ApplicationContext容器的refresh过程

spring源代码
spring
发布日期:   2018-03-05
字数:   2.6k
阅读时间:   12 分钟

前言

在Spring框架中要说最重要的方法就是AbstrctApplicationContext.refresh()方法,在这个方法中完成对容器的刷新和bean对象的加载过程,下面就详细对这个方法进行分析;

refresh()方法概述

@Override
public void refresh() throws BeansException, IllegalStateException {
	synchronized (this.startupShutdownMonitor) {
		//1.1 准备此上下文以进行刷新.
		prepareRefresh();

		//2.1 告诉子类刷新内部bean工厂.(获取beanFactory)
		ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory();

		//2.2 准备在这种情况下使用的bean工厂.(对beanFactory进行预处理)
		prepareBeanFactory(beanFactory);

		try {
			//2.3 在上下文子类中对bean工厂进行后置处理.
			postProcessBeanFactory(beanFactory);

			//3.1 调用在上下文中注册为Bean的工厂处理器.
			invokeBeanFactoryPostProcessors(beanFactory);

			//3.2 注册拦截Bean创建的Bean处理器.
			registerBeanPostProcessors(beanFactory);

			//4.1 为此上下文初始化消息源.
			initMessageSource();

			//4.2 为此上下文初始化事件广播器.
			initApplicationEventMulticaster();

			//5.1 在特定上下文子类中初始化其他特殊bean.
			onRefresh();

			//6 检查侦听器bean并注册它们.
			registerListeners();

			//7 实例化所有剩余的（非延迟初始化）单例bean.
			finishBeanFactoryInitialization(beanFactory);

			//8 最后一步：发布相应事件.
			finishRefresh();
		}

		catch (BeansException ex) {
			if (logger.isWarnEnabled()) {
				logger.warn("Exception encountered during context initialization - " +
						"cancelling refresh attempt: " + ex);
			}

			// 销毁已创建的单例以避免资源悬空.
			destroyBeans();

			// 重置“active”标志
			cancelRefresh(ex);

			// Propagate exception to caller.
			throw ex;
		}

		finally {
			//自检并重置spring中缓存的bean的元数据，因为可能不在使用
			resetCommonCaches();
		}
	}
}

通过源代码可以看到AbstrctApplicationContext.refresh()方法分为8个步骤

  1. 准备环境上下文
  2. 创建准备beanFactory
  3. 处理前置扩展点(BeanFactoryPostProcessor/BeanPostProcessor)
  4. 事件广播
  5. onRefresh
  6. 注册监听器
  7. 实例化剩下的bean
  8. 发布事件

下面根据步骤进一步分析refresh()方法的具体操作;

准备环境上下文

配置应用刷新上下文环境的方法主要有prepareRefresh()、obtainFreshBeanFactory()、prepareBeanFactory(beanFactory)

prepareRefresh()

/*
 * 准备此上下文以进行刷新，设置其启动日期和
 * 活动标志，以及执行属性源的任何初始化.
 */
protected void prepareRefresh() {
	//切换到活动状态.
	this.startupDate = System.currentTimeMillis();
	this.closed.set(false);
	this.active.set(true);

	if (logger.isDebugEnabled()) {
		if (logger.isTraceEnabled()) {
			logger.trace("Refreshing " + this);
		}
		else {
			logger.debug("Refreshing " + getDisplayName());
		}
	}

	// 初始化ProperySources容器.
	initPropertySources();

	// 验证所有标记为必需的属性都是可解析的:
	// see ConfigurablePropertyResolver#setRequiredProperties
	getEnvironment().validateRequiredProperties();

	// ApplicationListeners设置为预处理
	if (this.earlyApplicationListeners == null) {
		this.earlyApplicationListeners = new LinkedHashSet<>(this.applicationListeners);
	}
	else {
		// 将ApplicationListeners重新设置成预处理状态.
		this.applicationListeners.clear();
		this.applicationListeners.addAll(this.earlyApplicationListeners);
	}

prepareRefresh()方法只是在清理上下文环境、设置启动事件以及初始化PropertySources容器等；
初始化PropertySources容器方法对应web应用底层是调用

WebApplicationContextUtils.initServletPropertySources(getPropertySources(), servletContext, servletConfig)

实现将servletContext, servletConfig加载到PropertySources容器中的

  • servletContext是web应用服务器为每一个应用创建的一个服务上下文对象
  • servletConfig是操作一个servlet中的配置属性的接口

