Spring如何扫描工作目录下的Bean?|图文并茂讲解@Configuration的工作原理

揭秘@Configuration的秘密(一)

文章目录

      • 揭秘@Configuration的秘密(一)
        • 基础介绍
        • 流程图
          • 整体流程
          • 目前为止的bd类型
        • 代码分析
          • (1) processConfigBeanDefinitions(registry)
          • (2) checkConfigurationClassCandidate()
          • (3) ConfigurationClassParser.parse()
          • (4) processConfigurationClass()
          • (5) doProcessConfigurationClass()
          • (6) ComponentScanAnnotationParser.parse()
          • (7) ClassPathBeanDefinitionScanner.doScan()
          • (8) findCandidateComponents()
          • (9) ConfigurationClassParser.processImports()
          • (10) ConfigurationClassBeanDefinitionReader.loadBeanDefinitions()

基础介绍

前面我们谈到了后置处理器的加载过程,那么其中就有一个特殊的后置处理器——ConfigurationClassPostProcessor.class;他就是在Spring启动初始化时最先注入的bdinternalConfigurationAnnotationProcessor;由于这个类他实现了BeanDefinitionRegistryPostProcessor接口,因此Spring在执行后置处理器的时候,会先调用该后置处理器的该接口:

// ConfigurationClassPostProcessor	
@Override
public void postProcessBeanDefinitionRegistry(BeanDefinitionRegistry registry) {
    int registryId = System.identityHashCode(registry);
    this.registriesPostProcessed.add(registryId);
    // ...
    processConfigBeanDefinitions(registry);
}

流程图

Spring如何扫描工作目录下的Bean?|图文并茂讲解@Configuration的工作原理_第1张图片

整体流程
  1. 扫描当前bd(就是Spring内部注册的bd以及手动register()的类),筛选configurationClass字段合法的bd,将其进行排序;

    bd属性字段configurationClass设置为full: 是加@Configuration;

    bd属性字段configurationClass设置为lite:是加@Componnet||@ComponentScan||@Import||@ImportResource||@Bean

  2. 创建配置类分析器ConfigurationClassParse,将上面筛选的bd依稀调用该分析器的parse();

    1. 递归处理配置类内部的成员类;

    2. 处理资源属性配置@PropertySource;

    3. 循环扫描componentScans;

      1. 创建扫描解析器ComponentScanAnnotationParser,调用doScan()方法,将所有扫描的类转化成bdScannedGenericBeanDefinition,并加入bd集合中;
  3. 若扫描的类中还有配置类,则继续递归解析;

  4. 处理该配置类所有的@Import,ImportBeanDefinitionRegistrar,ImportResource,内部方法,@Bean等;

  5. 通过读取器ConfigurationClassBeanDefinitionReader将import,@Bean等注入的bd注册进bd集合中;

    被引入import进来,生成bdAnnotatedGenericBeanDefinition;

    @Bean,生成bdConfigurationClassBeanDefinition;

目前为止的bd类型

代码分析

请结合流程图查看

(1) processConfigBeanDefinitions(registry)

这个方法就是ConfigurationClassPostProcessor需要重写的postProcessBeanDefinitionRegistry()中的核心方法;

  • 首先传入的参数registry,实际上就是我们的DefaultListableBeanFactory,这个上一篇后置处理器文章有讲到;

  • 这个方法里面我们先取出我们工厂里已有的bd,就是spring定义的6个内置bd+我们注册的启动时的类;

  • Spring将这7个bd判断哪些是有加配置注解的,这里看方法2,将其加入集合并进行排序;

  • 定义了ConfigurationClassParser配置类分析器,循环将上述加配置注解的类调用配置类分析器的parse()方法;这里要跳到方法3去看;

  • 方法3执行完后,就把初始路径下所有的类全部扫描完生成bd注入进bean工厂了,目前,@Bean,importBeanDefinitionRegistrarsMap中的类还没有注入进bd中;因此这里创建了一个ConfigurationClassBeanDefinitionReader读取器去处理;这里调用this.reader.loadBeanDefinitions(configClasses)方法10

  • 当这些处理完,Spring再次扫描判断是否还有新的配置类,加入configCandidates集合中;

这个方法就分析完了;

// ConfigurationClassPostProcessor.class	
public void processConfigBeanDefinitions(BeanDefinitionRegistry registry) {
    List<BeanDefinitionHolder> configCandidates = new ArrayList<>();
    String[] candidateNames = registry.getBeanDefinitionNames();

