Spring - PostProcesser

PostProcesser

spring 有两个非常重要的PostProcesser，那就是BeanFactoryPostProcessor和BeanPostProcessor，这两个接口的方法调用逻辑主要在PostProcessorRegistrationDelegate类里。

BeanFactoryPostProcessor

BeanFactoryPostProcessor实现类，可以修改bean的定义属性。也就是说，Spring允许BeanFactoryPostProcessor在容器实例化任何其它bean之前读取配置元数据，并可以根据需要进行修改，例如可以把bean的scope从singleton改为prototype，也可以把property的值给修改掉。可以同时配置多个BeanFactoryPostProcessor，并通过设置’order’属性来控制各个BeanFactoryPostProcessor的执行次序。 注意：BeanFactoryPostProcessor是在spring容器加载了bean的定义文件之后，在bean实例化（调用构造方法）之前执行的。接口方法的入参是ConfigurrableListableBeanFactory，使用该参数，可以获取到相关bean的定义信息。

BeanPostProcessor

BeanPostProcessor实现类可以在bean初始化前后做一些事情，BeanPostProcessor的作用域是容器级的，它只和所在容器有关。

refresh

要想了解BeanFactoryPostProcessor和BeanPostProcessor 一定要先了解AbstractApplicationContext的refresh方法。spring 启动的时候，执行最重要的方法就是refresh方法，该方法源码如下：

@Override
    public void refresh() throws BeansException, IllegalStateException {
        synchronized (this.startupShutdownMonitor) {
            // 1. Prepare this context for refreshing.
            prepareRefresh();

            // 2. Tell the subclass to refresh the internal bean factory.
            ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory();

            // 3. Prepare the bean factory for use in this context.
            prepareBeanFactory(beanFactory);

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

                // 5. Invoke factory processors registered as beans in the context.
                invokeBeanFactoryPostProcessors(beanFactory);

                // 6. Register bean processors that intercept bean creation.
                registerBeanPostProcessors(beanFactory);

                // 7. Initialize message source for this context.
                initMessageSource();

                // 8. Initialize event multicaster for this context.
                initApplicationEventMulticaster();

                // 9. Initialize other special beans in specific context subclasses.
                onRefresh();

                // 10. Check for listener beans and register them.
                registerListeners();

                // 11. Instantiate all remaining (non-lazy-init) singletons.
                finishBeanFactoryInitialization(beanFactory);

                // 12. 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 Spring's core, since we
                // might not ever need metadata for singleton beans anymore...
                resetCommonCaches();
            }
        }
    }

• BeanPostProcessor 注册

prepareBeanFactory(beanFactory);

beanFactory.addBeanPostProcessor(new ApplicationContextAwareProcessor(this));
beanFactory.addBeanPostProcessor(new ApplicationListenerDetector(this));

postProcessBeanFactory(beanFactory)

beanFactory.addBeanPostProcessor(new WebApplicationContextServletContextAwareProcessor(this));

ConfigurationClassPostProcessor#postProcessBeanFactory

beanFactory.addBeanPostProcessor(newImportAwareBeanPostProcessor(beanFactory));

PostProcessorRegistrationDelegate#registerBeanPostProcessors(ConfigurableListableBeanFactory,AbstractApplicationContext)

 String[] postProcessorNames = beanFactory.getBeanNamesForType(BeanPostProcessor.class, true, false);

 beanFactory.addBeanPostProcessor(new BeanPostProcessorChecker(beanFactory, beanProcessorTargetCount));

分为3类

• PriorityOrdered
• Ordered

• other

• BeanPostProcessor 调用
  org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory#initializeBean(java.lang.String, java.lang.Object, org.springframework.beans.factory.support.RootBeanDefinition)

wrappedBean = applyBeanPostProcessorsBeforeInitialization(wrappedBean, beanName);

invokeInitMethods(beanName, wrappedBean, mbd);

wrappedBean = applyBeanPostProcessorsAfterInitialization(wrappedBean, beanName);

注册与调用

关于refresh方法中，本文主要关注PostProcessor的查找与调用时机。

BeanFactoryPostProcessor

在第5步中， invokeBeanFactoryPostProcessors方法里触发BeanFactoryPostProcessor的接口方法的调用，实际上是委托给PostProcessorRegistrationDelegate的静态方法invokeBeanFactoryPostProcessors。

