			synchronized (this.singletonObjects) {
				/**尝试从提前暴露缓存中拿到该bean
				 *这个earlySingletonObjects也是一个map
				 */
				singletonObject = this.earlySingletonObjects.get(beanName);
				if (singletonObject == null && allowEarlyReference) {
					/**
					 * 如果从提前暴露缓存中拿也没拿到，且是允许提前引用的
					 * 就尝试从singletonFactories中获取
					 */
					ObjectFactory<?> singletonFactory = this.singletonFactories.get(beanName);
					if (singletonFactory != null) {
						/**
						 * 如果获取到了该bean的单例工厂，就从单例工厂中来获取
						 * 该bean
						 */
						singletonObject = singletonFactory.getObject();
						/**
						 * 将获取到的对象加入，提前暴露缓存，这个时候，其实还不能算作bean
						 * 因为该对象还没有走完bean的生命周期
						 */
						this.earlySingletonObjects.put(beanName, singletonObject);
						//从单例工厂缓存中移除该bean的单例工厂
						this.singletonFactories.remove(beanName);
					}
				}
			}
		}
		return singletonObject;
	}

         if (!typeCheckOnly) {
	markBeanAsCreated(beanName);
}

final RootBeanDefinition mbd = getMergedLocalBeanDefinition(beanName);
checkMergedBeanDefinition(mbd, beanName, args);

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);
						}
					}
				}

protected Object createBean(String beanName, RootBeanDefinition mbd, @Nullable Object[] args)

if (mbd.isSingleton()) {
			instanceWrapper = this.factoryBeanInstanceCache.remove(beanName);
		}

instanceWrapper = createBeanInstance(beanName, mbd, args);

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");
			}
			/**
			 * 为避免后期循环依赖，可以在bean初始化完成之前将创建实例的ObjectFactory加入工厂
			 *getEarlyBeanReference需要注意，AOP就是在这将advice织入bean的
			 */
			addSingletonFactory(beanName, () -> getEarlyBeanReference(beanName, mbd, bean));
		}

populateBean(beanName, mbd, instanceWrapper);

exposedObject = initializeBean(beanName, exposedObject, mbd);

removeSingletonIfCreatedForTypeCheckOnly(dependentBean)for (String dependentBean : dependentBeans) {
						if (!removeSingletonIfCreatedForTypeCheckOnly(dependentBean)) {
							actualDependentBeans.add(dependentBean);
						}
					}

registerDisposableBeanIfNecessary(beanName, bean, mbd);

Class<?> beanClass = resolveBeanClass(mbd, beanName);

if (mbd.getFactoryMethodName() != null) {
			return instantiateUsingFactoryMethod(beanName, mbd, args);
		}

synchronized (mbd.constructorArgumentLock) {
				if (mbd.resolvedConstructorOrFactoryMethod != null) {
					resolved = true;
					autowireNecessary = mbd.constructorArgumentsResolved;
				}
			}

//如果已经解析过勒，则使用解析好的构造函数方法，而无需再次锁定
		if (resolved) {
			if (autowireNecessary) {
				//构造函数自动注入
				return autowireConstructor(beanName, mbd, null, null);
			}
			else {
				//使用默认构造函数注入
				return instantiateBean(beanName, mbd);
			}
		}

// Candidate constructors for autowiring?
		Constructor<?>[] ctors = determineConstructorsFromBeanPostProcessors(beanClass, beanName);
		if (ctors != null || mbd.getResolvedAutowireMode() == AUTOWIRE_CONSTRUCTOR ||
				mbd.hasConstructorArgumentValues() || !ObjectUtils.isEmpty(args)) {
			return autowireConstructor(beanName, mbd, ctors, args);
		}

ApplicationContext bf=new ClassPathXmlApplicationContext("beanFactory.xml");

public ClassPathXmlApplicationContext(String configLocation) throws BeansException {
		this(new String[] {configLocation}, true, null);
	}

public ClassPathXmlApplicationContext(
		String[] configLocations, boolean refresh, @Nullable ApplicationContext parent)
		throws BeansException {

	super(parent);
	//将配置文件以路径数组的方式传入
	setConfigLocations(configLocations);
	if (refresh) {
		refresh();
	}
}

public void refresh() throws BeansException, IllegalStateException {
		synchronized (this.startupShutdownMonitor) {
			// Prepare this context for refreshing.
			//准备刷新的上下文环境
			prepareRefresh();

