ConfigurationClassPostProcessor原理详解

叔牙

修改于 2022-01-05 10:01:27

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修改于 2022-01-05 10:01:27

一、概念介绍

BeanFactoryPostProcessor used for bootstrapping processing of @Configuration classes. Registered by default when usingor. Otherwise, may be declared manually as with any other BeanFactoryPostProcessor. This post processor is priority-ordered as it is important that any Bean methods declared in @Configuration classes have their corresponding bean definitions registered before any other BeanFactoryPostProcessor executes.

从spring官方介绍中,我们可以了解到ConfigurationClassPostProcessor是一个BeanFactoryPostProcessor,用于处理一些配置信息和注解扫描,并且该处理器执行的时候有优先级顺序,优先执行PriorityOrdered,然后执行Ordered,最后执行默认没有优先级的处理器。

并且ConfigurationClassPostProcessor只spring框架中最重要的BeanFactoryPostProcessor,也是最重要的内置组件之一。

二、作用

ConfigurationClassPostProcessor是一个BeanFactoryPostProcessor,同时也是BeanDefinitionRegistryPostProcessor,那么它发挥作用和执行逻辑就在于两个PostProcessor的方法,分别是postProcessBeanFactory和postProcessBeanDefinitionRegistry,对于执行优先级后边再分析,那么整个过程中做了哪些事情,发挥了哪些作用呢？

对于候选配置类使用CGLIB Enhancer增强
解析处理@PropertySource 注解
解析@ComponentScan注解,扫描@Configuration、@Service、@Controller、@Repository和@Component注解并注册BeanDefinition
解析@Import注解,然后进行实例化,并执行ImportBeanDefinitionRegistrar的registerBeanDefinitions逻辑,或者ImportSelector的selectImports逻辑
解析@ImportResource注解,并加载相关配置信息
解析方法级别@Bean注解并将返回值注册成BeanDefinition
注册ImportRegistry到容器中,用于处理ImportAware

三、原理分析

我们先看一下ConfigurationClassPostProcessor继承关系:

本质上是BeanFactoryPostProcessor,并且持有资源加载器、环境变量、类加载器,也是一个优先执行的处理器。

对于ConfigurationClassPostProcessor的原理分析,我们从加载注册BeanDefinition、实例化和调用时机以及逻辑几个维度来展开。

note:代码分析基于springboot2.1.3和spring5.1.5

1.ConfigurationClassPostProcessor加载与注册BeanDefinition

Springboot应用启动时会调用AbstractApplicationContext的refresh方法:

@Override
public void refresh() throws BeansException, IllegalStateException {
  synchronized (this.startupShutdownMonitor) {
    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);
      //...省略
    }

    catch (BeansException 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();
    }
  }
}

我们先看第6行调用obtainFreshBeanFactory方法:

protected ConfigurableListableBeanFactory obtainFreshBeanFactory() {
  refreshBeanFactory();
  return getBeanFactory();
}

然后调用子类AbstractRefreshableApplicationContext的refreshBeanFactory方法实现:

@Override
protected final void refreshBeanFactory() throws BeansException {
  if (hasBeanFactory()) {
    destroyBeans();
    closeBeanFactory();
  }
  try {
    DefaultListableBeanFactory beanFactory = createBeanFactory();
    beanFactory.setSerializationId(getId());
    customizeBeanFactory(beanFactory);
    loadBeanDefinitions(beanFactory);
    synchronized (this.beanFactoryMonitor) {
      this.beanFactory = beanFactory;
    }
  }
  catch (IOException ex) {
    throw new ApplicationContextException("I/O error parsing bean definition source for " + getDisplayName(), ex);
  }
}

接着又调用了子类AnnotationConfigWebApplicationContext的loadBeanDefinitions实现:

@Override
protected void loadBeanDefinitions(DefaultListableBeanFactory beanFactory) {
  AnnotatedBeanDefinitionReader reader = getAnnotatedBeanDefinitionReader(beanFactory);
  ClassPathBeanDefinitionScanner scanner = getClassPathBeanDefinitionScanner(beanFactory);

