一、前言

• Springboot源码解析是一件大工程，逐行逐句的去研究代码，会很枯燥，也不容易坚持下去。
• 我们不追求大而全，而是试着每次去研究一个小知识点，最终聚沙成塔，这就是我们的springboot源码管中窥豹系列。

二、BeanFactoryPostProcessor

BeanFactoryPostProcessor是在bean初始化之前对bean的统一操作

package org.springframework.beans.factory.config;
import org.springframework.beans.BeansException;

@FunctionalInterface
public interface BeanFactoryPostProcessor {

	void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory) throws BeansException;

}

它还有个子接口：BeanDefinitionRegistryPostProcessor

package org.springframework.beans.factory.support;

import org.springframework.beans.BeansException;
import org.springframework.beans.factory.config.BeanFactoryPostProcessor;

public interface BeanDefinitionRegistryPostProcessor extends BeanFactoryPostProcessor {

	void postProcessBeanDefinitionRegistry(BeanDefinitionRegistry registry) throws BeansException;

}

BeanDefinitionRegistryPostProcessor在BeanFactoryPostProcessor之前执行

三、源码分析

从main方法入口进入到SpringApplication的run方法

public ConfigurableApplicationContext run(String... args) {
    StopWatch stopWatch = new StopWatch();
    stopWatch.start();
    ConfigurableApplicationContext context = null;
    Collection<SpringBootExceptionReporter> exceptionReporters = new ArrayList<>();
    configureHeadlessProperty();
    SpringApplicationRunListeners listeners = getRunListeners(args);
    listeners.starting();
    try {
        ApplicationArguments applicationArguments = new DefaultApplicationArguments(
                args);
        ConfigurableEnvironment environment = prepareEnvironment(listeners,
                applicationArguments);
        configureIgnoreBeanInfo(environment);
        Banner printedBanner = printBanner(environment);
        context = createApplicationContext();
        exceptionReporters = getSpringFactoriesInstances(
                SpringBootExceptionReporter.class,
                new Class[] { ConfigurableApplicationContext.class }, context);
        prepareContext(context, environment, listeners, applicationArguments,
                printedBanner);
        refreshContext(context);
        afterRefresh(context, applicationArguments);
        stopWatch.stop();
        if (this.logStartupInfo) {
            new StartupInfoLogger(this.mainApplicationClass)
                    .logStarted(getApplicationLog(), stopWatch);
        }
        listeners.started(context);
        callRunners(context, applicationArguments);
    }
    catch (Throwable ex) {
        handleRunFailure(context, ex, exceptionReporters, listeners);
        throw new IllegalStateException(ex);
    }

    try {
        listeners.running(context);
    }
    catch (Throwable ex) {
        handleRunFailure(context, ex, exceptionReporters, null);
        throw new IllegalStateException(ex);
    }
    return context;
}

进入到refreshContext里面：

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

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

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

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

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

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

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

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

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

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

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

            // 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();
        }
    }
}

主要用到的就是postProcessBeanFactory方法和invokeBeanFactoryPostProcessors方法

@Override
protected void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory) {
    super.postProcessBeanFactory(beanFactory);
    if (this.basePackages != null && this.basePackages.length > 0) {
        this.scanner.scan(this.basePackages);
    }
    if (!this.annotatedClasses.isEmpty()) {
        this.reader.register(ClassUtils.toClassArray(this.annotatedClasses));
    }
}

postProcessBeanFactory主要是扫描包

protected void invokeBeanFactoryPostProcessors(ConfigurableListableBeanFactory beanFactory) {
    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()));
    }
}

调用在invokeBeanFactoryPostProcessors方法里面

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

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

    if (beanFactory instanceof BeanDefinitionRegistry) {
        // 先折叠上
        ...

