Dubbo源码解析之@DubboService、@DubboReference（Dubbo源码一）

更好的阅读体验：Dubbo源码解析之@DubboService、@DubboReference（Dubbo源码一）
视频讲解：https://www.bilibili.com/video/BV1nBsMejEbL

对于Dubbo用的最多的就是@DubboService、@DubboReference，与之对应的就是服务的提供方、调用方。

之所以加上注解就可以运行，定是生成了代理对象，这篇文章就来讲讲如何基于这两个注解生成代理对象。

不管是服务端还是客户端，在使用Dubbo的时候都会先使用@EnableDubbo，比如下面的demo

@SpringBootApplication
@EnableDubbo
public class App {public static void main(String[] args) {SpringApplication.run(App.class, args);}
}

@EnableDubbo 是一个组合注解，它头上还有@DubboComponentScan和@EnableDubboConfig，它们就是分别来解析@DubboService、@DubboReference

EnableDubbo

@EnableDubboConfig
@DubboComponentScan
public @interface EnableDubbo {}

DubboComponentScan

@Import(DubboComponentScanRegistrar.class)
public @interface DubboComponentScan {}

EnableDubboConfig

@Import(DubboConfigConfigurationRegistrar.class)
public @interface EnableDubboConfig {}

一、@DubboReference 注解解析

DubboConfigConfigurationRegistrar 里面注入了一个bean处理器 ReferenceAnnotationBeanPostProcessor，这个处理器会把带有下面三个注解的bean代理成一个 ReferenceBean

DubboReference
Reference
com.alibaba.dubbo.config.annotation.Reference

1、入口

入口跳的很多，全部把代码复制过来阅读体验不好，也全无必要，这里给出每个方法的关键代码

EnableDubbo

@EnableDubboConfig
@DubboComponentScan
public @interface EnableDubbo {}

EnableDubboConfig

@Import(DubboConfigConfigurationRegistrar.class)
public @interface EnableDubboConfig {}

DubboConfigConfigurationRegistrar

public class DubboConfigConfigurationRegistrar implements ImportBeanDefinitionRegistrar {@Overridepublic void registerBeanDefinitions(AnnotationMetadata importingClassMetadata, BeanDefinitionRegistry registry) {// initialize dubbo beansDubboSpringInitializer.initialize(registry);}
}

DubboSpringInitializer

public static void initialize(BeanDefinitionRegistry registry) {// ...// init dubbo contextinitContext(context, registry, beanFactory);
}private static void initContext(DubboSpringInitContext context, BeanDefinitionRegistry registry,ConfigurableListableBeanFactory beanFactory) {// ...// register common beansDubboBeanUtils.registerCommonBeans(registry);
}

DubboBeanUtils

static void registerCommonBeans(BeanDefinitionRegistry registry) {// ...// Since 2.5.7 Register @Reference Annotation Bean Processor as an infrastructure BeanregisterInfrastructureBean(registry, ReferenceAnnotationBeanPostProcessor.BEAN_NAME,ReferenceAnnotationBeanPostProcessor.class);// ...
}

2、bean处理器

所谓bean的后置处理器，其实就是在bean完成初始化之后，就会调用这个方法，给你所有的bean，然后你就可以对这个bean为所欲为了

bean处理器有很多，有前置处理器、后置处理器、bean工厂处理器

2-1、前、后置处理器

只需要实现BeanPostProcessor 接口，重写里面的前置、后置处理器就好了，系统会把每个bean作为参数去调用这个方法

public interface BeanPostProcessor {@Nullabledefault Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException {return bean;}@Nullabledefault Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException {return bean;}
}

2-2、bean工厂处理器

上面的前后置处理器，是系统拿到bean去调用这个方法，bean工厂处理器直接把bean工厂给你

public interface BeanFactoryPostProcessor {void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory) throws BeansException;}

