Spring 源码（四）解析配置类

作者: xiaolyuh | 来源:发表于2019-09-29 12:50 被阅读0次

我们要找出所有符合条件的业务Bean，首先我们需要知道在Spring中什么样的Bean是符合条件的，是需要容器来管理的：

使用组件标注注解的Bean（@Controller、@Service、@Repository、@Component），一般项目里面使用。
使用@Bean注解标准的方法，一般导入第三方组件的时候使用。
使用@Import注解导入的Bean，一般快速导入一批组件时使用。

doProcessConfigurationClass 配置类的解析过程

调用链路：

doProcessConfigurationClass:289, ConfigurationClassParser (org.springframework.context.annotation)
processConfigurationClass:247, ConfigurationClassParser (org.springframework.context.annotation)
parse:200, ConfigurationClassParser (org.springframework.context.annotation)
parse:169, ConfigurationClassParser (org.springframework.context.annotation)
processConfigBeanDefinitions:308, ConfigurationClassPostProcessor (org.springframework.context.annotation)
postProcessBeanDefinitionRegistry:228, ConfigurationClassPostProcessor (org.springframework.context.annotation)
invokeBeanDefinitionRegistryPostProcessors:272, PostProcessorRegistrationDelegate (org.springframework.context.support)
invokeBeanFactoryPostProcessors:92, PostProcessorRegistrationDelegate (org.springframework.context.support)
invokeBeanFactoryPostProcessors:687, AbstractApplicationContext (org.springframework.context.support)
refresh:525, AbstractApplicationContext (org.springframework.context.support)
<init>:84, AnnotationConfigApplicationContext (org.springframework.context.annotation)

源码：

// 解析配置类将业务Bean的定义BeanDefinition注册到容器
protected final SourceClass doProcessConfigurationClass(ConfigurationClass configClass, SourceClass sourceClass)
        throws IOException {

    // Recursively process any member (nested) classes first
    processMemberClasses(configClass, sourceClass);

    // Process any @PropertySource annotations
    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");
        }
    }

    // Process any @ComponentScan annotations
    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
            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
            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
    processImports(configClass, sourceClass, getImports(sourceClass), true);

    // Process any @ImportResource annotations
    if (sourceClass.getMetadata().isAnnotated(ImportResource.class.getName())) {
        AnnotationAttributes importResource =
                AnnotationConfigUtils.attributesFor(sourceClass.getMetadata(), ImportResource.class);
        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
    Set<MethodMetadata> beanMethods = retrieveBeanMethodMetadata(sourceClass);
    for (MethodMetadata methodMetadata : beanMethods) {
        configClass.addBeanMethod(new BeanMethod(methodMetadata, configClass));
    }

    // Process default methods on interfaces
    processInterfaces(configClass, sourceClass);

    // Process superclass, if any
    if (sourceClass.getMetadata().hasSuperClass()) {
        String superclass = sourceClass.getMetadata().getSuperClassName();
        if (!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;
}

从源码我们可以看到解析配置类的完整过程：

使用递归的方式处理嵌套类
处理@PropertySource注解，解析配置文件，将配置项加载到环境变量里面
处理@ComponentScan注解，将所有符合条件Bean的BeanDefinition注册到容器
处理@Import注解
处理@ImportResource注解
处理@Bean方法
处理接口的默认方法
处理父类

处理@ComponentScan注解

我们这里主要介绍下@ComponentScan注解的处理过程，最后主要的处理方法是ClassPathBeanDefinitionScanner#doScan()方法。

调用链路：

doScan:270, ClassPathBeanDefinitionScanner (org.springframework.context.annotation)
parse:135, ComponentScanAnnotationParser (org.springframework.context.annotation)
doProcessConfigurationClass:289, ConfigurationClassParser (org.springframework.context.annotation)
processConfigurationClass:247, ConfigurationClassParser (org.springframework.context.annotation)
parse:200, ConfigurationClassParser (org.springframework.context.annotation)
parse:169, ConfigurationClassParser (org.springframework.context.annotation)
processConfigBeanDefinitions:308, ConfigurationClassPostProcessor (org.springframework.context.annotation)
postProcessBeanDefinitionRegistry:228, ConfigurationClassPostProcessor (org.springframework.context.annotation)
invokeBeanDefinitionRegistryPostProcessors:272, PostProcessorRegistrationDelegate (org.springframework.context.support)
invokeBeanFactoryPostProcessors:92, PostProcessorRegistrationDelegate (org.springframework.context.support)
invokeBeanFactoryPostProcessors:687, AbstractApplicationContext (org.springframework.context.support)
refresh:525, AbstractApplicationContext (org.springframework.context.support)
<init>:84, AnnotationConfigApplicationContext (org.springframework.context.annotation)

源码：

//  @ComponentScan 执行包扫描
protected Set<BeanDefinitionHolder> doScan(String... basePackages) {
    Assert.notEmpty(basePackages, "At least one base package must be specified");
    Set<BeanDefinitionHolder> beanDefinitions = new LinkedHashSet<BeanDefinitionHolder>();
    for (String basePackage : basePackages) {
        // 根据包路径找到需要加载到容器的业务Bean
        Set<BeanDefinition> candidates = findCandidateComponents(basePackage);
        for (BeanDefinition candidate : candidates) {
            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);
            }
            if (candidate instanceof AnnotatedBeanDefinition) {
                AnnotationConfigUtils.processCommonDefinitionAnnotations((AnnotatedBeanDefinition) candidate);
            }
            if (checkCandidate(beanName, candidate)) {
                BeanDefinitionHolder definitionHolder = new BeanDefinitionHolder(candidate, beanName);
                definitionHolder =
                        AnnotationConfigUtils.applyScopedProxyMode(scopeMetadata, definitionHolder, this.registry);
                beanDefinitions.add(definitionHolder);
                // 将符合条件的Bean 定义注册到容器
                registerBeanDefinition(definitionHolder, this.registry);
            }
        }
    }
    return beanDefinitions;
}