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

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

        if (beanFactory instanceof BeanDefinitionRegistry) {
            BeanDefinitionRegistry registry = (BeanDefinitionRegistry) beanFactory;
            List<BeanFactoryPostProcessor> regularPostProcessors = new LinkedList<BeanFactoryPostProcessor>();
            List<BeanDefinitionRegistryPostProcessor> registryPostProcessors =
                    new LinkedList<BeanDefinitionRegistryPostProcessor>();

            for (BeanFactoryPostProcessor postProcessor : beanFactoryPostProcessors) {
                if (postProcessor instanceof BeanDefinitionRegistryPostProcessor) {
                    BeanDefinitionRegistryPostProcessor registryPostProcessor =
                            (BeanDefinitionRegistryPostProcessor) postProcessor;
                    registryPostProcessor.postProcessBeanDefinitionRegistry(registry);
                    registryPostProcessors.add(registryPostProcessor);
                }
                else {
                    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.
            String[] postProcessorNames =
                    beanFactory.getBeanNamesForType(BeanDefinitionRegistryPostProcessor.class, true, false);

            // First, invoke the BeanDefinitionRegistryPostProcessors that implement PriorityOrdered.
            List<BeanDefinitionRegistryPostProcessor> priorityOrderedPostProcessors = new ArrayList<BeanDefinitionRegistryPostProcessor>();
            for (String ppName : postProcessorNames) {
                if (beanFactory.isTypeMatch(ppName, PriorityOrdered.class)) {
                    priorityOrderedPostProcessors.add(beanFactory.getBean(ppName, BeanDefinitionRegistryPostProcessor.class));
                    processedBeans.add(ppName);
                }
            }
            sortPostProcessors(beanFactory, priorityOrderedPostProcessors);
            registryPostProcessors.addAll(priorityOrderedPostProcessors);
            invokeBeanDefinitionRegistryPostProcessors(priorityOrderedPostProcessors, registry);

            // Next, invoke the BeanDefinitionRegistryPostProcessors that implement Ordered.
            postProcessorNames = beanFactory.getBeanNamesForType(BeanDefinitionRegistryPostProcessor.class, true, false);
            List<BeanDefinitionRegistryPostProcessor> orderedPostProcessors = new ArrayList<BeanDefinitionRegistryPostProcessor>();
            for (String ppName : postProcessorNames) {
                if (!processedBeans.contains(ppName) && beanFactory.isTypeMatch(ppName, Ordered.class)) {
                    orderedPostProcessors.add(beanFactory.getBean(ppName, BeanDefinitionRegistryPostProcessor.class));
                    processedBeans.add(ppName);
                }
            }
            sortPostProcessors(beanFactory, orderedPostProcessors);
            registryPostProcessors.addAll(orderedPostProcessors);
            invokeBeanDefinitionRegistryPostProcessors(orderedPostProcessors, registry);

            // Finally, invoke all other BeanDefinitionRegistryPostProcessors until no further ones appear.
            boolean reiterate = true;
            while (reiterate) {
                reiterate = false;
                postProcessorNames = beanFactory.getBeanNamesForType(BeanDefinitionRegistryPostProcessor.class, true, false);
                for (String ppName : postProcessorNames) {
                    if (!processedBeans.contains(ppName)) {
                        BeanDefinitionRegistryPostProcessor pp = beanFactory.getBean(ppName, BeanDefinitionRegistryPostProcessor.class);
                        registryPostProcessors.add(pp);
                        processedBeans.add(ppName);
                        pp.postProcessBeanDefinitionRegistry(registry);
                        reiterate = true;
                    }
                }
            }

            // Now, invoke the postProcessBeanFactory callback of all processors handled so far.
            invokeBeanFactoryPostProcessors(registryPostProcessors, beanFactory);
            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!
        String[] postProcessorNames =
                beanFactory.getBeanNamesForType(BeanFactoryPostProcessor.class, true, false);

        // Separate between BeanFactoryPostProcessors that implement PriorityOrdered,
        // Ordered, and the rest.
        List<BeanFactoryPostProcessor> priorityOrderedPostProcessors = new ArrayList<BeanFactoryPostProcessor>();
        List<String> orderedPostProcessorNames = new ArrayList<String>();
        List<String> nonOrderedPostProcessorNames = new ArrayList<String>();
        for (String ppName : postProcessorNames) {
            if (processedBeans.contains(ppName)) {
                // skip - already processed in first phase above
            }
            else if (beanFactory.isTypeMatch(ppName, PriorityOrdered.class)) {
                priorityOrderedPostProcessors.add(beanFactory.getBean(ppName, BeanFactoryPostProcessor.class));
            }
            else if (beanFactory.isTypeMatch(ppName, Ordered.class)) {
                orderedPostProcessorNames.add(ppName);
            }
            else {
                nonOrderedPostProcessorNames.add(ppName);
            }
        }

        // First, invoke the BeanFactoryPostProcessors that implement PriorityOrdered.
        sortPostProcessors(beanFactory, priorityOrderedPostProcessors);
        invokeBeanFactoryPostProcessors(priorityOrderedPostProcessors, beanFactory);