3、循环所有的bean，找到使用注解的bean生成代理对象

ReferenceAnnotationBeanPostProcessor实现了BeanFactoryPostProcessor，重写了postProcessBeanFactory，在这个方法里面对使用了注解的bean进行代理

public void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory) throws BeansException {// 遍历所有的beanString[] beanNames = beanFactory.getBeanDefinitionNames();for (String beanName : beanNames) {Class<?> beanType;// 判断是不是工厂bean，显然我们不是if (beanFactory.isFactoryBean(beanName)) {// ...} else {// 走这个、拿到classbeanType = beanFactory.getType(beanName);}if (beanType != null) {// 找到需要被代理的 metadataAnnotatedInjectionMetadata metadata = findInjectionMetadata(beanName, beanType, null);try {// 进行代理生成prepareInjection(metadata);} catch (BeansException e) {throw e;} catch (Exception e) {throw new IllegalStateException("Prepare dubbo reference injection element failed", e);}}}
}

4、找到合适的bean

匹配逻辑，其实就是拿每一个Class 上面的注解，看看是否和DubboReference相关注解匹配，下面代码给出大概步骤，忽略一些判断逻辑

setp 1

protected AnnotatedInjectionMetadata findInjectionMetadata(String beanName, Class<?> clazz, PropertyValues pvs) {// ...try {// 走这里构建metadata = buildAnnotatedMetadata(clazz);this.injectionMetadataCache.put(cacheKey, metadata);} catch (NoClassDefFoundError err) {throw new IllegalStateException("Failed to introspect object class [" + clazz.getName() +"] for annotation metadata: could not find class that it depends on", err);} // ...return metadata;
}

setp 2

private AbstractAnnotationBeanPostProcessor.AnnotatedInjectionMetadata buildAnnotatedMetadata(final Class<?> beanClass) {// 这个方法就会找到合适匹配的beanCollection<AbstractAnnotationBeanPostProcessor.AnnotatedFieldElement> fieldElements = findFieldAnnotationMetadata(beanClass);Collection<AbstractAnnotationBeanPostProcessor.AnnotatedMethodElement> methodElements = findAnnotatedMethodMetadata(beanClass);return new AnnotatedInjectionMetadata(beanClass, fieldElements, methodElements);
}

setp 3

private List<AbstractAnnotationBeanPostProcessor.AnnotatedFieldElement> findFieldAnnotationMetadata(final Class<?> beanClass) {final List<AbstractAnnotationBeanPostProcessor.AnnotatedFieldElement> elements = new LinkedList<>();ReflectionUtils.doWithFields(beanClass, field -> {for (Class<? extends Annotation> annotationType : getAnnotationTypes()) {AnnotationAttributes attributes = AnnotationUtils.getAnnotationAttributes(field, annotationType, getEnvironment(), true, true);if (attributes != null) {if (Modifier.isStatic(field.getModifiers())) {if (logger.isWarnEnabled()) {logger.warn(CONFIG_DUBBO_BEAN_INITIALIZER, "", "", "@" + annotationType.getName() + " is not supported on static fields: " + field);}return;}elements.add(new AnnotatedFieldElement(field, attributes));}}});return elements;
}

getAnnotationTypes 就是在初始化的时候Set进去的

public ReferenceAnnotationBeanPostProcessor() {super(DubboReference.class, Reference.class, com.alibaba.dubbo.config.annotation.Reference.class);
}public AbstractAnnotationBeanPostProcessor(Class<? extends Annotation>... annotationTypes) {Assert.notEmpty(annotationTypes, "The argument of annotations' types must not empty");this.annotationTypes = annotationTypes;
}

5、注册 ReferenceBean类型的 beanDefinition

让我们再回到 ReferenceAnnotationBeanPostProcessor#postProcessBeanFactory 在这个方法里面循环每一个bean看它是否用到了 DubboReference 相关注解，如果有就进行代理对象