    }

    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<>();
    List<String> orderedPostProcessorNames = new ArrayList<>();
    List<String> nonOrderedPostProcessorNames = new ArrayList<>();
    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(priorityOrderedPostProcessors, beanFactory);
    invokeBeanFactoryPostProcessors(priorityOrderedPostProcessors, beanFactory);

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

    // Finally, invoke all other BeanFactoryPostProcessors.
    List<BeanFactoryPostProcessor> nonOrderedPostProcessors = new ArrayList<>();
    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();
}

• 折叠部分先不看，往下看
• 根据 beanFactory.getBeanNamesForType 取出BeanFactoryPostProcessor
• 根据priorityOrder , order , nonOrder分成三个list
• 对priorityOrderlist排序，执行invokeBeanFactoryPostProcessors
• 对orderlist排序，执行invokeBeanFactoryPostProcessors
• 对nonOrderlist排序，执行invokeBeanFactoryPostProcessors

private static void invokeBeanFactoryPostProcessors(
        Collection<? extends BeanFactoryPostProcessor> postProcessors, ConfigurableListableBeanFactory beanFactory) {

    for (BeanFactoryPostProcessor postProcessor : postProcessors) {
        postProcessor.postProcessBeanFactory(beanFactory);
    }
}

• 执行invokeBeanFactoryPostProcessors很简单，如上
• 我们在看一下折叠的部分

Set<String> processedBeans = new HashSet<>();

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

    for (BeanFactoryPostProcessor postProcessor : beanFactoryPostProcessors) {
        if (postProcessor instanceof BeanDefinitionRegistryPostProcessor) {
            BeanDefinitionRegistryPostProcessor registryProcessor =
                    (BeanDefinitionRegistryPostProcessor) postProcessor;
            registryProcessor.postProcessBeanDefinitionRegistry(registry);
            registryProcessors.add(registryProcessor);
        }
        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.
    List<BeanDefinitionRegistryPostProcessor> currentRegistryProcessors = new ArrayList<>();

    // First, invoke the BeanDefinitionRegistryPostProcessors that implement PriorityOrdered.
    String[] postProcessorNames =
            beanFactory.getBeanNamesForType(BeanDefinitionRegistryPostProcessor.class, true, false);
    for (String ppName : postProcessorNames) {
        if (beanFactory.isTypeMatch(ppName, PriorityOrdered.class)) {
            currentRegistryProcessors.add(beanFactory.getBean(ppName, BeanDefinitionRegistryPostProcessor.class));
            processedBeans.add(ppName);
        }
    }
    sortPostProcessors(currentRegistryProcessors, beanFactory);
    registryProcessors.addAll(currentRegistryProcessors);
    invokeBeanDefinitionRegistryPostProcessors(currentRegistryProcessors, registry);
    currentRegistryProcessors.clear();

    // Next, invoke the BeanDefinitionRegistryPostProcessors that implement Ordered.
    postProcessorNames = beanFactory.getBeanNamesForType(BeanDefinitionRegistryPostProcessor.class, true, false);
    for (String ppName : postProcessorNames) {
        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);
    invokeBeanDefinitionRegistryPostProcessors(currentRegistryProcessors, registry);
    currentRegistryProcessors.clear();

    // 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)) {
                currentRegistryProcessors.add(beanFactory.getBean(ppName, BeanDefinitionRegistryPostProcessor.class));
                processedBeans.add(ppName);
                reiterate = true;
            }
        }
        sortPostProcessors(currentRegistryProcessors, beanFactory);
        registryProcessors.addAll(currentRegistryProcessors);
        invokeBeanDefinitionRegistryPostProcessors(currentRegistryProcessors, registry);
        currentRegistryProcessors.clear();
    }

    // Now, invoke the postProcessBeanFactory callback of all processors handled so far.
    invokeBeanFactoryPostProcessors(registryProcessors, beanFactory);
    invokeBeanFactoryPostProcessors(regularPostProcessors, beanFactory);
}

else {
    // Invoke factory processors registered with the context instance.
    invokeBeanFactoryPostProcessors(beanFactoryPostProcessors, beanFactory);
}

• 如果类型是：BeanDefinitionRegistryPostProcessor，就执行registryProcessor.postProcessBeanDefinitionRegistry(registry);
• 同样按Priority,order,nonOrder的顺序执行registryProcessor.postProcessBeanDefinitionRegistry
• 分成两个list: regularPostProcessors(父接口)和registryProcessors（子接口）
• 先执行registryProcessors的invoke，再执行regularPostProcessors的invoke

总结一下：

• 如果类型是BeanDefinitionRegistryPostProcessor，就执行registryProcessor.postProcessBeanDefinitionRegistry(registry);
• 按Priority,order,nonOrder的顺序执行BeanDefinitionRegistryPostProcessor
• 上一步执行完了，执行registryProcessors的invoke, 再执行regularPostProcessors的invoke
• 最后按Priority,order,nonOrder的顺序执行普通的BeanFactoryPostProcessor

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