创建准备beanFactory

obtainFreshBeanFactory()

obtainFreshBeanFactory()

protected ConfigurableListableBeanFactory obtainFreshBeanFactory() {
	refreshBeanFactory();
	return getBeanFactory();
}
  1. refreshBeanFactory()刷新beanFactory，底层是调用DefaultListableBeanFactory.setSerializationId()方法去刷新工厂集合
   //这里使用的是ConcurrentHashMap
private static final Map<String, Reference<DefaultListableBeanFactory>> serializableFactories =
		new ConcurrentHashMap<>(8);

public void setSerializationId(@Nullable String serializationId) {
	if (serializationId != null) {
           //注意这里使用的是WeakReference保证了并发安全性
		serializableFactories.put(serializationId, new WeakReference<>(this));
	}
	else if (this.serializationId != null) {
		serializableFactories.remove(this.serializationId);
	}
	this.serializationId = serializationId;
}
  1. getBeanFactory()方法不同的实现都是返回DefaultListableBeanFactory

prepareBeanFactory(beanFactory)

protected void prepareBeanFactory(ConfigurableListableBeanFactory beanFactory) {
	// 告诉内部bean工厂使用上下文的类加载器等.
	beanFactory.setBeanClassLoader(getClassLoader());
	beanFactory.setBeanExpressionResolver(new StandardBeanExpressionResolver(beanFactory.getBeanClassLoader()));
	beanFactory.addPropertyEditorRegistrar(new ResourceEditorRegistrar(this, getEnvironment()));

	// 使用上下文回调配置Bean工厂.
	beanFactory.addBeanPostProcessor(new ApplicationContextAwareProcessor(this));
	beanFactory.ignoreDependencyInterface(EnvironmentAware.class);
	beanFactory.ignoreDependencyInterface(EmbeddedValueResolverAware.class);
	beanFactory.ignoreDependencyInterface(ResourceLoaderAware.class);
	beanFactory.ignoreDependencyInterface(ApplicationEventPublisherAware.class);
	beanFactory.ignoreDependencyInterface(MessageSourceAware.class);
	beanFactory.ignoreDependencyInterface(ApplicationContextAware.class);

	// BeanFactory接口不在普通工厂中注册设置为可解析类型.
	// MessageSource注册为Bean（并发现用于自动装配）.
	beanFactory.registerResolvableDependency(BeanFactory.class, beanFactory);
	beanFactory.registerResolvableDependency(ResourceLoader.class, this);
	beanFactory.registerResolvableDependency(ApplicationEventPublisher.class, this);
	beanFactory.registerResolvableDependency(ApplicationContext.class, this);

	// 注册早期的后置处理器以将内部bean检测为ApplicationListeners.
	beanFactory.addBeanPostProcessor(new ApplicationListenerDetector(this));

	// 如果发现LoadTimeWeaver，请准备织入。
	if (beanFactory.containsBean(LOAD_TIME_WEAVER_BEAN_NAME)) {
		beanFactory.addBeanPostProcessor(new LoadTimeWeaverAwareProcessor(beanFactory));
		// Set a temporary ClassLoader for type matching.
		beanFactory.setTempClassLoader(new ContextTypeMatchClassLoader(beanFactory.getBeanClassLoader()));
	}

	// 注册默认环境bean.
	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());
	}
}

prepareBeanFactory(beanFactory)主要是给beanFactory设置各种预设的属性的

小结

在开始加载bean之前需要做三件事情：

  1. 清理环境，设置启动时间，装载servletContext和servletConfig
  2. 获取DefaultListableBeanFactory
  3. 给获取到的DefaultListableBeanFactory设置各种属性

处理前置扩展点

postProcessBeanFactory是用来在应用上下文中注册一些特殊的BeanPostProrecessors

GenericWebApplicationContext分析

  • 代码展示
@Override
	protected void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory) {
		if (this.servletContext != null) {
			beanFactory.addBeanPostProcessor(new ServletContextAwareProcessor(this.servletContext));
			beanFactory.ignoreDependencyInterface(ServletContextAware.class);
		}
		WebApplicationContextUtils.registerWebApplicationScopes(beanFactory, this.servletContext);
		WebApplicationContextUtils.registerEnvironmentBeans(beanFactory, this.servletContext);
	}
  1. ServletContextAwareProcessor
  • WebApplicationContextUtils.registerWebApplicationScopes(beanFactory, this.servletContext)
	public static void registerWebApplicationScopes(ConfigurableListableBeanFactory beanFactory,
		@Nullable ServletContext sc) {

