需要前置知识，了解spring源码，springboot自动加载机制等

DubboBootstrap启动

详细信息可看学习Dubbo源码需要了解的基础内容源码详解

DubboBootstrap 启动所需要的信息

添加应用程序配置
添加注册中心配置
添加协议配置
添加服务配置
启动

SpringBoot启动Dubbo

@EnableDubbo注解中引用了 @DubboComponentScan和 @EnableDubboConfig注解

@DubboComponentScan注解中引用了 @Import(DubboComponentScanRegistrar.class) 所以以DubboComponentScanRegistrar类为起点

@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Import(DubboComponentScanRegistrar.class)
public @interface DubboComponentScan {String[] value() default {};String[] basePackages() default {};Class<?>[] basePackageClasses() default {};
}

DubboComponentScanRegistrar

实现自 ImportBeanDefinitionRegistrar 重写了 registerBeanDefinitions方法，在SpringBoot源码中会回调 registerBeanDefinitions方法，可见SpringBoot源码

@Override
public void registerBeanDefinitions(AnnotationMetadata importingClassMetadata, BeanDefinitionRegistry registry) {// initialize dubbo beans// 核心 初始化环境 包括注册监听器DubboSpringInitializer.initialize(registry);Set<String> packagesToScan = getPackagesToScan(importingClassMetadata);// 注册ServiceBean 和dubbo启动信息registerServiceAnnotationPostProcessor(packagesToScan, registry);
}

DubboSpringInitializer.initialize(registry) =》调用 initContext(context, registry, beanFactory) 初始化上下文

initContext(context, registry, beanFactory) =》调用 DubboBeanUtils.registerCommonBeans(registry);注册公共使用Bean对象

DubboBeanUtils.registerCommonBeans(registry);

static void registerCommonBeans(BeanDefinitionRegistry registry) {registerInfrastructureBean(registry, ServicePackagesHolder.BEAN_NAME, ServicePackagesHolder.class);registerInfrastructureBean(registry, ReferenceBeanManager.BEAN_NAME, ReferenceBeanManager.class);// Since 2.5.7 Register @Reference Annotation Bean Processor as an infrastructure BeanregisterInfrastructureBean(registry, ReferenceAnnotationBeanPostProcessor.BEAN_NAME,ReferenceAnnotationBeanPostProcessor.class);// TODO Whether DubboConfigAliasPostProcessor can be removed ?// Since 2.7.4 [Feature] https://github.com/apache/dubbo/issues/5093registerInfrastructureBean(registry, DubboConfigAliasPostProcessor.BEAN_NAME,DubboConfigAliasPostProcessor.class);// register ApplicationListeners// 核心，注册了部署调度监听器和应用程序监听器 registerInfrastructureBean(registry, DubboDeployApplicationListener.class.getName(), DubboDeployApplicationListener.class);registerInfrastructureBean(registry, DubboConfigApplicationListener.class.getName(), DubboConfigApplicationListener.class);// Since 2.7.6 Register DubboConfigDefaultPropertyValueBeanPostProcessor as an infrastructure BeanregisterInfrastructureBean(registry, DubboConfigDefaultPropertyValueBeanPostProcessor.BEAN_NAME,DubboConfigDefaultPropertyValueBeanPostProcessor.class);// Dubbo config initializerregisterInfrastructureBean(registry, DubboConfigBeanInitializer.BEAN_NAME, DubboConfigBeanInitializer.class);// register infra bean if not exists laterregisterInfrastructureBean(registry, DubboInfraBeanRegisterPostProcessor.BEAN_NAME, DubboInfraBeanRegisterPostProcessor.class);
}

注册服务配置信息SercviceBean

registerServiceAnnotationPostProcessor(packagesToScan, registry);

注册了 ServiceAnnotationPostProcessor

private void registerServiceAnnotationPostProcessor(Set<String> packagesToScan, BeanDefinitionRegistry registry) {// 注册 ServiceAnnotationPostProcessorBeanDefinitionBuilder builder = rootBeanDefinition(ServiceAnnotationPostProcessor.class);builder.addConstructorArgValue(packagesToScan);builder.setRole(BeanDefinition.ROLE_INFRASTRUCTURE);AbstractBeanDefinition beanDefinition = builder.getBeanDefinition();BeanDefinitionReaderUtils.registerWithGeneratedName(beanDefinition, registry);
}

ServiceAnnotationPostProcessor

实现了BeanDefinitionRegistryPostProcessor，所以会调用postProcessBeanDefinitionRegistry方法

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

scanServiceBeans(resolvedPackagesToScan, registry);

