Spring framework源码解析-BeanFactoryPostProcessor详解BeanFactoryPo

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1. BeanFactoryPostProcessor继承关系

BeanFactoryPostProcessor 主要用来处理注入Bean到BeanFactory中以及Bean类上面的注解，比如 @Configuration

PropertySourcesPlaceholderConfigurer和 PropertyPlaceholderConfigurer

//xml context 元素解析
public class ContextNamespaceHandler extends NamespaceHandlerSupport {

    @Override
    public void init() {
        registerBeanDefinitionParser("property-placeholder", new PropertyPlaceholderBeanDefinitionParser());
        registerBeanDefinitionParser("property-override", new PropertyOverrideBeanDefinitionParser());
        registerBeanDefinitionParser("annotation-config", new AnnotationConfigBeanDefinitionParser());
        registerBeanDefinitionParser("component-scan", new ComponentScanBeanDefinitionParser());
        registerBeanDefinitionParser("load-time-weaver", new LoadTimeWeaverBeanDefinitionParser());
        registerBeanDefinitionParser("spring-configured", new SpringConfiguredBeanDefinitionParser());
        registerBeanDefinitionParser("mbean-export", new MBeanExportBeanDefinitionParser());
        registerBeanDefinitionParser("mbean-server", new MBeanServerBeanDefinitionParser());
    }

}

class PropertyPlaceholderBeanDefinitionParser extends AbstractPropertyLoadingBeanDefinitionParser {

    private static final String SYSTEM_PROPERTIES_MODE_ATTRIBUTE = "system-properties-mode";

    private static final String SYSTEM_PROPERTIES_MODE_DEFAULT = "ENVIRONMENT";


    @Override
    protected Class<?> getBeanClass(Element element) {
        // As of Spring 3.1, the default value of system-properties-mode has changed from
        // 'FALLBACK' to 'ENVIRONMENT'. This latter value indicates that resolution of
        // placeholders against system properties is a function of the Environment and
        // its current set of PropertySources.
        if (SYSTEM_PROPERTIES_MODE_DEFAULT.equals(element.getAttribute(SYSTEM_PROPERTIES_MODE_ATTRIBUTE))) {
            return PropertySourcesPlaceholderConfigurer.class;
        }

        // The user has explicitly specified a value for system-properties-mode: revert to
        // PropertyPlaceholderConfigurer to ensure backward compatibility with 3.0 and earlier.
        return PropertyPlaceholderConfigurer.class;
    }

    @Override
    protected void doParse(Element element, ParserContext parserContext, BeanDefinitionBuilder builder) {
        super.doParse(element, parserContext, builder);

        builder.addPropertyValue("ignoreUnresolvablePlaceholders",
                Boolean.valueOf(element.getAttribute("ignore-unresolvable")));

        String systemPropertiesModeName = element.getAttribute(SYSTEM_PROPERTIES_MODE_ATTRIBUTE);
        if (StringUtils.hasLength(systemPropertiesModeName) &&
                !systemPropertiesModeName.equals(SYSTEM_PROPERTIES_MODE_DEFAULT)) {
            builder.addPropertyValue("systemPropertiesModeName", "SYSTEM_PROPERTIES_MODE_" + systemPropertiesModeName);
        }

        if (element.hasAttribute("value-separator")) {
            builder.addPropertyValue("valueSeparator", element.getAttribute("value-separator"));
        }
        if (element.hasAttribute("trim-values")) {
            builder.addPropertyValue("trimValues", element.getAttribute("trim-values"));
        }
        if (element.hasAttribute("null-value")) {
            builder.addPropertyValue("nullValue", element.getAttribute("null-value"));
        }
    }

