Spring啓動和Bean建立過程當中的可擴展接口

時間 2019-11-24

標籤 spring 啓動 bean 建立過程當中可擴展接口欄目 Spring 简体版

原文原文鏈接

1.前言

Spring中有一些能夠擴展的接口，能夠用來在工做中更深度的使用Spring，這些接口大多分佈在AbstractApplicationContext.refresh() 和 AbstractAutowireCapableBeanFactory.createBean()這兩個方法的執行過程當中。java

2.AbstractApplicationContext.refresh()

2.1 refresh()簡介

AbstractApplicationContext.refresh()是Spring環境啓動過程當中的一個重要方法，此方法中實例化了全部的bean，任何ApplicationContext的實現，都須要調用此方法。spring

如上圖所示，Spring中，全部的ApplicationContext，都繼承於AbstractApplicationContext。

爲節省篇幅，僅將要分析的幾個方法代碼片斷抽取出來，refresh()的所有實現可查看源碼中的AbstractApplicationContext.refresh()方法。app

// Prepare this context for refreshing.
prepareRefresh();

// Tell the subclass to refresh the internal bean factory.
ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory();

// Prepare the bean factory for use in this context.
prepareBeanFactory(beanFactory);

// Invoke factory processors registered as beans in the context.
invokeBeanFactoryPostProcessors(beanFactory);

// Register bean processors that intercept bean creation.
registerBeanPostProcessors(beanFactory);

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

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

調用了initPropertySources,初始化資源，如屬性文件中的佔位符等。由子類實現，如AbstractRefreshableWebApplicationContext。post

2.3 obtainFreshBeanFactory()

獲取ConfigurableListableBeanFactory:this

protected ConfigurableListableBeanFactory obtainFreshBeanFactory() {
	refreshBeanFactory();
	ConfigurableListableBeanFactory beanFactory = getBeanFactory();
	if (logger.isDebugEnabled()) {
		logger.debug("Bean factory for " + getDisplayName() + ": " + beanFactory);
	}
	return beanFactory;
}
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此方法中主要執行兩部分流程：spa

2.3.1 調用refreshBeanFactory()

調用抽象方法refreshBeanFactory()，由子類AbstractRefreshableApplicationContext實現，代碼片斷以下：debug

DefaultListableBeanFactory beanFactory = createBeanFactory();
beanFactory.setSerializationId(getId());
customizeBeanFactory(beanFactory);
loadBeanDefinitions(beanFactory);  //讀取xml,註冊BeanDefinition。
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loadBeanDefinitions是AbstractRefreshableApplicationContext的一個抽象方法，由其子類AbstractXmlApplicationContext實現，詳細瞭解AbstractXmlApplicationContext可參考Spring自定義配置的源碼解析與實現3d

2.3.2 調用getBeanFactory()

調用抽象方法getBeanFactory()，由子類AbstractRefreshableApplicationContext實現，返回一個接口ConfigurableListableBeanFactory的實現類DefaultListableBeanFactory的實例。代理

這個DefaultListableBeanFactory實例，由上面的refreshBeanFactory()中調用createBeanFactory()建立。code

2.4 prepareBeanFactory

配置ConfigurableListableBeanFactory。

ConfigurableListableBeanFactory繼承了BeanFactory，實現類是DefaultListableBeanFactory。

protected void prepareBeanFactory(ConfigurableListableBeanFactory beanFactory){....}

2.4.1 設置classLoader:

beanFactory.setBeanClassLoader(getClassLoader());

經過org.springframework.util.ClassUtils.getDefaultClassLoader()獲取ClassLoader。

2.4.2 建立ApplicationContextAwareProcessor

beanFactory.addBeanPostProcessor(new ApplicationContextAwareProcessor(this));

建立ApplicationContextAwareProcessor對象，而且添加到DefaultListableBeanFactory中。

ApplicationContextAwareProcessor實現了BeanPostProcessor，並在實現的BeanPostProcessor.postProcessBeforeInitialization中，定義了對一些列對org.springframework.beans.factory.Aware子接口的處理。

注：這裏只是添加了BeanPostProcessor，但並未執行。

private void invokeAwareInterfaces(Object bean) {
    if (bean instanceof Aware) {
		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);
		}
	}
}
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在後續建立Bean的流程中，會執行全部的BeanPostProcessor，也就是會執行ApplicationContextAwareProcessor.postProcessBeforeInitialization設置各類Aware接口。

2.4.3 設置默認的上下文bean

註冊Spring自身使用的一些Bean：

// Register default environment beans.
		if (!beanFactory.containsLocalBean(ENVIRONMENT_BEAN_NAME)) {
			beanFactory.registerSingleton(ENVIRONMENT_BEAN_NAME, getEnvironment());
		}
		if (!beanFactory.containsLocalBean(SYSTEM_PROPERTIES_BEAN_NAME)) {
			beanFactory.registerSingleton(SYSTEM_PROPERTIES_BEAN_NAME, getEnvironment().getSystemProperties());
		}
		if (!beanFactory.containsLocalBean(SYSTEM_ENVIRONMENT_BEAN_NAME)) {
			beanFactory.registerSingleton(SYSTEM_ENVIRONMENT_BEAN_NAME, getEnvironment().getSystemEnvironment());
		}
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其中：

String ENVIRONMENT_BEAN_NAME = "environment";
String SYSTEM_PROPERTIES_BEAN_NAME = "systemProperties";
String SYSTEM_ENVIRONMENT_BEAN_NAME = "systemEnvironment";
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2.5 invokeBeanFactoryPostProcessors

