揭开AnnotationConfigApplicationContext类运行的神秘面纱

一、运行大致流程图 在这里插入图片描述

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)
  

  在这里插入图片描述

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
  

  在这里插入图片描述

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.