    // 取出spring自己的bd和自己加的bd(入口注册的)
    for (String beanName : candidateNames) {
        BeanDefinition beanDef = registry.getBeanDefinition(beanName);
        // 判断bd是否已经执行过checkConfigurationClassCandidate()方法 修改过bd的属性字段
        if (ConfigurationClassUtils.isFullConfigurationClass(beanDef) ||
            ConfigurationClassUtils.isLiteConfigurationClass(beanDef)) {
            if (logger.isDebugEnabled()) {
                logger.debug("Bean definition has already been processed as a configuration class: " + beanDef);
            }
        }
        // bd属性字段configurationClass设置为full: 是加@Configuration
        // bd属性字段configurationClass设置为lite:是加@Componnet||@ComponentScan||@Import||@ImportResource||@Bean
        // 如果加了上述注解且又加了@order,该bd属性order字段设置order的值
        else if (ConfigurationClassUtils.checkConfigurationClassCandidate(beanDef, this.metadataReaderFactory)) {
            configCandidates.add(new BeanDefinitionHolder(beanDef, beanName));
        }
    }
    // Return immediately if no @Configuration classes were found
    // 如果没有任何加上述注解的,则直接返回
    if (configCandidates.isEmpty()) {
        return;
    }
    // Sort by previously determined @Order value, if applicable
    // 对这些bd按照order进行排序(没有@order的其value是Integer.MAX,值越大,优先级越小)
    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
    // 初始进来时 registry 是DefaultListableBeanFactory类型,实现了SingletonBeanRegistry
    SingletonBeanRegistry sbr = null;
    if (registry instanceof SingletonBeanRegistry) {
        sbr = (SingletonBeanRegistry) registry;
        if (!this.localBeanNameGeneratorSet) {
            // 从beanMap中取internalConfigurationBeanNameGenerator 但初始进来后,没有将该bean创建出来,因此是null
            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);
    // 去重 就是我们之前手动注册的带有上述注解的bd
    Set<BeanDefinitionHolder> candidates = new LinkedHashSet<>(configCandidates);
    // 标记已解析的class-避免重复解析
    Set<ConfigurationClass> alreadyParsed = new HashSet<>(configCandidates.size());
    do {
        // 将candidates集合中的所有包含的类解析成bd注入进bean工厂
        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());
        }
        this.reader.loadBeanDefinitions(configClasses);
        alreadyParsed.addAll(configClasses);

        candidates.clear();
        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();
    }
}
(2) checkConfigurationClassCandidate()

这个方法是ConfigurationClassUtils类中的方法,他是判断bd上面是否有配置类注解,如果有根据类型设置相应bd的configurationClass字段;

其中配置类注解分为两类:

  • 第一类是:@Configuration注解,会设置bd的属性configurationClass字段为full
  • 第二类是:加了@Component||@ComponentScan||@Import||@ImportResource||@Bean 设置bd的属性configurationClass字段为lite

除此之外,若加了@Order,则在bd中设置order值

// ConfigurationClassUtils.class
public static boolean checkConfigurationClassCandidate(BeanDefinition beanDef, MetadataReaderFactory metadataReaderFactory) {
    String className = beanDef.getBeanClassName();
    if (className == null || beanDef.getFactoryMethodName() != null) {
        return false;
    }
    // 内置注入的话是RootBeanDefinition,我们手动注入的是:AnnotatedGenericBeanDefinition
    // 这里是获取bd的元数据,根据元数据判断加注解的值
    AnnotationMetadata metadata;
    if (beanDef instanceof AnnotatedBeanDefinition &&
        className.equals(((AnnotatedBeanDefinition) beanDef).getMetadata().getClassName())) {
        // Can reuse the pre-parsed metadata from the given BeanDefinition...
        metadata = ((AnnotatedBeanDefinition) beanDef).getMetadata();
    }
    else if (beanDef instanceof AbstractBeanDefinition && ((AbstractBeanDefinition) beanDef).hasBeanClass()) {
        // Check already loaded Class if present...
        // since we possibly can't even load the class file for this Class.
        Class<?> beanClass = ((AbstractBeanDefinition) beanDef).getBeanClass();
        metadata = new StandardAnnotationMetadata(beanClass, true);
    }
    else {
        try {
            MetadataReader metadataReader = metadataReaderFactory.getMetadataReader(className);
            metadata = metadataReader.getAnnotationMetadata();
        }
        catch (IOException ex) {
            return false;
        }
    }
    // 根据元数据去处理,如果加了@Configuration注解,就设置bd的属性字段为full
    if (isFullConfigurationCandidate(metadata)) {
        beanDef.setAttribute(CONFIGURATION_CLASS_ATTRIBUTE, CONFIGURATION_CLASS_FULL);
    }
    // 如果加了@Component||@ComponentScan||@Import||@ImportResource||@Bean 设置配置字段为lite
    else if (isLiteConfigurationCandidate(metadata)) {
        beanDef.setAttribute(CONFIGURATION_CLASS_ATTRIBUTE, CONFIGURATION_CLASS_LITE);
    }
    else {
        return false;
    }

