Spring-bean的生命周期

标准bean生命周期

Bean工厂实现应该尽可能支持标准Bean生命周期接口。整套初始化方法及其标准顺序如下：

BeanNameAware.setBeanName,
BeanClassLoaderAware.setBeanClassLoader,
BeanFactoryAware.setBeanFactory,
org.springframework.context.EnvironmentAware.setEnvironment,
org.springframework.context.EmbeddedValueResolverAware.setEmbeddedValueResolver,
org.springframework.context.ResourceLoaderAware.setResourceLoader,
org.springframework.context.ApplicationEventPublisherAware.setApplicationEventPublisher,org.springframework.context.MessageSourceAware.setMessageSource,
org.springframework.context.ApplicationContextAware.setApplicationContext,
org.springframework.web.context.ServletContextAware.setServletContext,
org.springframework.beans.factory.config.BeanPostProcessor.postProcessBeforeInitialization,
InitializingBean.afterPropertiesSet,
org.springframework.beans.factory.support.RootBeanDefinition.getInitMethodName,
org.springframework.beans.factory.config.BeanPostProcessor.postProcessAfterInitialization,
org.springframework.beans.factory.config.DestructionAwareBeanPostProcessor.postProcessBeforDestruction,
DisposableBean.destroy,
org.springframework.beans.factory.support.RootBeanDefinition.getDestroyMethodName

bean生命周期分析

从ClassPathXmlApplicationContext的构造函数开始作为入口分析：

整个容器初始化过程大致如图所示：

bean初始化准备工作：

在obtainFreshBeanFactory方法中先loadBeanDefinitions加载bean定义，然后创建beanFactory实例，以及其他一些系统必要组件的加载

开始生命周期

1. 如果有则调用BeanDefinitionRegistryPostProcessor接口的postProcessBeanDefinitionRegistry
2. 如果有则调用BeanFactoryPostProcessor的postProcessBeanFactory方法
3. 如果有则调用InstantiationAwareBeanPostProcessor接口的postProcessBeforeInstantiation前置方法
   一个使用代理创建bean的机会，如果返回null，则开始正式创建bean
   如果不为null，则调用postProcessAfterInitialization后置方法
4. 实例化bean
5. 如果有则调用MergedBeanDefinitionPostProcessor的postProcessMergedBeanDefinition方法
6. 填充bean属性
7. 开始标准bean的声明周期（initializeBean(...)方法里）

xxAware实现原理

以ApplicationContextAware为例：
其实还是利用BeanPostProcessor的能力，关键代码如下：

class ApplicationContextAwareProcessor implements BeanPostProcessor {

	@Override
	@Nullable
	public Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException {
		if (!(bean instanceof EnvironmentAware || bean instanceof EmbeddedValueResolverAware ||
				bean instanceof ResourceLoaderAware || bean instanceof ApplicationEventPublisherAware ||
				bean instanceof MessageSourceAware || bean instanceof ApplicationContextAware)){
			return bean;
		}

		AccessControlContext acc = null;

		if (System.getSecurityManager() != null) {
			acc = this.applicationContext.getBeanFactory().getAccessControlContext();
		}

		if (acc != null) {
			AccessController.doPrivileged((PrivilegedAction<Object>) () -> {
				invokeAwareInterfaces(bean);
				return null;
			}, acc);
		}
		else {
                        // 通过调用这个方法
			invokeAwareInterfaces(bean);
		}

		return bean;
	}

	private void invokeAwareInterfaces(Object bean) {
		if (bean instanceof EnvironmentAware) {
			((EnvironmentAware) bean).setEnvironment(this.applicationContext.getEnvironment());
		}
		if (bean instanceof EmbeddedValueResolverAware) {
			((EmbeddedValueResolverAware) bean).setEmbeddedValueResolver(this.embeddedValueResolver);
		}
		if (bean instanceof ResourceLoaderAware) {
			((ResourceLoaderAware) bean).setResourceLoader(this.applicationContext);
		}
		if (bean instanceof ApplicationEventPublisherAware) {
			((ApplicationEventPublisherAware) bean).setApplicationEventPublisher(this.applicationContext);
		}
		if (bean instanceof MessageSourceAware) {
			((MessageSourceAware) bean).setMessageSource(this.applicationContext);
		}
		if (bean instanceof ApplicationContextAware) {
			((ApplicationContextAware) bean).setApplicationContext(this.applicationContext);
		}
	}

}