版本

• dubbo: 2.7.8
• springboot 2.3.2.RELEASE

SpringBoot中dubbo啟動(dòng)過(guò)程

1. @DubboService注解的bean是如何被注冊(cè)到容器中的

SpringBoot在啟動(dòng)時(shí)，通過(guò)ConfigurationClassPostProcessor.postProcessBeanFactory完成對(duì)依賴(lài)jar包中XxAutopConfiguration類(lèi)的注冊(cè)，自然DubboAutoConfiguration也會(huì)被注冊(cè)到容器內(nèi)部。

DubboAutoConfiguration中沛慢，定義了一個(gè)ServiceClassPostProcessor 确丢，同樣會(huì)被注冊(cè)到容器內(nèi)泥畅。

@Configuration
@AutoConfigureAfter({DubboRelaxedBindingAutoConfiguration.class})
@EnableConfigurationProperties({DubboConfigurationProperties.class})
@EnableDubboConfig
public class DubboAutoConfiguration implements ApplicationContextAware, BeanDefinitionRegistryPostProcessor {
    public DubboAutoConfiguration() {
    }

    @ConditionalOnProperty(
        prefix = "dubbo.scan.",
        name = {"base-packages"}
    )
    @ConditionalOnBean(
        name = {"dubbo-service-class-base-packages"}
    )
    @Bean
    public ServiceClassPostProcessor serviceClassPostProcessor(@Qualifier("dubbo-service-class-base-packages") Set<String> packagesToScan) {
        return new ServiceClassPostProcessor(packagesToScan);
    }

ServiceClassPostProcessor 實(shí)現(xiàn)了BeanDefinitionRegistryPostProcessor接口丁鹉，同樣他也是一個(gè)BeanFactoryPostProcessor瓜贾。

public class ServiceClassPostProcessor implements BeanDefinitionRegistryPostProcessor, EnvironmentAware, ResourceLoaderAware, BeanClassLoaderAware {

在SpringBoot刷新容器胆敞，調(diào)用所有BeanFactoryPostProcessors時(shí)着帽，對(duì)BeanDefinitionRegistryPostProcessor，會(huì)去調(diào)用其postProcessBeanDefinitionRegistry方法移层。

    public void postProcessBeanDefinitionRegistry(BeanDefinitionRegistry registry) throws BeansException {
        // 注冊(cè)監(jiān)聽(tīng)器仍翰，容器啟動(dòng)各個(gè)階段向監(jiān)聽(tīng)器發(fā)送消息
        BeanRegistrar.registerInfrastructureBean(registry, "dubboBootstrapApplicationListener", DubboBootstrapApplicationListener.class);
        Set<String> resolvedPackagesToScan = this.resolvePackagesToScan(this.packagesToScan);
        if (!CollectionUtils.isEmpty(resolvedPackagesToScan)) {
            // 從待掃描的包中獲取ServiceBean，然后注冊(cè)到容器
            this.registerServiceBeans(resolvedPackagesToScan, registry);
        } else if (this.logger.isWarnEnabled()) {
            this.logger.warn("packagesToScan is empty , ServiceBean registry will be ignored!");
        }

    }

    private void registerServiceBeans(Set<String> packagesToScan, BeanDefinitionRegistry registry) {
        DubboClassPathBeanDefinitionScanner scanner = new DubboClassPathBeanDefinitionScanner(registry, this.environment, this.resourceLoader);
        BeanNameGenerator beanNameGenerator = this.resolveBeanNameGenerator(registry);
        scanner.setBeanNameGenerator(beanNameGenerator);
        serviceAnnotationTypes.forEach((annotationType) -> {
            scanner.addIncludeFilter(new AnnotationTypeFilter(annotationType));
        });
        Iterator var5 = packagesToScan.iterator();

        // 獲取迭代器观话，遍歷待掃描的packages予借，獲取ServiceBean信息,封裝beanDefinition并注冊(cè)到IOC容器
        while(true) {
            while(var5.hasNext()) {
                String packageToScan = (String)var5.next();
                scanner.scan(new String[]{packageToScan});
                Set<BeanDefinitionHolder> beanDefinitionHolders = this.findServiceBeanDefinitionHolders(scanner, packageToScan, registry, beanNameGenerator);
                if (!CollectionUtils.isEmpty(beanDefinitionHolders)) {
                    Iterator var8 = beanDefinitionHolders.iterator();

                    while(var8.hasNext()) {
                        BeanDefinitionHolder beanDefinitionHolder = (BeanDefinitionHolder)var8.next();
                        this.registerServiceBean(beanDefinitionHolder, registry, scanner);
                    }