这个方法就包含了注册dubbo配置的bean的逻辑了，需要扫描自定义的注解来注册到spring的ioc容器中的套路大致都是相同的，和Mybatis一样，使用spring的扩展机制来扫描自定义的注解，然后注册为BeanDefinition，即可在Spring中注册为bean

private void scanServiceBeans(Set<String> packagesToScan, BeanDefinitionRegistry registry) {scanned = true;if (CollectionUtils.isEmpty(packagesToScan)) {if (logger.isWarnEnabled()) {logger.warn(CONFIG_NO_BEANS_SCANNED, "", "", "packagesToScan is empty , ServiceBean registry will be ignored!");}return;}// 创建扫描包类DubboClassPathBeanDefinitionScanner scanner =new DubboClassPathBeanDefinitionScanner(registry, environment, resourceLoader);BeanNameGenerator beanNameGenerator = resolveBeanNameGenerator(registry);scanner.setBeanNameGenerator(beanNameGenerator);// 添加有 @DubboService  @Service  的过滤条件 for (Class<? extends Annotation> annotationType : serviceAnnotationTypes) {scanner.addIncludeFilter(new AnnotationTypeFilter(annotationType));}ScanExcludeFilter scanExcludeFilter = new ScanExcludeFilter();scanner.addExcludeFilter(scanExcludeFilter);for (String packageToScan : packagesToScan) {// avoid duplicated scansif (servicePackagesHolder.isPackageScanned(packageToScan)) {if (logger.isInfoEnabled()) {logger.info("Ignore package who has already bean scanned: " + packageToScan);}continue;}// Registers @Service Bean first// 包扫描，扫描当前包路径下所有类（因为没开 @Indexed注解 ）scanner.scan(packageToScan);// 查找@Service的所有beandefinitionholder，无论@ComponentScan是否扫描  // 包装成 BeanDefinitionHolder 返回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) {// 核心 核心 对 每一个包装的 beanDefinitionHolder 处理processScannedBeanDefinition(beanDefinitionHolder);servicePackagesHolder.addScannedClass(beanDefinitionHolder.getBeanDefinition().getBeanClassName());}} else {if (logger.isWarnEnabled()) {logger.warn(CONFIG_NO_ANNOTATIONS_FOUND,"No annotations were found on the class","","No class annotated by Dubbo @Service was found under package ["+ packageToScan + "], ignore re-scanned classes: " + scanExcludeFilter.getExcludedCount());}}servicePackagesHolder.addScannedPackage(packageToScan);}
}

@DubboService注解的扫描使用原理

这里保证文档可读性，简单介绍，详情见 Dubbo注解 详细介绍

DubboClassPathBeanDefinitionScanner 扫描包类实现自 ClassPathBeanDefinitionScanner

在 scanServiceBeans 方法中通过以下代码添加了 DubboService Service 注解的过滤条件，从而才scan 扫描报的时候根据过滤条件寻找类，Scan扫描包去看Spring扫描包原理

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
);
// 添加有 @DubboService  @Service  的过滤条件 
for (Class<? extends Annotation> annotationType : serviceAnnotationTypes) {scanner.addIncludeFilter(new AnnotationTypeFilter(annotationType));
}
…… 
scanner.scan(packageToScan);

processScannedBeanDefinition

private void processScannedBeanDefinition(BeanDefinitionHolder beanDefinitionHolder) {Class<?> beanClass = resolveClass(beanDefinitionHolder);// 获取 @DubboServiceAnnotation service = findServiceAnnotation(beanClass);// 获取配置在注解@DubboService上的所有属性Map<String, Object> serviceAnnotationAttributes = AnnotationUtils.getAttributes(service, true);// 根据注解信息和类信息解析出接口信息String serviceInterface = resolveInterfaceName(serviceAnnotationAttributes, beanClass);// 拿到 @DubboSerivce修饰的类名String annotatedServiceBeanName = beanDefinitionHolder.getBeanName();// ServiceBean Bean nameString beanName = generateServiceBeanName(serviceAnnotationAttributes, serviceInterface);// 构造了关于Servicebean的 BeanDefinitionAbstractBeanDefinition serviceBeanDefinition =buildServiceBeanDefinition(serviceAnnotationAttributes, serviceInterface, annotatedServiceBeanName);// 把 关于Servicebean的 BeanDefinition 添加到spring中registerServiceBeanDefinition(beanName, serviceBeanDefinition, serviceInterface);}