  //...省略
}

该方法实例化了基于注解的BeanDefinitionReader和基于路径扫描的BeanDefinitionScanner,后边都会用到,接着看getAnnotatedBeanDefinitionReader实现:

protected AnnotatedBeanDefinitionReader getAnnotatedBeanDefinitionReader(DefaultListableBeanFactory beanFactory) {
  return new AnnotatedBeanDefinitionReader(beanFactory, getEnvironment());
}
//构造器
public AnnotatedBeanDefinitionReader(BeanDefinitionRegistry registry, Environment environment) {
  Assert.notNull(registry, "BeanDefinitionRegistry must not be null");
  Assert.notNull(environment, "Environment must not be null");
  this.registry = registry;
  this.conditionEvaluator = new ConditionEvaluator(registry, environment, null);
  AnnotationConfigUtils.registerAnnotationConfigProcessors(this.registry);
}

在创建AnnotatedBeanDefinitionReader的时候,调用了AnnotationConfigUtils的注册注解配置处理器方法:

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

  DefaultListableBeanFactory beanFactory = unwrapDefaultListableBeanFactory(registry);


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

  if (!registry.containsBeanDefinition(CONFIGURATION_ANNOTATION_PROCESSOR_BEAN_NAME)) {
    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;
}

这里把ConfigurationClassPostProcessor注册成RootBeanDefinition到容器中,并且把角色定义成ROLE_INFRASTRUCTURE,在应用启动后我们无法显式获取以及调用,同时也注册了其他处理器(AutowiredAnnotationBeanPostProcessor、CommonAnnotationBeanPostProcessor等)。

整个ConfigurationClassPostProcessor的BeanDefinition注册流程大致如下:

到这里只是完成了ConfigurationClassPostProcessor的定义和BeanDefinition注册,并没有执行实例化,框架层暂时无法调用其逻辑。

2.ConfigurationClassPostProcessor实例化与调用

之所以把实例化和调用放到一起分析,是因为两者在相同入口并且按照先后顺序一起触发。

同样入口是AbstractApplicationContext的refresh方法,调用invokeBeanFactoryPostProcessors方法:

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()));
  }
}

然后会调用到PostProcessorRegistrationDelegate的invokeBeanFactoryPostProcessors方法:

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

  // Invoke BeanDefinitionRegistryPostProcessors first, if any.
  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);
  }

  // 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();
}

这段代码的大概意思是如果BeanFactory中有已经实例化的BeanDefinitionRegistryPostProcessor,那么优先调用,然后调用实现PriorityOrdered接口的P,接着调用实现Ordered接口的,最后调用普通的,然后按照这个逻辑调用BeanFactoryPostProcessor逻辑。

我们的BeanFactory类型是DefaultListableBeanFactory,从其继承关系中可以看出它是BeanDefinitionRegistry类型。

所以会执行if分支逻辑,如果 BeanFactory中有BeanDefinitionRegistryPostProcessor类型PostProcessor,则优先执行一次,我们可以看出框架中有2个已经实例化的BeanDefinitionRegistryPostProcessor:

很明显我们的ConfigurationClassPostProcessor并没有实例化,这段代码不会调用到,继续往后边看后优先调用实现了PriorityOrdered接口的BeanDefinitionRegistryPostProcessor,ConfigurationClassPostProcessor实现了PriorityOrdered接口会优先调用。需要主要的是,中间有一行代码调用BeanFactory的getBean方法:

currentRegistryProcessors.add(beanFactory.getBean(ppName, BeanDefinitionRegistryPostProcessor.class));

会直接调用父类AbstractBeanFactory的getBean方法进行实例化:

@Override
public <T> T getBean(String name, Class<T> requiredType) throws BeansException {
  return doGetBean(name, requiredType, null, false);
}

实例化流程我们本篇不再展开分析,可以参考上一篇文章《@ComponentScan原理分析》有介绍:

回到invokeBeanFactoryPostProcessors方法,BeanDefinitionRegistryPostProcessor实例化之后,添加到列表中,然后按照PriorityOrdered优先级排序,然后调用invokeBeanDefinitionRegistryPostProcessors方法循环调用:

private static void invokeBeanDefinitionRegistryPostProcessors(
    Collection<? extends BeanDefinitionRegistryPostProcessor> postProcessors, BeanDefinitionRegistry registry) {

  for (BeanDefinitionRegistryPostProcessor postProcessor : postProcessors) {
    postProcessor.postProcessBeanDefinitionRegistry(registry);
  }
}

