dubbo（三）dubbo 服务暴露过程

关于dubbo服务暴露过程，首先我们之前在启动spring容器，注册自定义的dubbo的标签，解析xml时候

步骤一  DubboNamespaceHandler

public class DubboNamespaceHandler extends NamespaceHandlerSupport {

    static {
        Version.checkDuplicate(DubboNamespaceHandler.class);
    }

    @Override
    public void init() {
        registerBeanDefinitionParser("application", new DubboBeanDefinitionParser(ApplicationConfig.class, true));
        registerBeanDefinitionParser("module", new DubboBeanDefinitionParser(ModuleConfig.class, true));
        registerBeanDefinitionParser("registry", new DubboBeanDefinitionParser(RegistryConfig.class, true));
        registerBeanDefinitionParser("monitor", new DubboBeanDefinitionParser(MonitorConfig.class, true));
        registerBeanDefinitionParser("provider", new DubboBeanDefinitionParser(ProviderConfig.class, true));
        registerBeanDefinitionParser("consumer", new DubboBeanDefinitionParser(ConsumerConfig.class, true));
        registerBeanDefinitionParser("protocol", new DubboBeanDefinitionParser(ProtocolConfig.class, true));
        registerBeanDefinitionParser("service", new DubboBeanDefinitionParser(ServiceBean.class, true));
        registerBeanDefinitionParser("reference", new DubboBeanDefinitionParser(ReferenceBean.class, false));
        registerBeanDefinitionParser("annotation", new AnnotationBeanDefinitionParser());
    }

}

步骤二  ServiceBean

public class ServiceBean<T> extends ServiceConfig<T> implements InitializingBean, DisposableBean, ApplicationContextAware, ApplicationListener<ContextRefreshedEvent>, BeanNameAware {



    @Override
    public void onApplicationEvent(ContextRefreshedEvent event) {
        if (!isExported() && !isUnexported()) {
            if (logger.isInfoEnabled()) {
                logger.info("The service ready on spring started. service: " + getInterface());
            }
            export();
        }
    }

    @Override
    @SuppressWarnings({"unchecked", "deprecation"})
    public void afterPropertiesSet() throws Exception {

}

}

截取一点，一个是继承InitializingBean，当组件创建Servicebean对象以后会调用InitializingBean的唯一的方法afterPropertiesSet，Servicebean重写了afterPropertiesSet，这个afterPropertiesSet就是把spring配置文件中dubbo的标签内容保存起来。

 public void afterPropertiesSet() throws Exception {
        if (getProvider() == null) {
         
        }
        if (getApplication() == null
                && (getProvider() == null || getProvider().getApplication() == null)) {
       ..
        }
       ...
        if ((getRegistries() == null || getRegistries().isEmpty())
       ...
        }
      ......
        if ((getProtocols() == null || getProtocols().isEmpty())
   
        }
        if (getPath() == null || getPath().length() == 0) {
            if (beanName != null && beanName.length() > 0
                    && getInterface() != null && getInterface().length() > 0
                    && beanName.startsWith(getInterface())) {
                setPath(beanName);
            }
        }
        if (!supportedApplicationListener) {
            export();
        }
    }

ServiceBean还实现了ApplicationListener<ContextRefreshedEvent>接口，叫应用的监听器。它监听的事件是ContextRefreshedEvent，当我们ioc容器整个刷新完成，也就是ioc容器里面所有对象都创建完成以后来回调方法onApplicationEvent(ContextRefreshedEvent event)。onApplicationEvent这个export方法是暴露服务的过程

 @Override
    public void onApplicationEvent(ContextRefreshedEvent event) {
        if (!isExported() && !isUnexported()) {
            if (logger.isInfoEnabled()) {
                logger.info("The service ready on spring started. service: " + getInterface());
            }
            export();
        }
    }

步骤三  分析export方法

public synchronized void export() {
        if (provider != null) {
            if (export == null) {
                export = provider.getExport();
            }
            if (delay == null) {
                delay = provider.getDelay();
            }
        }
        if (export != null && !export) {
            return;
        }

        if (delay != null && delay > 0) {
            delayExportExecutor.schedule(new Runnable() {
                @Override
                public void run() {
                    doExport();
                }
            }, delay, TimeUnit.MILLISECONDS);
        } else {
            doExport();
        }
    }

