---

前言

文章基于3.1.0版本进行分析

		<dependency>
            <groupId>org.apache.dubbo</groupId>
            <artifactId>dubbo</artifactId>
            <version>3.1.0</version>
        </dependency>

一、服务监听ContextRefreshedEvent

在springboot 中，refresh 是 AbstractApplicationContext 中的一个方法，负责初始化 ApplicationContext 容器，容器必须调用 refresh 才能正常工作是进行，refresh的最后处理了 finishRefresh 方法，改方法会广播一个ContextRefreshedEvent容器刷新完成事件，所有监听了该事件的bean都会去执行相关逻辑处理。

1、AbstractApplicationContext.refresh

public void refresh() throws BeansException, IllegalStateException {
        synchronized(this.startupShutdownMonitor) {
            	// 省略无关代码***
                
                // 初始化生命周期处理器，调用生命周期处理器onRefresh方法，发布ContextRefreshedEvent事件，JMX相关处理
                this.finishRefresh();
            
            	// 省略无关代码***
        }
    }

2、AbstractApplicationContext.finishRefresh

	protected void finishRefresh() {
		// 清除上下文资源缓存（如扫描中的ASM元数据） scanning).
		clearResourceCaches();

		// Initialize lifecycle processor for this context.
		initLifecycleProcessor();

		// Propagate refresh to lifecycle processor first.
		getLifecycleProcessor().onRefresh();

		// 广播刷新完成事件
		publishEvent(new ContextRefreshedEvent(this));

		// Participate in LiveBeansView MBean, if active.
		if (!NativeDetector.inNativeImage()) {
			LiveBeansView.registerApplicationContext(this);
		}
	}

3、DubboDeployApplicationListener.onApplicationEvent

dubbo很好的结合了spring的这一个拓展点，在这个拓展点开始实现服务的发布。可以看到，DubboDeployApplicationListener实现了ContextRefreshedEvent的消息监听

public class DubboDeployApplicationListener implements ApplicationListener<ApplicationContextEvent>, ApplicationContextAware, Ordered {
    private static final Logger logger = LoggerFactory.getLogger(DubboDeployApplicationListener.class);

    private ApplicationContext applicationContext;
    private ApplicationModel applicationModel;
    private ModuleModel moduleModel;

    @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);
            }
        }
    }

    private void onContextRefreshedEvent(ContextRefreshedEvent event) {
    	// 获取配置的deployer 进行发布，默认是 DefaultModuleDeployer 
        ModuleDeployer deployer = moduleModel.getDeployer();
        Assert.notNull(deployer, "Module deployer is null");
        // start module
        Future future = deployer.start();

        // if the module does not start in background, await finish
        if (!deployer.isBackground()) {
            try {
            	// 等待发布结束
                future.get();
            } catch (InterruptedException e) {
                logger.warn("Interrupted while waiting for dubbo module start: " + e.getMessage());
            } catch (Exception e) {
                logger.warn("An error occurred while waiting for dubbo module start: " + e.getMessage(), e);
            }
        }
    }

}

4、DefaultModuleDeployer .referServices

DefaultModuleDeployer 中，真正核心的是ReferenceConfig，ReferenceConfig才是去实际发布的动作

public class DefaultModuleDeployer extends AbstractDeployer<ModuleModel> implements ModuleDeployer {
 
    // DefaultApplicationDeployer
    private ApplicationDeployer applicationDeployer;
 
    @Override
    public synchronized Future start() throws IllegalStateException {
 
        ...
        // 不管是 DefaultApplicationDeployer 还是DefaultModuleDeployer的initialize方法，都是处理相关配置文件
        // 其功能等价于监听器 DubboConfigApplicationListener
        applicationDeployer.initialize();
        initialize();
        // 真正触发 服务注册功能
        exportServices();
		// prepare application instance
        // exclude internal module to avoid wait itself
        if (moduleModel != moduleModel.getApplicationModel().getInternalModule()) {
            applicationDeployer.prepareInternalModule();
        }