                    if (this.logger.isInfoEnabled()) {
                        this.logger.info(beanDefinitionHolders.size() + " annotated Dubbo's @Service Components { " + beanDefinitionHolders + " } were scanned under package[" + packageToScan + "]");
                    }
                } else if (this.logger.isWarnEnabled()) {
                    this.logger.warn("No Spring Bean annotating Dubbo's @Service was found under package[" + packageToScan + "]");
                }
            }

            return;
        }

至此，便將ServiceBean注冊(cè)進(jìn)了Spring IOC容器。至于對(duì)象和代理對(duì)象的創(chuàng)建灵迫，那是后話了秦叛。

2. DubboService是如何對(duì)外暴露其url的

我們知道DubboService會(huì)被注冊(cè)到注冊(cè)中心，最終的結(jié)果是：將服務(wù)名瀑粥、服務(wù)對(duì)外暴露的url等信息通過(guò)網(wǎng)絡(luò)請(qǐng)求發(fā)送到注冊(cè)中心挣跋，那么對(duì)外暴露的時(shí)機(jī)是什么時(shí)候？它又是如何做到這件事情的狞换？
關(guān)于時(shí)機(jī)避咆，它應(yīng)該在容器刷新完成之后將所有DubboService對(duì)外暴露，那么如何感知到容器刷新呢修噪？SpringBoot中可以注冊(cè)listener查库，容器開(kāi)始啟動(dòng)、啟動(dòng)完成等事件會(huì)通知注冊(cè)進(jìn)來(lái)的listener黄琼。
ServiceClassPostProcessor 除了向容器注冊(cè)ServiceBean之外樊销，還注冊(cè)了一個(gè)監(jiān)聽(tīng)器：DubboBootstrapApplicationListener,當(dāng)感知到容器刷新完成和關(guān)閉事件時(shí)，做出相應(yīng)處理适荣，在這里關(guān)注刷新完成該如何處理现柠。

    public void onApplicationContextEvent(ApplicationContextEvent event) {
        if (event instanceof ContextRefreshedEvent) {
            this.onContextRefreshedEvent((ContextRefreshedEvent)event);
        } else if (event instanceof ContextClosedEvent) {
            this.onContextClosedEvent((ContextClosedEvent)event);
        }
    }

    private void onContextRefreshedEvent(ContextRefreshedEvent event) {
        this.dubboBootstrap.start();
    }

啟動(dòng)DubboBootStrap

    public DubboBootstrap start() {
            // ... 省略諸多初始化代碼

            // 服務(wù)暴露
            this.exportServices();
            if (!this.isOnlyRegisterProvider() || this.hasExportedServices()) {
                this.exportMetadataService();
                this.registerServiceInstance();
            }

           // 服務(wù)引用
            this.referServices();
            if (this.asyncExportingFutures.size() > 0) {
                (new Thread(() -> {
                    try {
                        this.awaitFinish();
                    } catch (Exception var2) {
                        this.logger.warn(NAME + " exportAsync occurred an exception.");
                    }

                    this.ready.set(true);
                    if (this.logger.isInfoEnabled()) {
                        this.logger.info(NAME + " is ready.");
                    }

                })).start();
            } else {
                this.ready.set(true);
                if (this.logger.isInfoEnabled()) {
                    this.logger.info(NAME + " is ready.");
                }
            }
            // log ... 
        }
        return this;
    }

    private void exportServices() {
        this.configManager.getServices().forEach((sc) -> {
            ServiceConfig serviceConfig = (ServiceConfig)sc;
            serviceConfig.setBootstrap(this);
            if (this.exportAsync) {
                ExecutorService executor = this.executorRepository.getServiceExporterExecutor();
                Future<?> future = executor.submit(() -> {
                    sc.export();
                    this.exportedServices.add(sc);
                });
                this.asyncExportingFutures.add(future);
            } else {
                sc.export();
                this.exportedServices.add(sc);
            }
        });
    }

至于Service如何暴露：如下圖

export過(guò)程

image.png

最后服務(wù)暴露到底對(duì)外暴露了個(gè)啥呢贪壳？其實(shí)就是invoker的url饱亿，當(dāng)consumer發(fā)起服務(wù)調(diào)用的時(shí)候，發(fā)起請(qǐng)求，當(dāng)provider接收到請(qǐng)求之后彪笼，將請(qǐng)求攜帶的信息(接口钻注、方法名、參數(shù)數(shù)組...)封裝為Invocation對(duì)象配猫，分派到相應(yīng)的invoker队寇，通過(guò)invoker.invoke(invocation)完成調(diào)用。
另外敖丙的文章也還不錯(cuò)章姓，Dubbo系列之服務(wù)暴露過(guò)程

