Spring声明周期简单介绍

介绍

Spring生命周期

1.第一部分 Spring生命周期为BeanFactory的初始化,这部分内容主要是Spring MetaData的加载,即如何将定义的Bean从xml,Annotation,JavaBean这三种形式变成Spring能识别的BeanDefinitions.这里有一个很关键的回调接口,BeanFactoryPostProcessor,完成BeanFactory的初始前后会回调这个接口。
2.第二部分 Spring对BeanDefinitions解析的一个过程,完成IOC和AOP的过程,这里Bean初始化过程为如图所示:1.实例化(new 一个Bean) 2.属性赋值(完成依赖注入) 3.初始化(调用Bean的构造器等) 4.销毁(destory),与BeanFactoryPostProcessor对应,完成Bean声明周期回调的接口为BeanPostPorcessor。

Spring声明周期调用图

以一个例子介绍

```Java
 package it.caoxin.ioctest4_beanlifecycle.bean;

import org.springframework.beans.factory.DisposableBean;
import org.springframework.beans.factory.InitializingBean;
import org.springframework.stereotype.Component;

import javax.annotation.PostConstruct;
import javax.annotation.PreDestroy;

/**
 * 功能描述:控制Spring Bean的声明周期
 * The InitializingBean and DisposableBean callback interfaces
 * Custom init() and destroy() methods
 * The @PostConstruct and @PreDestroy annotations. You can combine these mechanisms to control a given bean.
 * 修改日期:2020/3/9
 * 修改描述:
 */
@Component
public class BeanLifeCycle implements InitializingBean, DisposableBean {
	public BeanLifeCycle() {
		System.out.println("--------------------1.Constractor");
	}

	@PostConstruct
	public void postConstruct() {
		System.out.println("---------------------2.postConstruct");
	}

	@Override
	public void afterPropertiesSet() throws Exception {
		// 对应的代码配置代码
		// 
		System.out.println("--------------------3.afterPropertiesSet");
	}

	@PreDestroy
	public void preDestory() {
		System.out.println("---------------------4.preDestory");
	}
	@Override
	public void destroy() throws Exception {
		// 对应的配置代码
		// 
		System.out.println("--------------------5.destory");
	}
}

```

-- 程序的执行结果为：从Spring.io中声明周期部分可以找到以下部分代码
--------------------1.Constractor
---------------------2.postConstruct
--------------------3.afterPropertiesSet
---------------------4.preDestory
--------------------5.destory

如何证明BeanFactory初始化时会回调生命周期回调接口呢?

-- 从上图中可以看到Interface BeanDefinitionResgisterPostProcessor是实现了Interface BeanPostProcessor，我们先增加两个类，一个类实现BeanDefinitionResgisterPostProcessor另外一个类是实现了BeanPostProcessor；代码如下
BeanPostProcessor接口实现类

```Java
@Component
public class BeanLifeBeanPostProcess implements BeanPostProcessor {
	@Override
	public Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException {
		System.out.println(beanName+"---------1.BeanLifeBeanPost before------");
		return bean;
	}

	@Override
	public Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException {
		System.out.println(beanName+"---------2.BeanLifeBeanPost after------");
		return bean;
	}
}
```

BeanDefinitionRegistryPostProcessor接口实现类

```Java
@Component
public class BeanLifeBeanDefinitionRegisterPostProcess implements BeanDefinitionRegistryPostProcessor {
	@Override
	public void postProcessBeanDefinitionRegistry(BeanDefinitionRegistry registry) throws BeansException {
		System.out.println("1.BeanFactory----------------");
	}

	@Override
	public void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory) throws BeansException {
		System.out.println("2.BeanFactory-----------------");
	}
}
```

观察程序程序执行的结果我们可以发现
1.BeanFactory----------------
2.BeanFactory-----------------
3.BeanFactory-----------------
-------------------1.Constractor
--------------------2.postConstruct
-------------------3.afterPropertiesSet
--------------------4.preDestory
-------------------5.destory
这里我们证明了Spring BeanFactory初始化的回调。

如何证明Bean初始化时会回调生命周期回调接口呢?

我们再写两个类
第一个BeanPostProcessor

``` Java
@Component
public class BeanLifeBeanPostProcess implements BeanPostProcessor {
	@Override
	public Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException {
		System.out.println(beanName+"---------1.BeanLifeBeanPost before------");
		return bean;
	}

	@Override
	public Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException {
		System.out.println(beanName+"---------2.BeanLifeBeanPost after------");
		return bean;
	}
}
```

第二个InstantiationAwareBeanPostProcessor

``` Java
    @Component
public class BeanLifeInitilaztionBeanPostProcess implements InstantiationAwareBeanPostProcessor {
	@Override
	public Object postProcessBeforeInstantiation(Class beanClass, String beanName) throws BeansException {
		System.out.println(beanName+"--------1.BeanInitilaztion before---------");
		return null;
	}

	@Override
	public boolean postProcessAfterInstantiation(Object bean, String beanName) throws BeansException {
		System.out.println(beanName+"--------2.BeanInitilaztion after---------");
		return true;
	}

	@Override
	public PropertyValues postProcessProperties(PropertyValues pvs, Object bean, String beanName) throws BeansException {
		System.out.println(beanName+"--------3.BeanInitilaztion propertyvalue---------");
		return null;
	}
}
```

