06-Spring BeanFactoryPostProcessor的调用

实例化并调用所有的 BeanFactoryPostProcessor

BeanFactoryPostProcessor

在 Bean 未初始化之前，用于修改 BeanFactory 中定义的 BeanDefinition，可以修改其对应的属性值，覆盖或者增加属性值，甚至用于初始化 Bean。

void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory) throws BeansException

BeanDefinitionRegistryPostProcessor

继承自 BeanFactoryPostProcessor 接口，拥有独自的 BeanDefinitionRegistry 后置接口，可以直接向其注册更多的 BeanDefinition。注意，此接口和上述接口有本质区别，此接口可以对 BeanDefinition 进行增加或者删除，但上述接口只能对 BeanDefinition 里面的属性进行操作。其下一个非常关键的实现类即 ConfigurationClassPostProcessor。

void postProcessBeanDefinitionRegistry(BeanDefinitionRegistry registry) throws BeansException;

invokeBeanFactoryPostProcessors(beanFactory)

protected void invokeBeanFactoryPostProcessors(ConfigurableListableBeanFactory beanFactory) {
    // 获取到当前应用程序上下文的beanFactoryPostProcessors变量的值，并且实例化调用执行所有已经注册的beanFactoryPostProcessor
    // 默认情况下，通过getBeanFactoryPostProcessors()来获取已经注册的BFPP，但是默认是空的，那么问题来了，如果你想扩展，怎么进行扩展工作？
    PostProcessorRegistrationDelegate.invokeBeanFactoryPostProcessors(beanFactory, getBeanFactoryPostProcessors());

    // Detect a LoadTimeWeaver and prepare for weaving, if found in the meantime
    // (e.g. through an @Bean method registered by ConfigurationClassPostProcessor)
    if (beanFactory.getTempClassLoader() == null && beanFactory.containsBean(LOAD_TIME_WEAVER_BEAN_NAME)) {
        beanFactory.addBeanPostProcessor(new LoadTimeWeaverAwareProcessor(beanFactory));
        beanFactory.setTempClassLoader(new ContextTypeMatchClassLoader(beanFactory.getBeanClassLoader()));
    }
}

invokeBeanFactoryPostProcessors

此类中，会包含 GetBean 实例化单例，这个地方不做过多解析，只需要知道，主要是从 Spring IOC 中获取对应的单例对象即可。

执行流程

public static void invokeBeanFactoryPostProcessors(
    ConfigurableListableBeanFactory beanFactory, List beanFactoryPostProcessors) {

    // Invoke BeanDefinitionRegistryPostProcessors first, if any.
    // 无论是什么情况，优先执行BeanDefinitionRegistryPostProcessors
    // 将已经执行过的BFPP存储在processedBeans中，防止重复执行
    Set processedBeans = new HashSet<>();

    // 判断beanfactory是否是BeanDefinitionRegistry类型，此处是DefaultListableBeanFactory,实现了BeanDefinitionRegistry接口，所以为true
    if (beanFactory instanceof BeanDefinitionRegistry) {
        // 类型转换
        BeanDefinitionRegistry registry = (BeanDefinitionRegistry) beanFactory;
        // 此处希望大家做一个区分，两个接口是不同的，BeanDefinitionRegistryPostProcessor是BeanFactoryPostProcessor的子集
        // BeanFactoryPostProcessor主要针对的操作对象是BeanFactory，而BeanDefinitionRegistryPostProcessor主要针对的操作对象是BeanDefinition
        // 存放BeanFactoryPostProcessor的集合
        List regularPostProcessors = new ArrayList<>();
        // 存放BeanDefinitionRegistryPostProcessor的集合
        List registryProcessors = new ArrayList<>();

        // 首先处理入参中的beanFactoryPostProcessors,遍历所有的beanFactoryPostProcessors，将BeanDefinitionRegistryPostProcessor
        // 和BeanFactoryPostProcessor区分开
        for (BeanFactoryPostProcessor postProcessor : beanFactoryPostProcessors) {
            // 如果是BeanDefinitionRegistryPostProcessor
            if (postProcessor instanceof BeanDefinitionRegistryPostProcessor) {
                BeanDefinitionRegistryPostProcessor registryProcessor =
                    (BeanDefinitionRegistryPostProcessor) postProcessor;
                // 直接执行BeanDefinitionRegistryPostProcessor接口中的postProcessBeanDefinitionRegistry方法
                registryProcessor.postProcessBeanDefinitionRegistry(registry);
                // 添加到registryProcessors，用于后续执行postProcessBeanFactory方法
                registryProcessors.add(registryProcessor);
            } else {
                // 否则，只是普通的BeanFactoryPostProcessor，添加到regularPostProcessors，用于后续执行postProcessBeanFactory方法
                regularPostProcessors.add(postProcessor);
            }
        }