进入doExport方法

 protected synchronized void doExport() {
        ......
        checkApplication();
        checkRegistry();
        checkProtocol();
        appendProperties(this);
        checkStub(interfaceClass);
        checkMock(interfaceClass);
        if (path == null || path.length() == 0) {
            path = interfaceName;
        }
        doExportUrls();
        ProviderModel providerModel = new ProviderModel(getUniqueServiceName(), ref, interfaceClass);
        ApplicationModel.initProviderModel(getUniqueServiceName(), providerModel);
    }

进入doExportUrls（）

 private void doExportUrls() {
        List<URL> registryURLs = loadRegistries(true);
        for (ProtocolConfig protocolConfig : protocols) {
            doExportUrlsFor1Protocol(protocolConfig, registryURLs);
        }
    }

根据xml配置不同的协议，暴露服务地址，Dubbo支持dubbo、rmi、hessian、http、webservice、thrift、redis等多种协议

进入doExportUrlsFor1Protocol，分段解释

 第一段

 private void doExportUrlsFor1Protocol(ProtocolConfig protocolConfig, List<URL> registryURLs) {
        String name = protocolConfig.getName();
        if (name == null || name.length() == 0) {
            name = "dubbo";
        }

        Map<String, String> map = new HashMap<String, String>();
        map.put(Constants.SIDE_KEY, Constants.PROVIDER_SIDE);
        map.put(Constants.DUBBO_VERSION_KEY, Version.getProtocolVersion());
        map.put(Constants.TIMESTAMP_KEY, String.valueOf(System.currentTimeMillis()));
        if (ConfigUtils.getPid() > 0) {
            map.put(Constants.PID_KEY, String.valueOf(ConfigUtils.getPid()));
        }
        appendParameters(map, application);
        appendParameters(map, module);
        appendParameters(map, provider, Constants.DEFAULT_KEY);
        appendParameters(map, protocolConfig);
        appendParameters(map, this);
        if (methods != null && !methods.isEmpty()) {
            for (MethodConfig method : methods) {
                appendParameters(map, method, method.getName());
                String retryKey = method.getName() + ".retry";
                if (map.containsKey(retryKey)) {
                    String retryValue = map.remove(retryKey);
                    if ("false".equals(retryValue)) {
                        map.put(method.getName() + ".retries", "0");
                    }
                }
          ..............................
if (ProtocolUtils.isGeneric(generic)) {
            map.put(Constants.GENERIC_KEY, generic);
            map.put(Constants.METHODS_KEY, Constants.ANY_VALUE);
        } else {
            String revision = Version.getVersion(interfaceClass, version);
            if (revision != null && revision.length() > 0) {
                map.put("revision", revision);
            }

            String[] methods = Wrapper.getWrapper(interfaceClass).getMethodNames();
            if (methods.length == 0) {
                logger.warn("NO method found in service interface " + interfaceClass.getName());
                map.put(Constants.METHODS_KEY, Constants.ANY_VALUE);
            } else {
                map.put(Constants.METHODS_KEY, StringUtils.join(new HashSet<String>(Arrays.asList(methods)), ","));
            }
        }
   .................

没有设置protocal,默认使用dubbo协议，收集各种参数(方法重试，接口版本号..)

 第二段

        String host = this.findConfigedHosts(protocolConfig, registryURLs, map);
        Integer port = this.findConfigedPorts(protocolConfig, name, map);
        URL url = new URL(name, host, port, (contextPath == null || contextPath.length() == 0 ? "" : contextPath + "/") + path, map);

        if (ExtensionLoader.getExtensionLoader(ConfiguratorFactory.class)
                .hasExtension(url.getProtocol())) {
            url = ExtensionLoader.getExtensionLoader(ConfiguratorFactory.class)
                    .getExtension(url.getProtocol()).getConfigurator(url).configure(url);
        }

        String scope = url.getParameter(Constants.SCOPE_KEY);

findConfigedHosts方法

private String findConfigedHosts(ProtocolConfig protocolConfig, List<URL> registryURLs, Map<String, String> map) {
        boolean anyhost = false;

        String hostToBind = getValueFromConfig(protocolConfig, Constants.DUBBO_IP_TO_BIND);
        if (hostToBind != null && hostToBind.length() > 0 && isInvalidLocalHost(hostToBind)) {
            throw new IllegalArgumentException("Specified invalid bind ip from property:" + Constants.DUBBO_IP_TO_BIND + ", value:" + hostToBind);
        }

