源码分析--dubbo服务端暴露

服务暴露的入口方法是 ServiceBean 的 onApplicationEvent。onApplicationEvent 是一个事件响应方法，该方法会在收到 Spring 上下文刷新事件后执行服务导出操作。方法代码如下：

ServiceBean#onApplicationEvent

public void onApplicationEvent(ContextRefreshedEvent event) {
    //是不是已经暴露或 是不是被取消
    if (!isExported() && !isUnexported()) {
        if (logger.isInfoEnabled()) {
            logger.info("The service ready on spring started. service: " + getInterface());
        }
        export();
    }
}

下面我们看看export方法：

public synchronized void export() {
    //一开始进来这个是空的
    if (provider != null) {
        if (export == null) {
            export = provider.getExport();
        }
        if (delay == null) {
            delay = provider.getDelay();
        }
    }
    //表示是否服务已经暴露
    if (export != null && !export) {
        return;
    }
    //是否设置了延迟暴露
    if (delay != null && delay > 0) {
        delayExportExecutor.schedule(new Runnable() {
            @Override
            public void run() {
                doExport();
            }
        }, delay, TimeUnit.MILLISECONDS);
    } else {
        doExport();
    }
}

这个方法主要是进行校验服务有没有暴露过，有没有设置延迟。

然后进入到doExport方法中：

ServiceConfig#doExport

protected synchronized void doExport() {
    //如果已经取消暴露，则直接抛出异常
    if (unexported) {
        throw new IllegalStateException("Already unexported!");
    }
    //如果已经暴露过，则返回
    if (exported) {
        return;
    }
    exported = true;
    if (interfaceName == null || interfaceName.length() == 0) {
        throw new IllegalStateException("<dubbo:service interface=\"\" /> interface not allow null!");
    }
    //如果ProviderConfig为空，则给它进行赋值
    checkDefault();
    // 下面几个 if 语句用于检测 provider、application 等核心配置类对象是否为空，
    // 若为空，则尝试从其他配置类对象中获取相应的实例。
    if (provider != null) {
        if (application == null) {
            application = provider.getApplication();
        }
        if (module == null) {
            module = provider.getModule();
        }
        if (registries == null) {
            registries = provider.getRegistries();
        }
        if (monitor == null) {
            monitor = provider.getMonitor();
        }
        if (protocols == null) {
            protocols = provider.getProtocols();
        }
    }
    if (module != null) {
        if (registries == null) {
            registries = module.getRegistries();
        }
        if (monitor == null) {
            monitor = module.getMonitor();
        }
    }
    if (application != null) {
        if (registries == null) {
            registries = application.getRegistries();
        }
        if (monitor == null) {
            monitor = application.getMonitor();
        }
    }
    //泛型化
    if (ref instanceof GenericService) {
        interfaceClass = GenericService.class;
        if (StringUtils.isEmpty(generic)) {
            generic = Boolean.TRUE.toString();
        }
    } else {
        try {
            interfaceClass = Class.forName(interfaceName, true, Thread.currentThread()
                    .getContextClassLoader());
        } catch (ClassNotFoundException e) {
            throw new IllegalStateException(e.getMessage(), e);
        }
        //校验接口里面是否有设置的方法
        checkInterfaceAndMethods(interfaceClass, methods);
        //校验接口的实现类不能为空
        checkRef();
        generic = Boolean.FALSE.toString();
    }
    if (local != null) {
        if ("true".equals(local)) {
            local = interfaceName + "Local";
        }
        Class<?> localClass;
        try {
            localClass = ClassHelper.forNameWithThreadContextClassLoader(local);
        } catch (ClassNotFoundException e) {
            throw new IllegalStateException(e.getMessage(), e);
        }
        if (!interfaceClass.isAssignableFrom(localClass)) {
            throw new IllegalStateException("The local implementation class " + localClass.getName() + " not " +
                    "implement interface " + interfaceName);
        }
    }
    //本地存根
    if (stub != null) {
        if ("true".equals(stub)) {
            stub = interfaceName + "Stub";
        }
        Class<?> stubClass;
        try {
            stubClass = ClassHelper.forNameWithThreadContextClassLoader(stub);
        } catch (ClassNotFoundException e) {
            throw new IllegalStateException(e.getMessage(), e);
        }
        if (!interfaceClass.isAssignableFrom(stubClass)) {
            throw new IllegalStateException("The stub implementation class " + stubClass.getName() + " not " +
                    "implement interface " + interfaceName);
        }
    }
    //校验application，如果为空则从系统变量赋值
    checkApplication();
    //校验RegistryConfig，如果为空则从系统变量赋值
    checkRegistry();
    //校验protocols，如果为空则从系统变量赋值
    checkProtocol();
    //从系统变量为serviceconfig赋值
    appendProperties(this);
    //校验本地存根和本地伪装
    checkStub(interfaceClass);
    checkMock(interfaceClass);
    if (path == null || path.length() == 0) {
        path = interfaceName;
    }
    //服务暴露
    doExportUrls();
    // ProviderModel 表示服务提供者模型，此对象中存储了与服务提供者相关的信息。
    // 比如服务的配置信息，服务实例等。每个被导出的服务对应一个 ProviderModel。
    ProviderModel providerModel = new ProviderModel(getUniqueServiceName(), ref, interfaceClass);
    ApplicationModel.initProviderModel(getUniqueServiceName(), providerModel);
}

