Spring5源码解析5-ConfigurationClassPostProcessor (上)
- 2019 年 10 月 16 日
- 筆記
接上回，我们讲到了refresh()方法中的invokeBeanFactoryPostProcessors(beanFactory)方法主要在执行BeanFactoryPostProcessor和其子接口BeanDefinitionRegistryPostProcessor的方法。
在创建AnnotationConfigApplicationContext对象时Spring就添加了一个非常重要的BeanFactoryPostProcessor接口实现类：ConfigurationClassPostProcessor。注意，这里说的添加只是添加到容器的beanDefinitionMap中，还没有创建真正的实例Bean。
简单回顾一下ConfigurationClassPostProcessor是在什么时候被添加到容器中的：在AnnotationConfigApplicationContext的无参构造器中创建AnnotatedBeanDefinitionReader对象时会向传入的BeanDefinitionRegistry中注册解析注解配置类相关的processors的BeanDefinition，ConfigurationClassPostProcessor就是在此处被添加到容器中的。
ConfigurationClassPostProcessor
先看一些ConfigurationClassPostProcessor的继承体系：
ConfigurationClassPostProcessor实现了BeanDefinitionRegistryPostProcessor接口，也就拥有了在Spring容器启动时，往容器中注册BeanDefinition的能力。
我们知道，ConfigurationClassPostProcessor#postProcessBeanDefinitionRegistry方法是在refresh();方法中的invokeBeanFactoryPostProcessors(beanFactory);中被执行的，下面我们就一起来看一下该方法。
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); }主要的逻辑在processConfigBeanDefinitions(registry);中，点开源码：
public void processConfigBeanDefinitions(BeanDefinitionRegistry registry) { List<BeanDefinitionHolder> configCandidates = new ArrayList<>(); //获取所有的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); } } // 校验是否为配置类 // 配置类分为两种 Full @Configuration vs “lite” @Bean mode // 校验之后在 BeanDefinition 中添加标志属性 // 如果满足条件则加入到configCandidates else if (ConfigurationClassUtils.checkConfigurationClassCandidate(beanDef, this.metadataReaderFactory)) { // 如果是配置类,就放到 configCandidates 变量中 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; // 传入的 registry 是 DefaultListableBeanFactory if (registry instanceof SingletonBeanRegistry) { sbr = (SingletonBeanRegistry) registry; if (!this.localBeanNameGeneratorSet) { //获取自定义BeanNameGenerator,一般情况下为空 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,用来解析 @Configuration 类 ConfigurationClassParser parser = new ConfigurationClassParser( this.metadataReaderFactory, this.problemReporter, this.environment, this.resourceLoader, this.componentScanBeanNameGenerator, registry); // 将 configCandidates 转成 set candidates , 去重 Set<BeanDefinitionHolder> candidates = new LinkedHashSet<>(configCandidates); Set<ConfigurationClass> alreadyParsed = new HashSet<>(configCandidates.size()); do { // 解析配置类 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类,@Bean,@ImportResource 转化为 BeanDefinition this.reader.loadBeanDefinitions(configClasses); alreadyParsed.addAll(configClasses); candidates.clear(); // 再获取一下容器中BeanDefinition的数据,如果发现数量增加了,说明有新的BeanDefinition被注册了 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(); } }获取所有的BeanDefinitionNames，然后循环这个数组，判断其是否为配置类。
前5个是Spring注册的内置processor，最后一个是传入给AnnotationConfigApplicationContext的配置类AppConfig.class。
在Spring中存在两种ConfigurationClass，一种是FullConfigurationClass另一种是LiteConfigurationClass。关于这两者的区别，可以参看笔者文章之前关于Full @Configuration 和 lite @Bean mode的文章。
ConfigurationClassUtils#checkConfigurationClassCandidate方法内部就是在判断属于哪种配置类，并在BeanDefinition中标记判断结果。其具体的判断逻辑如下：
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; } }判断configCandidates变量中存放的
配置类是否为空，如果不为空，则对其进行排序。
创建ConfigurationClassParser对象，用于解析@Configuration类，完成包的扫描、BeanDefinition的注册。主要通过执行parser.parse(candidates);方法来完成。
执行parser.parse(candidates)方法前 ：
执行parser.parse(candidates)方法后 ：
解析完配置类之后，紧接着又执行了this.reader.loadBeanDefinitions(configClasses);方法。这个方法主要是用来处理Import类、@Bean和@ImportResource注解。关于这两个方法的具体细节，我们下次再讲。
最后又加了入了对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()); }关于对ImportAware接口的使用，我们也下次再讲。
未完待续……
源码学习笔记：https://github.com/shenjianeng/spring-code-study
欢迎各位关注公众号，大家一起学习成长。