    // It's a full or lite configuration candidate... Let's determine the order value, if any.
    // 若加了@Order,则设置order属性值
    Integer order = getOrder(metadata);
    if (order != null) {
        beanDef.setAttribute(ORDER_ATTRIBUTE, order);
    }
    return true;
}
(3) ConfigurationClassParser.parse()

从方法(1)中调用进来,这里传入的是配置类bd集合,根据bd类型去解析,其解析是调用parse()方法,实际是调用processConfigurationClass()方法,这里看方法4。解析完后,该方法还去处理该配置类中所标记的延迟导入类;

当全部扫描处理完后,再去处理延迟导入的类;延迟导入的类这里就不展开介绍了,其内部就是将所有延迟导入的类DeferredImportSelectorHolder进行排序,并按group进行分类,最后依旧循环调用processImports()方法,就是方法9

// ConfigurationClassParser.class
public void parse(Set<BeanDefinitionHolder> configCandidates) {
    // 初始化延迟导入队列
    this.deferredImportSelectors = new LinkedList<>();
    // 循环处理配置类bd并根据bd类型进行处理
    for (BeanDefinitionHolder holder : configCandidates) {
        BeanDefinition bd = holder.getBeanDefinition();
        try {
            if (bd instanceof AnnotatedBeanDefinition) {
                parse(((AnnotatedBeanDefinition) bd).getMetadata(), holder.getBeanName());
            }
            else if (bd instanceof AbstractBeanDefinition && ((AbstractBeanDefinition) bd).hasBeanClass()) {
                parse(((AbstractBeanDefinition) bd).getBeanClass(), holder.getBeanName());
            }
            else {
                parse(bd.getBeanClassName(), holder.getBeanName());
            }
        }
        catch (BeanDefinitionStoreException ex) {
            throw ex;
        }
    }
    // 处理延迟导入
    processDeferredImportSelectors();
}
(4) processConfigurationClass()

这个方法是将配置类bd进行封装解析的入口,他不仅解析它自身,如果它的内部类,他import的类,都将递归调用这个类;

它将配置类bd数据再次包装成SourceClass,然后循环调用doProcessConfigurationClass(),这里看方法5

方法5返回null时才结束,否则继续循环(不为null,则说明还有父类需要处理);

当全部处理完后,将配置类加入configurationClasses集合Map中;

// ConfigurationClassParser.class

protected final void parse(AnnotationMetadata metadata, String beanName) throws IOException {
    processConfigurationClass(new ConfigurationClass(metadata, beanName));
}

protected void processConfigurationClass(ConfigurationClass configClass) throws IOException {
    if (this.conditionEvaluator.shouldSkip(configClass.getMetadata(), ConfigurationPhase.PARSE_CONFIGURATION)) {
        return;
    }

    // 初始情况下 configurationClasses为empty
    ConfigurationClass existingClass = this.configurationClasses.get(configClass);
    // 初始情况下 configurationClasses为empty
    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.
    // 统一的源码包装类,还包含了AnnotationMetadata属性
    SourceClass sourceClass = asSourceClass(configClass);
    do {
        sourceClass = doProcessConfigurationClass(configClass, sourceClass);
    }
    while (sourceClass != null);
    // 将处理完的配置类class放入map中
    this.configurationClasses.put(configClass, configClass);
}
(5) doProcessConfigurationClass()

这个类就是核心解析配置类的方法了。建议配合我附上的源码解析和流程图看;

  • 它首先去处理内部类,如果其含有内部类,则判断是否是full或lite,然后再次递归调用入口函数processConfigurationClass();

  • 将所引用的配置文件,解析到Environment中;