这个方法里主要做了这么几件事：

1. 校验防止重复服务暴露
2. 创建ProviderConfig，并赋值
3. 泛型化校验
4. 校验要暴露的接口
5. 本地存根配置
6. 校验ApplicationConfig、RegistryConfig、ProtocolConfig
7. 服务暴露
8. 暴露完后将暴露的服务存入providedServices中
   
   所以，总体来说就是做校验和config的初始化工作，然后调用doExportUrls进行服务暴露。

接下来我们看看doExportUrls方法：

private void doExportUrls() {
    //将Registries封装成URL
    List<URL> registryURLs = loadRegistries(true);
    //遍历protocolConfig，并注册
    for (ProtocolConfig protocolConfig : protocols) {
        doExportUrlsFor1Protocol(protocolConfig, registryURLs);
    }
}

讲RegistryConfig转换为URL对象，然后调用doExportUrlsFor1Protocol方法。

private static final Protocol protocol = ExtensionLoader.getExtensionLoader(Protocol.class).getAdaptiveExtension();

private static final ProxyFactory proxyFactory = ExtensionLoader.getExtensionLoader(ProxyFactory.class).getAdaptiveExtension();

private void doExportUrlsFor1Protocol(ProtocolConfig protocolConfig, List<URL> registryURLs) {
    ....忽略不相关代码
    String scope = url.getParameter(Constants.SCOPE_KEY);
    // don't export when none is configured
    if (!Constants.SCOPE_NONE.equalsIgnoreCase(scope)) {
    //本地暴露
    // export to local if the config is not remote (export to remote only when config is remote)
    if (!Constants.SCOPE_REMOTE.equalsIgnoreCase(scope)) {
        exportLocal(url);
    }
    //远程暴露
    // export to remote if the config is not local (export to local only when config is local)
    if (!Constants.SCOPE_LOCAL.equalsIgnoreCase(scope)) {
        if (logger.isInfoEnabled()) {
            logger.info("Export dubbo service " + interfaceClass.getName() + " to url " + url);
        }
        if (registryURLs != null && !registryURLs.isEmpty()) {
            for (URL registryURL : registryURLs) {
                //有时候希望人工管理服务提供者的上线和下线，此时需将注册中心标识为非动态管理模式。
                //dynamic="false" 为人工管理服务模式
                url = url.addParameterIfAbsent(Constants.DYNAMIC_KEY,
                        registryURL.getParameter(Constants.DYNAMIC_KEY));
                //监控中心
                URL monitorUrl = loadMonitor(registryURL);
                if (monitorUrl != null) {
                    url = url.addParameterAndEncoded(Constants.MONITOR_KEY, monitorUrl.toFullString());
                }
                if (logger.isInfoEnabled()) {
                    logger.info("Register dubbo service " + interfaceClass.getName() + " url " + url + " to registry " + registryURL);
                }
                //配置是JdkProxyFactory还是JavassistProxyFactory
                // For providers, this is used to enable custom proxy to generate invoker
                String proxy = url.getParameter(Constants.PROXY_KEY);
                if (StringUtils.isNotEmpty(proxy)) {
                    registryURL = registryURL.addParameter(Constants.PROXY_KEY, proxy);
                }
                //ProxyFactory$Adaptive
                Invoker<?> invoker = proxyFactory.getInvoker(ref, (Class) interfaceClass, registryURL.addParameterAndEncoded(Constants.EXPORT_KEY, url.toFullString()));
                DelegateProviderMetaDataInvoker wrapperInvoker = new DelegateProviderMetaDataInvoker(invoker, this);
                //Protocol$Adaptive
                Exporter<?> exporter = protocol.export(wrapperInvoker);
                exporters.add(exporter);
            }
        } else {
            Invoker<?> invoker = proxyFactory.getInvoker(ref, (Class) interfaceClass, url);
            DelegateProviderMetaDataInvoker wrapperInvoker = new DelegateProviderMetaDataInvoker(invoker, this);

