Spring源码解析 – @Configuration配置类及注解Bean的解析

　　在分析Spring 容器创建过程时，我们知道容器默认会加载一些后置处理器PostProcessor，以AnnotationConfigApplicationContext为例，在构造函数中初始化reader时，加载默认后置处理器。其中 ConfigurationClassPostProcessor这个后置处理器专门处理带有@Configuration注解的类，ConfigurationClassPostProcessor后置处理实现了BeanDefinitionRegistryPostProcessor接口和PriorityOrdered接口，所以会在容器初始化refresh()方法中执行后置处理器时优先执行，主要负责解析所有@Configuration标签类，并将Bean定义注册到容器中。

BeanDefinitionRegistryPostProcessor解析配置类过程：

public void postProcessBeanDefinitionRegistry(BeanDefinitionRegistry registry) {
//生成唯一标识，用于重复处理验证
   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);
   //解析Java类配置bean
   processConfigBeanDefinitions(registry);
}

processConfigBeanDefinitions(registry)处理逻辑：

public void processConfigBeanDefinitions(BeanDefinitionRegistry registry) {
   List<BeanDefinitionHolder> configCandidates = new ArrayList<>();
　　//所有已经注册的bean 
   String[] candidateNames = registry.getBeanDefinitionNames();
   //遍历bean定义信息
   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);
         }
      }
　　//如果当前的bean是Javabean配置类（含有@Configuration注解的类），则加入到集合configCandidates中，
      else if (ConfigurationClassUtils.checkConfigurationClassCandidate(beanDef, this.metadataReaderFactory)) {
         configCandidates.add(new BeanDefinitionHolder(beanDef, beanName));
      }
   }

   // Return immediately if no @Configuration classes were found
　　// 没有@Configuration注解的类，直接退出
   if (configCandidates.isEmpty()) {
      return;
   }

   // 多个Java配置类，按@Ordered注解排序
   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
　　//初始化一个ConfigurationClassParser解析器，可以解析@Congiguration配置类
   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 {
　　　　//1.解析Java配置类
      parser.parse(candidates);
　　　　//主要校验配置类不能使用final修饰符（CGLIB代理是生成一个子类，因此原先的类不能使用final修饰）
      parser.validate();

      //排除已处理过的配置类
      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());
      }
　　　　//2.加载bean定义信息，主要实现将@Configuration @Import @ImportResource @ImportRegistrar注册为bean
      this.reader.loadBeanDefinitions(configClasses);
      alreadyParsed.addAll(configClasses);
      //清空已处理的配置类
      candidates.clear();
　　　　//再次获取容器中bean定义数量  如果大于 之前获取的bean定义数量，则说明有新的bean注册到容器中，需要再次解析
      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);
　　　　　　　　　　//新注册的bean如果也是@Configuration配置类,则添加到数据，等待解析
               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();
   }
}

1.解析Java配置类parser.parse(candidates)

parser.parse(candidates)方法最终调用processConfigurationClass方法来处理@Configuration配置类，ConfigurationClassParser. processConfigurationClass()方法实现代码如下：

protected void processConfigurationClass(ConfigurationClass configClass) throws IOException {
　　//判断是否需要解析
   if (this.conditionEvaluator.shouldSkip(configClass.getMetadata(), ConfigurationPhase.PARSE_CONFIGURATION)) {
      return;
   }
   //判断同一个配置类是否重复加载过，如果重复加载过，则合并，否则从集合中移除旧的配置类，后续逻辑将处理新的配置类
   ConfigurationClass existingClass = this.configurationClasses.get(configClass);
   if (existingClass != null) {
      if (configClass.isImported()) {
         if (existingClass.isImported()) {
            existingClass.mergeImportedBy(configClass);
         }
         // Otherwise ignore new imported config class; existing non-imported class overrides it.
         return;
      }
      else {
         // Explicit bean definition found, probably replacing an import.
         // Let's remove the old one and go with the new one.
         this.configurationClasses.remove(configClass);
         this.knownSuperclasses.values().removeIf(configClass::equals);
      }
   }

   // Recursively process the configuration class and its superclass hierarchy.
   SourceClass sourceClass = asSourceClass(configClass);
   do {
　　   //【真正解析配置类】
      sourceClass = doProcessConfigurationClass(configClass, sourceClass);
   }
   while (sourceClass != null);
   //再次添加到到集合中
   this.configurationClasses.put(configClass, configClass);
}

doProcessConfigurationClass方法主要实现从配置类中解析所有bean，包括处理内部类，父类以及各种注解

ConfigurationClassParser. doProcessConfigurationClass()解析配置类逻辑如下：

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

   //递归处理任何成员（嵌套）类
   processMemberClasses(configClass, sourceClass);