    关于@PropertySource的使用:https://www.cnblogs.com/517cn/p/10946213.html

  • 扫描@ComponentScans,@ComponentScan 指定的类,包路径等;这里就是核心的扫描注册进工厂的地方,通过调用this.componentScanParser.parse(),这里看方法6;这里扫描完,如果发现扫描的bd中还有配置类,则递归调用parse()方法;

    componentScanParser是什么时候创建的?实际上是ConfigurationClassParser在构建函数时创建的;

    this.componentScanParser = new ComponentScanAnnotationParser(environment, resourceLoader, componentScanBeanNameGenerator, registry);
    
  • 上述执行完后,就将配置类所在包下的所有类全部扫描成bd加入了bean工厂中,接下来处理的是配置类上加@Import注解,这里调用processImports()方法,处理import的类,见方法9

  • 若配置类有使用@ImportResource,则加入configClass的(importedResources)map中;

  • 处理定义在内部的@Bean,将其加入到configClass的(beanMethods)set中;

  • 如果有父类,则return父类,否则return null;

// ConfigurationClassParser.class

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

    // Recursively process any member (nested) classes first
    // 处理其中定义的内部类,是否是full或lite否则要再次递归调用processConfigurationClass
    processMemberClasses(configClass, sourceClass);

    // Process any @PropertySource annotations
    // 当使用配置文件中的值为属性赋值的时候,通过@PropertySource导入配置文件
    // 通过@PropertySource注解将properties配置文件中的值存储到Spring的 Environment中,Environment接口提供方法去读取配置文件中的值,参数是properties文件中定义的key值。
    // 关于@PropertySource的使用:https://www.cnblogs.com/517cn/p/10946213.html
    for (AnnotationAttributes propertySource : AnnotationConfigUtils.attributesForRepeatable(
        sourceClass.getMetadata(), PropertySources.class,
        org.springframework.context.annotation.PropertySource.class)) {
        if (this.environment instanceof ConfigurableEnvironment) {
            // 获得配置文件的Resource文件
            processPropertySource(propertySource);
        }
        else {
            logger.warn("Ignoring @PropertySource annotation on [" + sourceClass.getMetadata().getClassName() +
                        "]. Reason: Environment must implement ConfigurableEnvironment");
        }
    }

    // Process any @ComponentScan annotations
    // 扫描@ComponentScans,@ComponentScan 指定的类
    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) {
            // The config class is annotated with @ComponentScan -> perform the scan immediately
            // 扫描componentScan的类加入bd中
            // 它是自己new了ClassPathBeanDefinitionScanner去扫描的
            Set<BeanDefinitionHolder> scannedBeanDefinitions =
                this.componentScanParser.parse(componentScan, sourceClass.getMetadata().getClassName());
            // Check the set of scanned definitions for any further config classes and parse recursively if needed
            // 检查扫描的bdh集合是否有任何的配置类,并进行递归解析
            for (BeanDefinitionHolder holder : scannedBeanDefinitions) {
                BeanDefinition bdCand = holder.getBeanDefinition().getOriginatingBeanDefinition();
                if (bdCand == null) {
                    bdCand = holder.getBeanDefinition();
                }
                if (ConfigurationClassUtils.checkConfigurationClassCandidate(bdCand, this.metadataReaderFactory)) {
                    parse(bdCand.getBeanClassName(), holder.getBeanName());
                }
            }
        }
    }

    // Process any @Import annotations
    // 递归处理
    // ImportSelector 将返回的对象继续processImports
    // ImportBeanDefinitionRegistrar 加入configClass的(importBeanDefinitionRegistrars)map中
    // 其余的加入configClass的(imports)map中
    processImports(configClass, sourceClass, getImports(sourceClass), true);

    // Process any @ImportResource annotations
    //  定义的importResource加入configClass的(importedResources)map中
    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);
        }
    }

    // Process individual @Bean methods
    // 处理定义在内部的bean,将其加入到configClass的(beanMethods)set中
    Set<MethodMetadata> beanMethods = retrieveBeanMethodMetadata(sourceClass);
    for (MethodMetadata methodMetadata : beanMethods) {
        configClass.addBeanMethod(new BeanMethod(methodMetadata, configClass));
    }

    // Process default methods on interfaces
    // 将方法上加了@Bean的都加入到configClass的(beanMethods)set中
    processInterfaces(configClass, sourceClass);

    // Process superclass, if any
    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;
}
(6) ComponentScanAnnotationParser.parse()