3.ConfigurationClassPostProcessor逻辑执行

调用ConfigurationClassPostProcessor的postProcessBeanDefinitionRegistry方法:

@Override
public void postProcessBeanDefinitionRegistry(BeanDefinitionRegistry registry) {
  int registryId = System.identityHashCode(registry);
  if (this.registriesPostProcessed.contains(registryId)) {
    throw new IllegalStateException(
        "postProcessBeanDefinitionRegistry already called on this post-processor against " + registry);
  }
  if (this.factoriesPostProcessed.contains(registryId)) {
    throw new IllegalStateException(
        "postProcessBeanFactory already called on this post-processor against " + registry);
  }
  this.registriesPostProcessed.add(registryId);

  processConfigBeanDefinitions(registry);
}

这里生成registryId并添加到registriesPostProcessed中,然后调用processConfigBeanDefinitions(后边调用postProcessBeanFactory的时候不在调用processConfigBeanDefinitions):

public void processConfigBeanDefinitions(BeanDefinitionRegistry registry) {
  List<BeanDefinitionHolder> configCandidates = new ArrayList<>();
  String[] candidateNames = registry.getBeanDefinitionNames();
  //...省略

  // Detect any custom bean name generation strategy supplied through the enclosing application context
  SingletonBeanRegistry sbr = null;
  if (registry instanceof SingletonBeanRegistry) {
    sbr = (SingletonBeanRegistry) registry;
    if (!this.localBeanNameGeneratorSet) {
      BeanNameGenerator generator = (BeanNameGenerator) sbr.getSingleton(CONFIGURATION_BEAN_NAME_GENERATOR);
      if (generator != null) {
        this.componentScanBeanNameGenerator = generator;
        this.importBeanNameGenerator = generator;
      }
    }
  }

  if (this.environment == null) {
    this.environment = new StandardEnvironment();
  }

  // Parse each @Configuration class
  ConfigurationClassParser parser = new ConfigurationClassParser(
      this.metadataReaderFactory, this.problemReporter, this.environment,
      this.resourceLoader, this.componentScanBeanNameGenerator, registry);

  Set<BeanDefinitionHolder> candidates = new LinkedHashSet<>(configCandidates);
  Set<ConfigurationClass> alreadyParsed = new HashSet<>(configCandidates.size());
  do {
    parser.parse(candidates);
    parser.validate();

    Set<ConfigurationClass> configClasses = new LinkedHashSet<>(parser.getConfigurationClasses());
    configClasses.removeAll(alreadyParsed);

    // Read the model and create bean definitions based on its content
    if (this.reader == null) {
      this.reader = new ConfigurationClassBeanDefinitionReader(
          registry, this.sourceExtractor, this.resourceLoader, this.environment,
          this.importBeanNameGenerator, parser.getImportRegistry());
    }
    this.reader.loadBeanDefinitions(configClasses);
    alreadyParsed.addAll(configClasses);

    candidates.clear();
    if (registry.getBeanDefinitionCount() > candidateNames.length) {
      String[] newCandidateNames = registry.getBeanDefinitionNames();
      Set<String> oldCandidateNames = new HashSet<>(Arrays.asList(candidateNames));
      Set<String> alreadyParsedClasses = new HashSet<>();
      for (ConfigurationClass configurationClass : alreadyParsed) {
        alreadyParsedClasses.add(configurationClass.getMetadata().getClassName());
      }
      for (String candidateName : newCandidateNames) {
        if (!oldCandidateNames.contains(candidateName)) {
          BeanDefinition bd = registry.getBeanDefinition(candidateName);
          if (ConfigurationClassUtils.checkConfigurationClassCandidate(bd, this.metadataReaderFactory) &&
              !alreadyParsedClasses.contains(bd.getBeanClassName())) {
            candidates.add(new BeanDefinitionHolder(bd, candidateName));
          }
        }
      }
      candidateNames = newCandidateNames;
    }
  }
  while (!candidates.isEmpty());

