Spring-创建bean

preInstantiateSingletons

v1.0 preInstantiateSingletons

tips：最终调用getBean使用的是RootBeanDefinition进行构建的

	public void preInstantiateSingletons() throws BeansException {
		if (logger.isTraceEnabled()) {
			logger.trace("Pre-instantiating singletons in " + this);
		}

		//获取所有beanDefinition的名字
		List<String> beanNames = new ArrayList<>(this.beanDefinitionNames);

		//循环
		for (String beanName : beanNames) {
			// 获取合并后的BeanDefinition，看代码V1.1
			RootBeanDefinition bd = getMergedLocalBeanDefinition(beanName);
			//如果RootBeanDefinition不是抽象BeanDefinition，是单例bean，非懒加载，则创建bean对象
			if (!bd.isAbstract() && bd.isSingleton() && !bd.isLazyInit()) {
				if (isFactoryBean(beanName)) {
					// 获取FactoryBean对象
					Object bean = getBean(FACTORY_BEAN_PREFIX + beanName);
					if (bean instanceof FactoryBean) {
						FactoryBean<?> factory = (FactoryBean<?>) bean;
						boolean isEagerInit;
						if (System.getSecurityManager() != null && factory instanceof SmartFactoryBean) {
							isEagerInit = AccessController.doPrivileged(
									(PrivilegedAction<Boolean>) ((SmartFactoryBean<?>) factory)::isEagerInit,
									getAccessControlContext());
						}
						else {
							isEagerInit = (factory instanceof SmartFactoryBean &&
									((SmartFactoryBean<?>) factory).isEagerInit());
						}
						if (isEagerInit) {
							// 创建真正的Bean对象(getObject()返回的对象)
							getBean(beanName);
						}
					}
				}
				else {
					// 创建Bean对象
					getBean(beanName);
				}
			}
		}

		// 所有的非懒加载单例Bean都创建完了后
		//找出实现了SmartInitializingSingleton接口的单例bean，并执行afterSingletonsInstantiated（）方法
	
		for (String beanName : beanNames) {
			Object singletonInstance = getSingleton(beanName);
			if (singletonInstance instanceof SmartInitializingSingleton) {
				StartupStep smartInitialize = this.getApplicationStartup().start("spring.beans.smart-initialize")
						.tag("beanName", beanName);
				SmartInitializingSingleton smartSingleton = (SmartInitializingSingleton) singletonInstance;
				if (System.getSecurityManager() != null) {
					AccessController.doPrivileged((PrivilegedAction<Object>) () -> {
						smartSingleton.afterSingletonsInstantiated();
						return null;
					}, getAccessControlContext());
				}
				else {
					smartSingleton.afterSingletonsInstantiated();
				}
				smartInitialize.end();
			}
		}
	}

什么是抽象BeanDefinition？

V1.1 getMergedLocalBeanDefinition

合并BeanDefinition

protected RootBeanDefinition getMergedLocalBeanDefinition(String beanName) throws BeansException {
		// 先从RootBeanDefinitionMap中获取当前beanName对应的RootBeanDefinition对象
		RootBeanDefinition mbd = this.mergedBeanDefinitions.get(beanName);
		//如果已经存在，则直接返回
		if (mbd != null && !mbd.stale) {
			return mbd;
		}
		//如果不存在，则继续向下判断
		return getMergedBeanDefinition(beanName, getBeanDefinition(beanName));
	}
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	protected RootBeanDefinition getMergedBeanDefinition(
			String beanName, BeanDefinition bd, @Nullable BeanDefinition containingBd)
			throws BeanDefinitionStoreException {

		synchronized (this.mergedBeanDe