spring 5.0.x源码学习系列二: 从AnnotationConfigApplicationContext开始，进入spring世界

揭开AnnotationConfigApplicationContext类运行的神秘面纱

一、运行大致流程图

二、解析

2.1 无参构造方法

• AnnotationConfigApplicationContext无参构造方法

  	public AnnotationConfigApplicationContext() {
  		// 在执行此行代码之前, 先执行了父类的构造方法
  		// 此段代码做的事情:
  		// 1. 初始化bean工厂
  		// 2. 初始化一个注解BeanDefinition读取器
  		// 3. 将spring内置的6个类封装成RootBeanDefinition并注册到bean工厂, 
  		// 具体是哪6个类可以查看上述的原理图
  		this.reader = new AnnotatedBeanDefinitionReader(this);
  
  		// 并没啥用, 虽然ClassPathBeanDefinitionScanner
  		// 类的作用是扫描@ComponentScan注解提供的包路径。
  		// 但实际上它并没有做扫描工作, spring内部扫描路径
  		// 的时候, 是在内部新new了一个ClassPathBeanDefinitionScanner,
  		// 这个属性目前没啥用, 当然我们可以获取这个对象
  		// 调用它的scan方法, 但是没有必要! 因为
  		// @ComponentScan可以支持多个扫描路径。 
  		// 那这个类有什么用呢？跟刚刚的解释一样, 
  		// 我们可以自己new一个ClassPathBeanDefinitionScanner对象或者扩展他, 
  		// 利用它的扫描功能(因为它是使用ASM来扫描的)
  		// Mybatis源码中就是自己扩展了
  		// ClassPathBeanDefinitionScanner类
  		this.scanner = new ClassPathBeanDefinitionScanner(this);
  	}
  

  • AnnotationConfigApplicationContext父类GenericApplicationContext无参构造方法

  	public GenericApplicationContext() {
  	    // 实例化spring bean工厂: DefaultListableBeanFactory
  		this.beanFactory = new DefaultListableBeanFactory();
  	}
  

  • 注册spring内置的6个bean至bean工厂代码:org.springframework.context.annotation.AnnotationConfigUtils#registerAnnotationConfigProcessors(org.springframework.beans.factory.support.BeanDefinitionRegistry, java.lang.Object)

  public static Set<BeanDefinitionHolder> registerAnnotationConfigProcessors(
  			BeanDefinitionRegistry registry, @Nullable Object source) {
  		// 解析传入的registry, 获取bean工厂, 
  		// 根据调用链或debug可知, 它就是
  		// AnnotationConfigApplicationContext上下文, 
  		// 因为它的父类GenericApplicationContext维护了一个bean工厂, 
  		// 并提供了get方法, 那么它自然也能拥有bean工厂
  		DefaultListableBeanFactory beanFactory = unwrapDefaultListableBeanFactory(registry);
  		if (beanFactory != null) {
  			if (!(beanFactory.getDependencyComparator() instanceof AnnotationAwareOrderComparator)) {
  				beanFactory.setDependencyComparator(AnnotationAwareOrderComparator.INSTANCE);
  			}
  			if (!(beanFactory.getAutowireCandidateResolver() instanceof ContextAnnotationAutowireCandidateResolver)) {
  				beanFactory.setAutowireCandidateResolver(new ContextAnnotationAutowireCandidateResolver());
  			}
  		}
  
  		// 无啥用, 虽然方法返回了它, 但调用处压根没接收这个返回值
  		Set<BeanDefinitionHolder> beanDefs = new LinkedHashSet<>(8);
  
  		if (!registry.containsBeanDefinition(CONFIGURATION_ANNOTATION_PROCESSOR_BEAN_NAME)) {
  			RootBeanDefinition def = new RootBeanDefinition(ConfigurationClassPostProcessor.class);
  			def.setSource(source);
  			beanDefs.add(registerPostProcessor(registry, def, CONFIGURATION_ANNOTATION_PROCESSOR_BEAN_NAME));
  		}
  
  		if (!registry.containsBeanDefinition(AUTOWIRED_ANNOTATION_PROCESSOR_BEAN_NAME)) {
  			RootBeanDefinition def = new RootBeanDefinition(AutowiredAnnotationBeanPostProcessor.class);
  			def.setSource(source);
  			beanDefs.add(registerPostProcessor(registry, def, AUTOWIRED_ANNOTATION_PROCESSOR_BEAN_NAME));
  		}
  
  		if (!registry.containsBeanDefinition(REQUIRED_ANNOTATION_PROCESSOR_BEAN_NAME)) {
  			RootBeanDefinition def = new RootBeanDefinition(RequiredAnnotationBeanPostProcessor.class);
  			def.setSource(source);
  			beanDefs.add(registerPostProcessor(registry, def, REQUIRED_ANNOTATION_PROCESSOR_BEAN_NAME));
  		}
  