        // 服务消费
		// refer services
        referServices();
        ...
        return startFuture;
    }
 
    private void referServices() {
        configManager.getReferences().forEach(rc -> {
            try {
                ReferenceConfig<?> referenceConfig = (ReferenceConfig<?>) rc;
                // 刷新配置
				if (!referenceConfig.isRefreshed()) {
                    referenceConfig.refresh();
                }
	
                // 如果还没初始化
				if (rc.shouldInit()) {
                    // 是否异步注入
					if (referAsync || rc.shouldReferAsync()) {
                        ExecutorService executor = executorRepository.getServiceReferExecutor();
                        CompletableFuture<Void> future = CompletableFuture.runAsync(() -> {
                            try {
                                referenceCache.get(rc);
                            } catch (Throwable t) {
                                logger.error(getIdentifier() + " refer async catch error : " + t.getMessage(), t);
                            }
                        }, executor);

                        asyncReferringFutures.add(future);
                    } else {
						// 查询缓存中是否存在代理对象 对应的实现类SimpleReferenceCache
                        referenceCache.get(rc);
                    }
                }
            } catch (Throwable t) {
                logger.error(getIdentifier() + " refer catch error.");
                referenceCache.destroy(rc);
                throw t;
            }
        });
    }
}

5、SimpleReferenceCache.get

SimpleReferenceCache,一个用于缓存引用ReferenceConfigBase的util工具类。
ReferenceConfigBase是一个重对象，对于频繁创建ReferenceConfigBase的框架来说，有必要缓存这些对象。
如果需要使用复杂的策略，可以实现并使用自己的ReferenceConfigBase缓存
这个Cache是引用服务的开始如果我们想在代码中自定义一些服务引用的逻辑，可以直接创建SimpleReferenceCache类型对象然后调用其get方法进行引用服务。

	public <T> T get(ReferenceConfigBase<T> rc) {
        String key = generator.generateKey(rc);
		// 服务类型 如果是泛化调用则这个类型为GenericService
        Class<?> type = rc.getInterfaceClass();

        boolean singleton = rc.getSingleton() == null || rc.getSingleton();
        T proxy = null;
        // Check existing proxy of the same 'key' and 'type' first.
		// 单例
        if (singleton) {
			// 缓存数据找
            proxy = get(key, (Class<T>) type);
        } else {
            logger.warn("Using non-singleton ReferenceConfig and ReferenceCache at the same time may cause memory leak. " +
                "Call ReferenceConfig#get() directly for non-singleton ReferenceConfig instead of using ReferenceCache#get(ReferenceConfig)");
        }
		// 不存在消费的代理对象，创建rc.get()，最后走到ReferenceConfig.get()
        if (proxy == null) {
			// 获取或者创建值，为引用类型referencesOfType对象（类型为Map<Class<?>, List<ReferenceConfigBase<?>>>）缓存对象生成值（值不存咋时候会生成一个）
            List<ReferenceConfigBase<?>> referencesOfType = referenceTypeMap.computeIfAbsent(type, _t -> Collections.synchronizedList(new ArrayList<>()));
            // 每次走到这里都会添加一个ReferenceConfigBase 引用配置对象（单例的从缓存中拿到就可以直接返回了）
			referencesOfType.add(rc);
			// 与前面一样 前面是类型映射，这里是key映射
            List<ReferenceConfigBase<?>> referenceConfigList = referenceKeyMap.computeIfAbsent(key, _k -> Collections.synchronizedList(new ArrayList<>()));
            referenceConfigList.add(rc);
			// 开始引用服务
            proxy = rc.get();
        }

        return proxy;
    }

二、引用服务 ReferenceConfig

服务发现和引用就是从这里开始的

1、时序图

2、ReferenceConfig.get

获取引用的代理对象

	public T get() {
        if (destroyed) {
            throw new IllegalStateException("The invoker of ReferenceConfig(" + url + ") has already destroyed!");
        }

        if (ref == null) {
            // ensure start module, compatible with old api usage
			// 如果使用方直接调用了ReferenceConfigBase的get方法或者缓存对象SimpleReferenceCache类型的对象的get方法来引用服务端的时候就会造成很多配置没有初始化
			// 这个代码其实就是启动模块进行一些基础配置的初始化操作,比如元数据中心默认配置选择，注册中心默认配置选择这些都是比较重要的
            getScopeModel().getDeployer().start();