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

   // 处理@ComponentScan 
//获取@ComponentScan注解信息
   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) {

         // 按@CmponentScan注解扫描bean
         Set<BeanDefinitionHolder> scannedBeanDefinitions =
               this.componentScanParser.parse(componentScan, sourceClass.getMetadata().getClassName());
         // 遍历扫描出的bean定义是否是配置类bean
         for (BeanDefinitionHolder holder : scannedBeanDefinitions) {
            BeanDefinition bdCand = holder.getBeanDefinition().getOriginatingBeanDefinition();
            if (bdCand == null) {
               bdCand = holder.getBeanDefinition();
            }
//若果扫描出的bean定义是配置类（含有@COnfiguration）,则继续调用parse方法，内部再次调用doProcessConfigurationClas(),递归解析
            if (ConfigurationClassUtils.checkConfigurationClassCandidate(bdCand, this.metadataReaderFactory)) {
               parse(bdCand.getBeanClassName(), holder.getBeanName());
            }
         }
      }
   }

   //处理@Import注解
   processImports(configClass, sourceClass, getImports(sourceClass), true);

   //处理@ImportResource注解
   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);
      }
   }

   //处理@Bean注解 
   Set<MethodMetadata> beanMethods = retrieveBeanMethodMetadata(sourceClass);
   for (MethodMetadata methodMetadata : beanMethods) {
//将解析出的所有@Bean注解方法添加到configClass配置类信息中
      configClass.addBeanMethod(new BeanMethod(methodMetadata, configClass));
   }

   //处理接口中所有添加@Bean注解的方法，内部通过遍历所有接口，解析得到@Bean注解方法，并添加到configClass配置类信息中
   processInterfaces(configClass, sourceClass);

   // 如果有父类，则返回父类，递归执行doProcessConfigurationClass()解析父类
   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;
}

下面看两个很重要的注解@Bean和@ComponentScan的实现过程

@ComponentScan注解解析过程

Set<BeanDefinitionHolder> scannedBeanDefinitions =
               this.componentScanParser.parse(componentScan, sourceClass.getMetadata().getClassName());

@ComponentScan注解解析，从上面的代码可以看出@ComponentScan注解解析通过调用ComponentScanAnnotationParser的parse方法完成，而parse()方法内部处理了一些scanner属性(过滤器设置)和basePackages包名处理，最终通过调用ClassPathBeanDefinitionScanner.doScan方法实现扫面工作

public Set<BeanDefinitionHolder> parse(AnnotationAttributes componentScan, final String declaringClass) {
   ClassPathBeanDefinitionScanner scanner = new ClassPathBeanDefinitionScanner(this.registry,
         componentScan.getBoolean("useDefaultFilters"), this.environment, this.resourceLoader);

   Class<? extends BeanNameGenerator> generatorClass = componentScan.getClass("nameGenerator");
   boolean useInheritedGenerator = (BeanNameGenerator.class == generatorClass);
   scanner.setBeanNameGenerator(useInheritedGenerator ? this.beanNameGenerator :
         BeanUtils.instantiateClass(generatorClass));

   ScopedProxyMode scopedProxyMode = componentScan.getEnum("scopedProxy");
   if (scopedProxyMode != ScopedProxyMode.DEFAULT) {
      scanner.setScopedProxyMode(scopedProxyMode);
   }
   else {
      Class<? extends ScopeMetadataResolver> resolverClass = componentScan.getClass("scopeResolver");
      scanner.setScopeMetadataResolver(BeanUtils.instantiateClass(resolverClass));
   }

   scanner.setResourcePattern(componentScan.getString("resourcePattern"));

   for (AnnotationAttributes filter : componentScan.getAnnotationArray("includeFilters")) {
      for (TypeFilter typeFilter : typeFiltersFor(filter)) {
         scanner.addIncludeFilter(typeFilter);
      }
   }
   for (AnnotationAttributes filter : componentScan.getAnnotationArray("excludeFilters")) {
      for (TypeFilter typeFilter : typeFiltersFor(filter)) {
         scanner.addExcludeFilter(typeFilter);
      }
   }

   boolean lazyInit = componentScan.getBoolean("lazyInit");
   if (lazyInit) {
      scanner.getBeanDefinitionDefaults().setLazyInit(true);
   }