  // Register the ImportRegistry as a bean in order to support ImportAware @Configuration classes
  if (sbr != null && !sbr.containsSingleton(IMPORT_REGISTRY_BEAN_NAME)) {
    sbr.registerSingleton(IMPORT_REGISTRY_BEAN_NAME, parser.getImportRegistry());
  }
}

此方法先解析配置类,然后注册ImportRegistry,我们重点看一下ConfigurationClassParser的parse调用和ConfigurationClassBeanDefinitionReader的loadBeanDefinitions调用,先看ConfigurationClassParser的parse方法:

public void parse(Set<BeanDefinitionHolder> configCandidates) {
  for (BeanDefinitionHolder holder : configCandidates) {
    BeanDefinition bd = holder.getBeanDefinition();
    try {
      if (bd instanceof AnnotatedBeanDefinition) {
        parse(((AnnotatedBeanDefinition) bd).getMetadata(), holder.getBeanName());
      }
      else if (bd instanceof AbstractBeanDefinition && ((AbstractBeanDefinition) bd).hasBeanClass()) {
        parse(((AbstractBeanDefinition) bd).getBeanClass(), holder.getBeanName());
      }
      else {
        parse(bd.getBeanClassName(), holder.getBeanName());
      }
    }
    catch (BeanDefinitionStoreException ex) {
      throw ex;
    }
    catch (Throwable ex) {
      throw new BeanDefinitionStoreException(
          "Failed to parse configuration class [" + bd.getBeanClassName() + "]", ex);
    }
  }

  this.deferredImportSelectorHandler.process();
}

先执行解析逻辑,最后执行DeferredImportSelector相关逻辑调用,parse方法最终调用到doProcessConfigurationClass:

@Nullable
protected final SourceClass doProcessConfigurationClass(ConfigurationClass configClass, SourceClass sourceClass)
    throws IOException {

  //...省略
  // Process any @PropertySource annotations
  for (AnnotationAttributes propertySource : AnnotationConfigUtils.attributesForRepeatable(
      sourceClass.getMetadata(), PropertySources.class,
      org.springframework.context.annotation.PropertySource.class)) {
    if (this.environment instanceof ConfigurableEnvironment) {
      processPropertySource(propertySource);
    }
    else {
      logger.info("Ignoring @PropertySource annotation on [" + sourceClass.getMetadata().getClassName() +
          "]. Reason: Environment must implement ConfigurableEnvironment");
    }
  }

  // Process any @ComponentScan annotations
  Set<AnnotationAttributes> componentScans = AnnotationConfigUtils.attributesForRepeatable(
      sourceClass.getMetadata(), ComponentScans.class, ComponentScan.class);
  if (!componentScans.isEmpty() &&
      !this.conditionEvaluator.shouldSkip(sourceClass.getMetadata(), ConfigurationPhase.REGISTER_BEAN)) {
    for (AnnotationAttributes componentScan : componentScans) {
      // The config class is annotated with @ComponentScan -> perform the scan immediately
      Set<BeanDefinitionHolder> scannedBeanDefinitions =
          this.componentScanParser.parse(componentScan, sourceClass.getMetadata().getClassName());
      // Check the set of scanned definitions for any further config classes and parse recursively if needed
      for (BeanDefinitionHolder holder : scannedBeanDefinitions) {
        BeanDefinition bdCand = holder.getBeanDefinition().getOriginatingBeanDefinition();
        if (bdCand == null) {
          bdCand = holder.getBeanDefinition();
        }
        if (ConfigurationClassUtils.checkConfigurationClassCandidate(bdCand, this.metadataReaderFactory)) {
          parse(bdCand.getBeanClassName(), holder.getBeanName());
        }
      }
    }
  }

  // Process any @Import annotations
  processImports(configClass, sourceClass, getImports(sourceClass), true);

  // Process any @ImportResource annotations
  AnnotationAttributes importResource =
      AnnotationConfigUtils.attributesFor(sourceClass.getMetadata(), ImportResource.class);
  if (importResource != null) {
    String[] resources = importResource.getStringArray("locations");
    Class<? extends BeanDefinitionReader> readerClass = importResource.getClass("reader");
    for (String resource : resources) {
      String resolvedResource = this.environment.resolveRequiredPlaceholders(resource);
      configClass.addImportedResource(resolvedResource, readerClass);
    }
  }