            synchronized (this) {
                if (ref == null) {
                    init();
                }
            }
        }

        return ref;
    }

主要包括

• checkAndUpdateSubConfigs() – 检查并更新缺省配置
• init() – 消费者服务的初始化，核心逻辑。

3、ReferenceConfig.init

初始化代理对象

    protected synchronized void init() {
        // 初始化标记变量保证只初始化一次，这里又是加锁又是加标记变量的
		if (initialized && ref != null) {
            return;
        }
        try {
            // 刷新配置
			if (!this.isRefreshed()) {
                this.refresh();
            }
            
            // init serviceMetadata
            // 初始化元数据信息 如版本号，分组，服务接口名
            initServiceMetadata(consumer);
            // //继续初始化元数据信息 服务接口类型和key
            serviceMetadata.setServiceType(getServiceInterfaceClass());
            // TODO, uncomment this line once service key is unified
            serviceMetadata.setServiceKey(URL.buildKey(interfaceName, group, version));

            // 参数配置转成MAP
			Map<String, String> referenceParameters = appendConfig();
            // init service-application mapping
            // 初始化路径，参数转化成url，dubbo主要从url上面读取参数
			initServiceAppsMapping(referenceParameters);

            // 获取Module级别的服务存储仓库，其内部保存着服务提供者和服务消费者的缓存
            ModuleServiceRepository repository = getScopeModel().getServiceRepository();
            ServiceDescriptor serviceDescriptor;
            if (CommonConstants.NATIVE_STUB.equals(getProxy())) {
                serviceDescriptor = StubSuppliers.getServiceDescriptor(interfaceName);
                repository.registerService(serviceDescriptor);
            } else {
                serviceDescriptor = repository.registerService(interfaceClass);
            }
			// 创建消费者模型对象
            consumerModel = new ConsumerModel(serviceMetadata.getServiceKey(), proxy, serviceDescriptor,
                    getScopeModel(), serviceMetadata, createAsyncMethodInfo(), interfaceClassLoader);

            // Compatible with dependencies on ServiceModel#getReferenceConfig() , and will be removed in a future version.
            consumerModel.setConfig(this);

            repository.registerConsumer(consumerModel);

            serviceMetadata.getAttachments().putAll(referenceParameters);

            // 创建引用的代理对象 核心代码
			ref = createProxy(referenceParameters);

            serviceMetadata.setTarget(ref);
            serviceMetadata.addAttribute(PROXY_CLASS_REF, ref);

            consumerModel.setDestroyCaller(getDestroyRunner());
            consumerModel.setProxyObject(ref);
            consumerModel.initMethodModels();

            checkInvokerAvailable();
        } catch (Throwable t) {
            // *** 省略部分代码
            throw t;
        }
        initialized = true;
    }

主要流程

• 服务引用前初始化serviceMetadata服务元数据
• 获取服务仓库ModuleServiceRepository，并注册service 和 consumer
• 调用createProxy方法，根据服务引用参数map创建服务接口代理引用对象，并赋值给ref，核心逻辑

4、ReferenceConfig.createProxy

创建代理对象，实际调用需要通过这个代理对象进行调用

	private T createProxy(Map<String, String> referenceParameters) {
        // 本地引用
		if (shouldJvmRefer(referenceParameters)) {
            createInvokerForLocal(referenceParameters);
        } else {
            urls.clear();

            meshModeHandleUrl(referenceParameters);

            if (StringUtils.isNotEmpty(url)) {
                // user specified URL, could be peer-to-peer address, or register center's address.
				// url参数不为空，且可以配置多个。可以是点对点，也可以是注册中心，然后添加到urls
                parseUrl(referenceParameters);
            } else {
                // if protocols not in jvm checkRegistry
                if (!LOCAL_PROTOCOL.equalsIgnoreCase(getProtocol())) {
                    // 从注册表中获取URL并将其聚合。这个其实就是初始化一下注册中心的url配置
					aggregateUrlFromRegistry(referenceParameters);
                }
            }
			// 创建远程引用，创建远程引用调用器，承担服务调用的核心逻辑
            createInvokerForRemote();
        }

        if (logger.isInfoEnabled()) {
            logger.info("Referred dubbo service: [" + referenceParameters.get(INTERFACE_KEY) + "]." +
                    (Boolean.parseBoolean(referenceParameters.get(GENERIC_KEY)) ?
                            " it's GenericService reference" : " it's not GenericService reference"));
        }