        // Next, invoke the BeanFactoryPostProcessors that implement Ordered.
        List<BeanFactoryPostProcessor> orderedPostProcessors = new ArrayList<BeanFactoryPostProcessor>();
        for (String postProcessorName : orderedPostProcessorNames) {
            orderedPostProcessors.add(beanFactory.getBean(postProcessorName, BeanFactoryPostProcessor.class));
        }
        sortPostProcessors(beanFactory, orderedPostProcessors);
        invokeBeanFactoryPostProcessors(orderedPostProcessors, beanFactory);

        // Finally, invoke all other BeanFactoryPostProcessors.
        List<BeanFactoryPostProcessor> nonOrderedPostProcessors = new ArrayList<BeanFactoryPostProcessor>();
        for (String postProcessorName : nonOrderedPostProcessorNames) {
            nonOrderedPostProcessors.add(beanFactory.getBean(postProcessorName, BeanFactoryPostProcessor.class));
        }
        invokeBeanFactoryPostProcessors(nonOrderedPostProcessors, beanFactory);

        // Clear cached merged bean definitions since the post-processors might have
        // modified the original metadata, e.g. replacing placeholders in values...
        beanFactory.clearMetadataCache();
    }

BeanPostProcessor

在第6步中， registerBeanPostProcessors方法中注册BeanPostProcesser，实际上是委托给PostProcessorRegistrationDelegate的静态方法registerBeanPostProcessors。

    public static void registerBeanPostProcessors(
            ConfigurableListableBeanFactory beanFactory, AbstractApplicationContext applicationContext) {

                 //查找所有实现BeanPostProcessor接口的类
        String[] postProcessorNames = beanFactory.getBeanNamesForType(BeanPostProcessor.class, true, false);

        // Register BeanPostProcessorChecker that logs an info message when
        // a bean is created during BeanPostProcessor instantiation, i.e. when
        // a bean is not eligible for getting processed by all BeanPostProcessors.
        int beanProcessorTargetCount = beanFactory.getBeanPostProcessorCount() + 1 + postProcessorNames.length;
        beanFactory.addBeanPostProcessor(new BeanPostProcessorChecker(beanFactory, beanProcessorTargetCount));

        // Separate between BeanPostProcessors that implement PriorityOrdered,
        // Ordered, and the rest.
        List<BeanPostProcessor> priorityOrderedPostProcessors = new ArrayList<BeanPostProcessor>();
        List<BeanPostProcessor> internalPostProcessors = new ArrayList<BeanPostProcessor>();
        List<String> orderedPostProcessorNames = new ArrayList<String>();
        List<String> nonOrderedPostProcessorNames = new ArrayList<String>();
        for (String ppName : postProcessorNames) {
            if (beanFactory.isTypeMatch(ppName, PriorityOrdered.class)) {
                BeanPostProcessor pp = beanFactory.getBean(ppName, BeanPostProcessor.class);
                priorityOrderedPostProcessors.add(pp);
                if (pp instanceof MergedBeanDefinitionPostProcessor) {
                    internalPostProcessors.add(pp);
                }
            }
            else if (beanFactory.isTypeMatch(ppName, Ordered.class)) {
                orderedPostProcessorNames.add(ppName);
            }
            else {
                nonOrderedPostProcessorNames.add(ppName);
            }
        }

        // First, register the BeanPostProcessors that implement PriorityOrdered.
        sortPostProcessors(beanFactory, priorityOrderedPostProcessors);
        registerBeanPostProcessors(beanFactory, priorityOrderedPostProcessors);

        // Next, register the BeanPostProcessors that implement Ordered.
        List<BeanPostProcessor> orderedPostProcessors = new ArrayList<BeanPostProcessor>();
        for (String ppName : orderedPostProcessorNames) {
            BeanPostProcessor pp = beanFactory.getBean(ppName, BeanPostProcessor.class);
            orderedPostProcessors.add(pp);
            if (pp instanceof MergedBeanDefinitionPostProcessor) {
                internalPostProcessors.add(pp);
            }
        }
        sortPostProcessors(beanFactory, orderedPostProcessors);
        registerBeanPostProcessors(beanFactory, orderedPostProcessors);

        // Now, register all regular BeanPostProcessors.
        List<BeanPostProcessor> nonOrderedPostProcessors = new ArrayList<BeanPostProcessor>();
        for (String ppName : nonOrderedPostProcessorNames) {
            BeanPostProcessor pp = beanFactory.getBean(ppName, BeanPostProcessor.class);
            nonOrderedPostProcessors.add(pp);
            if (pp instanceof MergedBeanDefinitionPostProcessor) {
                internalPostProcessors.add(pp);
            }
        }
        registerBeanPostProcessors(beanFactory, nonOrderedPostProcessors);