  // Process individual @Bean methods
  Set<MethodMetadata> beanMethods = retrieveBeanMethodMetadata(sourceClass);
  for (MethodMetadata methodMetadata : beanMethods) {
    configClass.addBeanMethod(new BeanMethod(methodMetadata, configClass));
  }

  // Process default methods on interfaces
  processInterfaces(configClass, sourceClass);

  // Process superclass, if any
  if (sourceClass.getMetadata().hasSuperClass()) {
    String superclass = sourceClass.getMetadata().getSuperClassName();
    if (superclass != null && !superclass.startsWith("java") &&
        !this.knownSuperclasses.containsKey(superclass)) {
      this.knownSuperclasses.put(superclass, configClass);
      // Superclass found, return its annotation metadata and recurse
      return sourceClass.getSuperClass();
    }
  }

  // No superclass -> processing is complete
  return null;
}

从注释中我们清晰的看到,先解析@PropertySource注解,然后解析@ComponentScan注解扫描注册@Component以及衍生注解标注的类,接着处理@Import注解并执行ImportSelector或ImportBeanDefinitionRegistrar的方法调用,然后解析@ImportResource注解并加载资源,最后处理@Bean的方法并注册BeanDefinition返回调用。

这里把很多配置、或者用户自定义类都加载并且注册了BeanDefinition到容器中备用。然后我们回到processConfigBeanDefinitions方法循环体中的loadBeanDefinitions:

this.reader.loadBeanDefinitions(configClasses);

调用了ConfigurationClassBeanDefinitionReader的loadBeanDefinitions方法:

public void loadBeanDefinitions(Set<ConfigurationClass> configurationModel) {
  TrackedConditionEvaluator trackedConditionEvaluator = new TrackedConditionEvaluator();
  for (ConfigurationClass configClass : configurationModel) {
    loadBeanDefinitionsForConfigurationClass(configClass, trackedConditionEvaluator);
  }
}

循环调用loadBeanDefinitionsForConfigurationClass方法:

private void loadBeanDefinitionsForConfigurationClass(
    ConfigurationClass configClass, TrackedConditionEvaluator trackedConditionEvaluator) {

  //...省略

  if (configClass.isImported()) {
    registerBeanDefinitionForImportedConfigurationClass(configClass);
  }
  for (BeanMethod beanMethod : configClass.getBeanMethods()) {
    loadBeanDefinitionsForBeanMethod(beanMethod);
  }

  loadBeanDefinitionsFromImportedResources(configClass.getImportedResources());
  loadBeanDefinitionsFromRegistrars(configClass.getImportBeanDefinitionRegistrars());
}

如果配置类是通过@Import导入的,把配置类注册成BeanDefinition,然后如果配置类有@Bean标注的方法,则将其注册成BeanDefinition,接着将导入的xml配置资源加载解析成Resource并转换注册成BeanDefinition,最后调用已经初始化后的ImportBeanDefinitionRegistrar的registerBeanDefinitions方法。

同样在PostProcessorRegistrationDelegate的invokeBeanFactoryPostProcessors方法中也会对普通BeanFactoryPostProcessor的调用,而ConfigurationClassPostProcessor对BeanFactoryPostProcessor接口重写比较简单,可以理解为对配置类做了增强处理,也就不展开分析了,感兴趣可以自行翻阅源码。

这样我们完成了从类加载、BeanDefinition注册、实例化和逻辑调用维度对ConfigurationClassPostProcessor工作原理的分析,以及逻辑调用中执行了哪些核心逻辑。

总结

ConfigurationClassPostProcessor是spring框架中一个极其重要的类,我们平时工作中用到的能力,比如@Configuration、@Bean、@Service、@Component、@Controller、@Repository以及@Import等,都是由ConfigurationClassPostProcessor帮我们完成注解扫描和类定义注册,然后再由BeanFactory完成实例化以及初始化逻辑。

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原始发表：2021-12-28，如有侵权请联系 cloudcommunity@tencent.com 删除

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