Spring源码之BeanFactoryPostProcessor(后置处理器)

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Spring源码之BeanFactoryPostProcessor(后置处理器)。

有点水平的Spring开发人员想必都知道BeanFactoryPostProcessor也就是常说的后置管理器,这是Spirng生命周期中的一个接口,实现这个接口可以在beanFactory初始化前做一些事。

我们熟知的Spring和Mybatis的结合,正是因为Mybatis实现了BeanFactoryPostProcessor,它的重要性不言而喻,深入理解他对于切入Mybatis源码有着深刻的意义。

如下图是简单的应用:

还是先贴上refresh()的源码

    @Override
    public void refresh() throws BeansException, IllegalStateException 
        synchronized (this.startupShutdownMonitor) 
            // Prepare this context for refreshing.
            //1、刷新前的准备
            prepareRefresh();

            // Tell the subclass to refresh the internal bean factory.
            //2、将会初始化 BeanFactory、加载 Bean、注册 Bean
            ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory();

            // Prepare the bean factory for use in this context.
            //3、设置 BeanFactory 的类加载器,添加几个 BeanPostProcessor,手动注册几个特殊的 bean
            prepareBeanFactory(beanFactory);

            try 
                //4、模板方法
                // Allows post-processing of the bean factory in context subclasses.
                postProcessBeanFactory(beanFactory);

                // Invoke factory processors registered as beans in the context.
                //执行BeanFactory后置处理器
                invokeBeanFactoryPostProcessors(beanFactory);

                // 5、Register bean processors that intercept bean creation.
                //注册bean后置处理器
                registerBeanPostProcessors(beanFactory);

                // Initialize message source for this context.
                //国际化
                initMessageSource();

                // Initialize event multicaster for this context.
                initApplicationEventMulticaster();

                // Initialize other special beans in specific context subclasses.
                //6、模板方法--springboot实现了这个方法
                onRefresh();

                // Check for listener beans and register them.
                //7、注册监听器
                registerListeners();

                // Instantiate all remaining (non-lazy-init) singletons.
                //8、完成bean工厂的初始化**方法**********************************************
                finishBeanFactoryInitialization(beanFactory);

                //9、 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 Springs core, since we
                // might not ever need metadata for singleton beans anymore...
                resetCommonCaches();
            
        
    

benafactory源码的处理位于第三个位置。

主要涉及到两个方法postProcessBeanFactory(beanFactory);

和invokeBeanFactoryPostProcessors(beanFactory);

postProcessBeanFactory(beanFactory)点进去发现是一个空方法,具体的执行在invokeBeanFactoryPostProcessors(beanFactory);中

我们在invokeBeanFactoryPostProcessors方法上打断点一探究竟。第一次看的时候觉得这是什么玩意,这么长,耐住性子一步步的往下看。

方法虽长大概总结一下就是,判断beanFactory类型,然后将注册的BeanPostFactory放入、排好顺序、执行。

invokeBeanFactoryPostProcessors 方法的内容其实比较少,大部分过程在注释都已经写清楚,这边在稍微总结一下。

整个 invokeBeanFactoryPostProcessors 方法围绕两个接口,BeanDefinitionRegistryPostProcessor 和 BeanFactoryPostProcessor,其中 BeanDefinitionRegistryPostProcessor 继承了 BeanFactoryPostProcessor 。

BeanDefinitionRegistryPostProcessor 主要用来在常规 BeanFactoryPostProcessor 检测开始之前注册其他 Bean 定义,说的简单点,就是 BeanDefinitionRegistryPostProcessor 具有更高的优先级,执行顺序在 BeanFactoryPostProcessor 之前。

具体的过程看注释吧

    public static void invokeBeanFactoryPostProcessors(
            ConfigurableListableBeanFactory beanFactory, List<BeanFactoryPostProcessor> beanFactoryPostProcessors) 

        // Invoke BeanDefinitionRegistryPostProcessors first, if any.
        Set<String> processedBeans = new HashSet<>();

        // 1.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 ArrayList<>();
            // 用于存放BeanDefinitionRegistryPostProcessor
            List<BeanDefinitionRegistryPostProcessor> registryProcessors = new ArrayList<>();

            // 2.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) 
                    // 2.1 如果是BeanDefinitionRegistryPostProcessor
                    BeanDefinitionRegistryPostProcessor registryProcessor =
                            (BeanDefinitionRegistryPostProcessor) postProcessor;
                    // 2.1.1 直接执行BeanDefinitionRegistryPostProcessor接口的postProcessBeanDefinitionRegistry方法
                    registryProcessor.postProcessBeanDefinitionRegistry(registry);
                    // 2.1.2 添加到registryProcessors(用于最后执行postProcessBeanFactory方法)
                    registryProcessors.add(registryProcessor);
                
                else 
                    // 2.2 否则,只是普通的BeanFactoryPostProcessor
                    // 2.2.1 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<>();

            // First, invoke the BeanDefinitionRegistryPostProcessors that implement PriorityOrdered.
            // 3.调用所有实现PriorityOrdered接口的BeanDefinitionRegistryPostProcessor实现类
            // 3.1 找出所有实现BeanDefinitionRegistryPostProcessor接口的Bean的beanName
            String[] postProcessorNames =
                    beanFactory.getBeanNamesForType(BeanDefinitionRegistryPostProcessor.class, true, false);
            // 3.2 遍历postProcessorNames
            for (String ppName : postProcessorNames) 
                // 3.3 校验是否实现了PriorityOrdered接口
                if (beanFactory.isTypeMatch(ppName, PriorityOrdered.class)) 
                    // 3.4 获取ppName对应的bean实例, 添加到currentRegistryProcessors中,
                    currentRegistryProcessors.add(beanFactory.getBean(ppName, BeanDefinitionRegistryPostProcessor.class));
                    // 3.5 将要被执行的加入processedBeans,避免后续重复执行
                    processedBeans.add(ppName);
                