        // if bind ip is not found in environment, keep looking up
        if (hostToBind == null || hostToBind.length() == 0) {
            hostToBind = protocolConfig.getHost();
            if (provider != null && (hostToBind == null || hostToBind.length() == 0)) {
                hostToBind = provider.getHost();
            }
            if (isInvalidLocalHost(hostToBind)) {
                anyhost = true;
                try {
                    hostToBind = InetAddress.getLocalHost().getHostAddress();
                } catch (UnknownHostException e) {
                    logger.warn(e.getMessage(), e);
                }
                if (isInvalidLocalHost(hostToBind)) {
                    if (registryURLs != null && !registryURLs.isEmpty()) {
                        for (URL registryURL : registryURLs) {
                            if (Constants.MULTICAST.equalsIgnoreCase(registryURL.getParameter("registry"))) {
                                // skip multicast registry since we cannot connect to it via Socket
                                continue;
                            }
                            try {
                                Socket socket = new Socket();
                                try {
                                    SocketAddress addr = new InetSocketAddress(registryURL.getHost(), registryURL.getPort());
                                    socket.connect(addr, 1000);
                                    hostToBind = socket.getLocalAddress().getHostAddress();
                                    break;
                                } finally {
                                    try {
                                        socket.close();
                                    } catch (Throwable e) {
                                    }
                                }
                            } catch (Exception e) {
                                logger.warn(e.getMessage(), e);
                            }
                        }
                    }
                    if (isInvalidLocalHost(hostToBind)) {
                        hostToBind = getLocalHost();
                    }
                }
            }
        }
 ..................

getValueFromConfig()从ProtocolConfig配置中获取,没有的话，再从prividerConfig去获取host

dubbo解析IP地址的步骤如下：

1. 先从ProtocolConfig中取host
2. 再从ProviderConfig中取host
3. 若取出的是本地host, 则继续取host
4. 通过InetAddress.getLocalHost().getHostAddress();的方式获取Host
5. 通过Socket的方式尝试连接到注册中心，通过socket.getLocalAddress().getHostAddress()获取Host
6. 遍历本地网卡, 返回第一个合理的Host

 private Integer findConfigedPorts(ProtocolConfig protocolConfig, String name, Map<String, String> map) {
        Integer portToBind = null;

        // parse bind port from environment
        String port = getValueFromConfig(protocolConfig, Constants.DUBBO_PORT_TO_BIND);
        portToBind = parsePort(port);

        // if there's no bind port found from environment, keep looking up.
        if (portToBind == null) {
            portToBind = protocolConfig.getPort();
            if (provider != null && (portToBind == null || portToBind == 0)) {
                portToBind = provider.getPort();
            }
            final int defaultPort = ExtensionLoader.getExtensionLoader(Protocol.class).getExtension(name).getDefaultPort();
            if (portToBind == null || portToBind == 0) {
                portToBind = defaultPort;
            }
            if (portToBind == null || portToBind <= 0) {
                portToBind = getRandomPort(name);
                if (portToBind == null || portToBind < 0) {
                    portToBind = getAvailablePort(defaultPort);
                    putRandomPort(name, portToBind);
                }
                logger.warn("Use random available port(" + portToBind + ") for protocol " + name);
            }
        }

端口有则用，没有则随机

 

 第三段

      URL url = new URL(name, host, port, (contextPath == null || contextPath.length() == 0 ? "" : contextPath + "/") + path, map);

        if (ExtensionLoader.getExtensionLoader(ConfiguratorFactory.class)
                .hasExtension(url.getProtocol())) {
            url = ExtensionLoader.getExtensionLoader(ConfiguratorFactory.class)
                    .getExtension(url.getProtocol()).getConfigurator(url).configure(url);
        }

        String scope = url.getParameter(Constants.SCOPE_KEY);
        // don't export when none is configured
        if (!Constants.SCOPE_NONE.equalsIgnoreCase(scope)) {

            // 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);
            }
            // 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()) {
          .........................