			// Tell the subclass to refresh the internal bean factory.
			//初始化BeanFactory并进行xml文件的读取
			ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory();

			// Prepare the bean factory for use in this context.
			//对beanFactory进行功能上的填充
			prepareBeanFactory(beanFactory);

			try {
				// Allows post-processing of the bean factory in context subclasses.
				//子类覆盖方法做额外的处理
				postProcessBeanFactory(beanFactory);

				// Invoke factory processors registered as beans in the context.
				//调用各种beanFactory处理器
				invokeBeanFactoryPostProcessors(beanFactory);

				// Register bean processors that intercept bean creation.
				//注册拦截bean创建的bean处理器
				registerBeanPostProcessors(beanFactory);

				// Initialize message source for this context.
				//为上下文初始化message源，即不同的语言的消息体，国际化处理
				initMessageSource();

				// Initialize event multicaster for this context.
				//初始化应用消息广播器
				initApplicationEventMulticaster();

				// Initialize other special beans in specific context subclasses.
				//留给子类来初始化其它的bean
				onRefresh();

				// Check for listener beans and register them.
				//在所有的bean中查找listener bean，并注册到消息广播器中
				registerListeners();

				// Instantiate all remaining (non-lazy-init) singletons.
				//初始化剩下的非懒加载的单实例
				finishBeanFactoryInitialization(beanFactory);

				// Last step: publish corresponding event.
				//完成刷新过程
				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();
			}
		}
	}

protected ConfigurableListableBeanFactory obtainFreshBeanFactory() {
	refreshBeanFactory();
	//这一步就创建了一个BeanFactory
	ConfigurableListableBeanFactory beanFactory = getBeanFactory();
	if (logger.isDebugEnabled()) {
		logger.debug("Bean factory for " + getDisplayName() + ": " + beanFactory);
	}
	return beanFactory;
}

//留给子类覆盖的，这个方法内部是空的
initPropertySources();
//验证所需的属性文件是否都已经放入环境中了
getEnvironment().validateRequiredProperties();

ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory();

public classs TestEvent extends ApplicationEvent{
    public String msg;
    public TestEvent(Object source){
        super(source);
    }
    public TestEvent(Object source,String msg){
        super(source);
        this.msg=msg;
    }
    
    public void print(){
        System.out.println(msg);
    }
}

public class TestListener implements ApplicationListener{
    public void onApplicationEvent(ApplicationEvent event){
        if(event instanceof TestEvent){
            TestEvent testEvent=(TestEvent)event;
            testEvent.print();
        }
    }
}

<bean id="testListener" class="com.test.event.TestListener"/>

public class Test{
    public static void main(String[] args){
        ApplicationContext context=new ClassPathXmlApplicationContext("classpath:applicationContext.xml");
        TestEvent event=new TestEvent("hello","msg");
        context.publishEvent(event);
    }
}

protected void registerListeners() {
		//硬编码方式注册的监听器处理
		for (ApplicationListener<?> listener : getApplicationListeners()) {
			getApplicationEventMulticaster().addApplicationListener(listener);
		}
		// 配置文件注册的监听器处理
		String[] listenerBeanNames = getBeanNamesForType(ApplicationListener.class, true, false);
		for (String listenerBeanName : listenerBeanNames) {
			getApplicationEventMulticaster().addApplicationListenerBean(listenerBeanName);
		}

		// Publish early application events now that we finally have a multicaster...
		Set<ApplicationEvent> earlyEventsToProcess = this.earlyApplicationEvents;
		this.earlyApplicationEvents = null;
		if (earlyEventsToProcess != null) {
			for (ApplicationEvent earlyEvent : earlyEventsToProcess) {
				getApplicationEventMulticaster().multicastEvent(earlyEvent);
			}
		}
	}