简介

本文基于Spring Boot 2.6.6，dubbo-spring-boot-starter 3.0.6环境。

本文主要分析Dubbo中注解DubboService的使用方式，并从源码分析其生效的实现原理；

使用

常用的使用方式有两种，下面分别介绍；

方式一

在实现类上使用@DubboService，表示该Bean为Dubbo Service，示例代码如下：

@DubboService
public class DemoServiceImpl implements DemoService {}

方式二

官方推荐在BeanMethod上使用@DubboService；

示例代码如下：

@Configuration
public class ReferenceConfig {@Bean@DubboServicepublic DemoService demoServiceImpl() {return new DemoServiceImpl();}
}

解析

注解DubboService的解析由ServiceAnnotationPostProcessor完成，它会将标注了@DubboService的类或者Bean以ServiceBean形式注册到Spring容器中，以便后续创建Dubbo Service；

其postProcessBeanDefinitionRegistry方法用于解析方式一的@DubboService；
其postProcessBeanFactory方法用于解析方式二的@DubboService；

方式一

ServiceAnnotationPostProcessor实现了BeanDefinitionRegistryPostProcessor接口，在其postProcessBeanDefinitionRegistry方法中，会根据设置的resolvedPackagesToScan(待扫描路径)，处理对应路径下标注了@DubboService（本文仅关注DubboService，实际还包括：org.apache.dubbo.config.annotation.Service、com.alibaba.dubbo.config.annotation.Service）的类，代码如下：

public void postProcessBeanDefinitionRegistry(BeanDefinitionRegistry registry) throws BeansException {this.registry = registry;// 扫描resolvedPackagesToScan路径下标注了@DubboService的类// packagesToScan由参数dubbo.scan.base-packages配置// 若该参数不存在，那么ServiceAnnotationPostProcessor也不会存在于Spring容器scanServiceBeans(resolvedPackagesToScan, registry);
}private void scanServiceBeans(Set<String> packagesToScan, BeanDefinitionRegistry registry) {// 设置扫描标识，避免重复扫描scaned = true;if (CollectionUtils.isEmpty(packagesToScan)) {// 无路径需要扫描，则直接退出if (logger.isWarnEnabled()) {logger.warn("packagesToScan is empty , ServiceBean registry will be ignored!");}return;}// 配置DubboClassPathBeanDefinitionScannerDubboClassPathBeanDefinitionScanner scanner =new DubboClassPathBeanDefinitionScanner(registry, environment, resourceLoader);BeanNameGenerator beanNameGenerator = resolveBeanNameGenerator(registry);scanner.setBeanNameGenerator(beanNameGenerator);for (Class<? extends Annotation> annotationType : serviceAnnotationTypes) {// 基于注解的类型过滤器scanner.addIncludeFilter(new AnnotationTypeFilter(annotationType));}ScanExcludeFilter scanExcludeFilter = new ScanExcludeFilter();scanner.addExcludeFilter(scanExcludeFilter);// 扫描各个包路径for (String packageToScan : packagesToScan) {// 如果已经扫描过则跳过if (servicePackagesHolder.isPackageScanned(packageToScan)) {if (logger.isInfoEnabled()) {logger.info("Ignore package who has already bean scanned: " + packageToScan);}continue;}// 扫描包路径下被Dubbo Service注解标注的类，并生成BeanDefinitionscanner.scan(packageToScan);// 查找Dubbo Service的BeanDefinitionHolder// 结果会在scan中缓存，故此次直接从缓存中得到Set<BeanDefinitionHolder> beanDefinitionHolders =findServiceBeanDefinitionHolders(scanner, packageToScan, registry, beanNameGenerator);if (!CollectionUtils.isEmpty(beanDefinitionHolders)) {if (logger.isInfoEnabled()) {List<String> serviceClasses = new ArrayList<>(beanDefinitionHolders.size());for (BeanDefinitionHolder beanDefinitionHolder : beanDefinitionHolders) {serviceClasses.add(beanDefinitionHolder.getBeanDefinition().getBeanClassName());}logger.info("Found " + beanDefinitionHolders.size() + " classes annotated by Dubbo @Service under package [" + packageToScan + "]: " + serviceClasses);}for (BeanDefinitionHolder beanDefinitionHolder : beanDefinitionHolders) {// 向容器中注册该beanDefinitionHolderprocessScannedBeanDefinition(beanDefinitionHolder, registry, scanner);// 缓存已扫描过的类servicePackagesHolder.addScannedClass(beanDefinitionHolder.getBeanDefinition().getBeanClassName());}} else {if (logger.isWarnEnabled()) {logger.warn("No class annotated by Dubbo @Service was found under package ["+ packageToScan + "], ignore re-scanned classes: " + scanExcludeFilter.getExcludedCount());}}// 缓存已扫描过的包路径servicePackagesHolder.addScannedPackage(packageToScan);}
}

主要逻辑为：

扫描标注@DubboService的Class，并注册到Spring容器；
将注册的BeanDefinition，再以ServiceBean注册到Spring容器