        // Do not initialize FactoryBeans here: We need to leave all regular beans
        // uninitialized to let the bean factory post-processors apply to them!
        // Separate between BeanDefinitionRegistryPostProcessors that implement
        // PriorityOrdered, Ordered, and the rest.
        // 用于保存本次要执行的BeanDefinitionRegistryPostProcessor
        List currentRegistryProcessors = new ArrayList<>();

        // First, invoke the BeanDefinitionRegistryPostProcessors that implement PriorityOrdered.
        // 调用所有实现PriorityOrdered接口的BeanDefinitionRegistryPostProcessor实现类
        // 找到所有实现BeanDefinitionRegistryPostProcessor接口bean的beanName
        String[] postProcessorNames =
            beanFactory.getBeanNamesForType(BeanDefinitionRegistryPostProcessor.class, true, false);
        // 遍历处理所有符合规则的postProcessorNames
        for (String ppName : postProcessorNames) {
            // 检测是否实现了PriorityOrdered接口
            if (beanFactory.isTypeMatch(ppName, PriorityOrdered.class)) {
                // 获取名字对应的bean实例，添加到currentRegistryProcessors中
                currentRegistryProcessors.add(beanFactory.getBean(ppName, BeanDefinitionRegistryPostProcessor.class));
                // 将要被执行的BFPP名称添加到processedBeans，避免后续重复执行
                processedBeans.add(ppName);
            }
        }
        // 按照优先级进行排序操作
        sortPostProcessors(currentRegistryProcessors, beanFactory);
        // 添加到registryProcessors中，用于最后执行postProcessBeanFactory方法
        registryProcessors.addAll(currentRegistryProcessors);
        // 遍历currentRegistryProcessors，执行postProcessBeanDefinitionRegistry方法
        invokeBeanDefinitionRegistryPostProcessors(currentRegistryProcessors, registry);
        // 执行完毕之后，清空currentRegistryProcessors
        currentRegistryProcessors.clear();

        // Next, invoke the BeanDefinitionRegistryPostProcessors that implement Ordered.
        // 调用所有实现Ordered接口的BeanDefinitionRegistryPostProcessor实现类
        // 找到所有实现BeanDefinitionRegistryPostProcessor接口bean的beanName，
        // 此处需要重复查找的原因在于上面的执行过程中可能会新增其他的BeanDefinitionRegistryPostProcessor
        postProcessorNames = beanFactory.getBeanNamesForType(BeanDefinitionRegistryPostProcessor.class, true, false);
        for (String ppName : postProcessorNames) {
            // 检测是否实现了Ordered接口，并且还未执行过
            if (!processedBeans.contains(ppName) && beanFactory.isTypeMatch(ppName, Ordered.class)) {
                // 获取名字对应的bean实例，添加到currentRegistryProcessors中
                currentRegistryProcessors.add(beanFactory.getBean(ppName, BeanDefinitionRegistryPostProcessor.class));
                // 将要被执行的BFPP名称添加到processedBeans，避免后续重复执行
                processedBeans.add(ppName);
            }
        }
        // 按照优先级进行排序操作
        sortPostProcessors(currentRegistryProcessors, beanFactory);
        // 添加到registryProcessors中，用于最后执行postProcessBeanFactory方法
        registryProcessors.addAll(currentRegistryProcessors);
        // 遍历currentRegistryProcessors，执行postProcessBeanDefinitionRegistry方法
        invokeBeanDefinitionRegistryPostProcessors(currentRegistryProcessors, registry);
        // 执行完毕之后，清空currentRegistryProcessors
        currentRegistryProcessors.clear();

