如何解析SpringFramework的@Configuration/@Import注解
这篇文章主要介绍"如何解析SpringFramework的@Configuration/@Import注解"，在日常操作中，相信很多人在如何解析SpringFramework的@Configuration/@Import注解问题上存在疑惑，小编查阅了各式资料，整理出简单好用的操作方法，希望对大家解答"如何解析SpringFramework的@Configuration/@Import注解"的疑惑有所帮助！接下来，请跟着小编一起来学习吧！
Spring版本是5.0.9.release，Springboot版本是2.0.3.release
Springboot中，Servlet web应用，使用的是AnnotationConfigServletWebServerApplicationContext，它的构造方法中实例化了AnnotatedBeanDefinitionReader，如下List-1，调用了AnnotationConfigUtils.registerAnnotationConfigProcessors(this.registry)，如List-2所示:
List-1
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);}List-2
public static SetregisterAnnotationConfigProcessors( BeanDefinitionRegistry registry, @Nullable Object source) { ... 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)); } ...
如List-2所示，ConfigurationClassPostProcessor转换为BeanDefinition，注册到registry中。ConfigurationClassPostProcessor实现了BeanFacotryPostProcessor接口，如果熟悉SpringIOC，应该知道这个的作用。
图1
AnnotationConfigServletWebServerApplicationContext继承了AbstractApplicationContext，AbstractApplicationContext的refresh()如下List-3所示，refresh()中调用了this.invokeBeanFactoryPostProcessors(beanFactory)，接着调用了PostProcessorRegistrationDelegate.invokeBeanFactoryPostProcessors(beanFactory, this.getBeanFactoryPostProcessors())，从BeanFactory方法中获取所有BeanFactoryPostProcessor，之后调用BeanFactoryPostProcessor的postProcessBeanFactory()。
List-3
public void refresh() throws BeansException, IllegalStateException { synchronized(this.startupShutdownMonitor) { this.prepareRefresh(); ConfigurableListableBeanFactory beanFactory = this.obtainFreshBeanFactory(); this.prepareBeanFactory(beanFactory); try { this.postProcessBeanFactory(beanFactory); this.invokeBeanFactoryPostProcessors(beanFactory); this.registerBeanPostProcessors(beanFactory); this.initMessageSource(); this.initApplicationEventMulticaster(); this.onRefresh(); this.registerListeners(); this.finishBeanFactoryInitialization(beanFactory); this.finishRefresh(); } catch (BeansException var9) { if (this.logger.isWarnEnabled()) { this.logger.warn("Exception encountered during context initialization - cancelling refresh attempt: " + var9); } this.destroyBeans(); this.cancelRefresh(var9); throw var9; } finally { this.resetCommonCaches(); } }}回到ConfigurationClassPostProcessor，看它的postProcessBeanFactory()，调用了processConfigBeanDefinitions()，如下List-4，代码很多，不过看关键部分就好了，1处的ConfigurationClassUtils.checkConfigurationClassCandidate要重点看，这个方法中判断类上是否有Configuration/ComponentScan/Import/ImportResource注解，如果有这些注解，那么会加入到configCandidates中，循环处理configCandidates，交给ConfigurationClassParser.pase()进行解析。
List-4
public void processConfigBeanDefinitions(BeanDefinitionRegistry registry) { List configCandidates = new ArrayList<>(); String[] candidateNames = registry.getBeanDefinitionNames(); for (String beanName : candidateNames) { BeanDefinition beanDef = registry.getBeanDefinition(beanName); if (ConfigurationClassUtils.isFullConfigurationClass(beanDef) || ConfigurationClassUtils.isLiteConfigurationClass(beanDef)) { if (logger.isDebugEnabled()) { logger.debug("Bean definition has already been processed as a configuration class: " + beanDef); } } //1 else if (ConfigurationClassUtils.checkConfigurationClassCandidate(beanDef, this.metadataReaderFactory)) { configCandidates.add(new BeanDefinitionHolder(beanDef, beanName)); } } // Return immediately if no @Configuration classes were found if (configCandidates.isEmpty()) { return; } // Sort by previously determined @Order value, if applicable configCandidates.sort((bd1, bd2) -> { int i1 = ConfigurationClassUtils.getOrder(bd1.getBeanDefinition()); int i2 = ConfigurationClassUtils.getOrder(bd2.getBeanDefinition()); return Integer.compare(i1, i2); }); // 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 candidates = new LinkedHashSet<>(configCandidates); Set alreadyParsed = new HashSet<>(configCandidates.size()); do { parser.parse(candidates); parser.validate(); Set 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 oldCandidateNames = new HashSet<>(Arrays.asList(candidateNames)); Set 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()); } if (this.metadataReaderFactory instanceof CachingMetadataReaderFactory) { // Clear cache in externally provided MetadataReaderFactory; this is a no-op // for a shared cache since it'll be cleared by the ApplicationContext. ((CachingMetadataReaderFactory) this.metadataReaderFactory).clearCache(); }} 自动装配中EnableXX注解上的Import引入的Selector的处理就是在这里处理的，有趣的是Selector返回的String[]中的值需要是类的完全路径累名，这是因为使用Class.forName()将String类型的beanName转换为对应的Class类型。
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