        URL consumerUrl = new ServiceConfigURL(CONSUMER_PROTOCOL, referenceParameters.get(REGISTER_IP_KEY), 0,
                referenceParameters.get(INTERFACE_KEY), referenceParameters);
        consumerUrl = consumerUrl.setScopeModel(getScopeModel());
        consumerUrl = consumerUrl.setServiceModel(consumerModel);
        MetadataUtils.publishServiceDefinition(consumerUrl, consumerModel.getServiceModel(), getApplicationModel());

        // create service proxy
		// 构建一个代理对象，代理客户端的请求
        return (T) proxyFactory.getProxy(invoker, ProtocolUtils.isGeneric(generic));
    }

5、ReferenceConfig.createInvokerForRemote

远程引用或者直连引用情况下，将会调用该方法，创建远程引用Invoker。对于一个注册中心url和多个注册中心url的处理是不一样的，一个注册中心对应一个invoker，最后封装到集群路由invoker

	private void createInvokerForRemote() {
        // 只有一个，秩序创建一个invoker
		if (urls.size() == 1) {
            URL curUrl = urls.get(0);
			// 自适应扩展类，这里和服务发布类似，先进入了RegistryProtocol.refer
            invoker = protocolSPI.refer(interfaceClass, curUrl);
            if (!UrlUtils.isRegistry(curUrl)) {
                List<Invoker<?>> invokers = new ArrayList<>();
                invokers.add(invoker);
                invoker = Cluster.getCluster(scopeModel, Cluster.DEFAULT).join(new StaticDirectory(curUrl, invokers), true);
            }
        } else {
            List<Invoker<?>> invokers = new ArrayList<>();
            URL registryUrl = null;
			// 创建多个invoker
            for (URL url : urls) {
                // For multi-registry scenarios, it is not checked whether each referInvoker is available.
                // Because this invoker may become available later.
				// 
                invokers.add(protocolSPI.refer(interfaceClass, url));

                if (UrlUtils.isRegistry(url)) {
                    // use last registry url
                    registryUrl = url;
                }
            }

            // 创建一个集群路由invoker
			if (registryUrl != null) {
                // registry url is available
                // for multi-subscription scenario, use 'zone-aware' policy by default
                String cluster = registryUrl.getParameter(CLUSTER_KEY, ZoneAwareCluster.NAME);
                // The invoker wrap sequence would be: ZoneAwareClusterInvoker(StaticDirectory) -> FailoverClusterInvoker
                // (RegistryDirectory, routing happens here) -> Invoker
                invoker = Cluster.getCluster(registryUrl.getScopeModel(), cluster, false).join(new StaticDirectory(registryUrl, invokers), false);
            } else {
                // not a registry url, must be direct invoke.
				// 直连
                if (CollectionUtils.isEmpty(invokers)) {
                    throw new IllegalArgumentException("invokers == null");
                }
                URL curUrl = invokers.get(0).getUrl();
                String cluster = curUrl.getParameter(CLUSTER_KEY, Cluster.DEFAULT);
                invoker = Cluster.getCluster(scopeModel, cluster).join(new StaticDirectory(curUrl, invokers), true);
            }
        }
    }

服务发布的时候讲到 protocolSPI，protocolSPI.refer形成的调用链为
-Protocol$Adaptie -> ProtocolSerializationWrapper -> ProtocolFilterWrapper -> QosProtocolWrapper -> ProtocolListenerWrapper -> RegistryProtocol -> RegistryProtocol