@Override
public void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory) throws BeansException {String[] beanNames = beanFactory.getBeanDefinitionNames();for (String beanName : beanNames) {// ...if (beanType != null) {// 找到满足代理的bean，上一节已经讲了AnnotatedInjectionMetadata metadata = findInjectionMetadata(beanName, beanType, null);try {// 进行代理prepareInjection(metadata);}}// ... }
}

protected void prepareInjection(AnnotatedInjectionMetadata metadata) throws BeansException {try {//find and register bean definition for @DubboReference/@Referencefor (AnnotatedFieldElement fieldElement : metadata.getFieldElements()) {if (fieldElement.injectedObject != null) {continue;}Class<?> injectedType = fieldElement.field.getType();AnnotationAttributes attributes = fieldElement.attributes;// 注册代理beanString referenceBeanName = registerReferenceBean(fieldElement.getPropertyName(), injectedType, attributes, fieldElement.field);//associate fieldElement and reference beanfieldElement.injectedObject = referenceBeanName;injectedFieldReferenceBeanCache.put(fieldElement, referenceBeanName);}// ...} catch (ClassNotFoundException e) {throw new BeanCreationException("prepare reference annotation failed", e);}
}

registerReferenceBean 方法很长，前面有一系列的校验和缓存处理，这里为了简便，只给出后面注册 beanDefinition 部分

public String registerReferenceBean(String propertyName, Class<?> injectedType, Map<String, Object> attributes, Member member) throws BeansException {// ... 省略一大段校验缓存逻辑// Register the reference bean definition to the beanFactoryRootBeanDefinition beanDefinition = new RootBeanDefinition();// 看看看看，找到了，注册的这个 beanDefinition ，是 ReferenceBean.classbeanDefinition.setBeanClassName(ReferenceBean.class.getName());// ... 省略赋值的逻辑// 注册BeanDefinition， 被注册的 BeanDefinition，会生成一个对象beanDefinitionRegistry.registerBeanDefinition(referenceBeanName, beanDefinition);logger.info("Register dubbo reference bean: " + referenceBeanName + " = " + referenceKey + " at " + member);return referenceBeanName;
}

6、生成代理对象 ReferenceBean

ReferenceBean 是一个FactoryBean，所以在需要这个bean的时候会调用getObject 获取bean

ReferenceBean<T> implements FactoryBean<T>,ApplicationContextAware, BeanClassLoaderAware, BeanNameAware, InitializingBean, DisposableBean

@Override
public T getObject() {if (lazyProxy == null) {createLazyProxy();}return (T) lazyProxy;
}

private void createLazyProxy() {// ....// 这里默认走的就是Javassist代理if (StringUtils.isEmpty(this.proxy) || CommonConstants.DEFAULT_PROXY.equalsIgnoreCase(this.proxy)) {generateFromJavassistFirst(interfaces);}if (this.lazyProxy == null) {generateFromJdk(interfaces);}
}

好啦，到这里代理对象就生成完毕了，这里看到它在代理对象里面注册了一个 LazyTargetInvocationHandler，它本质上是一个 InvocationHandler，所以当执行这个代理对象的时候就会执行org.apache.LazyTargetInvocationHandler#invoke 这就行下一期要讲的，运行原理

private void generateFromJavassistFirst(List<Class<?>> interfaces) {try {this.lazyProxy = Proxy.getProxy(interfaces.toArray(new Class[0])).newInstance(new LazyTargetInvocationHandler(new DubboReferenceLazyInitTargetSource()));} catch (Throwable fromJavassist) {// ...}
}

二、@DubboService 注解解析

相较于@DubboReference，@DubboService的解析要复杂不少，先是扫描到带有注解的实体，生成 ServiceBean，再基于ServiceBean生成CallbackRegistrationInvoker对象

1、入口

@EnableDubbo > @DubboComponentScan > DubboComponentScanRegistrar.class

DubboComponentScanRegistrar implements ImportBeanDefinitionRegistrar，重写了registerBeanDefinitions，这个方法里面就注入了Service处理器，通过扫描包下面使用相关注解的bean