  		// Check for JSR-250 support, and if present add the CommonAnnotationBeanPostProcessor.
  		if (jsr250Present && !registry.containsBeanDefinition(COMMON_ANNOTATION_PROCESSOR_BEAN_NAME)) {
  			RootBeanDefinition def = new RootBeanDefinition(CommonAnnotationBeanPostProcessor.class);
  			def.setSource(source);
  			beanDefs.add(registerPostProcessor(registry, def, COMMON_ANNOTATION_PROCESSOR_BEAN_NAME));
  		}
  
  		// Check for JPA support, and if present add the PersistenceAnnotationBeanPostProcessor.
  		if (jpaPresent && !registry.containsBeanDefinition(PERSISTENCE_ANNOTATION_PROCESSOR_BEAN_NAME)) {
  			RootBeanDefinition def = new RootBeanDefinition();
  			try {
  				def.setBeanClass(ClassUtils.forName(PERSISTENCE_ANNOTATION_PROCESSOR_CLASS_NAME,
  						AnnotationConfigUtils.class.getClassLoader()));
  			}
  			catch (ClassNotFoundException ex) {
  				throw new IllegalStateException(
  						"Cannot load optional framework class: " + PERSISTENCE_ANNOTATION_PROCESSOR_CLASS_NAME, ex);
  			}
  			def.setSource(source);
  			beanDefs.add(registerPostProcessor(registry, def, PERSISTENCE_ANNOTATION_PROCESSOR_BEAN_NAME));
  		}
  
  		if (!registry.containsBeanDefinition(EVENT_LISTENER_PROCESSOR_BEAN_NAME)) {
  			RootBeanDefinition def = new RootBeanDefinition(EventListenerMethodProcessor.class);
  			def.setSource(source);
  			beanDefs.add(registerPostProcessor(registry, def, EVENT_LISTENER_PROCESSOR_BEAN_NAME));
  		}
  
  		if (!registry.containsBeanDefinition(EVENT_LISTENER_FACTORY_BEAN_NAME)) {
  			RootBeanDefinition def = new RootBeanDefinition(DefaultEventListenerFactory.class);
  			def.setSource(source);
  			beanDefs.add(registerPostProcessor(registry, def, EVENT_LISTENER_FACTORY_BEAN_NAME));
  		}
  
  		return beanDefs;
  	}
  

2.2 register方法

• 源码

  	 /**
  	 * 传入的是一个被注解类的Class数组, 可以是配置类也可以是普通类
  	 * (什么叫配置类什么叫普通类, 在后续的源码系列中会更新)
  	 * @param annotatedClasses one or more annotated classes
  	 */
  	public void register(Class<?>... annotatedClasses) {
  		Assert.notEmpty(annotatedClasses, "At least one annotated class must be specified");
  		// 此处用到了构造方法new出来的AnnotatedBeanDefinitionReader, 
  		// 这里解释下, 为什么能用这个类来将传入的类注册到bean工厂中: 因为它内
  		// 部维护了一个registry, 这个registry就是AnnotationConfigApplicationContext
  		this.reader.register(annotatedClasses);
  	}
  

• 作用: 将传入的被注解的类以AnnotatedGenericBeanDefinition的类型注册到bean工厂。 至此， 还没有一个bean被创建出来。以下为注册AnnotatedGenericBeanDefinition的具体代码逻辑, 可以看到注册bean调用了这个方法: registerBeanDefinition(这个方法很重要. 后续注册beanDefinition到bean工厂基本上都会用到这个方法)
  

2.3 refresh方法

• 这个方法可以说是spring的核心入口方法了, 在内部做了太多太多的事情。

• 源码(每行代码执行意义在注释中有写到, 先使用黑箱理论, 大致了解它是干啥的, 具体先解析到invokeBeanFactoryPostProcessors此方法, 后续的方法还没往后读, 以后补充):

  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.
  		// 这个方法执行完成, spring的bean单例容器中会存在三个bean,
  		// 分别是systemEnvironment, environment, systemProperties
  		prepareBeanFactory(beanFactory);
  
  		try {
  			// 该方法没有做任何事, 内部无任何逻辑
  			postProcessBeanFactory(beanFactory);
  
  			// 调用后置处理器, 此方法太重要了, 调用过程参考下图		
  			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);
  			}
  
  			// Destroy already created singletons to avoid dangling resources.
  			destroyBeans();
  
  			// Reset 'active' flag.
  			cancelRefresh(ex);
  
  			// Propagate exception to caller.
  			throw ex;
  		}
  
  		finally {
  			// Reset common introspection caches in Spring's core, since we
  			// might not ever need metadata for singleton beans anymore...
  			resetCommonCaches();
  		}
  	}
  }
  

• invokeBeanFactoryPostProcessors方法运行原理图, 该方法大致包含: 调用手动添加的BeanFactoryPostProcessor后置处理器、调用spring内置后置处理器ConfigrationClassPostProcessor, 主要解析配置类、给全注解类添加cglib代理等等这里先把它晒出来, 后续再详细
  

三、小结

• 上述为本次博客内容
• github地址: https://github.com/AvengerEug
• I am a slow walker, but I never walk backwards.