// 根据包路径找到需要加载到容器的业务Bean
public Set<BeanDefinition> findCandidateComponents(String basePackage) {
    Set<BeanDefinition> candidates = new LinkedHashSet<BeanDefinition>();
    try {
        // 根据包路径找到需要加载到容器class文件
        String packageSearchPath = ResourcePatternResolver.CLASSPATH_ALL_URL_PREFIX +
                resolveBasePackage(basePackage) + '/' + this.resourcePattern;
                
        // 根据资源加载器加载所有在对应包路径下的class文件到内存
        Resource[] resources = this.resourcePatternResolver.getResources(packageSearchPath);
        boolean traceEnabled = logger.isTraceEnabled();
        boolean debugEnabled = logger.isDebugEnabled();
        for (Resource resource : resources) {
            if (traceEnabled) {
                logger.trace("Scanning " + resource);
            }
            // 判断是否是可读
            if (resource.isReadable()) {
                try {
                    MetadataReader metadataReader = this.metadataReaderFactory.getMetadataReader(resource);
                    // 判断是否是@Component组件
                    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);
                        }
                        ...
    return candidates;
}

// 判断是否是@Component组件
protected boolean isCandidateComponent(MetadataReader metadataReader) throws IOException {
    // 执行excludeFilters
    for (TypeFilter tf : this.excludeFilters) {
        if (tf.match(metadataReader, this.metadataReaderFactory)) {
            return false;
        }
    }
    // 执行includeFilters
    for (TypeFilter tf : this.includeFilters) {
        if (tf.match(metadataReader, this.metadataReaderFactory)) {
            return isConditionMatch(metadataReader);
        }
    }
    return false;
}

findCandidateComponents方法最终会调用AnnotationMetadataReadingVisitor类的hasAnnotation和hasMetaAnnotation方法来判断是否是@Component组件。
调用链路：

hasMetaAnnotation:112, AnnotationMetadataReadingVisitor (org.springframework.core.type.classreading)
matchSelf:86, AnnotationTypeFilter (org.springframework.core.type.filter)
match:61, AbstractTypeHierarchyTraversingFilter (org.springframework.core.type.filter)
isCandidateComponent:354, ClassPathScanningCandidateComponentProvider (org.springframework.context.annotation)
findCandidateComponents:288, ClassPathScanningCandidateComponentProvider (org.springframework.context.annotation)
doScan:272, ClassPathBeanDefinitionScanner (org.springframework.context.annotation)
parse:135, ComponentScanAnnotationParser (org.springframework.context.annotation)
doProcessConfigurationClass:289, ConfigurationClassParser (org.springframework.context.annotation)
processConfigurationClass:247, ConfigurationClassParser (org.springframework.context.annotation)
parse:200, ConfigurationClassParser (org.springframework.context.annotation)
parse:169, ConfigurationClassParser (org.springframework.context.annotation)
processConfigBeanDefinitions:308, ConfigurationClassPostProcessor (org.springframework.context.annotation)
postProcessBeanDefinitionRegistry:228, ConfigurationClassPostProcessor (org.springframework.context.annotation)
invokeBeanDefinitionRegistryPostProcessors:272, PostProcessorRegistrationDelegate (org.springframework.context.support)
invokeBeanFactoryPostProcessors:92, PostProcessorRegistrationDelegate (org.springframework.context.support)
invokeBeanFactoryPostProcessors:687, AbstractApplicationContext (org.springframework.context.support)
refresh:525, AbstractApplicationContext (org.springframework.context.support)
<init>:84, AnnotationConfigApplicationContext (org.springframework.context.annotation)

源码：

// 判断是否是@Component组件
public class AnnotationMetadataReadingVisitor extends ClassMetadataReadingVisitor implements AnnotationMetadata {

    ...
    // 判断是否是业务Bean
    @Override
    public boolean hasAnnotation(String annotationName) {
        return this.annotationSet.contains(annotationName);
    }
    
    // 判断是否是业务Bean
    @Override
    public boolean hasMetaAnnotation(String metaAnnotationType) {
        // 如果业务Bean是加的@Service注解，那么在metaAnnotationMap中将会以 
        // org.springframework.stereotype.Service=org.springframework.stereotype.Component的形式存储，
        // 将@Service注解映射成@Component注解。其他继承自@Component注解的处理方式也一样
        Collection<Set<String>> allMetaTypes = this.metaAnnotationMap.values();
        for (Set<String> metaTypes : allMetaTypes) {
            if (metaTypes.contains(metaAnnotationType)) {
                return true;
            }
        }
        return false;
    }
    ...
}

执行流程：

根据@ComponentScan注解配置的包范围找到所有符合条件的class文件
根据资源加载器，将所有的class文件加载到内存
循环遍历class找出符合条件的@Component组件
执行@ComponentScan的excludeFilters
执行@ComponentScan的includeFilters
获取当前class的metaAnnotationMap，判断是否是@Component组件
将符合条件的class的BeanDefinition注册到容器

如果业务Bean是加的@Service注解，那么在metaAnnotationMap中将会以 org.springframework.stereotype.Service=org.springframework.stereotype.Component的形式存储，将@Service注解映射成@Component注解。其他继承自@Component注解的处理方式也一样

Spring 源码（四）解析配置类

doProcessConfigurationClass 配置类的解析过程

处理@ComponentScan注解

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