Spring源码-BeanFactoryPostProcessor

查看构造函数

public AnnotationConfigApplicationContext() {
   // 继续查看这步
   this.reader = new AnnotatedBeanDefinitionReader(this); 
   this.scanner = new ClassPathBeanDefinitionScanner(this);
}

/**
* 可以看出，将自身转换为BeanDefinitionRegistry，
* 这说明AnnotationConfigApplicationContext实现了BeanDefinitionRegistry接口
*/
public AnnotatedBeanDefinitionReader(BeanDefinitionRegistry registry) {
    this(registry, getOrCreateEnvironment(registry));
}

public AnnotatedBeanDefinitionReader(BeanDefinitionRegistry registry, Environment environment) {
    Assert.notNull(registry, "BeanDefinitionRegistry must not be null");
    Assert.notNull(environment, "Environment must not be null");
    this.registry = registry;
    this.conditionEvaluator = new ConditionEvaluator(registry, environment, null);
    // 这一行是查看reader的关键，它将定义了最初的几个Bean的后置处理器
    AnnotationConfigUtils.registerAnnotationConfigProcessors(this.registry);
}

public static void registerAnnotationConfigProcessors(BeanDefinitionRegistry registry) {
    registerAnnotationConfigProcessors(registry, null);
}

public static Set<BeanDefinitionHolder> registerAnnotationConfigProcessors(
            BeanDefinitionRegistry registry, @Nullable Object source) {
    // 获取BeanFacotry,即DefaultListableBeanFactory
    DefaultListableBeanFactory beanFactory = unwrapDefaultListableBeanFactory(registry);
    Set<BeanDefinitionHolder> beanDefs = new LinkedHashSet<>(8);
    if (!registry.containsBeanDefinition(CONFIGURATION_ANNOTATION_PROCESSOR_BEAN_NAME)) {
        //添加ConfigurationClassPostProcessor后置处理器，它是工厂级的后置处理器，它实现了BeanDefinitionRegistryPostProcessor，它继承了了BeanFactoryPostProcessor，后面的重点也会集中在这个后置处理器上。
        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)) {
        // 名字是不是很熟悉，自动注入后置处理器，它是Bean级别的，实现了自动注入
        RootBeanDefinition def = new RootBeanDefinition(AutowiredAnnotationBeanPostProcessor.class);
        def.setSource(source);
        beanDefs.add(registerPostProcessor(registry, def, AUTOWIRED_ANNOTATION_PROCESSOR_BEAN_NAME));
    }
    if (jsr250Present && !registry.containsBeanDefinition(COMMON_ANNOTATION_PROCESSOR_BEAN_NAME)) {
        // 也是Bean级别的后置处理器，为@PostConstruct和@PreDestroy等提供支持
        RootBeanDefinition def = new RootBeanDefinition(CommonAnnotationBeanPostProcessor.class);
        def.setSource(source);
        beanDefs.add(registerPostProcessor(registry, def, COMMON_ANNOTATION_PROCESSOR_BEAN_NAME));
    }
    // 如果存在JPA，则提供对JPA的支持，也是后置处理器
    if (jpaPresent && !registry.containsBeanDefinition(PERSISTENCE_ANNOTATION_PROCESSOR_BEAN_NAME)) {
        RootBeanDefinition def = new RootBeanDefinition();
        def.setBeanClass(ClassUtils.forName(PERSISTENCE_ANNOTATION_PROCESSOR_CLASS_NAME,
                                            AnnotationConfigUtils.class.getClassLoader()));
    }
    return beanDefs;
}