調用全部的 BeanFactoryPostProcessor.postProcessBeanFactory。 PostProcessorRegistrationDelegate.invokeBeanFactoryPostProcessors(beanFactory, getBeanFactoryPostProcessors());

public static void invokeBeanFactoryPostProcessors( ConfigurableListableBeanFactory beanFactory, List<BeanFactoryPostProcessor> beanFactoryPostProcessors){....}
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2.6 registerBeanPostProcessors

註冊全部的BeanPostProcessor

protected void registerBeanPostProcessors(ConfigurableListableBeanFactory beanFactory) {
		PostProcessorRegistrationDelegate.registerBeanPostProcessors(beanFactory, this);
	}
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2.7 initApplicationEventMulticaster

初始化ApplicationEventMulticaster，實現類是SimpleApplicationEventMulticaster。

this.applicationEventMulticaster = new SimpleApplicationEventMulticaster(beanFactory);
beanFactory.registerSingleton(APPLICATION_EVENT_MULTICASTER_BEAN_NAME, this.applicationEventMulticaster);
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public static final String APPLICATION_EVENT_MULTICASTER_BEAN_NAME = "applicationEventMulticaster";

2.8 registerListeners

向ApplicationEventMulticaster註冊ApplicationListner。

/** * Add beans that implement ApplicationListener as listeners. * Doesn't affect other listeners, which can be added without being beans. */
	protected void registerListeners() {
		// Register statically specified listeners first.
		for (ApplicationListener<?> listener : getApplicationListeners()) {
			getApplicationEventMulticaster().addApplicationListener(listener);
		}

		// Do not initialize FactoryBeans here: We need to leave all regular beans
		// uninitialized to let post-processors apply to them!
		String[] listenerBeanNames = getBeanNamesForType(ApplicationListener.class, true, false);
		for (String listenerBeanName : listenerBeanNames) {
			getApplicationEventMulticaster().addApplicationListenerBean(listenerBeanName);
		}

		// Publish early application events now that we finally have a multicaster...
		Set<ApplicationEvent> earlyEventsToProcess = this.earlyApplicationEvents;
		this.earlyApplicationEvents = null;
		if (earlyEventsToProcess != null) {
			for (ApplicationEvent earlyEvent : earlyEventsToProcess) {
				getApplicationEventMulticaster().multicastEvent(earlyEvent);
			}
		}
	}
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3 AbstractAutowireCapableBeanFactory.createBean()

3.1 DefaultListableBeanFactory

如上圖所示， DefaultListableBeanFactory是ListableBeanFactory和BeanDefinitionRegistry的默認實現，是全部BeanFactory的始祖。最終建立bean的，是它的直接父類AbstractAutowireCapableBeanFactory.createBean 。

3.2 createBean

protected Object createBean(String beanName, RootBeanDefinition mbd, Object[] args) throws BeanCreationException {....}

主要執行了兩個方法：

Object bean = resolveBeforeInstantiation(beanName, mbdToUse); 執行了InstantiationAwareBeanPostProcessor，這個接口是BeanPostProcessor的子類，接口文檔提到爲內部使用。
Object beanInstance = doCreateBean(beanName, mbdToUse, args);

3.3 AbstractAutowireCapableBeanFactory.doCreateBean

3.3.1 createBeanInstance

BeanWrapper createBeanInstance(String beanName, RootBeanDefinition mbd, Object[] args) 主要作了如下工做：

Class<?> beanClass = resolveBeanClass(mbd, beanName); 根據beanName加載class；
BeanWrapper instantiateBean(final String beanName, final RootBeanDefinition mbd);
getInstantiationStrategy().instantiate(RootBeanDefinition bd, String beanName, BeanFactory owner)生成bean實例，InstantiationStrategy默認的實現爲CglibSubclassingInstantiationStrategy；
使用BeanWrapper的實現類BeanWrapperImpl封裝上面實例化的對象；
使用initBeanWrapper(BeanWrapper bw)處理後返回。

3.3.2 populateBean

populateBean(String beanName, RootBeanDefinition mbd, BeanWrapper bw) 根據BeanDefinition爲BeanWrapper封裝的bean代理對象設置屬性值。設置的方式，是建立了BeanDefinitionValueResolver對象，並BeanDefinitionValueResolver.resolveValueIfNecessary實現。resolveValueIfNecessary執行了一系列判斷和遞歸調用，將屬性值填充。

3.3.3 initializeBean

Object initializeBean(final String beanName, final Object bean, RootBeanDefinition mbd)

1 invokeAwareMethods : 執行 BeanNameAware, BeanClassLoaderAware , BeanFactoryAware
2 applyBeanPostProcessorsBeforeInitialization: 調用了全部BeanPostProcessor的postProcessBeforeInitialization方法。
3 invokeInitMethods:
- 1）執行 InitializingBean.afterPropertiesSet；
- 2）執行 init-method;
4 applyBeanPostProcessorsAfterInitialization: 執行全部的 BeanPostProcessor 的 postProcessAfterInitialization方法。

3.3.4 registerDisposableBeanIfNecessary

註冊Bean銷燬事件。 protected void registerDisposableBeanIfNecessary(String beanName, Object bean, RootBeanDefinition mbd)

1 執行 DisposableBean.destroy();
2 執行destroy-method；

4 總結

4.1 **Aware

實現**Aware類的接口，用於獲取到Spring環境中的各類信息或對象：

經常使用的有：

ApplicationContextAware：獲取當前的ApplicationContext；
BeanNameAware：獲取當前的beanName;
BeanClassLoaderAware：獲取當前的ClassLoader;
BeanFactoryAware：獲取當前的BeanFactory;
ApplicationEventPublisherAware：獲取當前的ApplicationEventPublisher，用於發佈事件；要接收事件的類能夠實現ApplicationListener接口，並實現其中的onApplicationEvent方法。

其餘還有：