一、前言
- Springboot源码解析是一件大工程，逐行逐句的去钻研代码，会很干燥，也不容易坚持下去。
- 咱们不谋求大而全，而是试着每次去钻研一个小知识点，最终聚沙成塔，这就是咱们的springboot源码管中窥豹系列。
二、ApplicationContextAware
- 假如咱们想应用某个bean, 如果是在@Component类上面，间接用@Autowired援用就行了
- 假如咱们想在某个静态方法外面用，就不能用下面的办法了
- 你可能想用new Bean()的形式，new一个，然而这个bean外面的@Autowired援用用不了
- 如果有一个动态的全局ApplicationContext就好了，用spring的能力获取bean: ApplicationContext.getBean(clazz)
- ApplicationContextAware就是这个用途
public interface ApplicationContextAware extends Aware { void setApplicationContext(ApplicationContext applicationContext) throws BeansException;}public interface Aware {}咱们写一个实现类：
import org.springframework.beans.BeansException;import org.springframework.context.ApplicationContext;import org.springframework.context.ApplicationContextAware;import org.springframework.stereotype.Component;@Componentpublic class SpringContextUtil implements ApplicationContextAware { private static ApplicationContext applicationContext; @Override public void setApplicationContext(ApplicationContext applicationContext) throws BeansException { SpringContextUtil.applicationContext = applicationContext; } private static ApplicationContext getApplicationContext() { return applicationContext; } public static <T> T getBean(Class<T> clazz){ return getApplicationContext().getBean(clazz); }}- 通过setApplicationContext，把applicationContext赋值到本地动态变量
- 通过ApplicationContext的getBean就能够在静态方法中应用任何bean的能力了
三、源码剖析
咱们进入SpringApplication的run办法：
public ConfigurableApplicationContext run(String... args) { ... try { ... refreshContext(context); ... } catch (Throwable ex) { ... } ... return context;}咱们进入refreshContext(context)外部：
public void refresh() throws BeansException, IllegalStateException { synchronized (this.startupShutdownMonitor) { // 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); try { // Allows post-processing of the bean factory in context subclasses. postProcessBeanFactory(beanFactory); // Invoke factory processors registered as beans in the context. invokeBeanFactoryPostProcessors(beanFactory); // Register bean processors that intercept bean creation. 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. finishBeanFactoryInitialization(beanFactory); // Last step: publish corresponding event. finishRefresh(); } catch (BeansException ex) { if (logger.isWarnEnabled()) { logger.warn("Exception encountered during context initialization - " + "cancelling refresh attempt: " + ex); } destroyBeans(); cancelRefresh(ex); throw ex; } finally { resetCommonCaches(); } }}这个refresh是spring的外围办法，当前会屡次用到，内容太多，咱们这次只关注一个办法：
- prepareBeanFactory(beanFactory);
public void refresh() throws BeansException, IllegalStateException { synchronized (this.startupShutdownMonitor) { ... // Prepare the bean factory for use in this context. prepareBeanFactory(beanFactory); ... }}咱们先看prepareBeanFactory(beanFactory)：
protected void prepareBeanFactory(ConfigurableListableBeanFactory beanFactory) { ... // Configure the bean factory with context callbacks. beanFactory.addBeanPostProcessor(new ApplicationContextAwareProcessor(this)); ... }咱们看一下这个addBeanPostProcessor办法
private final List<BeanPostProcessor> beanPostProcessors = new CopyOnWriteArrayList<>();@Overridepublic void addBeanPostProcessor(BeanPostProcessor beanPostProcessor) { Assert.notNull(beanPostProcessor, "BeanPostProcessor must not be null"); // Remove from old position, if any this.beanPostProcessors.remove(beanPostProcessor); // Track whether it is instantiation/destruction aware if (beanPostProcessor instanceof InstantiationAwareBeanPostProcessor) { this.hasInstantiationAwareBeanPostProcessors = true; } if (beanPostProcessor instanceof DestructionAwareBeanPostProcessor) { this.hasDestructionAwareBeanPostProcessors = true; } // Add to end of list this.beanPostProcessors.add(beanPostProcessor);}- 先remove,再add
- beanPostProcessors是一个线程平安的list: CopyOnWriteArrayList
- 咱们往下看看new ApplicationContextAwareProcessor(this)，留神：this是ApplicationContext
class ApplicationContextAwareProcessor implements BeanPostProcessor { private final ConfigurableApplicationContext applicationContext; private final StringValueResolver embeddedValueResolver; /** * Create a new ApplicationContextAwareProcessor for the given context. */ public ApplicationContextAwareProcessor(ConfigurableApplicationContext applicationContext) { this.applicationContext = applicationContext; this.embeddedValueResolver = new EmbeddedValueResolver(applicationContext.getBeanFactory()); } @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 { 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); } }}- 构造方法，把applicationContext设到本地变量上
- 实现接口的办法：postProcessBeforeInitialization，回调的时候会用，次要是校验权限
- 最上面的invokeAwareInterfaces是个公有的外围回调办法，依据不同类型，有不同回调
咱们看到除了ApplicationContextAware，还有其它的aware, 总共6个
- EnvironmentAware：环境变量
- EmbeddedValueResolverAware：值解析器
- ResourceLoaderAware：资源加载器
- ApplicationEventPublisherAware：事件公布器
- MessageSourceAware：信息处理器
- ApplicationContextAware：spring容器
比方咱们想用全局的环境变量，就有EnvironmentAware，想用spring的事件就用ApplicationEventPublisherAware，等等
- 起源找到了，ApplicationContextAwareProcessor什么时候执行的呢？
- 这个比拟麻烦，咱们前面单开一节再具体的去看。
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