Spring源码之invokeBeanFactoryPostProcessors

Spring源码之invokeBeanFactoryPostProcessors

invokeBeanFactoryPostProcessors方法中主要是处理BeanDefinitionRegistryPostProcessor和BeanFactoryPostProcessor，BeanDefinitionRegistryPostProcessor是BeanFactoryPostProcessor的子接口，具有更强大的功能。这两个接口是Spring再初始化前一个重要的扩展点。

invokeBeanFactoryPostProcessors源码分析

public static void invokeBeanFactoryPostProcessors(
        ConfigurableListableBeanFactory beanFactory, List<BeanFactoryPostProcessor> beanFactoryPostProcessors) {
 
    // Invoke BeanDefinitionRegistryPostProcessors first, if any.
    Set<String> processedBeans = new HashSet<String>();
 
    // 判断beanFactory是否为BeanDefinitionRegistry，beanFactory为DefaultListableBeanFactory,
    // 而DefaultListableBeanFactory实现了BeanDefinitionRegistry接口，因此这边为true
    if (beanFactory instanceof BeanDefinitionRegistry) {
        BeanDefinitionRegistry registry = (BeanDefinitionRegistry) beanFactory;
        // 用于存放普通的BeanFactoryPostProcessor
        List<BeanFactoryPostProcessor> regularPostProcessors = new LinkedList<BeanFactoryPostProcessor>();
        // 用于存放BeanDefinitionRegistryPostProcessor
        List<BeanDefinitionRegistryPostProcessor> registryProcessors = new LinkedList<BeanDefinitionRegistryPostProcessor>();
 
        // 首先处理入参中的beanFactoryPostProcessors
        // 遍历所有的beanFactoryPostProcessors, 将BeanDefinitionRegistryPostProcessor和普通BeanFactoryPostProcessor区分开
        for (BeanFactoryPostProcessor postProcessor : beanFactoryPostProcessors) {
            if (postProcessor instanceof BeanDefinitionRegistryPostProcessor) {
                //  如果是BeanDefinitionRegistryPostProcessor
                BeanDefinitionRegistryPostProcessor registryProcessor =
                        (BeanDefinitionRegistryPostProcessor) postProcessor;
                // 直接执行BeanDefinitionRegistryPostProcessor接口的postProcessBeanDefinitionRegistry方法
                registryProcessor.postProcessBeanDefinitionRegistry(registry); //@3
                //  添加到registryProcessors(用于最后执行postProcessBeanFactory方法)
                registryProcessors.add(registryProcessor);
            } else {
                // 否则，只是普通的BeanFactoryPostProcessor
                // 添加到regularPostProcessors(用于最后执行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<BeanDefinitionRegistryPostProcessor> currentRegistryProcessors = new ArrayList<BeanDefinitionRegistryPostProcessor>();
 
        // First, invoke the BeanDefinitionRegistryPostProcessors that implement PriorityOrdered.
        // 调用所有实现PriorityOrdered接口的BeanDefinitionRegistryPostProcessor实现类
        //  找出所有实现BeanDefinitionRegistryPostProcessor接口的Bean的beanName
        //@1
        String[] postProcessorNames =
                beanFactory.getBeanNamesForType(BeanDefinitionRegistryPostProcessor.class, true, false);
        //遍历postProcessorNames
        for (String ppName : postProcessorNames) {
            // 校验是否实现了PriorityOrdered接口
            if (beanFactory.isTypeMatch(ppName, PriorityOrdered.class)) {
                //  获取ppName对应的bean实例, 添加到currentRegistryProcessors中,
                // beanFactory.getBean: 这边getBean方法会触发创建ppName对应的bean对象, 目前暂不深入解析
                currentRegistryProcessors.add(beanFactory.getBean(ppName, BeanDefinitionRegistryPostProcessor.class));
                // 将要被执行的加入processedBeans，避免后续重复执行
                processedBeans.add(ppName);
            }
        }
        //进行排序(根据是否实现PriorityOrdered、Ordered接口和order值来排序)
        sortPostProcessors(currentRegistryProcessors, beanFactory);
        //  添加到registryProcessors(用于最后执行postProcessBeanFactory方法)
        registryProcessors.addAll(currentRegistryProcessors);
        // 遍历currentRegistryProcessors, 执行postProcessBeanDefinitionRegistry方法
        invokeBeanDefinitionRegistryPostProcessors(currentRegistryProcessors, registry);
        // 执行完毕后, 清空currentRegistryProcessors
        currentRegistryProcessors.clear();
 