}

这类加载了。

ConfigurationClassPostProcessor

这个类注入分为两种：

XML的情况下注入

public class ContextNamespaceHandler extends NamespaceHandlerSupport {
    @Override
    public void init() {
        registerBeanDefinitionParser("property-placeholder", new PropertyPlaceholderBeanDefinitionParser());
        registerBeanDefinitionParser("property-override", new PropertyOverrideBeanDefinitionParser());
        //这个类注入
        registerBeanDefinitionParser("annotation-config", new AnnotationConfigBeanDefinitionParser());
        //这个类注入
        registerBeanDefinitionParser("component-scan", new ComponentScanBeanDefinitionParser());
        registerBeanDefinitionParser("load-time-weaver", new LoadTimeWeaverBeanDefinitionParser());
        registerBeanDefinitionParser("spring-configured", new SpringConfiguredBeanDefinitionParser());
        registerBeanDefinitionParser("mbean-export", new MBeanExportBeanDefinitionParser());
        registerBeanDefinitionParser("mbean-server", new MBeanServerBeanDefinitionParser());
    }
}

注解的情况下注入

AnnotationConfigUtils.registerAnnotationConfigProcessors(parserContext.getRegistry(), source);这个方法里面注入了

    public static Set<BeanDefinitionHolder> registerAnnotationConfigProcessors(
            BeanDefinitionRegistry registry, @Nullable Object source) {

        DefaultListableBeanFactory beanFactory = unwrapDefaultListableBeanFactory(registry);
        if (beanFactory != null) {
            if (!(beanFactory.getDependencyComparator() instanceof AnnotationAwareOrderComparator)) {
                beanFactory.setDependencyComparator(AnnotationAwareOrderComparator.INSTANCE);
            }
            if (!(beanFactory.getAutowireCandidateResolver() instanceof ContextAnnotationAutowireCandidateResolver)) {
                beanFactory.setAutowireCandidateResolver(new ContextAnnotationAutowireCandidateResolver());
            }
        }

        Set<BeanDefinitionHolder> beanDefs = new LinkedHashSet<>(8);

        if (!registry.containsBeanDefinition(CONFIGURATION_ANNOTATION_PROCESSOR_BEAN_NAME)) {
            //注入ConfigurationClassPostProcessor
            RootBeanDefinition def = new RootBeanDefinition(ConfigurationClassPostProcessor.class);
        def.setSource(source);
            beanDefs.add(registerPostProcessor(registry, def, CONFIGURATION_ANNOTATION_PROCESSOR_BEAN_NAME));
        }

        if (!registry.containsBeanDefinition(AUTOWIRED_ANNOTATION_PROCESSOR_BEAN_NAME)) {
            RootBeanDefinition def = new RootBeanDefinition(AutowiredAnnotationBeanPostProcessor.class);
            def.setSource(source);
            beanDefs.add(registerPostProcessor(registry, def, AUTOWIRED_ANNOTATION_PROCESSOR_BEAN_NAME));
        }

        // Check for JSR-250 support, and if present add the CommonAnnotationBeanPostProcessor.
        if (jsr250Present && !registry.containsBeanDefinition(COMMON_ANNOTATION_PROCESSOR_BEAN_NAME)) {
            RootBeanDefinition def = new RootBeanDefinition(CommonAnnotationBeanPostProcessor.class);
            def.setSource(source);
            beanDefs.add(registerPostProcessor(registry, def, COMMON_ANNOTATION_PROCESSOR_BEAN_NAME));
        }

        // Check for JPA support, and if present add the PersistenceAnnotationBeanPostProcessor.
        if (jpaPresent && !registry.containsBeanDefinition(PERSISTENCE_ANNOTATION_PROCESSOR_BEAN_NAME)) {
            RootBeanDefinition def = new RootBeanDefinition();
            try {
                def.setBeanClass(ClassUtils.forName(PERSISTENCE_ANNOTATION_PROCESSOR_CLASS_NAME,
                        AnnotationConfigUtils.class.getClassLoader()));
            }
            catch (ClassNotFoundException ex) {
                throw new IllegalStateException(
                        "Cannot load optional framework class: " + PERSISTENCE_ANNOTATION_PROCESSOR_CLASS_NAME, ex);
            }
            def.setSource(source);
            beanDefs.add(registerPostProcessor(registry, def, PERSISTENCE_ANNOTATION_PROCESSOR_BEAN_NAME));
        }

        if (!registry.containsBeanDefinition(EVENT_LISTENER_PROCESSOR_BEAN_NAME)) {
            RootBeanDefinition def = new RootBeanDefinition(EventListenerMethodProcessor.class);
            def.setSource(source);
            beanDefs.add(registerPostProcessor(registry, def, EVENT_LISTENER_PROCESSOR_BEAN_NAME));
        }