            Exporter<?> exporter = protocol.export(wrapperInvoker);
            exporters.add(exporter);
        }
    }
}
}

doExportUrlsFor1Protocol代码里面有很多配置和设值的代码，我这里就不贴出来了，有兴趣的可以自己去看看是怎么设值的。

这段代码我们只需要看这个if判断就可以了。在这个if判断里面，如果scope配置的不是none，并且不是remote，那么就会进行本地暴露和远程暴露。

下面我只对远程暴露进行讲解。

首先会对url进行dynamic和monitorUrl校验和配置，然后会调用proxyFactory#getInvoker生成一个invoker对象。proxyFactory是由dubbo的spi生成的代理对象ProxyFactory$Adaptive，我们来看看具体的代码：

public class ProxyFactory$Adaptive implements ProxyFactory {
    private static final Logger logger = LoggerFactory.getLogger(ExtensionLoader.class);
    private AtomicInteger count = new AtomicInteger(0);

    public Object getProxy(Invoker var1) throws RpcException {
        if (var1 == null) {
            throw new IllegalArgumentException("org.apache.dubbo.rpc.Invoker argument == null");
        } else if (var1.getUrl() == null) {
            throw new IllegalArgumentException("org.apache.dubbo.rpc.Invoker argument getUrl() == null");
        } else {
            URL var2 = var1.getUrl();
            String var3 = var2.getParameter("proxy", "javassist");
            if (var3 == null) {
                throw new IllegalStateException("Fail to get extension(org.apache.dubbo.rpc.ProxyFactory) name from url(" + var2.toString() + ") use keys([proxy])");
            } else {
                ProxyFactory var4 = null;

                try {
                    var4 = (ProxyFactory)ExtensionLoader.getExtensionLoader(ProxyFactory.class).getExtension(var3);
                } catch (Exception var6) {
                    if (this.count.incrementAndGet() == 1) {
                        logger.warn("Failed to find extension named " + var3 + " for type org.apache.dubbo.rpc.ProxyFactory, will use default extension javassist instead.", var6);
                    }

                    var4 = (ProxyFactory)ExtensionLoader.getExtensionLoader(ProxyFactory.class).getExtension("javassist");
                }

                return var4.getProxy(var1);
            }
        }
    }

    public Object getProxy(Invoker var1, boolean var2) throws RpcException {
        if (var1 == null) {
            throw new IllegalArgumentException("org.apache.dubbo.rpc.Invoker argument == null");
        } else if (var1.getUrl() == null) {
            throw new IllegalArgumentException("org.apache.dubbo.rpc.Invoker argument getUrl() == null");
        } else {
            URL var3 = var1.getUrl();
            String var4 = var3.getParameter("proxy", "javassist");
            if (var4 == null) {
                throw new IllegalStateException("Fail to get extension(org.apache.dubbo.rpc.ProxyFactory) name from url(" + var3.toString() + ") use keys([proxy])");
            } else {
                ProxyFactory var5 = null;

                try {
                    var5 = (ProxyFactory)ExtensionLoader.getExtensionLoader(ProxyFactory.class).getExtension(var4);
                } catch (Exception var7) {
                    if (this.count.incrementAndGet() == 1) {
                        logger.warn("Failed to find extension named " + var4 + " for type org.apache.dubbo.rpc.ProxyFactory, will use default extension javassist instead.", var7);
                    }

                    var5 = (ProxyFactory)ExtensionLoader.getExtensionLoader(ProxyFactory.class).getExtension("javassist");
                }

