Spring中的AnnotatedBeanDefinitionReader

在Spring Boot中，不管是servlet还是reactive类型的应用上下文的构造器中都会创建该对象，倒不是说要考它来读取bean的定义，而是在它的构造方法中有一个关键操作，本文就来看一下这个关键操作是什么。

创建过程

创建时机

在Spring Boot中，不管是servlet还是reactive类型的应用上下文，在其构造方法中都会创建AnnotatedBeanDefinitionReader对象。

servlet上下文

reactive上下文

java

spring-boot-project/spring-boot/src/main/java/org/springframework/boot/web/servlet/context/AnnotationConfigServletWebServerApplicationContext.java

public AnnotationConfigServletWebServerApplicationContext() {
    /*
     * 创建BeanDefinition的reader和scanner
     */
    this.reader = new AnnotatedBeanDefinitionReader(this);
    this.scanner = new ClassPathBeanDefinitionScanner(this);
}

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java

spring-boot-project/spring-boot/src/main/java/org/springframework/boot/web/reactive/context/AnnotationConfigReactiveWebServerApplicationContext.java

public AnnotationConfigReactiveWebServerApplicationContext() {
    this.reader = new AnnotatedBeanDefinitionReader(this);
    this.scanner = new ClassPathBeanDefinitionScanner(this);
}

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另外在AnnotationConfigWebApplicationContext的loadBeanDefinitions方法中也会创建AnnotatedBeanDefinitionReader对象。但一般很少使用AnnotationConfigWebApplicationContext，一般都是XmlWebApplicationContext。

注册注解相关后置处理器

java

spring-context/src/main/java/org/springframework/context/annotation/AnnotationConfigUtils.java

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

public static Set<BeanDefinitionHolder> registerAnnotationConfigProcessors(
        BeanDefinitionRegistry registry, @Nullable Object source) {

    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());
        }
    }

    // 保存一些默认用到的PostProcessor，默认提供了下面6个，虽然initialCapacity是8
    Set<BeanDefinitionHolder> beanDefs = new LinkedHashSet<>(8);

    /*
     * ConfigurationClassPostProcessor是一个BeanFactoryPostProcessor
     */
    if (!registry.containsBeanDefinition(CONFIGURATION_ANNOTATION_PROCESSOR_BEAN_NAME)) {
        // 创建bean定义
        RootBeanDefinition def = new RootBeanDefinition(ConfigurationClassPostProcessor.class);
        def.setSource(source);
        beanDefs.add(registerPostProcessor(registry, def, CONFIGURATION_ANNOTATION_PROCESSOR_BEAN_NAME));
    }

    // 处理@Autowired注解
    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));
    }

    // Check for JSR-250 support, and if present add the CommonAnnotationBeanPostProcessor.
    // 如果存在javax.annotation.Resource依赖，那么添加针对JSR-250的BeanPostProcessor
    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;
}

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在上面的方法中，会注册一些后置处理器，既有BeanFactoryPostProcessor，也有BeanPostProcessor。