Spring 三大生命周期

简介（What）

与大多数框架一样，Spring也提供了其生命周期回调，以方便开发者Spring的默认行为进行修改或扩展。

Spring将整个生命周期划分为以下三大类：

生命周期类型 描述 回调接口对象
SpringApplicaton Spring 应用程序 SpringApplicationRunListener
BeanFactory Bean工厂 BeanFactoryPostProcessor
Bean Bean对象 BeanPostProcessor

SpringApplication

SpringApplication是Spring Boot提供的可以从Java main方法直接启动Spring容器的类，使用方法如下：

@SpringBootApplication
public class MySpringApplication{
    public static void main(String[] args){
        SpringApplication.run(MySpringApplication.class,args);
    }
}

SpringApplication将应用的启动过程run()拆分为以下几个阶段：

graph LR
    starting --> environmentPrepared --> contextPrepared --> contextLoaded --> started --> running --> failed

并提供了SpringApplicationRunListener回调接口用于监听上述生命周期，SpringApplicationRunListener的实现需要声明在/META-INF/spring.factories文件中以被SpringApplication加载。

Spring提供了一个内置的实现类EventPublishingRunListener，用于发布ApplicationEvent事件，各个回调对应的具体事件对象如下：

方法 Event 描述
starting ApplicationStartingEvent 应用启动
environmentPrepared ApplicationEnvironmentPreparedEvent 环境准备好
contextPrepared ApplicationContextInitializedEvent 容器准备好
contextLoaded ApplicationPreparedEvent 容器加载完成
started ApplicationStartedEvent 应用启动完成
running ApplicationReadyEvent 应用运行中
failed ApplicationFailedEvent 应用启动失败

BeanFactoryPostProcessor

BeanFacotry是Spring容器的核心接口，ApplicationContext也实现了该接口：

classDiagram
	BeanFacotry <-- ListableBeanFactory
	BeanFacotry <-- HierarchicalBeanFactory
	ListableBeanFactory <-- ApplicationContext
	HierarchicalBeanFactory <-- ApplicationContext
类 方法 描述  
BeanDefinitionRegistryPostProcessor postProcessBeanDefinitionRegistry(BeanDefinitionRegistry registry)    
BeanFactoryPostProcessor postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory)    

BeanPostProcessor

类 方法 描述  
InstantiationAwareBeanPostProcessor postProcessBeforeInstantiation(beanClass, beanName) 自定义创建对象，如AOP  
InstantiationAwareBeanPostProcessor postProcessAfterInitialization(result, beanName) 当对象被创建后回调  
SmartInstantiationAwareBeanPostProcessor determineCandidateConstructors(beanClass, beanName) 推断构造方法，如@Autowried  
MergedBeanDefinitionPostProcessor postProcessMergedBeanDefinition(mbd, beanType, beanName)    
SmartInstantiationAwareBeanPostProcessor getEarlyBeanReference(exposedObject, beanName)    
InstantiationAwareBeanPostProcessor postProcessAfterInstantiation(bw.getWrappedInstance(), beanName)    
InstantiationAwareBeanPostProcessor postProcessProperties(pvs, bw.getWrappedInstance(), beanName)    
InstantiationAwareBeanPostProcessor postProcessPropertyValues(pvs, filteredPds, bw.getWrappedInstance(), beanName)    
BeanPostProcessor postProcessBeforeInitialization(result, beanName)    
BeanPostProcessor postProcessAfterInitialization(result, beanName)    
DestructionAwareBeanPostProcessor requiresDestruction(bean)