 这段主要是拼接URL，Dubbo框架是以URL为总线的模式，即运行过程中所有的状态数据信息都可以通过URL来获取，比如当前系统采用什么序列化，采用什么通信，采用什么负载均衡等信息，都是通过URL的参数来呈现的，所以在框架运行过程中，运行到某个阶段需要相应的数据，都可以通过对应的Key从URL的参数列表中获取。根据scope的配置决定是作本地暴露还是远程暴露，做服务暴露从结果上看就是产生了一个特定服务的 Exporter 类，并将其存储在对应的ServiceBean实例的 exporters属性中

 URL示例：dubbo://192.168.10.247:10080/org.huxin.dubbo.test.user.service.UserInterface?anyhost=true&application=dubbo-provider&default.retries=0&default.timeout=5000&dubbo=2.8.4&generic=false&getUserById.0.callback=true&interface=org.huxin.dubbo.test.user.service.UserInterface&methods=getUserById,getUserList,updateUsers&organization=huxin&owner=programmer&pid=6020&retries=0&serialization=kryo&side=provider&timestamp=1512955717318

第四段

...........
for (URL registryURL : registryURLs) {
                        url = url.addParameterIfAbsent(Constants.DYNAMIC_KEY, registryURL.getParameter(Constants.DYNAMIC_KEY));
                        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);
                        }

                        // 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);
                        }

                        Invoker<?> invoker = proxyFactory.getInvoker(ref, (Class) interfaceClass, registryURL.addParameterAndEncoded(Constants.EXPORT_KEY, url.toFullString()));
                        DelegateProviderMetaDataInvoker wrapperInvoker = new DelegateProviderMetaDataInvoker(invoker, this);

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

                    }
                } else {  //这个是用来没有注册中心情况下的暴露，应该是用于直连的场景
                    Invoker<?> invoker = proxyFactory.getInvoker(ref, (Class) interfaceClass, url);

                    Exporter<?> exporter = protocol.export(invoker);
                    exporters.add(exporter);
                }
            }
        }
        this.urls.add(url);

进行暴露服务过程,这里的protocol，当前的Url的协议是registry，进入registryprotocol

@Override
    public <T> Exporter<T> export(final Invoker<T> originInvoker) throws RpcException {
        //export invoker
        final ExporterChangeableWrapper<T> exporter = doLocalExport(originInvoker);

        URL registryUrl = getRegistryUrl(originInvoker);

        //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) {
            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);
        registry.subscribe(overrideSubscribeUrl, overrideSubscribeListener);
        //Ensure that a new exporter instance is returned every time export
        return new DestroyableExporter<T>(exporter, originInvoker, overrideSubscribeUrl, registeredProviderUrl);
    }

进入doLocalExport(originInvoker)

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));
                    exporter = new ExporterChangeableWrapper<T>((Exporter<T>) protocol.export(invokerDelegete), originInvoker);
                    bounds.put(key, exporter);
                }
            }
        }
        return exporter;
    }

 

这里的protocol.export（..）是DubboProtocol的方法，protocol.export，这时候url发生了变化不再是registryUrl了，而是存放在registryUrl的export参数中的providerUrl，根据不同协议会定位到不同的扩展，示例配置是dubbo协议，对应的实现是DubboProtocol，同样地根据Wrapper扩展点加载机制会加载出ProtocolListenerWrapper和 ListenerExporterWrapper两个Wrapper，然后依次调用ProtocolListenerWrapper->ListenerExporterWrapper->DubboProtocol的export方法。从上面的代码可以看到，ProtocolListenerWrapper.export会创建一个ListenerExporterWrapper实例，并添加所有激活的ExporterListener到ListenerExporterWrapper实例中，再经过ProtocolFilterWrapper处理，加载所有激活的Filter，并且构建Invoker-Filter链包装成新的Invoker。接着会调用DubboProtocol.export方法生成一个DubboExporter对象，Exporter中持有上面包装Filter链后的Invoker对象引用和url对应的key（key的生成规则在com.alibaba.dubbo.rpc.support.ProtocolUtils.serviceKey(URL)方法中），该Exporter对象会注册到DubboProtocol的exporterMap中，服务器监听到服务调用之后会在这个map中查找Exporter，并封装的Invoke
 

进入DubboProtocol方法

 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);
            }
        }

        openServer(url);
        optimizeSerialization(url);
        return exporter;
    }

