SpringBoot之Bean初始化

一、refresh 方法

SpringBoot 加载 bean 操作主要在 AbstractApplicationContext 类 refresh 方法里，它的流程图如下：

代码如下：

@Override
public void refresh() throws BeansException, IllegalStateException {
	synchronized (this.startupShutdownMonitor) {
		// 容器状态设置，初始化属性设置，检查必备属性是否存在
		prepareRefresh();

		// 设置beanFactory序列化id，获取beanFactory 
		ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory();

		// 设置 beanFactory 属性，添加后置处理器，设置忽略的自动装配接口，注册部分组件
		prepareBeanFactory(beanFactory);

		try {
			// 子类重写以在 BeanFactory 完成创建后做进一步设置
			postProcessBeanFactory(beanFactory);

			// 调用BeanDefinitionRegistryPostProcessor实现向容器内添加bean的定义
            // 调用BeanFactoryPostProcessor实现向容器内添加bean的定义添加属性
			invokeBeanFactoryPostProcessors(beanFactory);

			// 找到BeanPostPocessor的实现，排序后注册进容器内
			registerBeanPostProcessors(beanFactory);

			// 初始化国际化相关属性
			initMessageSource();

			// 初始化事件广播器。注册到容器当中
			initApplicationEventMulticaster();

			// 创建web容器。如果是web环境当中，构建一个web容器，如tomcat，jetty等。
			onRefresh();

            // 添加容器内事件监听器至事件广播器中
			// 派发早期事件
			registerListeners();

			// 初始化剩下的单实例 Bean
			registerListeners(beanFactory);

			// 初始化生命周期处理器
			// 调用生命周期处理器的onRefresh方法
			// 发布ContextRefreshedEvent 事件
			//	JMX相关处理
			finishRefresh();
		} catch (BeansException ex) {
			if (logger.isWarnEnabled()) {
				logger.warn("Exception encountered during context initialization - " +
						"cancelling refresh attempt: " + ex);
			}

			// 销毁已创建的单例
			destroyBeans();

			// 重置标记
			cancelRefresh(ex);

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

二、Bean实例化流程

bean 实例化流程流程是在 onRefresh方法的 finishBeanFactoryInitialization中，进入该方法：

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();
}