这个方法创建了一个ClassPathBeanDefinitionScanner扫描器,而不是用刚开始Spring初始化的时候定义的ClassPathBeanDefinitionScanner

每次扫描指定的路径时,调用该方法都会创建一个扫描器,这里面就是初始化扫描器的一些基本配置,比如bean名生成器,代理,懒加载等默认值,都是根据@ComponentScans配置的数据;

这里如果没有指定要扫描的包路径,则包路径设置为当前类所在包;这也解释了,每次启动Spring的时候,会自动扫描当前入口类所在包及其子包下的所有类;

最终调用扫描器的扫描方法;scanner.doScan();这里见方法7;并将扫描完的bdh集合返回;

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

    // 设置bean名称生成器
    Class<? extends BeanNameGenerator> generatorClass = componentScan.getClass("nameGenerator");
    boolean useInheritedGenerator = (BeanNameGenerator.class == generatorClass);
    scanner.setBeanNameGenerator(useInheritedGenerator ? this.beanNameGenerator :
                                 BeanUtils.instantiateClass(generatorClass));
    // 若有代理则扫描器需要set代理
    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"));
    // 添加需要扫描的类
    for (AnnotationAttributes filter : componentScan.getAnnotationArray("includeFilters")) {
        for (TypeFilter typeFilter : typeFiltersFor(filter)) {
            scanner.addIncludeFilter(typeFilter);
        }
    }
    // 添加需要过滤的类
    for (AnnotationAttributes filter : componentScan.getAnnotationArray("excludeFilters")) {
        for (TypeFilter typeFilter : typeFiltersFor(filter)) {
            scanner.addExcludeFilter(typeFilter);
        }
    }
    // 判断是否需要懒加载
    boolean lazyInit = componentScan.getBoolean("lazyInit");
    if (lazyInit) {
        scanner.getBeanDefinitionDefaults().setLazyInit(true);
    }
    // 获取扫描包路径
    Set<String> basePackages = new LinkedHashSet<>();
    String[] basePackagesArray = componentScan.getStringArray("basePackages");
    for (String pkg : basePackagesArray) {
        // 将指定的路径中特殊字符替换掉并加入basePackages集合中
        String[] tokenized = StringUtils.tokenizeToStringArray(this.environment.resolvePlaceholders(pkg),
                                                               ConfigurableApplicationContext.CONFIG_LOCATION_DELIMITERS);
        Collections.addAll(basePackages, tokenized);
    }
    // 扫描某个指定类所在包下的所有类
    for (Class<?> clazz : componentScan.getClassArray("basePackageClasses")) {
        basePackages.add(ClassUtils.getPackageName(clazz));
    }
    // 若当前类并没有指定所在包,则他会默认扫描该类所在的目录下的所有类
    if (basePackages.isEmpty()) {
        basePackages.add(ClassUtils.getPackageName(declaringClass));
    }

    scanner.addExcludeFilter(new AbstractTypeHierarchyTraversingFilter(false, false) {
        @Override
        protected boolean matchClassName(String className) {
            return declaringClass.equals(className);
        }
    });
    // 上面一大段都是初始化扫描器
    // 这里才开始扫描
    return scanner.doScan(StringUtils.toStringArray(basePackages));
}
(7) ClassPathBeanDefinitionScanner.doScan()

这个方法就是实际的扫描逻辑了;

通过调用findCandidateComponents()方法,通过ASM将包路径下的类全部扫描生成ScannedGenericBeanDefinition并包装成bdr返回,具体看方法8

将得到的bd进行初始化,以及配置该bean是否懒加载,依赖@DependsOn,@Primary等属性值;

bean工厂对该bd进行检查,判断是否不存在bean工厂中,就将bd注入进bean工厂中;

最终将bdh集合返回;

