lazy init控制加载在Spring中如何实现源码分析

<bean id="testBean" class="com.fhx.TestBean">

<bean id="testBean" class="com.fhx.TestBean" lazy-init="false">

<beans default-lazy-init="true"><!-- no beans will be eagerly pre-instantiated... --></beans>

//解析bean的属性值
 public AbstractBeanDefinition parseBeanDefinitionAttributes(Element ele, String beanName, BeanDefinition containingBean, AbstractBeanDefinition bd) {
 // 省略
 //如果当前元素没有设置 lazyInit 懒加载；则去 this.defaults.getLazyInit()；这个defaults是上一篇分析过的；整个xml文件全局的默认值；
        String lazyInit = ele.getAttribute(LAZY_INIT_ATTRIBUTE);
        if (DEFAULT_VALUE.equals(lazyInit)) {
            lazyInit = this.defaults.getLazyInit();
        }
//省略....
}

@Override
	public void refresh() throws BeansException, IllegalStateException {
	// 忽略..
	// 实例化所有剩余非 lazy-init 为true的单例对象
		finishBeanFactoryInitialization(beanFactory);
	// 忽略..		
	}

	@Override
	public void preInstantiateSingletons() throws BeansException {
		if (this.logger.isDebugEnabled()) {
			this.logger.debug("Pre-instantiating singletons in " + this);
		}
		// Iterate over a copy to allow for init methods which in turn register new bean definitions.
		// While this may not be part of the regular factory bootstrap, it does otherwise work fine.
		List<String> beanNames = new ArrayList<String>(this.beanDefinitionNames);
		// 遍历所有bean
		for (String beanName : beanNames) {
			RootBeanDefinition bd = getMergedLocalBeanDefinition(beanName);
			//1.bd的abstract属性是false；<bean abstract="false"> 不能被实例化，它主要作用是被用作被子bean继承属性用的；
			//2.单例对象并且 lazy-init为false
			//满足上面条件才行
			if (!bd.isAbstract() && bd.isSingleton() && !bd.isLazyInit()) {
			/**
			*如果实现了FactoryBean接口
			*1.先将FactoryBean的实现类实例化；
			*2.判断是否将FactoryBean实现类的getObject方法返回的实例对象也实例化；判断依据
			*  2.1如果当前bean实现了SmartFactoryBean接口，并且isEagerInit()返回true；才会调用工厂类的方法
			*/
				if (isFactoryBean(beanName)) {
					final FactoryBean<?> factory = (FactoryBean<?>) getBean(FACTORY_BEAN_PREFIX + beanName);
					boolean isEagerInit;
					if (System.getSecurityManager() != null && factory instanceof SmartFactoryBean) {
						isEagerInit = AccessController.doPrivileged(new PrivilegedAction<Boolean>() {
							@Override
							public Boolean run() {
								return ((SmartFactoryBean<?>) factory).isEagerInit();
							}
						}, getAccessControlContext());
					}
					else {
						isEagerInit = (factory instanceof SmartFactoryBean &&
								((SmartFactoryBean<?>) factory).isEagerInit());
					}
					if (isEagerInit) {
						getBean(beanName);
					}
				}
				else {//如果不是FactoryBean接口之间实例化
					getBean(beanName);
				}
			}
		}
		// 调用所有SmartInitializingSingleton类型的实现类的afterSingletonsInstantiated方法；通过名字可以知道它表示 单例对象实例化后需要做的操作
		for (String beanName : beanNames) {
			Object singletonInstance = getSingleton(beanName);
			if (singletonInstance instanceof SmartInitializingSingleton) {
				final SmartInitializingSingleton smartSingleton = (SmartInitializingSingleton) singletonInstance;
				if (System.getSecurityManager() != null) {
					AccessController.doPrivileged(new PrivilegedAction<Object>() {
						@Override
						public Object run() {
							smartSingleton.afterSingletonsInstantiated();
							return null;
						}
					}, getAccessControlContext());
				}
				else {
					smartSingleton.afterSingletonsInstantiated();
				}
			}
		}
	}