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Create ConfigurationClassPostProcessor.txt
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‎spring/ConfigurationClassPostProcessor.txt

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ConfigurationClassPostProcessor
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@Override
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public void postProcessBeanDefinitionRegistry(BeanDefinitionRegistry registry) {
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... // 忽略不必要的代码
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processConfigBeanDefinitions(registry);
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}
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public void processConfigBeanDefinitions(BeanDefinitionRegistry registry) {
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List<BeanDefinitionHolder> configCandidates = new ArrayList<>();
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// 从当前beandifinition注册表中取出所有的候选类，这里面有很多都是spring 的内置bean ，所以这些不需要处理。
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String[] candidateNames = registry.getBeanDefinitionNames();
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for (String beanName : candidateNames) {
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BeanDefinition beanDef = registry.getBeanDefinition(beanName);
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if (beanDef.getAttribute(ConfigurationClassUtils.CONFIGURATION_CLASS_ATTRIBUTE) != null) {
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if (logger.isDebugEnabled()) {
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logger.debug("Bean definition has already been processed as a configuration class: " + beanDef);
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}
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}
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else if (ConfigurationClassUtils.checkConfigurationClassCandidate(beanDef, this.metadataReaderFactory)) {
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// 将不是spring 的内置bean 取出来。这里的判断条件是有注解@Configuration 所标识的类才会被识别并添加。
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configCandidates.add(new BeanDefinitionHolder(beanDef, beanName));
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}
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}
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// Return immediately if no @Configuration classes were found
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if (configCandidates.isEmpty()) {
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return;
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}
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// 支持@Order 注解，以及Ordered 接口，排序能力。
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// Sort by previously determined @Order value, if applicable
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configCandidates.sort((bd1, bd2) -> {
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int i1 = ConfigurationClassUtils.getOrder(bd1.getBeanDefinition());
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int i2 = ConfigurationClassUtils.getOrder(bd2.getBeanDefinition());
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return Integer.compare(i1, i2);
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});
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// Detect any custom bean name generation strategy supplied through the enclosing application context
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// 是否有用户自定义的spring bean name 的生成器，如果有就取出使用。
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SingletonBeanRegistry sbr = null;
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if (registry instanceof SingletonBeanRegistry) {
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sbr = (SingletonBeanRegistry) registry;
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if (!this.localBeanNameGeneratorSet) {
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BeanNameGenerator generator = (BeanNameGenerator) sbr.getSingleton(
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AnnotationConfigUtils.CONFIGURATION_BEAN_NAME_GENERATOR);
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if (generator != null) {
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this.componentScanBeanNameGenerator = generator;
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this.importBeanNameGenerator = generator;
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}
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}
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}
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if (this.environment == null) {
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this.environment = new StandardEnvironment();
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}
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// Parse each @Configuration class
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// 构建出一个解析器，对前面使用@Configuration 标识的类，进行解析。
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ConfigurationClassParser parser = new ConfigurationClassParser(
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this.metadataReaderFactory, this.problemReporter, this.environment,
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this.resourceLoader, this.componentScanBeanNameGenerator, registry);
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Set<BeanDefinitionHolder> candidates = new LinkedHashSet<>(configCandidates);
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Set<ConfigurationClass> alreadyParsed = new HashSet<>(configCandidates.size());
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do {
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StartupStep processConfig = this.applicationStartup.start("spring.context.config-classes.parse");
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// 解析动作，进去。
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parser.parse(candidates);
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parser.validate();
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... // 后面的没有详细看，但核心功能不在这里面，基本都是跳过的。
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}
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while (!candidates.isEmpty());
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... // 不太关心的代码。
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}
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ConfigurationClassParser
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public void parse(Set<BeanDefinitionHolder> configCandidates) {
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for (BeanDefinitionHolder holder : configCandidates) {
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BeanDefinition bd = holder.getBeanDefinition();
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try {
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if (bd instanceof AnnotatedBeanDefinition) {
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// 基本都是走的这一条分支，但是这三个分支，最终调用的都是同一个方法 processConfigurationClass(..)
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parse(((AnnotatedBeanDefinition) bd).getMetadata(), holder.getBeanName());
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}
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else if (bd instanceof AbstractBeanDefinition && ((AbstractBeanDefinition) bd).hasBeanClass()) {
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parse(((AbstractBeanDefinition) bd).getBeanClass(), holder.getBeanName());
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}
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else {
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parse(bd.getBeanClassName(), holder.getBeanName());
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}
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}
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catch (BeanDefinitionStoreException ex) {
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throw ex;
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}
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catch (Throwable ex) {
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throw new BeanDefinitionStoreException(
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"Failed to parse configuration class [" + bd.getBeanClassName() + "]", ex);
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}
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}
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// 这里是一个后置处理，前端的逻辑会为其填充基本数据，在这里做实际的动作。
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this.deferredImportSelectorHandler.process();
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}
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protected void processConfigurationClass(ConfigurationClass configClass, Predicate<String> filter) throws IOException {
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// 是否添加了@Conditional 注解，并校验。
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if (this.conditionEvaluator.shouldSkip(configClass.getMetadata(), ConfigurationPhase.PARSE_CONFIGURATION)) {
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return;
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}
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... // 这些不关心
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// Recursively process the configuration class and its superclass hierarchy.