// ClassPathBeanDefinitionScanner.class
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) {
        // 将包路径下的class转为bd
        Set<BeanDefinition> candidates = findCandidateComponents(basePackage);
        for (BeanDefinition candidate : candidates) {
            // 生成元数据 若有指定代理则设置元数据中代理属性
            // Spring在注册bean的时候。会通过bean的作用域来决定是否使用代理模式去创建bean。如果是单例模式,那么不会使用代理,非单例就会使用。并且如果这个bean实现了接口,就会使用JDK动态代理,如果继承类,就会使用Cglib代理。
            ScopeMetadata scopeMetadata = this.scopeMetadataResolver.resolveScopeMetadata(candidate);
            // bd设置元数据
            candidate.setScope(scopeMetadata.getScopeName());
            // 获取bd的名称
            String beanName = this.beanNameGenerator.generateBeanName(candidate, this.registry);
            // 初始时,findCandidateComponents()扫描创建的都是ScannedGenericBeanDefinition
            // 他都是实现AbstractBeanDefinition和AnnotatedBeanDefinition的
            if (candidate instanceof AbstractBeanDefinition) {
                // bd设置初始默认值(不懒加载,默认不注入,不进行依赖检查,无初始执行方法,无销毁执行方法)
                // 以及是否设置某个bean自动注入的时候是否为作为候选bean
                postProcessBeanDefinition((AbstractBeanDefinition) candidate, beanName);
            }
            if (candidate instanceof AnnotatedBeanDefinition) {
                // 根据实际配置设置该bean是否懒加载,依赖@DependsOn,@Primary等属性值
                AnnotationConfigUtils.processCommonDefinitionAnnotations((AnnotatedBeanDefinition) candidate);
            }
            // 检测当前bf没有冲突 (判断bd是否注册,若已有bd那判断与现有bd是否冲突)
            if (checkCandidate(beanName, candidate)) {
                BeanDefinitionHolder definitionHolder = new BeanDefinitionHolder(candidate, beanName);
                definitionHolder =
                    AnnotationConfigUtils.applyScopedProxyMode(scopeMetadata, definitionHolder, this.registry);
                beanDefinitions.add(definitionHolder);
                // 注册进入bean工厂
                registerBeanDefinition(definitionHolder, this.registry);
            }
        }
    }
    return beanDefinitions;
}

(8) findCandidateComponents()

这个方法会调用scanCandidateComponents()方法;

它通过ASM读取包路径下的类,将合法可以转为bd类转换成bdScannedGenericBeanDefinition

最终将路径下的所有bd放入集合返回;

其中判断类是正常的类(不是接口或抽象类)如果是抽象类@Lookup注入也算正常类;

// ClassPathScanningCandidateComponentProvider.class
// ClassPathBeanDefinitionScanner.class是它的子类
// 这里调用的是父类的findCandidateComponents()
public Set<BeanDefinition> findCandidateComponents(String basePackage) {
    if (this.componentsIndex != null && indexSupportsIncludeFilters()) {
        return addCandidateComponentsFromIndex(this.componentsIndex, basePackage);
    }
    else {
        // 初始化进入的是这里
        return scanCandidateComponents(basePackage);
    }
}

private Set<BeanDefinition> scanCandidateComponents(String basePackage) {
    Set<BeanDefinition> candidates = new LinkedHashSet<>();
    try {
        // 转换成 classpath*:${basePackage}/**/*.class
        String packageSearchPath = ResourcePatternResolver.CLASSPATH_ALL_URL_PREFIX +
            resolveBasePackage(basePackage) + '/' + this.resourcePattern;
        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);
                    // 判断是否需要过滤
                    if (isCandidateComponent(metadataReader)) {
                        // 通过扫描的都是 ScannedGenericBeanDefinition
                        ScannedGenericBeanDefinition sbd = new ScannedGenericBeanDefinition(metadataReader);
                        sbd.setSource(resource);
                        // 判断是正常的类(不是接口或抽象类)如果是抽象类@Lookup注入也算正常类
                        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;
}

(9) ConfigurationClassParser.processImports()

这个类将Import导入进来的类进行分类处理;

  • 如果实现了ImportSelector接口,若实现的是DeferredImportSelector接口,则加入延迟导入队列中;否则就调用ImportSelector.selectImports()方法,递归调用processImports()方法;
  • 如果实现了ImportBeanDefinitionRegistrar接口,就将其加入进importBeanDefinitionRegistrarsMap中;
  • 如果都没有实现上述两个接口,就将该类当作配置类,调用processConfigurationClass()方法;
// ConfigurationClassParser.class
private void processImports(ConfigurationClass configClass, SourceClass currentSourceClass,
                            Collection<SourceClass> importCandidates, boolean checkForCircularImports) {