        // Finally, invoke all other BeanDefinitionRegistryPostProcessors until no further ones appear.
        // 最后，调用所有剩下的BeanDefinitionRegistryPostProcessors
        boolean reiterate = true;
        while (reiterate) {
            reiterate = false;
            // 找出所有实现BeanDefinitionRegistryPostProcessor接口的类
            postProcessorNames = beanFactory.getBeanNamesForType(BeanDefinitionRegistryPostProcessor.class, true, false);
            // 遍历执行
            for (String ppName : postProcessorNames) {
                // 跳过已经执行过的BeanDefinitionRegistryPostProcessor
                if (!processedBeans.contains(ppName)) {
                    // 获取名字对应的bean实例，添加到currentRegistryProcessors中
                    currentRegistryProcessors.add(beanFactory.getBean(ppName, BeanDefinitionRegistryPostProcessor.class));
                    // 将要被执行的BFPP名称添加到processedBeans，避免后续重复执行
                    processedBeans.add(ppName);
                    reiterate = true;
                }
            }
            // 按照优先级进行排序操作
            sortPostProcessors(currentRegistryProcessors, beanFactory);
            // 添加到registryProcessors中，用于最后执行postProcessBeanFactory方法
            registryProcessors.addAll(currentRegistryProcessors);
            // 遍历currentRegistryProcessors，执行postProcessBeanDefinitionRegistry方法
            invokeBeanDefinitionRegistryPostProcessors(currentRegistryProcessors, registry);
            // 执行完毕之后，清空currentRegistryProcessors
            currentRegistryProcessors.clear();
        }

        // Now, invoke the postProcessBeanFactory callback of all processors handled so far.
        // 调用所有BeanDefinitionRegistryPostProcessor的postProcessBeanFactory方法
        invokeBeanFactoryPostProcessors(registryProcessors, beanFactory);
        // 最后，调用入参beanFactoryPostProcessors中的普通BeanFactoryPostProcessor的postProcessBeanFactory方法
        invokeBeanFactoryPostProcessors(regularPostProcessors, beanFactory);
    } else {
        // Invoke factory processors registered with the context instance.
        // 如果beanFactory不归属于BeanDefinitionRegistry类型，那么直接执行postProcessBeanFactory方法
        invokeBeanFactoryPostProcessors(beanFactoryPostProcessors, beanFactory);
    }

    // 到这里为止，入参beanFactoryPostProcessors和容器中的所有BeanDefinitionRegistryPostProcessor已经全部处理完毕，下面开始处理容器中
    // 所有的BeanFactoryPostProcessor
    // 可能会包含一些实现类，只实现了BeanFactoryPostProcessor，并没有实现BeanDefinitionRegistryPostProcessor接口

    // Do not initialize FactoryBeans here: We need to leave all regular beans
    // uninitialized to let the bean factory post-processors apply to them!
    // 找到所有实现BeanFactoryPostProcessor接口的类
    String[] postProcessorNames =
        beanFactory.getBeanNamesForType(BeanFactoryPostProcessor.class, true, false);

    // Separate between BeanFactoryPostProcessors that implement PriorityOrdered,
    // Ordered, and the rest.
    // 用于存放实现了PriorityOrdered接口的BeanFactoryPostProcessor
    List priorityOrderedPostProcessors = new ArrayList<>();
    // 用于存放实现了Ordered接口的BeanFactoryPostProcessor的beanName
    List orderedPostProcessorNames = new ArrayList<>();
    // 用于存放普通BeanFactoryPostProcessor的beanName
    List nonOrderedPostProcessorNames = new ArrayList<>();
    // 遍历postProcessorNames,将BeanFactoryPostProcessor按实现PriorityOrdered、实现Ordered接口、普通三种区分开
    for (String ppName : postProcessorNames) {
        // 跳过已经执行过的BeanFactoryPostProcessor
        if (processedBeans.contains(ppName)) {
            // skip - already processed in first phase above
        }
        // 添加实现了PriorityOrdered接口的BeanFactoryPostProcessor到priorityOrderedPostProcessors
        else if (beanFactory.isTypeMatch(ppName, PriorityOrdered.class)) {
            priorityOrderedPostProcessors.add(beanFactory.getBean(ppName, BeanFactoryPostProcessor.class));
        }
        // 添加实现了Ordered接口的BeanFactoryPostProcessor的beanName到orderedPostProcessorNames
        else if (beanFactory.isTypeMatch(ppName, Ordered.class)) {
            orderedPostProcessorNames.add(ppName);
        } else {
            // 添加剩下的普通BeanFactoryPostProcessor的beanName到nonOrderedPostProcessorNames
            nonOrderedPostProcessorNames.add(ppName);
        }
    }