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SourceClass sourceClass = asSourceClass(configClass, filter);
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do {
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// 关键在这里
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sourceClass = doProcessConfigurationClass(configClass, sourceClass, filter);
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}
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while (sourceClass != null);
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this.configurationClasses.put(configClass, configClass);
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}
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// 处理配置类的解析工作
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protected final SourceClass doProcessConfigurationClass(
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ConfigurationClass configClass, SourceClass sourceClass, Predicate<String> filter)
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throws IOException {
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if (configClass.getMetadata().isAnnotated(Component.class.getName())) {
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// Recursively process any member (nested) classes first
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// 这里并不重要，因为基本没人这么实现
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// 它会检查当前类里面的内部类，对该内部类也要进行解析。
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// 如果有，那最终也会在某个位置递归到当前方法来的。
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processMemberClasses(configClass, sourceClass, filter);
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}
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// Process any @PropertySource annotations
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// 对存在注解@PropertySource 的类进行解析，并处理对应的逻辑
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for (AnnotationAttributes propertySource : AnnotationConfigUtils.attributesForRepeatable(
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sourceClass.getMetadata(), PropertySources.class,
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org.springframework.context.annotation.PropertySource.class)) {
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if (this.environment instanceof ConfigurableEnvironment) {
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processPropertySource(propertySource);
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}
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else {
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logger.info("Ignoring @PropertySource annotation on [" + sourceClass.getMetadata().getClassName() +
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"]. Reason: Environment must implement ConfigurableEnvironment");
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}
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}
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// Process any @ComponentScan annotations
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// 对存在注解@ComponentScan 的类进行解析，并处理对应的逻辑
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// 对于spring-boot 应用这里是很关键的一点，@SpringBootApplication 的解析，这里就是入口。
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Set<AnnotationAttributes> componentScans = AnnotationConfigUtils.attributesForRepeatable(
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sourceClass.getMetadata(), ComponentScans.class, ComponentScan.class);
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if (!componentScans.isEmpty() &&
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!this.conditionEvaluator.shouldSkip(sourceClass.getMetadata(), ConfigurationPhase.REGISTER_BEAN)) {
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for (AnnotationAttributes componentScan : componentScans) {
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// The config class is annotated with @ComponentScan -> perform the scan immediately
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// 这里将对应的扫描包路径下面的所有被识别为Bean 的Class 都解析出来，并将其相关的信息封闭到BeanDefinition 中，最终包装到BeanDefinitionHolder 中。
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Set<BeanDefinitionHolder> scannedBeanDefinitions =
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this.componentScanParser.parse(componentScan, sourceClass.getMetadata().getClassName());
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// Check the set of scanned definitions for any further config classes and parse recursively if needed
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for (BeanDefinitionHolder holder : scannedBeanDefinitions) {
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BeanDefinition bdCand = holder.getBeanDefinition().getOriginatingBeanDefinition();
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if (bdCand == null) {
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bdCand = holder.getBeanDefinition();
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}
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// 如果对应的Class 被注解@Configuration 标识，那么会递归调用 parse(..) 方法，继续处理。
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// 我们要知道：当前方法也是从某个 parse(..) 方法调用进来的。
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if (ConfigurationClassUtils.checkConfigurationClassCandidate(bdCand, this.metadataReaderFactory)) {
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parse(bdCand.getBeanClassName(), holder.getBeanName());
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}
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}
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}
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}
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// Process any @Import annotations
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// 处理@Import 注解
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processImports(configClass, sourceClass, getImports(sourceClass), filter, true);
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// Process any @ImportResource annotations
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// 处理@ImportResource 注解
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AnnotationAttributes importResource =
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AnnotationConfigUtils.attributesFor(sourceClass.getMetadata(), ImportResource.class);
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if (importResource != null) {
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String[] resources = importResource.getStringArray("locations");
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Class<? extends BeanDefinitionReader> readerClass = importResource.getClass("reader");
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for (String resource : resources) {
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String resolvedResource = this.environment.resolveRequiredPlaceholders(resource);
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configClass.addImportedResource(resolvedResource, readerClass);
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}
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}
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// Process individual @Bean methods
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// 对@Bean 注解标注的方法的处理
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Set<MethodMetadata> beanMethods = retrieveBeanMethodMetadata(sourceClass);
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for (MethodMetadata methodMetadata : beanMethods) {
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configClass.addBeanMethod(new BeanMethod(methodMetadata, configClass));
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}
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// Process default methods on interfaces
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// 对于jdk 1.8 之后，接口上面也有默认方法的实现，对这些方法的处理。
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processInterfaces(configClass, sourceClass);
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// Process superclass, if any
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// 处理父类的
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if (sourceClass.getMetadata().hasSuperClass()) {
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String superclass = sourceClass.getMetadata().getSuperClassName();
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if (superclass != null && !superclass.startsWith("java") &&
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!this.knownSuperclasses.containsKey(superclass)) {
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this.knownSuperclasses.put(superclass, configClass);
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// Superclass found, return its annotation metadata and recurse
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return sourceClass.getSuperClass();
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}
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}
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// No superclass -> processing is complete
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return null;
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}

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