程序运行结果
1.BeanFactory----------------
2.BeanFactory-----------------
3.BeanFactory-----------------
读者可以先不看appConfig
appConfig--------1.BeanInitilaztion before---------
appConfig--------2.BeanInitilaztion after---------
appConfig--------3.BeanInitilaztion propertyvalue---------
appConfig---------1.BeanLifeBeanPost before------
appConfig---------2.BeanLifeBeanPost after------
读者可以先不看appConfig
beanLifeCycle--------1.BeanInitilaztion before---------
-------------------1.Constractor
beanLifeCycle--------2.BeanInitilaztion after---------
beanLifeCycle--------3.BeanInitilaztion propertyvalue---------
beanLifeCycle---------1.BeanLifeBeanPost before------
---------------------2.postConstruct
--------------------3.afterPropertiesSet
beanLifeCycle---------2.BeanLifeBeanPost after------
---------------------4.preDestory
--------------------5.destory
最终的结果是:
1.BeanFactory----------------
2.BeanFactory-----------------
3.BeanFactory-----------------
beanLifeCycle--------1.BeanInitilaztion before---------
-------------------1.Constractor
beanLifeCycle--------2.BeanInitilaztion after---------
beanLifeCycle--------3.BeanInitilaztion propertyvalue---------
beanLifeCycle---------1.BeanLifeBeanPost before------
---------------------2.postConstruct
--------------------3.afterPropertiesSet
beanLifeCycle---------2.BeanLifeBeanPost after------
---------------------4.preDestory
--------------------5.destory
可以看出实现InstantiationAwareBeanPostProcessor的三个方法会先于BeanPostProcessor的三个方法执行并穿插在BeanLifeCycle中。这里分析一下BeanPostProcessor接口，大家可以使用Idea展示一下BeanPostProcessor，实现类众多其实大致可以分为三类：
第一类：
影响多个Bean接口；BeanPostProcessor接口用于用户自定义扩展，BeanPostProcessor执行阶段的源码穿插在Aware接口调用。
第二类：
只调用一次的接口
1.Aware接口顾名思义可以拿到资源如BeanNameAware接口，稍后Dubbo服务导出中会分析到。分类他们会在org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory#invokeAwareMethods中进行调用
一组
BeanNameAware 获取BeanDefinition的名字
BeanClassLoaderAware 获取类加载器
BeanFactoryAware 获取BeanFactory
二组
EnvironmentAware 获取Spring环境
ApplicationContextAware
ApplicationEventPulisherAware
MessageSoureAware
ResourceLoaderAware

最后介绍一个Spring源码中声明周期的大致调用链

org.springframework.context.support.AbstractApplicationContext#refresh中

```Java
// Allows post-processing of the bean factory in context subclasses.
	postProcessBeanFactory(beanFactory);

    // Invoke factory processors registered as beans in the context.
	// BeanFactoryProcessors调用点(重要)--1.ConfigurationClassPostProcessor
	invokeBeanFactoryPostProcessors(beanFactory);

	// Register bean processors that intercept bean creation.
	// 所有BeanPostProcessors注册的调用点
	registerBeanPostProcessors(beanFactory);
	
    // Initialize message source for this context.
	initMessageSource();

	// Initialize event multicaster for this context.
	initApplicationEventMulticaster();

	// Initialize other special beans in specific context subclasses.
	onRefresh();

	// Check for listener beans and register them.
	registerListeners();

	// Instantiate all remaining (non-lazy-init) singletons.
	// 实例化所有非懒加载的单例Bean的调用点(重要)
	finishBeanFactoryInitialization(beanFactory);

	// Last step: publish corresponding event.
	finishRefresh();
```

Bean的初始化流程在finishBeanFactoryInitialization中有兴趣的读者可以详细了解一下，具体创建Bean的过程在
org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory#doCreateBean中

 对应实例化阶段
```Java
	    // Instantiate the bean.
		BeanWrapper instanceWrapper = null;
		if (mbd.isSingleton()) {
			instanceWrapper = this.factoryBeanInstanceCache.remove(beanName);
		}
		if (instanceWrapper == null) {
			// 1.Bean声明周期 实例化阶段
			//  第2次调用PostProcessor
			instanceWrapper = createBeanInstance(beanName, mbd, args);
		}
```

 对应属性赋值阶段
```Java
			// 2.Bean声明周期 属性赋值阶段 平常所说的依赖注入就时在这个过程
			// 第5和第6次调用PostProcessor
			populateBean(beanName, mbd, instanceWrapper);
```

 对应初始化阶段
```Java
   			// 3.Bean声明周期 初始化阶段
			// 第7和第8次调用PostProcessor
			exposedObject = initializeBean(beanName, exposedObject, mbd);
```

 对应销毁阶段
```Java
   ApplicationConfigAnnotation context new ApplicationConfigAnnotation();
   context.close();
```

框架 Spring生命周期分析(1)