三、注册协议 RegistryProtocol

应用级服务远程协议以service-discovery-registry开头，其对应的Protocol实现就是RegistryProtocol

1、RegistryProtocol.refer

    public <T> Invoker<T> refer(Class<T> type, URL url) throws RpcException {
		// 组装配置中心的地址
        url = getRegistryUrl(url);
		// 获取用于操作Zookeeper的Registry类型 
        Registry registry = getRegistry(url);
        if (RegistryService.class.equals(type)) {
            return proxyFactory.getInvoker((T) registry, type, url);
        }

        // group="a,b" or group="*"
        Map<String, String> qs = (Map<String, String>) url.getAttribute(REFER_KEY);
        String group = qs.get(GROUP_KEY);
        if (StringUtils.isNotEmpty(group)) {
            if ((COMMA_SPLIT_PATTERN.split(group)).length > 1 || "*".equals(group)) {
                return doRefer(Cluster.getCluster(url.getScopeModel(), MergeableCluster.NAME), registry, type, url, qs);
            }
        }
		// 降级容错的逻辑处理对象 类型为Cluster 实际类型为MockClusterWrapper 内部包装的是FailoverCluster
        // 后续调用服务失败时候会先失效转移再降级
        Cluster cluster = Cluster.getCluster(url.getScopeModel(), qs.get(CLUSTER_KEY));
		// 主要干活的地方 生成引用 invoker
        return doRefer(cluster, registry, type, url, qs);
    }

生成配置中心的url

zookeeper://127.0.0.1:2181/org.apache.dubbo.registry.RegistryService?application=dubbo-springboot-start-consumer
&dubbo=2.0.2
&pid=8896
&qos.enable=false
&release=3.1.0
&timestamp=1725379058285

2、RegistryProtocol.doRefer

    protected <T> Invoker<T> doRefer(Cluster cluster, Registry registry, Class<T> type, URL url, Map<String, String> parameters) {
        Map<String, Object> consumerAttribute = new HashMap<>(url.getAttributes());
        consumerAttribute.remove(REFER_KEY);
        String p = isEmpty(parameters.get(PROTOCOL_KEY)) ? CONSUMER : parameters.get(PROTOCOL_KEY);
		// 消费者url信息
        URL consumerUrl = new ServiceConfigURL (
            p,
            null,
            null,
            parameters.get(REGISTER_IP_KEY),
            0, getPath(parameters, type),
            parameters,
            consumerAttribute
        );
        url = url.putAttribute(CONSUMER_URL_KEY, consumerUrl);
		// 带迁移性质的Invoker对象
        ClusterInvoker<T> migrationInvoker = getMigrationInvoker(this, cluster, registry, type, url, consumerUrl);
		// 执行迁移规则创建应用级优先的服务发现Invoker对象
        return interceptInvoker(migrationInvoker, url, consumerUrl);
    }

consumerUrl如下

consumer://192.168.0.101/org.sjl.dubbo.AsyncProvider?application=dubbo-springboot-start-consumer
&background=false
&dubbo=2.0.2
&interface=org.sjl.dubbo.AsyncProvider
&methods=sayHiAsync,sayHello,sayHelloAsync&pid=33100
&qos.enable=false
&register.ip=192.168.0.101
&release=3.1.0
&side=consumer
&sticky=false
&timeout=30000
&timestamp=1725379319215

3、RegistryProtocol.interceptInvoker

    protected <T> Invoker<T> interceptInvoker(ClusterInvoker<T> invoker, URL url, URL consumerUrl) {
        // 获取激活的注册协议监听器扩展里面registry.protocol.listener，这里激活的类型为MigrationRuleListener
		List<RegistryProtocolListener> listeners = findRegistryProtocolListeners(url);
        if (CollectionUtils.isEmpty(listeners)) {
            return invoker;
        }

        for (RegistryProtocolListener listener : listeners) {
			// MigrationRuleListener
			// 迁移规则应用级引用
            listener.onRefer(this, invoker, consumerUrl, url);
        }
        return invoker;
    }

接下来就进入了迁移规则的应用级服务发现了，参考 dubbo 服务消费原理分析之应用级服务发现