                return var5.getProxy(var1, var2);
            }
        }
    }
    //var1 = ref
    //var2 = (Class) interfaceClass
    //var3 = url 对象
    public Invoker getInvoker(Object var1, Class var2, URL var3) throws RpcException {
        if (var3 == null) {
            throw new IllegalArgumentException("url == null");
        } else {
            //获取代理方式，默认是javassist
            String var5 = var3.getParameter("proxy", "javassist");
            if (var5 == null) {
                throw new IllegalStateException("Fail to get extension(org.apache.dubbo.rpc.ProxyFactory) name from url(" + var3.toString() + ") use keys([proxy])");
            } else {
                ProxyFactory var6 = null;

                try {
                    //通过spi获取ProxyFactory实例JavassistProxyFactory
                    var6 = (ProxyFactory)ExtensionLoader.getExtensionLoader(ProxyFactory.class).getExtension(var5);
                } catch (Exception var8) {
                    if (this.count.incrementAndGet() == 1) {
                        logger.warn("Failed to find extension named " + var5 + " for type org.apache.dubbo.rpc.ProxyFactory, will use default extension javassist instead.", var8);
                    }

                    var6 = (ProxyFactory)ExtensionLoader.getExtensionLoader(ProxyFactory.class).getExtension("javassist");
                }
                //调用JavassistProxyFactory实例的invoker方法
                return var6.getInvoker(var1, var2, var3);
            }
        }
    }

    public ProxyFactory$Adaptive() {
    }
}

所以proxyFactory#getInvoker最终会通过 ProxyFactory$Adaptive生成一个invoker对象。

然后封装成wrapperInvoker实例传入到protocol#export中。protocol是生成的代理类Protocol$Adaptive。

我们看一下Protocol$Adaptive生成的代码是怎么样的：

public class Protocol$Adaptive implements Protocol {
    private static final Logger logger = LoggerFactory.getLogger(ExtensionLoader.class);
    private AtomicInteger count = new AtomicInteger(0);

    public void destroy() {
        throw new UnsupportedOperationException("method public abstract void org.apache.dubbo.rpc.Protocol.destroy() of interface org.apache.dubbo.rpc.Protocol is not adaptive method!");
    }

    public int getDefaultPort() {
        throw new UnsupportedOperationException("method public abstract int org.apache.dubbo.rpc.Protocol.getDefaultPort() of interface org.apache.dubbo.rpc.Protocol is not adaptive method!");
    }

    public Exporter export(Invoker var1) throws RpcException {
        if (var1 == null) {
            throw new IllegalArgumentException("org.apache.dubbo.rpc.Invoker argument == null");
        } else if (var1.getUrl() == null) {
            throw new IllegalArgumentException("org.apache.dubbo.rpc.Invoker argument getUrl() == null");
        } else {
            URL var2 = var1.getUrl();
            String var3 = var2.getProtocol() == null ? "dubbo" : var2.getProtocol();
            if (var3 == null) {
                throw new IllegalStateException("Fail to get extension(org.apache.dubbo.rpc.Protocol) name from url(" + var2.toString() + ") use keys([protocol])");
            } else {
                Protocol var4 = null;

                try {
                    var4 = (Protocol)ExtensionLoader.getExtensionLoader(Protocol.class).getExtension(var3);
                } catch (Exception var6) {
                    if (this.count.incrementAndGet() == 1) {
                        logger.warn("Failed to find extension named " + var3 + " for type org.apache.dubbo.rpc.Protocol, will use default extension dubbo instead.", var6);
                    }

                    var4 = (Protocol)ExtensionLoader.getExtensionLoader(Protocol.class).getExtension("dubbo");
                }

                return var4.export(var1);
            }
        }
    }

    public Invoker refer(Class var1, URL var2) throws RpcException {
        if (var2 == null) {
            throw new IllegalArgumentException("url == null");
        } else {
            String var4 = var2.getProtocol() == null ? "dubbo" : var2.getProtocol();
            if (var4 == null) {
                throw new IllegalStateException("Fail to get extension(org.apache.dubbo.rpc.Protocol) name from url(" + var2.toString() + ") use keys([protocol])");
            } else {
                Protocol var5 = null;

                try {
                    var5 = (Protocol)ExtensionLoader.getExtensionLoader(Protocol.class).getExtension(var4);
                } catch (Exception var7) {
                    if (this.count.incrementAndGet() == 1) {
                        logger.warn("Failed to find extension named " + var4 + " for type org.apache.dubbo.rpc.Protocol, will use default extension dubbo instead.", var7);
                    }

                    var5 = (Protocol)ExtensionLoader.getExtensionLoader(Protocol.class).getExtension("dubbo");
                }

                return var5.refer(var1, var2);
            }
        }
    }

    public Protocol$Adaptive() {
    }
}

最后会通过下面代码，获得ProtocolListenerWrapper实例，并调用其export方法进行暴露。

var4 = (Protocol)ExtensionLoader.getExtensionLoader(Protocol.class).getExtension(var3);