        // Finally, re-register all internal BeanPostProcessors.
        sortPostProcessors(beanFactory, internalPostProcessors);
        registerBeanPostProcessors(beanFactory, internalPostProcessors);

        // Re-register post-processor for detecting inner beans as ApplicationListeners,
        // moving it to the end of the processor chain (for picking up proxies etc).
        beanFactory.addBeanPostProcessor(new ApplicationListenerDetector(applicationContext));
    }

其实在第3步prepareBeanFactory中也注册了一些BeanPostProcessor，比如ApplicationContextAwareProcessor，ApplicationListenerDetector等。

最终BeanPostProcessor调用逻辑是在AbstractAutowireCapableBeanFactory的initializeBean方法实现的

protected Object initializeBean(final String beanName, final Object bean, RootBeanDefinition mbd) {
        if (System.getSecurityManager() != null) {
            AccessController.doPrivileged(new PrivilegedAction<Object>() {
                @Override
                public Object run() {
                    invokeAwareMethods(beanName, bean);
                    return null;
                }
            }, getAccessControlContext());
        }
        else {
            invokeAwareMethods(beanName, bean);
        }

        Object wrappedBean = bean;
        if (mbd == null || !mbd.isSynthetic()) {
           //调用postProcessBeforeInitialization方法
            wrappedBean = applyBeanPostProcessorsBeforeInitialization(wrappedBean, beanName);
        }

        try {
            invokeInitMethods(beanName, wrappedBean, mbd);
        }
        catch (Throwable ex) {
            throw new BeanCreationException(
                    (mbd != null ? mbd.getResourceDescription() : null),
                    beanName, "Invocation of init method failed", ex);
        }

        if (mbd == null || !mbd.isSynthetic()) {
           //调用postProcessBeforeInitialization方法
            wrappedBean = applyBeanPostProcessorsAfterInitialization(wrappedBean, beanName);
        }
        return wrappedBean;
    }

调用顺序

BeanPostProcessor是在bean的初始化前后调用的，那么它和各种初始化方法调用的顺序，和BeanFactoryPostProcesser调用顺序如何：

• 1、BeanFactoryPostProcessor.postProcessBeanFactory
• 2、构造方法
• 3、设置属性
• 4、BeanPostProcesser.postProcessBeforeInitialization
• 5、@PostConstruct 注解方法
• 6、InitializingBean.afterPropertiesSet
• 7、自定义init方法
• 8、BeanPostProcesser.postProcessAfterInitialization
• 9、@PreDestroy方法
• 10、DisposableBean.destroy
• 11、自定义destroy方法

1、在获取BeanFactory之后调用的，此时已经读取了Bean的定义BeanDefinition。

4、BeanPostProcesser在调用bean的初始化方法，实例化之后

5、@PostConstruct也是通过BeanPostProcesser(InitDestroyAnnotationBeanPostProcessor)实现的，但是InitDestroyAnnotationBeanPostProcessor定义了最低优先级(Ordered.LOWEST_PRECEDENCE)，所以在4之后

6、可以看AbstractAutowireCapableBeanFactory的initializeBean方法，下边的源码只保留关键部分，可以看到先后顺序如下，初始化方法在BeanPostProcessor之后，所以在5之后。

1）BeanPostProcesser的postProcessBeforeInitialization

2）初始化方法，invokeInitMethods里先是调用
InitializingBean.afterPropertiesSet()，然后调用自定义init方法

3）BeanPostProcesser的postProcessAfterInitialization

protected Object initializeBean(final String beanName, final Object bean, RootBeanDefinition mbd) {
    Object wrappedBean = bean;
    wrappedBean = applyBeanPostProcessorsBeforeInitialization(wrappedBean, beanName);

    invokeInitMethods(beanName, wrappedBean, mbd);

    wrappedBean = applyBeanPostProcessorsAfterInitialization(wrappedBean, beanName);

    return wrappedBean;
}

8、 9、 10、11 可以看DisposableBeanAdapter的destroy方法核心代码：

public void destroy() {
     // 8、9
    if (!CollectionUtils.isEmpty(this.beanPostProcessors)) {
        for (DestructionAwareBeanPostProcessor processor : this.beanPostProcessors) {
            processor.postProcessBeforeDestruction(this.bean, this.beanName);
        }
    }
    // 10
    if (this.invokeDisposableBean) {
        ((DisposableBean) bean).destroy();
    }
    // 11
    if (this.destroyMethod != null) {
        invokeCustomDestroyMethod(this.destroyMethod);
    }
    else if (this.destroyMethodName != null) {
        Method methodToCall = determineDestroyMethod();
        if (methodToCall != null) {
            invokeCustomDestroyMethod(methodToCall);
        }
    }
}