lazy init控制載入在Spring中如何實現原始碼分析

<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的屬性值
 public AbstractBeanDefinition parseBeanDefinitionAttributes(Element ele, String beanName, BeanDefinition containingBean, AbstractBeanDefinition bd) {
 // 省略
 //如果當前元素沒有設定 lazyInit 懶載入；則去 this.defaults.getLazyInit()；這個defaults是上一篇分析過的；整個xml檔案全域性的預設值；
        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..
	// 範例化所有剩餘非 lazy-init 為true的單例物件
		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);
		// 遍歷所有bean
		for (String beanName : beanNames) {
			RootBeanDefinition bd = getMergedLocalBeanDefinition(beanName);
			//1.bd的abstract屬性是false；<bean abstract="false"> 不能被範例化，它主要作用是被用作被子bean繼承屬性用的；
			//2.單例物件並且 lazy-init為false
			//滿足上面條件才行
			if (!bd.isAbstract() && bd.isSingleton() && !bd.isLazyInit()) {
			/**
			*如果實現了FactoryBean介面
			*1.先將FactoryBean的實現類範例化；
			*2.判斷是否將FactoryBean實現類的getObject方法返回的範例物件也範例化；判斷依據
			*  2.1如果當前bean實現了SmartFactoryBean介面，並且isEagerInit()返回true；才會呼叫工廠類的方法
			*/
				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介面之間範例化
					getBean(beanName);
				}
			}
		}
		// 呼叫所有SmartInitializingSingleton型別的實現類的afterSingletonsInstantiated方法；通過名字可以知道它表示 單例物件範例化後需要做的操作
		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();
				}
			}
		}
	}