然后调用链：ProtocolListenerWrapper->ProtocolFilterWrapper->RegistryProtocol

最后调用RegistryProtocol#export方法。

public <T> Exporter<T> export(final Invoker<T> originInvoker) throws RpcException {
    //服务端开启服务
    //export invoker
    final ExporterChangeableWrapper<T> exporter = doLocalExport(originInvoker);

    URL registryUrl = getRegistryUrl(originInvoker);

    //获取注册中心实例
    //registry provider
    final Registry registry = getRegistry(originInvoker);
    final URL registeredProviderUrl = getRegisteredProviderUrl(originInvoker);

    //to judge to delay publish whether or not
    boolean register = registeredProviderUrl.getParameter("register", true);

    ProviderConsumerRegTable.registerProvider(originInvoker, registryUrl, registeredProviderUrl);

    if (register) {
        //注册
        register(registryUrl, registeredProviderUrl);
        ProviderConsumerRegTable.getProviderWrapper(originInvoker).setReg(true);
    }

    // Subscribe the override data
    // FIXME When the provider subscribes, it will affect the scene : a certain JVM exposes the service and call
    //  the same service. Because the subscribed is cached key with the name of the service, it causes the
    //  subscription information to cover.
    final URL overrideSubscribeUrl = getSubscribedOverrideUrl(registeredProviderUrl);
    final OverrideListener overrideSubscribeListener = new OverrideListener(overrideSubscribeUrl, originInvoker);
    overrideListeners.put(overrideSubscribeUrl, overrideSubscribeListener);
    //订阅监听
    registry.subscribe(overrideSubscribeUrl, overrideSubscribeListener);
    //Ensure that a new exporter instance is returned every time export
    return new DestroyableExporter<T>(exporter, originInvoker, overrideSubscribeUrl, registeredProviderUrl);
}

我们先看doLocalExport这个方法，这个方法里面实现了服务端的服务暴露。

private <T> ExporterChangeableWrapper<T> doLocalExport(final Invoker<T> originInvoker) {
    String key = getCacheKey(originInvoker);
    ExporterChangeableWrapper<T> exporter = (ExporterChangeableWrapper<T>) bounds.get(key);
    if (exporter == null) {
        synchronized (bounds) {
            exporter = (ExporterChangeableWrapper<T>) bounds.get(key);
            if (exporter == null) {
                final Invoker<?> invokerDelegete = new InvokerDelegete<T>(originInvoker,
                        getProviderUrl(originInvoker));
                //通过spi调用dubboProtocol进行服务暴露
                exporter = new ExporterChangeableWrapper<T>((Exporter<T>) protocol.export(invokerDelegete),
                        originInvoker);
                //缓存暴露过的服务
                bounds.put(key, exporter);
            }
        }
    }
    return exporter;
}

在doLocalExport方法里面，会通过spi调用

ProtocolListenerWrapper->ProtocolFilterWrapper->DubboProtocol

DubboProtocol#export

public <T> Exporter<T> export(Invoker<T> invoker) throws RpcException {
    URL url = invoker.getUrl();

    // export service.
    String key = serviceKey(url);
    DubboExporter<T> exporter = new DubboExporter<T>(invoker, key, exporterMap);
    exporterMap.put(key, exporter);