    if (importCandidates.isEmpty()) {
        return;
    }

    if (checkForCircularImports && isChainedImportOnStack(configClass)) {
        this.problemReporter.error(new CircularImportProblem(configClass, this.importStack));
    }
    else {
        this.importStack.push(configClass);
        try {
            for (SourceClass candidate : importCandidates) {
                // 若@Import的类实现了ImportSelector
                if (candidate.isAssignable(ImportSelector.class)) {
                    // Candidate class is an ImportSelector -> delegate to it to determine imports
                    Class<?> candidateClass = candidate.loadClass();
                    ImportSelector selector = BeanUtils.instantiateClass(candidateClass, ImportSelector.class);
                    // 设置selector 的bean工厂,环境,类加载器,资源加载器
                    ParserStrategyUtils.invokeAwareMethods(
                        selector, this.environment, this.resourceLoader, this.registry);
                    if (this.deferredImportSelectors != null && selector instanceof DeferredImportSelector) {
                        this.deferredImportSelectors.add(
                            new DeferredImportSelectorHolder(configClass, (DeferredImportSelector) selector));
                    }
                    else {
                        // selector获取import的class 递归调用processImports
                        String[] importClassNames = selector.selectImports(currentSourceClass.getMetadata());
                        Collection<SourceClass> importSourceClasses = asSourceClasses(importClassNames);
                        processImports(configClass, currentSourceClass, importSourceClasses, false);
                    }
                }
                // 若@Import的类实现了ImportBeanDefinitionRegistrar
                else if (candidate.isAssignable(ImportBeanDefinitionRegistrar.class)) {
                    // Candidate class is an ImportBeanDefinitionRegistrar ->
                    // delegate to it to register additional bean definitions
                    Class<?> candidateClass = candidate.loadClass();
                    ImportBeanDefinitionRegistrar registrar =
                        BeanUtils.instantiateClass(candidateClass, ImportBeanDefinitionRegistrar.class);
                    // 设置registrar 的bean工厂,环境,类加载器,资源加载器
                    ParserStrategyUtils.invokeAwareMethods(
                        registrar, this.environment, this.resourceLoader, this.registry);
                    // 加入进importBeanDefinitionRegistrarsMap中
                    configClass.addImportBeanDefinitionRegistrar(registrar, currentSourceClass.getMetadata());
                }
                // 若@Import的类没有实现上述两个接口
                else {
                    // Candidate class not an ImportSelector or ImportBeanDefinitionRegistrar ->
                    // process it as an @Configuration class
                    // importStackMap中加入
                    this.importStack.registerImport(
                        currentSourceClass.getMetadata(), candidate.getMetadata().getClassName());
                    // 将他当作@Configuration 修饰的类去递归调用processConfigurationClass
                    processConfigurationClass(candidate.asConfigClass(configClass));
                }
            }
        }
        catch (BeanDefinitionStoreException ex) {
            throw ex;
        }
        catch (Throwable ex) {
            throw new BeanDefinitionStoreException(
                "Failed to process import candidates for configuration class [" +
                configClass.getMetadata().getClassName() + "]", ex);
        }
        finally {
            this.importStack.pop();
        }
    }
}

(10) ConfigurationClassBeanDefinitionReader.loadBeanDefinitions()

这个读取器,将被@Import导入的类生成bd(AnnotatedGenericBeanDefinition);

将@Bean创建的Bean生成bd(ConfigurationClassBeanDefinition);

将所有的ImportBeanDefinitionRegistrar调用其registerBeanDefinitions()方法;

// ConfigurationClassBeanDefinitionReader.class
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;
    }
    // 被引入import进来
    if (configClass.isImported()) {
        // 生成AnnotatedGenericBeanDefinition
        registerBeanDefinitionForImportedConfigurationClass(configClass);
    }
    for (BeanMethod beanMethod : configClass.getBeanMethods()) {
        // 生成ConfigurationClassBeanDefinition
        loadBeanDefinitionsForBeanMethod(beanMethod);
    }
    // 加载资源
    loadBeanDefinitionsFromImportedResources(configClass.getImportedResources());
    // 调用注册的ImportBeanDefinitionRegistrar.registerBeanDefinitions()方法
    loadBeanDefinitionsFromRegistrars(configClass.getImportBeanDefinitionRegistrars());
}

// 将所有的ImportBeanDefinitionRegistrar调用其registerBeanDefinitions()方法
private void loadBeanDefinitionsFromRegistrars(Map<ImportBeanDefinitionRegistrar, AnnotationMetadata> registrars) {
    registrars.forEach((registrar, metadata) ->
                       registrar.registerBeanDefinitions(metadata, this.registry));
}

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