        // Next, invoke the BeanDefinitionRegistryPostProcessors that implement Ordered.
        // 调用所有实现了Ordered接口的BeanDefinitionRegistryPostProcessor实现类（过程跟上面的步骤3基本一样）
        // 找出所有实现BeanDefinitionRegistryPostProcessor接口的类, 这边重复查找是因为执行完上面的BeanDefinitionRegistryPostProcessor,
        // 可能会新增了其他的BeanDefinitionRegistryPostProcessor, 因此需要重新查找
       // @2
        postProcessorNames = beanFactory.getBeanNamesForType(BeanDefinitionRegistryPostProcessor.class, true, false);
        for (String ppName : postProcessorNames) {
            // 校验是否实现了Ordered接口，并且还未执行过
            if (!processedBeans.contains(ppName) && beanFactory.isTypeMatch(ppName, Ordered.class)) {
                currentRegistryProcessors.add(beanFactory.getBean(ppName, BeanDefinitionRegistryPostProcessor.class));
                processedBeans.add(ppName);
            }
        }
        sortPostProcessors(currentRegistryProcessors, beanFactory);
        registryProcessors.addAll(currentRegistryProcessors);
        //  遍历currentRegistryProcessors, 执行postProcessBeanDefinitionRegistry方法
        invokeBeanDefinitionRegistryPostProcessors(currentRegistryProcessors, registry);
        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);
            for (String ppName : postProcessorNames) {
                // 跳过已经执行过的
                if (!processedBeans.contains(ppName)) {
                    currentRegistryProcessors.add(beanFactory.getBean(ppName, BeanDefinitionRegistryPostProcessor.class));
                    processedBeans.add(ppName);
                    //  如果有BeanDefinitionRegistryPostProcessor被执行, 则有可能会产生新的BeanDefinitionRegistryPostProcessor,
                    // 因此这边将reiterate赋值为true, 代表需要再循环查找一次
                    reiterate = true;
                }
            }
            sortPostProcessors(currentRegistryProcessors, beanFactory);
            registryProcessors.addAll(currentRegistryProcessors);
            // 遍历currentRegistryProcessors, 执行postProcessBeanDefinitionRegistry方法
            invokeBeanDefinitionRegistryPostProcessors(currentRegistryProcessors, registry);
            currentRegistryProcessors.clear();
        }
 
        // Now, invoke the postProcessBeanFactory callback of all processors handled so far.
        //调用所有BeanDefinitionRegistryPostProcessor的postProcessBeanFactory方法(BeanDefinitionRegistryPostProcessor继承自BeanFactoryPostProcessor)
        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.
        invokeBeanFactoryPostProcessors(beanFactoryPostProcessors, beanFactory);
    }
 
    // 到这里 , 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的所有BeanFactoryPostProcessor
 
    // Do not initialize FactoryBeans here: We need to leave all regular beans
    // uninitialized to let the bean factory post-processors apply to them!
    // 找出所有实现BeanFactoryPostProcessor接口的类
    //@3
    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<BeanFactoryPostProcessor> priorityOrderedPostProcessors = new ArrayList<BeanFactoryPostProcessor>();
    // 用于存放实现了Ordered接口的BeanFactoryPostProcessor的beanName
    List<String> orderedPostProcessorNames = new ArrayList<String>();
    // 用于存放普通BeanFactoryPostProcessor的beanName
    List<String> nonOrderedPostProcessorNames = new ArrayList<String>();
    // 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
        if (processedBeans.contains(ppName)) {
            // skip - already processed in first phase above
        } else if (beanFactory.isTypeMatch(ppName, PriorityOrdered.class)) {
            // 添加实现了PriorityOrdered接口的BeanFactoryPostProcessor
            priorityOrderedPostProcessors.add(beanFactory.getBean(ppName, BeanFactoryPostProcessor.class));
        } else if (beanFactory.isTypeMatch(ppName, Ordered.class)) {
            //  添加实现了Ordered接口的BeanFactoryPostProcessor的beanName
            orderedPostProcessorNames.add(ppName);
        } else {
            // 添加剩下的普通BeanFactoryPostProcessor的beanName
            nonOrderedPostProcessorNames.add(ppName);
        }
    }
 
    // First, invoke the BeanFactoryPostProcessors that implement PriorityOrdered.
    // 调用所有实现PriorityOrdered接口的BeanFactoryPostProcessor
    // 对priorityOrderedPostProcessors排序
    sortPostProcessors(priorityOrderedPostProcessors, beanFactory);
    // 遍历priorityOrderedPostProcessors, 执行postProcessBeanFactory方法
    invokeBeanFactoryPostProcessors(priorityOrderedPostProcessors, beanFactory);
 