3. 服務(wù)引入及遠(yuǎn)程調(diào)用

從springboot解析@DubboReference開(kāi)始講起佳遣。
DubboAutoConfiguration被@EnableDubboConfig注解，通過(guò)該注解引入了DubboConfigConfigurationRegistrar類(lèi)凡伊。

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

DubboConfigConfigurationRegistrar::registerBeanDefinitions(args)

    public void registerBeanDefinitions(AnnotationMetadata importingClassMetadata, BeanDefinitionRegistry registry) {
        //...省略一些代碼
        DubboBeanUtils.registerCommonBeans(registry);
    }

public interface DubboBeanUtils {
    static void registerCommonBeans(BeanDefinitionRegistry registry) {
        BeanRegistrar.registerInfrastructureBean(registry, "referenceAnnotationBeanPostProcessor", ReferenceAnnotationBeanPostProcessor.class);
        // ... 省略
    }
}

ReferenceAnnotationBeanPostProcessor是一個(gè)InstantiationAwareBeanPostProcessorAdapter零渐，在對(duì)象實(shí)例化后，填充屬性中系忙，會(huì)調(diào)用其postProcessPropertyValues

public class ReferenceAnnotationBeanPostProcessor extends AbstractAnnotationBeanPostProcessor implements ApplicationContextAware {
    // ... 省略

    public PropertyValues postProcessPropertyValues(PropertyValues pvs, PropertyDescriptor[] pds, Object bean, String beanName) throws BeanCreationException {
        InjectionMetadata metadata = this.findInjectionMetadata(beanName, bean.getClass(), pvs);

        try {
            // 這里的metadata就是AbstractAnnotationBeanPostProcessor.AnnotatedFieldElement對(duì)象
            metadata.inject(bean, beanName, pvs);
            return pvs;
        } catch (BeanCreationException var7) {
            throw var7;
        } catch (Throwable var8) {
            throw new BeanCreationException(beanName, "Injection of @" + this.getAnnotationType().getSimpleName() + " dependencies is failed", var8);
        }
    }
}

    public class AnnotatedFieldElement extends InjectedElement {
        // ...

        protected void inject(Object bean, String beanName, PropertyValues pvs) throws Throwable {
            Class<?> injectedType = this.resolveInjectedType(bean, this.field);
            Object injectedObject = AbstractAnnotationBeanPostProcessor.this.getInjectedObject(this.attributes, bean, beanName, injectedType, this);
            ReflectionUtils.makeAccessible(this.field);
            this.field.set(bean, injectedObject);
        }
}

最終到達(dá)referenceBean.get()方法诵盼，返回代理對(duì)象，并注入到目標(biāo)對(duì)象的field银还。

    protected Object doGetInjectedBean(AnnotationAttributes attributes, Object bean, String beanName, Class<?> injectedType, InjectedElement injectedElement) throws Exception {
        String referencedBeanName = this.buildReferencedBeanName(attributes, injectedType);
        String referenceBeanName = this.getReferenceBeanName(attributes, injectedType);
        ReferenceBean referenceBean = this.buildReferenceBeanIfAbsent(referenceBeanName, attributes, injectedType);
        boolean localServiceBean = this.isLocalServiceBean(referencedBeanName, referenceBean, attributes);
        this.prepareReferenceBean(referencedBeanName, referenceBean, localServiceBean);
        this.registerReferenceBean(referencedBeanName, referenceBean, attributes, localServiceBean, injectedType);
        this.cacheInjectedReferenceBean(referenceBean, injectedElement);
        return referenceBean.get();
    }

如果拋開(kāi)SpringBoot如何注入被@DubboReference注解的Bean风宁，可以說(shuō)referenceBean.get()就是服務(wù)引用的入口。

    // ... 省略諸多代碼
    private transient volatile T ref;
    // 線程安全單例
    public synchronized T get() {
        if (this.destroyed) {
            throw new IllegalStateException("The invoker of ReferenceConfig(" + this.url + ") has already destroyed!");
        } else {
            if (this.ref == null) {
                this.init();
            }

            return this.ref;
        }
    }
 // ...
}

后面的事情就是Dubbo內(nèi)部要完成的了蛹疯，大概過(guò)程如這樣：

image.png