@Override
public void registerBeanDefinitions(AnnotationMetadata importingClassMetadata, BeanDefinitionRegistry registry) {// initialize dubbo beansDubboSpringInitializer.initialize(registry);Set<String> packagesToScan = getPackagesToScan(importingClassMetadata);// 注册Service处理器registerServiceAnnotationPostProcessor(packagesToScan, registry);
}

2、bean 处理器

通过扫描指定包下的bean来筛选是否满足生成 ServiceBean

org.apache.dubbo.config.spring.beans.factory.annotation.ServiceAnnotationPostProcessor#postProcessBeanDefinitionRegistry

@Override
public void postProcessBeanDefinitionRegistry(BeanDefinitionRegistry registry) throws BeansException {this.registry = registry;scanServiceBeans(resolvedPackagesToScan, registry);
}

scanServiceBeans

看看这里把 serviceAnnotationTypes 装进去了，下面判断的时候会用到

private void scanServiceBeans(Set<String> packagesToScan, BeanDefinitionRegistry registry) {// 循环每个包for (String packageToScan : packagesToScan) {DubboClassPathBeanDefinitionScanner scanner = new DubboClassPathBeanDefinitionScanner(registry, environment, resourceLoader);// 🌈🌈🌈🌈构建需要包含哪些bean， serviceAnnotationTypes 就是上面定义的注解for (Class<? extends Annotation> annotationType : serviceAnnotationTypes) {scanner.addIncludeFilter(new AnnotationTypeFilter(annotationType));}// 扫描每个包scanner.scan(packageToScan);// 找到合适的 BeanDefinitionSet<BeanDefinitionHolder> beanDefinitionHolders =findServiceBeanDefinitionHolders(scanner, packageToScan, registry, beanNameGenerator);// 循环每一个合适的 BeanDefinitionfor (BeanDefinitionHolder beanDefinitionHolder : beanDefinitionHolders) {// 生成 ServiceBeanprocessScannedBeanDefinition(beanDefinitionHolder);servicePackagesHolder.addScannedClass(beanDefinitionHolder.getBeanDefinition().getBeanClassName());}servicePackagesHolder.addScannedPackage(packageToScan);}
}

serviceAnnotationTypes

private final static List<Class<? extends Annotation>> serviceAnnotationTypes = asList(// @since 2.7.7 Add the @DubboService , the issue : https://github.com/apache/dubbo/issues/6007DubboService.class,// @since 2.7.0 the substitute @com.alibaba.dubbo.config.annotation.ServiceService.class,// @since 2.7.3 Add the compatibility for legacy Dubbo's @Service , the issue : https://github.com/apache/dubbo/issues/4330com.alibaba.dubbo.config.annotation.Service.class
);

3、找到合适的 BeanDefinition

这里寻找的过程有一点绕，还是和之前一起，给出每个关键节点的关键代码

本质上就是扫描包下面的BeanDefinition看看是否有包含 @DubboService相关注解

findServiceBeanDefinitionHolders

org.apache.dubbo.config.spring.beans.factory.annotation.ServiceAnnotationPostProcessor#findServiceBeanDefinitionHolders

private Set<BeanDefinitionHolder> findServiceBeanDefinitionHolders(ClassPathBeanDefinitionScanner scanner, String packageToScan, BeanDefinitionRegistry registry,BeanNameGenerator beanNameGenerator) {Set<BeanDefinition> beanDefinitions = scanner.findCandidateComponents(packageToScan);Set<BeanDefinitionHolder> beanDefinitionHolders = new LinkedHashSet<>(beanDefinitions.size());for (BeanDefinition beanDefinition : beanDefinitions) {String beanName = beanNameGenerator.generateBeanName(beanDefinition, registry);BeanDefinitionHolder beanDefinitionHolder = new BeanDefinitionHolder(beanDefinition, beanName);beanDefinitionHolders.add(beanDefinitionHolder);}return beanDefinitionHolders;}

findCandidateComponents

org.apache.dubbo.config.spring.context.annotation.DubboClassPathBeanDefinitionScanner#findCandidateComponents