        if (!registry.containsBeanDefinition(EVENT_LISTENER_FACTORY_BEAN_NAME)) {
            RootBeanDefinition def = new RootBeanDefinition(DefaultEventListenerFactory.class);
            def.setSource(source);
            beanDefs.add(registerPostProcessor(registry, def, EVENT_LISTENER_FACTORY_BEAN_NAME));
        }

        return beanDefs;
    }

在Spring源码中主要可以关注一下上面的三个实现类。

主要关注下面这两个接口：

BeanFactoryPostProcessor

BeanDefinitionRegistryPostProcessor (可以注入bean)

2. BeanFactoryPostProcessor在Spring中如何工作的源码分析

首先我们应该知道，不管是什么在Spring的容器中都是一个Bean ，经过bean的扫描或者xml定义后加载。代码首先会在这里进入：

AbstractApplicationContext#refresh#invokeBeanFactoryPostProcessors 方法中来处理

    protected void invokeBeanFactoryPostProcessors(ConfigurableListableBeanFactory beanFactory) {
        //这个方法主要处理实现了BeanFactoryPostProcessor接口的java类
        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()));
        }
    }

PostProcessorRegistrationDelegate.invokeBeanFactoryPostProcessors(beanFactory, getBeanFactoryPostProcessors()) 这个方法主要处理BeanFactoryPostProcessor实现的类。

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


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

        //判断BeanFactory是否为BeanDefinitionRegistry的实例(BeanDefinitionRegistry可以注入bean)
        if (beanFactory instanceof BeanDefinitionRegistry) {
            BeanDefinitionRegistry registry = (BeanDefinitionRegistry) beanFactory;

            //存放实现BeanFactoryPostProcessor的实例
            List<BeanFactoryPostProcessor> regularPostProcessors = new ArrayList<>();

            //存放实现BeanDefinitionRegistryPostProcessor
            List<BeanDefinitionRegistryPostProcessor> registryProcessors = new ArrayList<>();

            for (BeanFactoryPostProcessor postProcessor : beanFactoryPostProcessors) {

                //分类存放BeanDefinitionRegistryPostProcessor 和 BeanFactoryPostProcessor
                if (postProcessor instanceof BeanDefinitionRegistryPostProcessor) {
                    BeanDefinitionRegistryPostProcessor registryProcessor =
                            (BeanDefinitionRegistryPostProcessor) postProcessor;
                    //执行postProcessBeanDefinitionRegistry方法
                    registryProcessor.postProcessBeanDefinitionRegistry(registry);
                    registryProcessors.add(registryProcessor);
                }
                else {
                    regularPostProcessors.add(postProcessor);
                }
            }


            //处理当前BeanDefinitionRegistryPostProcessor实现类
            List<BeanDefinitionRegistryPostProcessor> currentRegistryProcessors = new ArrayList<>();

            // 首先执行实现了PriorityOrdered的BeanDefinitionRegistryPostProcessor实现类
            // 在beanFacotry中通过BeanDefinitionRegistryPostProcessor类型获取名称
            String[] postProcessorNames =
                    beanFactory.getBeanNamesForType(BeanDefinitionRegistryPostProcessor.class, true, false);
            for (String ppName : postProcessorNames) {

                //过滤出来PriorityOrdered的实现类
                if (beanFactory.isTypeMatch(ppName, PriorityOrdered.class)) {
                    currentRegistryProcessors.add(beanFactory.getBean(ppName, BeanDefinitionRegistryPostProcessor.class));
                    processedBeans.add(ppName);
                }
            }
            //排序按照PriorityOrdered
            sortPostProcessors(currentRegistryProcessors, beanFactory);
            registryProcessors.addAll(currentRegistryProcessors);
            //执行BeanDefinitionRegistryPostProcessor#postProcessBeanDefinitionRegistry()方法
            invokeBeanDefinitionRegistryPostProcessors(currentRegistryProcessors, registry);
            currentRegistryProcessors.clear();

            // 执行BeanDefinitionRegistryPostProcessors实现了Ordered接口的类.
            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();

            // 最后执行那些实现了BeanDefinitionRegistryPostProcessor类的
            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();
            }