	beanFactory.registerScope(WebApplicationContext.SCOPE_REQUEST, new RequestScope());
	beanFactory.registerScope(WebApplicationContext.SCOPE_SESSION, new SessionScope());
	if (sc != null) {
		ServletContextScope appScope = new ServletContextScope(sc);
		beanFactory.registerScope(WebApplicationContext.SCOPE_APPLICATION, appScope);
		// Register as ServletContext attribute, for ContextCleanupListener to detect it.
		sc.setAttribute(ServletContextScope.class.getName(), appScope);
	}

	beanFactory.registerResolvableDependency(ServletRequest.class, new RequestObjectFactory());
	beanFactory.registerResolvableDependency(ServletResponse.class, new ResponseObjectFactory());
	beanFactory.registerResolvableDependency(HttpSession.class, new SessionObjectFactory());
	beanFactory.registerResolvableDependency(WebRequest.class, new WebRequestObjectFactory());
	if (jsfPresent) {
		FacesDependencyRegistrar.registerFacesDependencies(beanFactory);
	}
}
  1. 主要是用于注册web应用程序bean的注册范围增加request、session、application
  • WebApplicationContextUtils.registerEnvironmentBeans(beanFactory, this.servletContext)
public static void registerEnvironmentBeans(ConfigurableListableBeanFactory bf,
		@Nullable ServletContext servletContext, @Nullable ServletConfig servletConfig) {

	if (servletContext != null && !bf.containsBean(WebApplicationContext.SERVLET_CONTEXT_BEAN_NAME)) {
		bf.registerSingleton(WebApplicationContext.SERVLET_CONTEXT_BEAN_NAME, servletContext);
	}

	if (servletConfig != null && !bf.containsBean(ConfigurableWebApplicationContext.SERVLET_CONFIG_BEAN_NAME)) {
		bf.registerSingleton(ConfigurableWebApplicationContext.SERVLET_CONFIG_BEAN_NAME, servletConfig);
	}
	//省略...
	bf.registerSingleton(WebApplicationContext.CONTEXT_PARAMETERS_BEAN_NAME,
		Collections.unmodifiableMap(parameterMap));
	}
	//省略...
	bf.registerSingleton(WebApplicationContext.CONTEXT_ATTRIBUTES_BEAN_NAME,
		Collections.unmodifiableMap(attributeMap));
	}
}
  1. 将servletContext、servletConfig、contextParameters、contextParameters注册到容器中

postProcessBeanFactory方法就是在bean初始化之前将一些特殊的bean注册到容器中去，从而完成接下来的初始化操作

invokeBeanFactoryPostProcessors

invokeBeanFactoryPostProcessors方法是执行实现BeanFactoryPostProcessor接口的方法

protected void invokeBeanFactoryPostProcessors(ConfigurableListableBeanFactory beanFactory) {
	PostProcessorRegistrationDelegate.invokeBeanFactoryPostProcessors(beanFactory,getBeanFactoryPostProcessors());

	// Detect a LoadTimeWeaver and prepare for weaving, if found in the meantime
	// (e.g. through an @Bean method registered by ConfigurationClassPostProcessor)
	if (beanFactory.getTempClassLoader() == null && beanFactory.containsBean(LOAD_TIME_WEAVER_BEAN_NAME)) {
		beanFactory.addBeanPostProcessor(new LoadTimeWeaverAwareProcessor(beanFactory));
		beanFactory.setTempClassLoader(new ContextTypeMatchClassLoader(beanFactory.getBeanClassLoader()));
	}
}

getBeanFactoryPostProcessors()中返回的bean是在初始化化环境prepareContext中加载的

invokeBeanFactoryPostProcessors的代码：

public static void invokeBeanFactoryPostProcessors(
		ConfigurableListableBeanFactory beanFactory, List<BeanFactoryPostProcessor> beanFactoryPostProcessors) {