            
            // 3.6 进行排序(根据是否实现PriorityOrdered、Ordered接口和order值来排序)
            sortPostProcessors(currentRegistryProcessors, beanFactory);
            // 3.7 添加到registryProcessors(用于最后执行postProcessBeanFactory方法)
            registryProcessors.addAll(currentRegistryProcessors);
            // 3.8 遍历currentRegistryProcessors, 执行postProcessBeanDefinitionRegistry方法
            invokeBeanDefinitionRegistryPostProcessors(currentRegistryProcessors, registry);
            // 3.9 执行完毕后, 清空currentRegistryProcessors
            currentRegistryProcessors.clear();

            // Next, invoke the BeanDefinitionRegistryPostProcessors that implement Ordered.
            // 4.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)
            // 4.1 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
            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);
            // 4.2 遍历currentRegistryProcessors, 执行postProcessBeanDefinitionRegistry方法
            invokeBeanDefinitionRegistryPostProcessors(currentRegistryProcessors, registry);
            currentRegistryProcessors.clear();

            // Finally, invoke all other BeanDefinitionRegistryPostProcessors until no further ones appear.
            // 5.最后, 调用所有剩下的BeanDefinitionRegistryPostProcessors
            boolean reiterate = true;
            while (reiterate) 
                reiterate = false;
                // 5.1 找出所有实现BeanDefinitionRegistryPostProcessor接口的类
                postProcessorNames = beanFactory.getBeanNamesForType(BeanDefinitionRegistryPostProcessor.class, true, false);
                for (String ppName : postProcessorNames) 
                    // 5.2 跳过已经执行过的
                    if (!processedBeans.contains(ppName)) 
                        currentRegistryProcessors.add(beanFactory.getBean(ppName, BeanDefinitionRegistryPostProcessor.class));
                        processedBeans.add(ppName);
                        // 5.3 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);
                // 5.4 遍历currentRegistryProcessors, 执行postProcessBeanDefinitionRegistry方法
                invokeBeanDefinitionRegistryPostProcessors(currentRegistryProcessors, registry);
                currentRegistryProcessors.clear();
            

            // Now, invoke the postProcessBeanFactory callback of all processors handled so far.
            // 6.调用所有BeanDefinitionRegistryPostProcessor的postProcessBeanFactory方法(BeanDefinitionRegistryPostProcessor继承自BeanFactoryPostProcessor)
            invokeBeanFactoryPostProcessors(registryProcessors, beanFactory);
            // 7.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);
        

        // Do not initialize FactoryBeans here: We need to leave all regular beans
        // uninitialized to let the bean factory post-processors apply to them!
        // 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!
        // 8.找出所有实现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<BeanFactoryPostProcessor> priorityOrderedPostProcessors = new ArrayList<>();
        // 用于存放实现了Ordered接口的BeanFactoryPostProcessor的beanName
        List<String> orderedPostProcessorNames = new ArrayList<>();
        // 用于存放普通BeanFactoryPostProcessor的beanName
        List<String> nonOrderedPostProcessorNames = new ArrayList<>();
        // 8.1 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) 
            // 8.2 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)) 
                // 8.3 添加实现了PriorityOrdered接口的BeanFactoryPostProcessor
                priorityOrderedPostProcessors.add(beanFactory.getBean(ppName, BeanFactoryPostProcessor.class));
            
            else if (beanFactory.isTypeMatch(ppName, Ordered.class)) 
                // 8.4 添加实现了Ordered接口的BeanFactoryPostProcessor的beanName
                orderedPostProcessorNames.add(ppName);
            
            else 
                // 8.5 添加剩下的普通BeanFactoryPostProcessor的beanName
                nonOrderedPostProcessorNames.add(ppName);
            
        

        // First, invoke the BeanFactoryPostProcessors that implement PriorityOrdered.
        // 9.调用所有实现PriorityOrdered接口的BeanFactoryPostProcessor
        // 9.1 对priorityOrderedPostProcessors排序
        sortPostProcessors(priorityOrderedPostProcessors, beanFactory);
        // 9.2 遍历priorityOrderedPostProcessors, 执行postProcessBeanFactory方法
        invokeBeanFactoryPostProcessors(priorityOrderedPostProcessors, beanFactory);

        // Next, invoke the BeanFactoryPostProcessors that implement Ordered.
        // 10.调用所有实现Ordered接口的BeanFactoryPostProcessor
        List<BeanFactoryPostProcessor> orderedPostProcessors = new ArrayList<>();
        for (String postProcessorName : orderedPostProcessorNames) 
            // 10.1 获取postProcessorName对应的bean实例, 添加到orderedPostProcessors, 准备执行
            orderedPostProcessors.add(beanFactory.getBean(postProcessorName, BeanFactoryPostProcessor.class));
        
        // 10.2 对orderedPostProcessors排序
        sortPostProcessors(orderedPostProcessors, beanFactory);
        // 10.3 遍历orderedPostProcessors, 执行postProcessBeanFactory方法
        invokeBeanFactoryPostProcessors(orderedPostProcessors, beanFactory);

        // Finally, invoke all other BeanFactoryPostProcessors.
        // 11.调用所有剩下的BeanFactoryPostProcessor
        List<BeanFactoryPostProcessor> nonOrderedPostProcessors = new ArrayList<>();
        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));
        
        // 11.2 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...
        // 12.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();
    

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