            //调用BeanFactoryPostProcessor的postProcessBeanFactory
            invokeBeanFactoryPostProcessors(registryProcessors, beanFactory);
            invokeBeanFactoryPostProcessors(regularPostProcessors, beanFactory);
        }

        else {
            //直接调用postProcessor#postProcessBeanFactory
            invokeBeanFactoryPostProcessors(beanFactoryPostProcessors, beanFactory);
        }

        //下面处理的是实现了BeanFactoryPostProcessor的类
        String[] postProcessorNames =
                beanFactory.getBeanNamesForType(BeanFactoryPostProcessor.class, true, false);

        /**
         * 三种：
         * 1 实现了PriorityOrdered 和 BeanFactoryPostProcessor
         * 2 实现了Ordered 和 BeanFactoryPostProcessor
         * 3 只实现了BeanFactoryPostProcessor
         */
        List<BeanFactoryPostProcessor> priorityOrderedPostProcessors = new ArrayList<>();
        List<String> orderedPostProcessorNames = new ArrayList<>();
        List<String> nonOrderedPostProcessorNames = new ArrayList<>();
        for (String ppName : postProcessorNames) {

            if (processedBeans.contains(ppName)) {
                // 如果是BeanDefinitionRegistryPostProcessor处理过的就什么也不做
            }
            else if (beanFactory.isTypeMatch(ppName, PriorityOrdered.class)) {
                //保存实现了PriorityOrdered接口的BeanFactoryPostProcessor
                priorityOrderedPostProcessors.add(beanFactory.getBean(ppName, BeanFactoryPostProcessor.class));
            }
            else if (beanFactory.isTypeMatch(ppName, Ordered.class)) {
                //保存实现了Ordered接口的BeanFactoryPostProcessor
                orderedPostProcessorNames.add(ppName);
            }
            else {
                //正常的接口
                nonOrderedPostProcessorNames.add(ppName);
            }
        }

        //对priorityOrderedPostProcessors进行排序
        sortPostProcessors(priorityOrderedPostProcessors, beanFactory);
        //执行BeanFactoryPostProcessor#postProcessBeanFactory()方法
        invokeBeanFactoryPostProcessors(priorityOrderedPostProcessors, beanFactory);

        // 执行完实现了Ordered接口的BeanFactoryPostProcessor
        List<BeanFactoryPostProcessor> orderedPostProcessors = new ArrayList<>();
        for (String postProcessorName : orderedPostProcessorNames) {
            orderedPostProcessors.add(beanFactory.getBean(postProcessorName, BeanFactoryPostProcessor.class));
        }
        sortPostProcessors(orderedPostProcessors, beanFactory);
        invokeBeanFactoryPostProcessors(orderedPostProcessors, beanFactory);

        // 执行完剩下的BeanFactoryPostProcessor(没有实现Ordered和PriorityOrdered接口)
        List<BeanFactoryPostProcessor> nonOrderedPostProcessors = new ArrayList<>();
        for (String postProcessorName : nonOrderedPostProcessorNames) {
            nonOrderedPostProcessors.add(beanFactory.getBean(postProcessorName, BeanFactoryPostProcessor.class));
        }
        invokeBeanFactoryPostProcessors(nonOrderedPostProcessors, beanFactory);


        beanFactory.clearMetadataCache();
    }

通过上面的代码可以看出来，AbstractApplicationContext#refresh#invokeBeanFactoryPostProcessors 这个方法主要用来执行 BeanFactoryPostProcessor 和 BeanDefinitionRegistryPostProcessor 这两个类的接口。 BeanDefinitionRegistryPostProcessor 继承了 BeanFactoryPostProcessor 接口。从这里可以看出来Spring容器是如何调用这两个类的。这两个类执行的顺序

BeanDefinitionRegistryPostProcessor#postProcessBeanDefinitionRegistry
BeanFactoryPostProcessor#postProcessBeanFactory

3. 总结

BeanFactoryPostProcessor 的实现类主要处理类上面的注解比如：

@Configuration
@Order
@Component
@PropertySources
@ComponentScans
@ComponentScan
@Import
@ImportResource
@Bean(类内部方法上)

处理顺序图：

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