@Override
public Set<BeanDefinition> findCandidateComponents(String basePackage) {Set<BeanDefinition> beanDefinitions = beanDefinitionMap.get(basePackage);// if beanDefinitions size is null => scanif (Objects.isNull(beanDefinitions)) {beanDefinitions = super.findCandidateComponents(basePackage);beanDefinitionMap.put(basePackage, beanDefinitions);}return beanDefinitions;
}

scanCandidateComponents

org.springframework.context.annotation.ClassPathScanningCandidateComponentProvider#scanCandidateComponents

private Set<BeanDefinition> scanCandidateComponents(String basePackage) {Set<BeanDefinition> candidates = new LinkedHashSet();// ...MetadataReader metadataReader = this.getMetadataReaderFactory().getMetadataReader(resource);if (this.isCandidateComponent(metadataReader)) {ScannedGenericBeanDefinition sbd = new ScannedGenericBeanDefinition(metadataReader);// 判断当前bean是不是满足if (this.isCandidateComponent((AnnotatedBeanDefinition)sbd)) {if (debugEnabled) {this.logger.debug("Identified candidate component class: " + resource);}candidates.add(sbd);} else if (debugEnabled) {this.logger.debug("Ignored because not a concrete top-level class: " + resource);}} // ...return candidates;
}

isCandidateComponent

includeFilters 数据就是在scanServiceBeans 里面设置进去的

org.springframework.context.annotation.ClassPathScanningCandidateComponentProvider#isCandidateComponent(org.springframework.core.type.classreading.MetadataReader)

protected boolean isCandidateComponent(MetadataReader metadataReader) throws IOException {Iterator var2 = this.excludeFilters.iterator();TypeFilter tf;do {if (!var2.hasNext()) {var2 = this.includeFilters.iterator();do {if (!var2.hasNext()) {return false;}tf = (TypeFilter)var2.next();} while(!tf.match(metadataReader, this.getMetadataReaderFactory()));return this.isConditionMatch(metadataReader);}tf = (TypeFilter)var2.next();} while(!tf.match(metadataReader, this.getMetadataReaderFactory()));return false;
}

4、生成ServiceBean

org.apache.dubbo.config.spring.beans.factory.annotation.ServiceAnnotationPostProcessor#processScannedBeanDefinition


private void processScannedBeanDefinition(BeanDefinitionHolder beanDefinitionHolder) {Class<?> beanClass = resolveClass(beanDefinitionHolder);Annotation service = findServiceAnnotation(beanClass);// The attributes of @Service annotationMap<String, Object> serviceAnnotationAttributes = AnnotationUtils.getAttributes(service, true);String serviceInterface = resolveInterfaceName(serviceAnnotationAttributes, beanClass);String annotatedServiceBeanName = beanDefinitionHolder.getBeanName();// ServiceBean Bean nameString beanName = generateServiceBeanName(serviceAnnotationAttributes, serviceInterface);AbstractBeanDefinition serviceBeanDefinition =buildServiceBeanDefinition(serviceAnnotationAttributes, serviceInterface, annotatedServiceBeanName);registerServiceBeanDefinition(beanName, serviceBeanDefinition, serviceInterface);}

生成beanName

private String generateServiceBeanName(Map<String, Object> serviceAnnotationAttributes, String serviceInterface) {ServiceBeanNameBuilder builder = create(serviceInterface, environment).group((String) serviceAnnotationAttributes.get("group")).version((String) serviceAnnotationAttributes.get("version"));return builder.build();
}