	// Invoke BeanDefinitionRegistryPostProcessors first, if any.
	Set<String> processedBeans = new HashSet<>();

	if (beanFactory instanceof BeanDefinitionRegistry) {
		BeanDefinitionRegistry registry = (BeanDefinitionRegistry) beanFactory;
		List<BeanFactoryPostProcessor> regularPostProcessors = new ArrayList<>();
		List<BeanDefinitionRegistryPostProcessor> registryProcessors = new ArrayList<>();

		for (BeanFactoryPostProcessor postProcessor : beanFactoryPostProcessors) {
			if (postProcessor instanceof BeanDefinitionRegistryPostProcessor) {
				BeanDefinitionRegistryPostProcessor registryProcessor =
						(BeanDefinitionRegistryPostProcessor) postProcessor;
				registryProcessor.postProcessBeanDefinitionRegistry(registry);
				registryProcessors.add(registryProcessor);
			}
			else {
				regularPostProcessors.add(postProcessor);
			}
		}
		List<BeanDefinitionRegistryPostProcessor> currentRegistryProcessors = new ArrayList<>();

		// First, invoke the BeanDefinitionRegistryPostProcessors that implement PriorityOrdered.
		String[] postProcessorNames =
				beanFactory.getBeanNamesForType(BeanDefinitionRegistryPostProcessor.class, true, false);
		sortPostProcessors(currentRegistryProcessors, beanFactory);
		registryProcessors.addAll(currentRegistryProcessors);
		invokeBeanDefinitionRegistryPostProcessors(currentRegistryProcessors, registry);
		currentRegistryProcessors.clear();
		//省略....
		// Next, invoke the BeanDefinitionRegistryPostProcessors that implement Ordered.

		// Finally, invoke all other BeanDefinitionRegistryPostProcessors until no further ones appear.
		boolean reiterate = true;
		while (reiterate) {
			sortPostProcessors(currentRegistryProcessors, beanFactory);
			registryProcessors.addAll(currentRegistryProcessors);
			invokeBeanDefinitionRegistryPostProcessors(currentRegistryProcessors, registry);
			currentRegistryProcessors.clear();
		}

		// Now, invoke the postProcessBeanFactory callback of all processors handled so far.
		invokeBeanFactoryPostProcessors(registryProcessors, beanFactory);
		invokeBeanFactoryPostProcessors(regularPostProcessors, beanFactory);
		//省略....
	}

以上代码的作用就是

  1. 先处理BeanDefinitionRegistryPostProcessor，按照PriorityOrdered > Ordered > 普通的顺序一次执行postProcessBeanDefinitionRegistry方法；
  2. 再处理BeanFactoryPostProcessors，按照PriorityOrdered > Ordered > 普通的顺序一次执行postProcessBeanFactory方法；

小结

invokeBeanFactoryPostProcessors方法就是执行实现BeanDefinitionRegistryPostProcessor接口的postProcessBeanDefinitionRegistry以及执行实现BeanFactoryPostProcessors接口的postProcessBeanFactory方法

运行示例
3LvlRO.png

registerBeanPostProcessors分析

  • 代码示例
public static void registerBeanPostProcessors(
		ConfigurableListableBeanFactory beanFactory, AbstractApplicationContext applicationContext) {

	String[] postProcessorNames = beanFactory.getBeanNamesForType(BeanPostProcessor.class, true, false);

	// Register BeanPostProcessorChecker that logs an info message when
	// a bean is created during BeanPostProcessor instantiation, i.e. when
	// a bean is not eligible for getting processed by all BeanPostProcessors.
	int beanProcessorTargetCount = beanFactory.getBeanPostProcessorCount() + 1 + postProcessorNames.length;
	beanFactory.addBeanPostProcessor(new BeanPostProcessorChecker(beanFactory, beanProcessorTargetCount));

	// Separate between BeanPostProcessors that implement PriorityOrdered,
	// Ordered, and the rest.
	List<BeanPostProcessor> priorityOrderedPostProcessors = new ArrayList<>();
	List<BeanPostProcessor> internalPostProcessors = new ArrayList<>();
	List<String> orderedPostProcessorNames = new ArrayList<>();
	List<String> nonOrderedPostProcessorNames = new ArrayList<>();

	// First, register the BeanPostProcessors that implement PriorityOrdered.
	sortPostProcessors(priorityOrderedPostProcessors, beanFactory);
	registerBeanPostProcessors(beanFactory, priorityOrderedPostProcessors);

	//省略代码...
	// Next, register the BeanPostProcessors that implement Ordered.
	List<BeanPostProcessor> orderedPostProcessors = new ArrayList<>(orderedPostProcessorNames.size());
	sortPostProcessors(orderedPostProcessors, beanFactory);
	registerBeanPostProcessors(beanFactory, orderedPostProcessors);