进入openserver(url)方法

private void openServer(URL url) {
        // find server.
        String key = url.getAddress();
        //client can export a service which's only for server to invoke
        boolean isServer = url.getParameter(Constants.IS_SERVER_KEY, true);
        if (isServer) {
            ExchangeServer server = serverMap.get(key);
            if (server == null) {
                synchronized (this) {
                    server = serverMap.get(key);
                    if (server == null) {
                        serverMap.put(key, createServer(url));
                    }
                }
            } else {
                // server supports reset, use together with override
                server.reset(url);
            }
        }
    }

进入creatServer（url）创建netty服务器

private ExchangeServer createServer(URL url) {
        // send readonly event when server closes, it's enabled by default
        url = url.addParameterIfAbsent(Constants.CHANNEL_READONLYEVENT_SENT_KEY, Boolean.TRUE.toString());
        // enable heartbeat by default
        url = url.addParameterIfAbsent(Constants.HEARTBEAT_KEY, String.valueOf(Constants.DEFAULT_HEARTBEAT));
        String str = url.getParameter(Constants.SERVER_KEY, Constants.DEFAULT_REMOTING_SERVER);

        if (str != null && str.length() > 0 && !ExtensionLoader.getExtensionLoader(Transporter.class).hasExtension(str)) {
            throw new RpcException("Unsupported server type: " + str + ", url: " + url);
        }

        url = url.addParameter(Constants.CODEC_KEY, DubboCodec.NAME);
        ExchangeServer server;
        try {
            server = Exchangers.bind(url, requestHandler);
        } catch (RemotingException e) {
            throw new RpcException("Fail to start server(url: " + url + ") " + e.getMessage(), e);
        }
        str = url.getParameter(Constants.CLIENT_KEY);
        if (str != null && str.length() > 0) {
            Set<String> supportedTypes = ExtensionLoader.getExtensionLoader(Transporter.class).getSupportedExtensions();
            if (!supportedTypes.contains(str)) {
                throw new RpcException("Unsupported client type: " + str);
            }
        }
        return server;
    }

上面已经生成了服务代理，为了能收到消费端的服务请求，还要在上面选中的端口上监听消费端的请求，调用DubboProtocol的openServer方法，dubbo使用了Netty、grizzly、Mina三种网络框架，框架默认使用Netty，示例配置没有特殊配置，主要看一下Netty。启动服务时组件的调用顺序：Exchanger.bind->Transporter.bind->Server，Exchanger和Transporter也是通过ExtensionLoader来加载，会加载到NettyTransporter实现，它会创建生成一个NettyServer实例，在构造NettyServer实例时调用doOpen打开端口监听， 并添加三个IO事件处理器，NettyCodecAdapter负责请求解码、响应编码，nettyHandler处理请求，把NettyCodecAdapter.decoder->NettyCodecAdapter.encoder->NettyHandler IO事件处理器链到Netty框架中，服务调用消息由多层框架内部的Handler转发最终会转发到DubboProcotol的requestHandler中处理

dubboprotocol启动服务器后回到registerprotocol

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

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

FailbackRegistry

@Override
    public void register(URL url) {
        super.register(url);
        failedRegistered.remove(url);
        failedUnregistered.remove(url);
        try {
            // Sending a registration request to the server side
            doRegister(url);
        } catch (Exception e) {
.....

ZookeeperRegistry是FailbackRegistry子类

    @Override
    protected void doRegister(URL url) {
        try {
            zkClient.create(toUrlPath(url), url.getParameter(Constants.DYNAMIC_KEY, true));
        } catch (Throwable e) {
            throw new RpcException("Failed to register " + url + " to zookeeper " + getUrl() + ", cause: " + e.getMessage(), e);
        }
    }

zookeeper注册中心通过zookeeper框架的监听回调接口进行监听（redis注册中心通过订阅命令（subscribe）监听），服务器缓存注册中心的配置，当配置发生变更时，服务会刷新本地缓存，代码在ZookeeperRegistry的doSubscribe方法。