buildServiceBeanDefinition

构建了一个BeanDefinition，设置他的BeanClass = ServiceBean，每个接口都会生成一个BeanDefinition

到这里位置，就已经把所以扫描到@DubboService（包括兼容历史所需要的 @Service ）注解的类，全部注册为了BeanDefinition，开始进行spring bean的初始化，开始初始化设置的ServiceBean

private AbstractBeanDefinition buildServiceBeanDefinition(Map<String, Object> serviceAnnotationAttributes,String serviceInterface,String refServiceBeanName) {// 创建 ServiceBean 的BuilderBeanDefinitionBuilder builder = rootBeanDefinition(ServiceBean.class);AbstractBeanDefinition beanDefinition = builder.getBeanDefinition();// 设置ServiceBean需要的相关参数，例如  protocol，ref 等MutablePropertyValues propertyValues = beanDefinition.getPropertyValues();String[] ignoreAttributeNames = of("provider", "monitor", "application", "module", "registry", "protocol","methods", "interfaceName", "parameters");…… …… ……return builder.getBeanDefinition();}

ServiceBean初始化

初始化会调用 InitializingBean的 afterPropertiesSet 方法，详解见Dubbo前置知识

DubboDeployApplicationListener

在ServiceBean初始化后 DubboDeployApplicationListener 监听器监听了 ContextRefreshedEvent 时间，在spring初始化完成后该监听器会被执行

onApplicationEvent监听事件

@Override
public void onApplicationEvent(ApplicationContextEvent event) {if (nullSafeEquals(applicationContext, event.getSource())) {if (event instanceof ContextRefreshedEvent) {onContextRefreshedEvent((ContextRefreshedEvent) event);} else if (event instanceof ContextClosedEvent) {onContextClosedEvent((ContextClosedEvent) event);}}
}

onContextRefreshedEvent

private void onContextRefreshedEvent(ContextRefreshedEvent event) {ModuleDeployer deployer = moduleModel.getDeployer();Assert.notNull(deployer, "Module deployer is null");// start module// 核心 部署器启动Future future = deployer.start();// if the module does not start in background, await finishif (!deployer.isBackground()) {try {future.get();} catch (InterruptedException e) {logger.warn(CONFIG_FAILED_START_MODEL, "", "", "Interrupted while waiting for dubbo module start: " + e.getMessage());} catch (Exception e) {logger.warn(CONFIG_FAILED_START_MODEL, "", "", "An error occurred while waiting for dubbo module start: " + e.getMessage(), e);}}
}

DefaultModuleDeployer#start

部署器启动

@Override
public Future start() throws IllegalStateException {// initialize，maybe deadlock applicationDeployer lock & moduleDeployer lock// 初始化部署applicationDeployer.initialize();return startSync();
}

DefaultApplicationDeployer#initialize

初始化，包括配置中心，应用程序配置，元数据配置等

对应DubboBootstrap 代码启动的加载

@Override
public void initialize() {if (initialized) {return;}// Ensure that the initialization is completed when concurrent callssynchronized (startLock) {if (initialized) {return;}// register shutdown hookregisterShutdownHook();startConfigCenter();loadApplicationConfigs();initModuleDeployers();// @since 2.7.8startMetadataCenter();initialized = true;if (logger.isInfoEnabled()) {logger.info(getIdentifier() + " has been initialized!");}}
}

DefaultModuleDeployer#startSync()

private synchronized Future startSync() throws IllegalStateException {if (isStopping() || isStopped() || isFailed()) {throw new IllegalStateException(getIdentifier() + " is stopping or stopped, can not start again");}try {if (isStarting() || isStarted()) {return startFuture;}// 却换模块启动状态 STARTINGonModuleStarting();//如果为初始化则初始化initialize();// export services//服务暴漏exportServices();// prepare application instance// exclude internal module to avoid wait itselfif (moduleModel != moduleModel.getApplicationModel().getInternalModule()) {applicationDeployer.prepareInternalModule();}// refer services//引用服务referServices();// if no async export/refer services, just set started//非异步启动直接转换状态为STARTEDif (asyncExportingFutures.isEmpty() && asyncReferringFutures.isEmpty()) {onModuleStarted();} else {//如果是异步启动，等待服务发布和服务引用的回调frameworkExecutorRepository.getSharedExecutor().submit(() -> {try {// wait for export finishwaitExportFinish();// wait for refer finishwaitReferFinish();} catch (Throwable e) {logger.warn(CONFIG_FAILED_WAIT_EXPORT_REFER, "", "", "wait for export/refer services occurred an exception", e);} finally {onModuleStarted();}});}} catch (Throwable e) {onModuleFailed(getIdentifier() + " start failed: " + e, e);throw e;}return startFuture;
}