	//省略代码...
	// Now, register all regular BeanPostProcessors.
	List<BeanPostProcessor> nonOrderedPostProcessors = new ArrayList<>(nonOrderedPostProcessorNames.size());
	registerBeanPostProcessors(beanFactory, nonOrderedPostProcessors);

	//省略代码...
	// Re-register post-processor for detecting inner beans as ApplicationListeners,
	// moving it to the end of the processor chain (for picking up proxies etc).
	beanFactory.addBeanPostProcessor(new ApplicationListenerDetector(applicationContext));
}

主要是往beanFactory中注册BeanProcessor的实现，在beanFactory中是用CopyOnWriteArrayList来作为缓存容器的。

/** AbstractBeanFactory内部是用CopyOnWriteArrayList来保证安全性的 */
private final List<BeanPostProcessor> beanPostProcessors = new CopyOnWriteArrayList<>();

事件广播

initMessageSource()

initMessageSource是初始化消息源的，也就是进行初始化国际化配置相关的

initApplicationEventMulticaster

initApplicationEventMulticaster进行初始化事件发布器。beanFactory中存在ApplicationEventMulticaster就进行注册，没有就注册SimpleApplicationEventMulticaster。

onRefresh()

onRefresh,用于子类实现容器refresh的过程中执行其他特殊操作，这是一个模板方法，允许子类去扩展

注册监听器

registerListeners注册监听器

protected void registerListeners() {
	// 首先注册指定的静态侦听器.
	for (ApplicationListener<?> listener : getApplicationListeners()) {
		getApplicationEventMulticaster().addApplicationListener(listener);
	}

	// 不要在这里初始化FactoryBeans：我们需要保留所有常规bean
	//否则后置处理器将无法对他们进行处理!
	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);
		}
	}
}

实例化剩下的bean

finishBeanFactoryInitialization(beanFactory)实列化剩下的bean,这个方法也是绝大多数bean初始化的方式。这个方法的解析放在下一篇文章

发布事件

finishRefresh完成容器的刷新

protected void finishRefresh() {
	// 清除上下文级别的资源缓存（例如来自扫描的ASM元数据）.
	clearResourceCaches();

	// 为容器初始化处理器.注册一个LifecycleProcessor
	initLifecycleProcessor();

	// 对生命周期处理器进行刷新.
	getLifecycleProcessor().onRefresh();

	// 广播容器初始化完成的消息.
	publishEvent(new ContextRefreshedEvent(this));

	// 先LiveBeanView中注册ApplicationContext.
	LiveBeansView.registerApplicationContext(this);
}

initLifecycleProcessor容器执行容器初始化周期过程中的控制

  • 代码运行
    3OuocQ.png

总结

  1. 配置资源初始化环境
    1. 清理环境，设置启动时间，装载servletContext和servletConfig
    2. 获取DefaultListableBeanFactory
    3. 给DefaultListableBeanFactory设置各种属性
  2. postProcessBeanFactory()
    1. 注册ServletContextAwareProcessor
    2. 主要是用于注册web应用程序bean的注册范围增加request、session、application
    3. 将servletContext、servletConfig、contextParameters、contextParameters注册到容器中
  3. invokeBeanFactoryPostProcessors()
    1. 先处理BeanDefinitionRegistryPostProcessor，按照PriorityOrdered > Ordered > 普通的顺序一次执行postProcessBeanDefinitionRegistry方法
    2. 再处理BeanFactoryPostProcessors，按照PriorityOrdered > Ordered > 普通的顺序一次执行postProcessBeanFactory方法
  4. registerBeanPostProcessors()
    1. 往beanFactory中注册BeanProcessor的实现
  5. initMessageSource进行国际化配置处理
  6. initApplicationEventMulticaster进行初始化事件发布器。beanFactory中存在ApplicationEventMulticaster就进行注册，没有就注册SimpleApplicationEventMulticaster
  7. onRefresh,用于子类实现容器refresh的过程中执行其他特殊操作，这是一个模板方法，允许子类去扩展
  8. registerListeners注册监听器
  9. finishBeanFactoryInitialization()加载bean
  10. finishRefresh完成容器的刷新
  • 流程图
    3OMqYV.png

参考资料

spring源代码
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