    // First, invoke the BeanFactoryPostProcessors that implement PriorityOrdered.
    // 对实现了PriorityOrdered接口的BeanFactoryPostProcessor进行排序
    sortPostProcessors(priorityOrderedPostProcessors, beanFactory);
    // 遍历实现了PriorityOrdered接口的BeanFactoryPostProcessor，执行postProcessBeanFactory方法
    invokeBeanFactoryPostProcessors(priorityOrderedPostProcessors, beanFactory);

    // Next, invoke the BeanFactoryPostProcessors that implement Ordered.
    // 创建存放实现了Ordered接口的BeanFactoryPostProcessor集合
    List orderedPostProcessors = new ArrayList<>(orderedPostProcessorNames.size());
    // 遍历存放实现了Ordered接口的BeanFactoryPostProcessor名字的集合
    for (String postProcessorName : orderedPostProcessorNames) {
        // 将实现了Ordered接口的BeanFactoryPostProcessor添加到集合中
        orderedPostProcessors.add(beanFactory.getBean(postProcessorName, BeanFactoryPostProcessor.class));
    }
    // 对实现了Ordered接口的BeanFactoryPostProcessor进行排序操作
    sortPostProcessors(orderedPostProcessors, beanFactory);
    //        sortPostProcessors(orderedPostProcessor, beanFactory);
    // 遍历实现了Ordered接口的BeanFactoryPostProcessor，执行postProcessBeanFactory方法
    invokeBeanFactoryPostProcessors(orderedPostProcessors, beanFactory);
    //        invokeBeanFactoryPostProcessors(orderedPostProcessor, beanFactory);

    // Finally, invoke all other BeanFactoryPostProcessors.
    // 最后，创建存放普通的BeanFactoryPostProcessor的集合
    List nonOrderedPostProcessors = new ArrayList<>(nonOrderedPostProcessorNames.size());
    // 遍历存放实现了普通BeanFactoryPostProcessor名字的集合
    for (String postProcessorName : nonOrderedPostProcessorNames) {
        // 将普通的BeanFactoryPostProcessor添加到集合中
        nonOrderedPostProcessors.add(beanFactory.getBean(postProcessorName, BeanFactoryPostProcessor.class));
    }
    // 遍历普通的BeanFactoryPostProcessor，执行postProcessBeanFactory方法
    invokeBeanFactoryPostProcessors(nonOrderedPostProcessors, beanFactory);
    //        invokeBeanFactoryPostProcessors(nonOrderedPostProcessorNames, beanFactory);

    // Clear cached merged bean definitions since the post-processors might have
    // modified the original metadata, e.g. replacing placeholders in values...
    // 清除元数据缓存(mergeBeanDefinitions、allBeanNamesByType、singletonBeanNameByType)
    // 因为后置处理器可能已经修改了原始元数据，例如，替换值中的占位符
    beanFactory.clearMetadataCache();
}

invokeBeanFactoryPostProcessors(regularPostProcessors, beanFactory)

调用给定的 BeanFactoryPostProcessor类型Bean对象

private static void invokeBeanFactoryPostProcessors(
    Collection postProcessors, ConfigurableListableBeanFactory beanFactory) {

    //遍历postProcessors
    for (BeanFactoryPostProcessor postProcessor : postProcessors) {
        //回调 BeanFactoryPostProcessor 的 postProcessBeanFactory 方法，使得每个postProcessor对象都可以对
        // beanFactory进行调整
        postProcessor.postProcessBeanFactory(beanFactory);
    }
}

invokeBeanDefinitionRegistryPostProcessors(currentRegistryProcessors, registry)

调用给定 BeanDefinitionRegistryPostProcessor Bean对象

private static void invokeBeanDefinitionRegistryPostProcessors(
    Collection postProcessors, BeanDefinitionRegistry registry) {

    //遍历 postProcessors
    for (BeanDefinitionRegistryPostProcessor postProcessor : postProcessors) {
        //调用 postProcessor 的 postProcessBeanDefinitionRegistry以使得postProcess往registry注册BeanDefinition对象
        postProcessor.postProcessBeanDefinitionRegistry(registry);
    }
}