    //export an stub service for dispatching event
    Boolean isStubSupportEvent = url.getParameter(Constants.STUB_EVENT_KEY, Constants.DEFAULT_STUB_EVENT);
    Boolean isCallbackservice = url.getParameter(Constants.IS_CALLBACK_SERVICE, false);
    if (isStubSupportEvent && !isCallbackservice) {
        String stubServiceMethods = url.getParameter(Constants.STUB_EVENT_METHODS_KEY);
        if (stubServiceMethods == null || stubServiceMethods.length() == 0) {
            if (logger.isWarnEnabled()) {
                logger.warn(new IllegalStateException("consumer [" + url.getParameter(Constants.INTERFACE_KEY) +
                        "], has set stubproxy support event ,but no stub methods founded."));
            }
        } else {
            stubServiceMethodsMap.put(url.getServiceKey(), stubServiceMethods);
        }
    }
    //实现服务的暴露
    openServer(url);
    optimizeSerialization(url);
    return exporter;
}

private void openServer(URL url) {
    ...忽略代码
    if (server == null) {
        //创建服务
        serverMap.put(key, createServer(url));
    }
}

private ExchangeServer createServer(URL url) {
    ...忽略代码
    //启动服务
    server = Exchangers.bind(url, requestHandler);
    ...忽略代码
    return server;
}

最终会通过Exchangers#bind来启动服务

Exchangers#bind->HeaderExchanger#bind->Transporters#bind->NettyTransporter#bind->NettyServer#doOpen

最后会在NettyServer调用doOpen方法启动服务。

我们再回到RegistryProtocol#export往下走

register(registryUrl, registeredProviderUrl)，这句代码就是用来注册到注册中心的，如果用的是zk，那么就是注册到Zookeeper的。

我们进到这个方法里瞧瞧。

public void register(URL registryUrl, URL registedProviderUrl) {
    //ZookeeperRegistry
    Registry registry = registryFactory.getRegistry(registryUrl);
    registry.register(registedProviderUrl);
}

registryFactory是spi实现的代理类：

public class RegistryFactory$Adaptive implements RegistryFactory {
    private static final Logger logger = LoggerFactory.getLogger(ExtensionLoader.class);
    private AtomicInteger count = new AtomicInteger(0);

    public Registry getRegistry(URL var1) {
        if (var1 == null) {
            throw new IllegalArgumentException("url == null");
        } else {
            String var3 = var1.getProtocol() == null ? "dubbo" : var1.getProtocol();
            if (var3 == null) {
                throw new IllegalStateException("Fail to get extension(org.apache.dubbo.registry.RegistryFactory) name from url(" + var1.toString() + ") use keys([protocol])");
            } else {
                RegistryFactory var4 = null;

                try {
                    var4 = (RegistryFactory)ExtensionLoader.getExtensionLoader(RegistryFactory.class).getExtension(var3);
                } catch (Exception var6) {
                    if (this.count.incrementAndGet() == 1) {
                        logger.warn("Failed to find extension named " + var3 + " for type org.apache.dubbo.registry.RegistryFactory, will use default extension dubbo instead.", var6);
                    }

                    var4 = (RegistryFactory)ExtensionLoader.getExtensionLoader(RegistryFactory.class).getExtension("dubbo");
                }

                return var4.getRegistry(var1);
            }
        }
    }

    public RegistryFactory$Adaptive() {
    }
}

然后通过调用RegistryFactory$Adaptive的getRegistry方法获取Registry的实现类ZookeeperRegistry实例。

ZookeeperRegistry继承关系图如下所示：

所以调用ZookeeperRegistry#register会先调用到父类的register方法。

FailbackRegistry#register

public void register(URL url) {
    super.register(url);
    //从失败集合中移除
    failedRegistered.remove(url);
    //从失败取消注册的集合中移除
    failedUnregistered.remove(url);
    try {
        // Sending a registration request to the server side
        //调用子类的方法进行注册
        doRegister(url);
    } catch (Exception e) {
        Throwable t = e;

        // If the startup detection is opened, the Exception is thrown directly.
        boolean check = getUrl().getParameter(Constants.CHECK_KEY, true)
                && url.getParameter(Constants.CHECK_KEY, true)
                && !Constants.CONSUMER_PROTOCOL.equals(url.getProtocol());
        boolean skipFailback = t instanceof SkipFailbackWrapperException;
        if (check || skipFailback) {
            if (skipFailback) {
                t = t.getCause();
            }
            throw new IllegalStateException("Failed to register " + url + " to registry " + getUrl().getAddress() + ", cause: " + t.getMessage(), t);
        } else {
            logger.error("Failed to register " + url + ", waiting for retry, cause: " + t.getMessage(), t);
        }

        // Record a failed registration request to a failed list, retry regularly
        failedRegistered.add(url);
    }
}

通过调用doRegister回到ZookeeperRegistry的doRegister方法中，然后调用zk的spi进行注册。

到这里，服务端的暴露也就讲完了。