   Set<String> basePackages = new LinkedHashSet<>();
   String[] basePackagesArray = componentScan.getStringArray("basePackages");
   for (String pkg : basePackagesArray) {
      String[] tokenized = StringUtils.tokenizeToStringArray(this.environment.resolvePlaceholders(pkg),
            ConfigurableApplicationContext.CONFIG_LOCATION_DELIMITERS);
      Collections.addAll(basePackages, tokenized);
   }
   for (Class<?> clazz : componentScan.getClassArray("basePackageClasses")) {
      basePackages.add(ClassUtils.getPackageName(clazz));
   }
   if (basePackages.isEmpty()) {
      basePackages.add(ClassUtils.getPackageName(declaringClass));
   }

   scanner.addExcludeFilter(new AbstractTypeHierarchyTraversingFilter(false, false) {
      @Override
      protected boolean matchClassName(String className) {
         return declaringClass.equals(className);
      }
   });
   return scanner.doScan(StringUtils.toStringArray(basePackages));
}

doScan扫描basePackages下所有bean

protected Set<BeanDefinitionHolder> doScan(String... basePackages) {
   Assert.notEmpty(basePackages, "At least one base package must be specified");
   Set<BeanDefinitionHolder> beanDefinitions = new LinkedHashSet<>();
   for (String basePackage : basePackages) {
　　　　//根据basePackage加载包下所有java文件，并扫描出所有bean组件, findCandidateComponents方法内部调用ClassPathScanningCandidateComponentProvider.scanCandidateComponents(backPackages)
      Set<BeanDefinition> candidates = findCandidateComponents(basePackage);
　　　　//遍历beandefition
      for (BeanDefinition candidate : candidates) {
　　　　　　//解析作用域Scope
         ScopeMetadata scopeMetadata = this.scopeMetadataResolver.resolveScopeMetadata(candidate);
         candidate.setScope(scopeMetadata.getScopeName());
         String beanName = this.beanNameGenerator.generateBeanName(candidate, this.registry);
//
         if (candidate instanceof AbstractBeanDefinition) {
            postProcessBeanDefinition((AbstractBeanDefinition) candidate, beanName);
         }
　　　　　　//通用注解解析到candidate结构中，主要是处理Lazy, primary DependsOn, Role ,Description这五个注解
         if (candidate instanceof AnnotatedBeanDefinition) {
            AnnotationConfigUtils.processCommonDefinitionAnnotations((AnnotatedBeanDefinition) candidate);
         }
　　　　　　//检查当前bean是否已经注册，不存在则注册
         if (checkCandidate(beanName, candidate)) {
            BeanDefinitionHolder definitionHolder = new BeanDefinitionHolder(candidate, beanName);
            definitionHolder =
                  AnnotationConfigUtils.applyScopedProxyMode(scopeMetadata, definitionHolder, this.registry);
            beanDefinitions.add(definitionHolder);
　　　　　　　　// 注册到ioc容器中，主要是一些@Component组件，@Bean注解方法并没有在此处注册， definitionHolder: beanname和beandefinition 键值对
            registerBeanDefinition(definitionHolder, this.registry);
         }
      }
   }
   return beanDefinitions;
}

ClassPathBeanDefinitionScanner.scanCandidateComponents实现bean定义信息扫描

private Set<BeanDefinition> scanCandidateComponents(String basePackage) {
   Set<BeanDefinition> candidates = new LinkedHashSet<>();
   try {
　　　　// @ComponentScan("com.sl.springlearning.extension")包路径处理：packageSearchPath = classpath*:com/sl/springlearning/extension/**/*.class
      String packageSearchPath = ResourcePatternResolver.CLASSPATH_ALL_URL_PREFIX +
            resolveBasePackage(basePackage) + '/' + this.resourcePattern;
　　　　//获取当前包下所有的class文件
      Resource[] resources = getResourcePatternResolver().getResources(packageSearchPath);
      boolean traceEnabled = logger.isTraceEnabled();
      boolean debugEnabled = logger.isDebugEnabled();
      for (Resource resource : resources) {
         if (traceEnabled) {
            logger.trace("Scanning " + resource);
         }
         if (resource.isReadable()) {
            try {
               MetadataReader metadataReader = getMetadataReaderFactory().getMetadataReader(resource);
　　　　　　　　　　//按照scanner过滤器过滤，比如配置类本身将被果过滤掉，没有@Component等组件注解的类将过滤掉
               if (isCandidateComponent(metadataReader)) {
                  ScannedGenericBeanDefinition sbd = new ScannedGenericBeanDefinition(metadataReader);
                  sbd.setResource(resource);
                  sbd.setSource(resource);
                  if (isCandidateComponent(sbd)) {
                     if (debugEnabled) {
                        logger.debug("Identified candidate component class: " + resource);
                     }
                     candidates.add(sbd);
                  }
                  else {
                     if (debugEnabled) {
                        logger.debug("Ignored because not a concrete top-level class: " + resource);
                     }
                  }
               }
               else {
                  if (traceEnabled) {
                     logger.trace("Ignored because not matching any filter: " + resource);
                  }
               }
            }
            catch (Throwable ex) {
               throw new BeanDefinitionStoreException(
                     "Failed to read candidate component class: " + resource, ex);
            }
         }
         else {
            if (traceEnabled) {
               logger.trace("Ignored because not readable: " + resource);
            }
         }
      }
   }
   catch (IOException ex) {
      throw new BeanDefinitionStoreException("I/O failure during classpath scanning", ex);
   }
   return candidates;
}