    // Next, invoke the BeanFactoryPostProcessors that implement Ordered.
    // 调用所有实现Ordered接口的BeanFactoryPostProcessor
    List<BeanFactoryPostProcessor> orderedPostProcessors = new ArrayList<BeanFactoryPostProcessor>();
    for (String postProcessorName : orderedPostProcessorNames) {
        //  获取postProcessorName对应的bean实例, 添加到orderedPostProcessors, 准备执行
        orderedPostProcessors.add(beanFactory.getBean(postProcessorName, BeanFactoryPostProcessor.class));
    }
    //  对orderedPostProcessors排序
    sortPostProcessors(orderedPostProcessors, beanFactory);
    // 遍历orderedPostProcessors, 执行postProcessBeanFactory方法
    invokeBeanFactoryPostProcessors(orderedPostProcessors, beanFactory);
 
    // Finally, invoke all other BeanFactoryPostProcessors.
    // 调用所有剩下的BeanFactoryPostProcessor
    List<BeanFactoryPostProcessor> nonOrderedPostProcessors = new ArrayList<BeanFactoryPostProcessor>();
    for (String postProcessorName : nonOrderedPostProcessorNames) {
        // 11.1 获取postProcessorName对应的bean实例, 添加到nonOrderedPostProcessors, 准备执行
        nonOrderedPostProcessors.add(beanFactory.getBean(postProcessorName, BeanFactoryPostProcessor.class));
    }
    // 遍历nonOrderedPostProcessors, 执行postProcessBeanFactory方法
    invokeBeanFactoryPostProcessors(nonOrderedPostProcessors, 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（mergedBeanDefinitions、allBeanNamesByType、singletonBeanNamesByType），
    // 因为后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();
}

@1这里会我们可以看下beanFactory中只有7个beanDefinition，其中只有ConfigurationClassPostProcessor是实现了BeanDefinitionRegistryPostProcessor接口
所以它会被优先执行。

ConfigurationClassPostProcessor后置处理器是在run()--->createApplicationContext()--->ApplicationContextFactory.create()--->
AnnotationConfigApplicationContext---->AnnotatedBeanDefinitionReader()--->
AnnotationConfigUtils.registerAnnotationConfigProcessors()添加的默认处理器。
@2由于加载了ConfigurationClassPostProcessor，系统中可能新增一些实现了BeanDefinitionRegistryPostProcessor的类，对他们进行排序，遍历执行postProcessBeanDefinitionRegistry方法。
@3加载所有实现了BeanFactoryPostProcessor，执行postProcessBeanFactory方法
从代码执行的顺序也可以知道BeanDefinitionRegistryPostProcessor是在BeanFactoryPostProcessor之前执行

@Component
public class BeanDefinitionRegistryPostProcessorOrder1 implements BeanDefinitionRegistryPostProcessor, Ordered {

    @Override
    public void postProcessBeanDefinitionRegistry(BeanDefinitionRegistry registry) throws BeansException {
        System.out.println("BeanDefinitionRegistryPostProcessorOrder1:::"+"postProcessBeanDefinitionRegistry");
    }

    @Override
    public void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory) throws BeansException {
        System.out.println("BeanDefinitionRegistryPostProcessorOrder1:::"+"postProcessBeanFactory");
    }

    @Override
    public int getOrder() {
        return 1;
    }
}

@Component
public class BeanDefinitionRegistryPostProcessorOrder2 implements BeanDefinitionRegistryPostProcessor, Ordered {

    @Override
    public void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory) throws BeansException {
        System.out.println("BeanDefinitionRegistryPostProcessorOrder2:::" + "postProcessBeanFactory");
    }

    @Override
    public void postProcessBeanDefinitionRegistry(BeanDefinitionRegistry registry) throws BeansException {
        System.out.println("BeanDefinitionRegistryPostProcessorOrder2:::" + "postProcessBeanDefinitionRegistry");
    }
    
    @Override
    public int getOrder() {
        return 2;
    }
}


@Component
public class BeanFactoryPostProcessorOrder1 implements BeanFactoryPostProcessor, Ordered {

    @Override
    public void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory) throws BeansException {
        System.out.println("BeanFactoryPostProcessorOrder1:::"+"postProcessBeanFactory");
    }

    @Override
    public int getOrder() {
        return 1;
    }
}


@Component
public class BeanFactoryPostProcessorOrder2 implements BeanFactoryPostProcessor, Ordered {

    @Override
    public void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory) throws BeansException {
        System.out.println("BeanFactoryPostProcessorOrder2:::" + "postProcessBeanFactory");
    }

    @Override
    public int getOrder() {
        return 2;
    }
}


输出结果：

BeanDefinitionRegistryPostProcessorOrder1:::postProcessBeanDefinitionRegistry
BeanDefinitionRegistryPostProcessorOrder2:::postProcessBeanDefinitionRegistry
BeanDefinitionRegistryPostProcessorOrder1:::postProcessBeanFactory
BeanDefinitionRegistryPostProcessorOrder2:::postProcessBeanFactory
BeanFactoryPostProcessorOrder1:::postProcessBeanFactory
BeanFactoryPostProcessorOrder2:::postProcessBeanFactory