SpringBoot之Bean初始化

一、refresh 方法

SpringBoot 加載 bean 操作主要在 AbstractApplicationContext 類 refresh 方法里，它的流程圖如下：

代碼如下：

@Override
public void refresh() throws BeansException, IllegalStateException {
	synchronized (this.startupShutdownMonitor) {
		// 容器狀態設置，初始化屬性設置，檢查必備屬性是否存在
		prepareRefresh();

		// 設置beanFactory序列化id，獲取beanFactory 
		ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory();

		// 設置 beanFactory 屬性，添加后置處理器，設置忽略的自動裝配接口，注冊部分組件
		prepareBeanFactory(beanFactory);

		try {
			// 子類重寫以在 BeanFactory 完成創建后做進一步設置
			postProcessBeanFactory(beanFactory);

			// 調用BeanDefinitionRegistryPostProcessor實現向容器內添加bean的定義
            // 調用BeanFactoryPostProcessor實現向容器內添加bean的定義添加屬性
			invokeBeanFactoryPostProcessors(beanFactory);

			// 找到BeanPostPocessor的實現，排序后注冊進容器內
			registerBeanPostProcessors(beanFactory);

			// 初始化國際化相關屬性
			initMessageSource();

			// 初始化事件廣播器。注冊到容器當中
			initApplicationEventMulticaster();

			// 創建web容器。如果是web環境當中，構建一個web容器，如tomcat，jetty等。
			onRefresh();

            // 添加容器內事件監聽器至事件廣播器中
			// 派發早期事件
			registerListeners();

			// 初始化剩下的單實例 Bean
			registerListeners(beanFactory);

			// 初始化生命周期處理器
			// 調用生命周期處理器的onRefresh方法
			// 發布ContextRefreshedEvent 事件
			//	JMX相關處理
			finishRefresh();
		} catch (BeansException ex) {
			if (logger.isWarnEnabled()) {
				logger.warn("Exception encountered during context initialization - " +
						"cancelling refresh attempt: " + ex);
			}

			// 銷毀已創建的單例
			destroyBeans();

			// 重置標記
			cancelRefresh(ex);

			// Propagate exception to caller.
			throw ex;
		} finally {
			// 清除緩存
			resetCommonCaches();
		}
	}
}

二、Bean實例化流程

bean 實例化流程流程是在 onRefresh方法的 finishBeanFactoryInitialization中，進入該方法：

protected void finishBeanFactoryInitialization(ConfigurableListableBeanFactory beanFactory) {
    // Initialize conversion service for this context.
    if (beanFactory.containsBean(CONVERSION_SERVICE_BEAN_NAME) &&
            beanFactory.isTypeMatch(CONVERSION_SERVICE_BEAN_NAME, ConversionService.class)) {
        beanFactory.setConversionService(
                beanFactory.getBean(CONVERSION_SERVICE_BEAN_NAME, ConversionService.class));
    }

    // Register a default embedded value resolver if no bean post-processor
    // (such as a PropertyPlaceholderConfigurer bean) registered any before:
    // at this point, primarily for resolution in annotation attribute values.
    if (!beanFactory.hasEmbeddedValueResolver()) {
        beanFactory.addEmbeddedValueResolver(strVal -> getEnvironment().resolvePlaceholders(strVal));
    }

    // Initialize LoadTimeWeaverAware beans early to allow for registering their transformers early.
    String[] weaverAwareNames = beanFactory.getBeanNamesForType(LoadTimeWeaverAware.class, false, false);
    for (String weaverAwareName : weaverAwareNames) {
        getBean(weaverAwareName);
    }

    // Stop using the temporary ClassLoader for type matching.
    beanFactory.setTempClassLoader(null);

    // Allow for caching all bean definition metadata, not expecting further changes.
    beanFactory.freezeConfiguration();

    // Instantiate all remaining (non-lazy-init) singletons.
    beanFactory.preInstantiateSingletons();
}