扫描标注@DubboService的Class

ClassPathBeanDefinitionScanner.scan(packageToScan)内部使用doScan实现，其代码如下：

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) {// 查找满足要求的候选组件Dubbo Service Class// 对basePackage路径下所有类经过isCandidateComponent筛选//     先经过excludeFilters（优先），再经过includeFiltersSet<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);}// 校验当前容器是否已存在该BeanDefinition// 1. 若不存在则校验通过// 2. 若存在，但兼容，则校验不通过// 3. 若存在，且不兼容，则抛出异常if (checkCandidate(beanName, candidate)) {BeanDefinitionHolder definitionHolder = new BeanDefinitionHolder(candidate, beanName);definitionHolder =AnnotationConfigUtils.applyScopedProxyMode(scopeMetadata, definitionHolder, this.registry);beanDefinitions.add(definitionHolder);// 注册BeanDefinition，此时beanName根据原始类名生成registerBeanDefinition(definitionHolder, this.registry);}}}return beanDefinitions;
}

注册ServiceBean

processScannedBeanDefinition代码如下：

private void processScannedBeanDefinition(BeanDefinitionHolder beanDefinitionHolder, BeanDefinitionRegistry registry,DubboClassPathBeanDefinitionScanner scanner) {Class<?> beanClass = resolveClass(beanDefinitionHolder);// 获取类上标注的Dubbo Service注解Annotation service = findServiceAnnotation(beanClass);// 获取注解的属性Map<String, Object> serviceAnnotationAttributes = AnnotationUtils.getAttributes(service, true);String serviceInterface = resolveInterfaceName(serviceAnnotationAttributes, beanClass);String annotatedServiceBeanName = beanDefinitionHolder.getBeanName();// 构造ServiceBean BeanName// ServiceBean:interfaceNameString beanName = generateServiceBeanName(serviceAnnotationAttributes, serviceInterface);// 构造ServiceBean BeanDefinitionAbstractBeanDefinition serviceBeanDefinition =buildServiceBeanDefinition(serviceAnnotationAttributes, serviceInterface, annotatedServiceBeanName);// 注册ServiceBean BeanDefinition// 此时beanName为ServiceBean:interfaceNameregisterServiceBeanDefinition(beanName, serviceBeanDefinition, serviceInterface);
}

方式二

ServiceAnnotationPostProcessor.postProcessBeanFactory方法中，会处理标注了@DubboService（本文仅关注DubboService，实际还包括：org.apache.dubbo.config.annotation.Service、com.alibaba.dubbo.config.annotation.Service）的BeanMethod，代码如下：

public void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory) throws BeansException {if (this.registry == null) {// 未在postProcessBeanDefinitionRegistry中设置，则此时设置this.registry = (BeanDefinitionRegistry) beanFactory;}// 处理由标注了Dubbo Service注解的BeanMethod得到的BeanDefinitionString[] beanNames = beanFactory.getBeanDefinitionNames();for (String beanName : beanNames) {BeanDefinition beanDefinition = beanFactory.getBeanDefinition(beanName);Map<String, Object> annotationAttributes = getServiceAnnotationAttributes(beanDefinition);// 存在则说明BeanMethod上存在Dubbo Service注解if (annotationAttributes != null) {// 注册为Dubbo Service BeanDefinitionprocessAnnotatedBeanDefinition(beanName, (AnnotatedBeanDefinition) beanDefinition, annotationAttributes);}}if (!scaned) {// 还未扫描过，则扫描scanServiceBeans(resolvedPackagesToScan, registry);}
}private void processAnnotatedBeanDefinition(String refServiceBeanName, AnnotatedBeanDefinition refServiceBeanDefinition, Map<String, Object> attributes) {Map<String, Object> serviceAnnotationAttributes = new LinkedHashMap<>(attributes);// get bean class from return typeString returnTypeName = SpringCompatUtils.getFactoryMethodReturnType(refServiceBeanDefinition);Class<?> beanClass = resolveClassName(returnTypeName, classLoader);String serviceInterface = resolveInterfaceName(serviceAnnotationAttributes, beanClass);// 构造ServiceBean BeanName// ServiceBean:interfaceNameString serviceBeanName = generateServiceBeanName(serviceAnnotationAttributes, serviceInterface);AbstractBeanDefinition serviceBeanDefinition = buildServiceBeanDefinition(serviceAnnotationAttributes, serviceInterface, refServiceBeanName);// set idserviceBeanDefinition.getPropertyValues().add(Constants.ID, serviceBeanName);// 注册ServiceBean BeanDefinition// 此时beanName为ServiceBean:interfaceNameregisterServiceBeanDefinition(serviceBeanName, serviceBeanDefinition, serviceInterface);
}

至此，@DubboService的源码分析就结束啦，ServiceBean的实例化请见下文分析。

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相关阅读

简介

使用

方式一

方式二

解析

方式一

扫描标注@DubboService的Class

注册ServiceBean

方式二

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