Spring5源碼解析5-ConfigurationClassPostProcessor (上)
- 2019 年 10 月 16 日
- 筆記
接上回，我們講到了refresh()方法中的invokeBeanFactoryPostProcessors(beanFactory)方法主要在執行BeanFactoryPostProcessor和其子接口BeanDefinitionRegistryPostProcessor的方法。
在創建AnnotationConfigApplicationContext對象時Spring就添加了一個非常重要的BeanFactoryPostProcessor接口實現類：ConfigurationClassPostProcessor。注意，這裡說的添加只是添加到容器的beanDefinitionMap中，還沒有創建真正的實例Bean。
簡單回顧一下ConfigurationClassPostProcessor是在什麼時候被添加到容器中的：在AnnotationConfigApplicationContext的無參構造器中創建AnnotatedBeanDefinitionReader對象時會向傳入的BeanDefinitionRegistry中註冊解析註解配置類相關的processors的BeanDefinition，ConfigurationClassPostProcessor就是在此處被添加到容器中的。
ConfigurationClassPostProcessor
先看一些ConfigurationClassPostProcessor的繼承體系：
ConfigurationClassPostProcessor實現了BeanDefinitionRegistryPostProcessor接口，也就擁有了在Spring容器啟動時，往容器中註冊BeanDefinition的能力。
我們知道，ConfigurationClassPostProcessor#postProcessBeanDefinitionRegistry方法是在refresh();方法中的invokeBeanFactoryPostProcessors(beanFactory);中被執行的，下面我們就一起來看一下該方法。
ConfigurationClassPostProcessor#postProcessBeanDefinitionRegistry
@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); }主要的邏輯在processConfigBeanDefinitions(registry);中，點開源碼：
public void processConfigBeanDefinitions(BeanDefinitionRegistry registry) { List<BeanDefinitionHolder> configCandidates = new ArrayList<>(); //獲取所有的BeanDefinitionName String[] candidateNames = registry.getBeanDefinitionNames(); for (String beanName : candidateNames) { BeanDefinition beanDef = registry.getBeanDefinition(beanName); // https://docs.spring.io/spring/docs/5.1.8.RELEASE/spring-framework-reference/core.html#beans-java-basic-concepts // Full @Configuration vs 「lite」 @Bean mode if (ConfigurationClassUtils.isFullConfigurationClass(beanDef) || ConfigurationClassUtils.isLiteConfigurationClass(beanDef)) { if (logger.isDebugEnabled()) { logger.debug("Bean definition has already been processed as a configuration class: " + beanDef); } } // 校驗是否為配置類 // 配置類分為兩種 Full @Configuration vs 「lite」 @Bean mode // 校驗之後在 BeanDefinition 中添加標誌屬性 // 如果滿足條件則加入到configCandidates else if (ConfigurationClassUtils.checkConfigurationClassCandidate(beanDef, this.metadataReaderFactory)) { // 如果是配置類,就放到 configCandidates 變量中 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; // 傳入的 registry 是 DefaultListableBeanFactory if (registry instanceof SingletonBeanRegistry) { sbr = (SingletonBeanRegistry) registry; if (!this.localBeanNameGeneratorSet) { //獲取自定義BeanNameGenerator,一般情況下為空 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 // new ConfigurationClassParser,用來解析 @Configuration 類 ConfigurationClassParser parser = new ConfigurationClassParser( this.metadataReaderFactory, this.problemReporter, this.environment, this.resourceLoader, this.componentScanBeanNameGenerator, registry); // 將 configCandidates 轉成 set candidates , 去重 Set<BeanDefinitionHolder> candidates = new LinkedHashSet<>(configCandidates); Set<ConfigurationClass> alreadyParsed = new HashSet<>(configCandidates.size()); do { // 解析配置類 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()); } // Import類,@Bean,@ImportResource 轉化為 BeanDefinition this.reader.loadBeanDefinitions(configClasses); alreadyParsed.addAll(configClasses); candidates.clear(); // 再獲取一下容器中BeanDefinition的數據,如果發現數量增加了,說明有新的BeanDefinition被註冊了 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()); } 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(); } }獲取所有的BeanDefinitionNames，然後循環這個數組，判斷其是否為配置類。
前5個是Spring註冊的內置processor，最後一個是傳入給AnnotationConfigApplicationContext的配置類AppConfig.class。
在Spring中存在兩種ConfigurationClass，一種是FullConfigurationClass另一種是LiteConfigurationClass。關於這兩者的區別，可以參看筆者文章之前關於Full @Configuration 和 lite @Bean mode的文章。
ConfigurationClassUtils#checkConfigurationClassCandidate方法內部就是在判斷屬於哪種配置類，並在BeanDefinition中標記判斷結果。其具體的判斷邏輯如下：
public static boolean isFullConfigurationCandidate(AnnotationMetadata metadata) { return metadata.isAnnotated(Configuration.class.getName()); } private static final Set<String> candidateIndicators = new HashSet<>(8); static { candidateIndicators.add(Component.class.getName()); candidateIndicators.add(ComponentScan.class.getName()); candidateIndicators.add(Import.class.getName()); candidateIndicators.add(ImportResource.class.getName()); } public static boolean isLiteConfigurationCandidate(AnnotationMetadata metadata) { // Do not consider an interface or an annotation... if (metadata.isInterface()) { return false; } // Any of the typical annotations found? for (String indicator : candidateIndicators) { if (metadata.isAnnotated(indicator)) { return true; } } // Finally, let's look for @Bean methods... try { return metadata.hasAnnotatedMethods(Bean.class.getName()); } catch (Throwable ex) { if (logger.isDebugEnabled()) { logger.debug("Failed to introspect @Bean methods on class [" + metadata.getClassName() + "]: " + ex); } return false; } }判斷configCandidates變量中存放的
配置類是否為空，如果不為空，則對其進行排序。
創建ConfigurationClassParser對象，用於解析@Configuration類，完成包的掃描、BeanDefinition的註冊。主要通過執行parser.parse(candidates);方法來完成。
執行parser.parse(candidates)方法前 ：
執行parser.parse(candidates)方法後 ：
解析完配置類之後，緊接着又執行了this.reader.loadBeanDefinitions(configClasses);方法。這個方法主要是用來處理Import類、@Bean和@ImportResource註解。關於這兩個方法的具體細節，我們下次再講。
最後又加了入了對ImportAware接口支持所需要的Bean。
// 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()); }關於對ImportAware接口的使用，我們也下次再講。
未完待續……
源碼學習筆記：https://github.com/shenjianeng/spring-code-study
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