@Bean注解解析过程

retrieveBeanMethodMetadata方法实现了@Bean方法的解析，并未将实现bean实例的创建。

private Set<MethodMetadata> retrieveBeanMethodMetadata(SourceClass sourceClass) {
   AnnotationMetadata original = sourceClass.getMetadata();
//获取所有@Bean注解的方法
   Set<MethodMetadata> beanMethods = original.getAnnotatedMethods(Bean.class.getName());
// 如果配置类中有多个@Bean注解的方法，则排序
   if (beanMethods.size() > 1 && original instanceof StandardAnnotationMetadata) {
      // Try reading the class file via ASM for deterministic declaration order...
      // Unfortunately, the JVM's standard reflection returns methods in arbitrary
      // order, even between different runs of the same application on the same JVM.
      try {
         AnnotationMetadata asm =
               this.metadataReaderFactory.getMetadataReader(original.getClassName()).getAnnotationMetadata();
         Set<MethodMetadata> asmMethods = asm.getAnnotatedMethods(Bean.class.getName());
         if (asmMethods.size() >= beanMethods.size()) {
            Set<MethodMetadata> selectedMethods = new LinkedHashSet<>(asmMethods.size());
            for (MethodMetadata asmMethod : asmMethods) {
               for (MethodMetadata beanMethod : beanMethods) {
                  if (beanMethod.getMethodName().equals(asmMethod.getMethodName())) {
                     selectedMethods.add(beanMethod);
                     break;
                  }
               }
            }
            if (selectedMethods.size() == beanMethods.size()) {
               // All reflection-detected methods found in ASM method set -> proceed
               beanMethods = selectedMethods;
            }
         }
      }
      catch (IOException ex) {
         logger.debug("Failed to read class file via ASM for determining @Bean method order", ex);
         // No worries, let's continue with the reflection metadata we started with...
      }
   }
   return beanMethods;
}

2.加载bean定义信息  this.reader.loadBeanDefinitions(configClasses)

　　ConfigurationClassBeanDefinitionReader.loadBeanDefinitions()方法的功能就是将之前解析出的configClasses配置类信息中所有配置相关的信息添加到spring的bean定义，主要是配置类中的@Bean注解方法，配置类@ImportResource和@Import(实现ImportBeanDefinitionRegistrar接口方式)的bean注册

ConfigurationClassBeanDefinitionReader.loadBeanDefinitions()方法 实现逻辑如下：

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

private void loadBeanDefinitionsForConfigurationClass(
      ConfigurationClass configClass, TrackedConditionEvaluator trackedConditionEvaluator) {
     if (trackedConditionEvaluator.shouldSkip(configClass)) {
      String beanName = configClass.getBeanName();
      if (StringUtils.hasLength(beanName) && this.registry.containsBeanDefinition(beanName)) {
         this.registry.removeBeanDefinition(beanName);
      }
      this.importRegistry.removeImportingClass(configClass.getMetadata().getClassName());
      return;
   }

   if (configClass.isImported()) {
      registerBeanDefinitionForImportedConfigurationClass(configClass);
   }
　　//将@Bean方法注册为bean
   for (BeanMethod beanMethod : configClass.getBeanMethods()) {
      loadBeanDefinitionsForBeanMethod(beanMethod);
   }
   //将configClass中中ImportResource指定的资源注册为bean
   loadBeanDefinitionsFromImportedResources(configClass.getImportedResources());
//将configClass中ImportedRegistrar注册为bean
   loadBeanDefinitionsFromRegistrars(configClass.getImportBeanDefinitionRegistrars());
}

处理逻辑理了一遍后，看一下ConfigurationClassPostProcessor处理器解析@configuration配置类主要过程：

　　1. Spring容器初始化时注册默认后置处理器ConfigurationClassPostProcessor

　　2. Spring容器初始化执行refresh()方法中调用ConfigurationClassPostProcessor

　　3. ConfigurationClassPostProcessor处理器借助ConfigurationClassParser完成配置类解析

　　4. ConfigurationClassParser配置内解析过程中完成嵌套的MemberClass、@PropertySource注解、@ComponentScan注解（扫描package下的所有Class并进行迭代解析，主要是@Component组件解析及注册）、@ImportResource、@Bean等处理

　　5. 完成@Bean注册， @ImportResource指定bean的注册以及@Import(实现ImportBeanDefinitionRegistrar接口方式)的bean注册