构建bean参数

定义 BeanDefinition 的class，并且解析注解上的参数，放入BeanDefinition

private AbstractBeanDefinition buildServiceBeanDefinition(Map<String, Object> serviceAnnotationAttributes,String serviceInterface,String refServiceBeanName) {// 设置class                                                            BeanDefinitionBuilder builder = rootBeanDefinition(ServiceBean.class);AbstractBeanDefinition beanDefinition = builder.getBeanDefinition();beanDefinition.setAutowireMode(AbstractBeanDefinition.AUTOWIRE_CONSTRUCTOR);MutablePropertyValues propertyValues = beanDefinition.getPropertyValues();String[] ignoreAttributeNames = ObjectUtils.of("provider", "monitor", "application", "module", "registry", "protocol","methods", "interfaceName", "parameters", "executor");propertyValues.addPropertyValues(new AnnotationPropertyValuesAdapter(serviceAnnotationAttributes, environment, ignoreAttributeNames));addPropertyReference(builder, "ref", refServiceBeanName);// Set interfacebuilder.addPropertyValue("interface", serviceInterface);// ... 设置各种参数return builder.getBeanDefinition();
}

注册到 BeanDefinitionRegistry

private void registerServiceBeanDefinition(String serviceBeanName, AbstractBeanDefinition serviceBeanDefinition, String serviceInterface) {// check service bean// ...registry.registerBeanDefinition(serviceBeanName, serviceBeanDefinition);// ...
}

5、ServiceBean

一般生成代理对象，都会有一个 invoker方法，但ServiceBean没有，这是因为ServiceBean 只是存储DubboService的相关信息，后面还会生成一个真正invoker。

先来看一下ServiceBean的继承关系

public class ServiceBean<T> extends ServiceConfig<T> implements InitializingBean, DisposableBean,ApplicationContextAware, BeanNameAware, ApplicationEventPublisherAware {}

真正的invoker是在 ServiceConfig中生成的

ServiceBean 重写了 afterPropertiesSet ，把自己注册到了moduleConfigManager（这个后面会看到）

@Override
public void afterPropertiesSet() throws Exception {if (StringUtils.isEmpty(getPath())) {if (StringUtils.isNotEmpty(getInterface())) {setPath(getInterface());}}//register service beanModuleModel moduleModel = DubboBeanUtils.getModuleModel(applicationContext);moduleModel.getConfigManager().addService(this);moduleModel.getDeployer().setPending();
}

6、invoker生成

Dubbo注册了一个事件监听器，这个事件监听器会做很多初始化的工作，就会到生成Invoker的地方，这里的调用链路太长了，给一个Debug的图

在这里插入图片描述

最终会到当前类的org.apache.dubbo.config.ServiceConfig#doExportUrl方法

private void doExportUrl(URL url, boolean withMetaData, RegisterTypeEnum registerType) {if (!url.getParameter(REGISTER_KEY, true)) {registerType = RegisterTypeEnum.MANUAL_REGISTER;}if (registerType == RegisterTypeEnum.NEVER_REGISTER ||registerType == RegisterTypeEnum.MANUAL_REGISTER ||registerType == RegisterTypeEnum.AUTO_REGISTER_BY_DEPLOYER) {url = url.addParameter(REGISTER_KEY, false);}Invoker<?> invoker = proxyFactory.getInvoker(ref, (Class) interfaceClass, url);if (withMetaData) {invoker = new DelegateProviderMetaDataInvoker(invoker, this);}Exporter<?> exporter = protocolSPI.export(invoker);exporters.computeIfAbsent(registerType, k -> new CopyOnWriteArrayList<>()).add(exporter);
}

interfaceClass 取的是刚刚解析ServiceBean来的，也就是使用DubboService注解的类，invoker 返回的是Java生成的代理对象，Dubbo会再把它包装一层，所谓的包装就是用 Filter去包它，一层层的。最终生成 CallbackRegistrationInvoker。

在这里插入图片描述