    @Override
    protected void doSubscribe(final URL url, final NotifyListener listener) {
        try {
            if (Constants.ANY_VALUE.equals(url.getServiceInterface())) {
                String root = toRootPath();
                ConcurrentMap<NotifyListener, ChildListener> listeners = zkListeners.get(url);
                if (listeners == null) {
                    zkListeners.putIfAbsent(url, new ConcurrentHashMap<NotifyListener, ChildListener>());
                    listeners = zkListeners.get(url);
                }
                ChildListener zkListener = listeners.get(listener);
                if (zkListener == null) {
                    listeners.putIfAbsent(listener, new ChildListener() {
                        @Override
                        public void childChanged(String parentPath, List<String> currentChilds) {
                            for (String child : currentChilds) {
                                child = URL.decode(child);
                                if (!anyServices.contains(child)) {
                                    anyServices.add(child);
                                    subscribe(url.setPath(child).addParameters(Constants.INTERFACE_KEY, child,
                                            Constants.CHECK_KEY, String.valueOf(false)), listener);
                                }
                            }
                        }
                    });
                    zkListener = listeners.get(listener);
                }
                zkClient.create(root, false);
                List<String> services = zkClient.addChildListener(root, zkListener);
                if (services != null && !services.isEmpty()) {
                    for (String service : services) {
                        service = URL.decode(service);
                        anyServices.add(service);
                        subscribe(url.setPath(service).addParameters(Constants.INTERFACE_KEY, service,
                                Constants.CHECK_KEY, String.valueOf(false)), listener);
                    }
                }
            } else {
                List<URL> urls = new ArrayList<URL>();
                for (String path : toCategoriesPath(url)) {
                    ConcurrentMap<NotifyListener, ChildListener> listeners = zkListeners.get(url);
                    if (listeners == null) {
                        zkListeners.putIfAbsent(url, new ConcurrentHashMap<NotifyListener, ChildListener>());
                        listeners = zkListeners.get(url);
                    }
                    ChildListener zkListener = listeners.get(listener);
                    if (zkListener == null) {
                        listeners.putIfAbsent(listener, new ChildListener() {
                            @Override
                            public void childChanged(String parentPath, List<String> currentChilds) {
                                ZookeeperRegistry.this.notify(url, listener, toUrlsWithEmpty(url, parentPath, currentChilds));
                            }
                        });
                        zkListener = listeners.get(listener);
                    }
                    zkClient.create(path, false);
                    List<String> children = zkClient.addChildListener(path, zkListener);
                    if (children != null) {
                        urls.addAll(toUrlsWithEmpty(url, path, children));
                    }
                }
                notify(url, listener, urls);
            }
        } catch (Throwable e) {
            throw new RpcException("Failed to subscribe " + url + " to zookeeper " + getUrl() + ", cause: " + e.getMessage(), e);
        }
    }

 

 关于文章中在serviceConfig类中为什么使用dubboprotocol，为什么使用Registryprotocol

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

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

怎么知道是Registryprotocol;dubbo spi机制是

ExtensionLoader.getExtensionLoader(Protocol.class).getAdaptiveExtension(“name值”)

显然这里没有名字啊  

import com.alibaba.dubbo.common.extension.ExtensionLoader;
public class Protocol$Adpative implements Protocol {
  public Invoker refer(Class arg0, URL arg1) throws Class {
    if (arg1 == null) throw new IllegalArgumentException("url == null");

    URL url = arg1;
    String extName = ( url.getProtocol() == null ? "dubbo" : url.getProtocol() );

    if(extName == null) throw new IllegalStateException("Fail to get extension(Protocol) name from url(" + url.toString() + ") use keys([protocol])");
    
    Protocol extension = (Protocol)ExtensionLoader.getExtensionLoader(Protocol.class).getExtension(extName);
    
    return extension.refer(arg0, arg1);
  }
  
  public Exporter export(Invoker arg0) throws Invoker {
    if (arg0 == null) throw new IllegalArgumentException("Invoker argument == null");
    
    if (arg0.getUrl() == null) throw new IllegalArgumentException("Invoker argument getUrl() == null");URL url = arg0.getUrl();
    //这里会根据url中的信息获取具体的实现类名
    String extName = ( url.getProtocol() == null ? "dubbo" : url.getProtocol() );
    
    if(extName == null) throw new IllegalStateException("Fail to get extension(Protocol) name from url(" + url.toString() + ") use keys([protocol])");
    //根据上面的实现类名，会在运行时，通过Dubbo的扩展机制加载具体实现类
    Protocol extension = (Protocol)ExtensionLoader.getExtensionLoader(Protocol.class).getExtension(extName);
    
    return extension.export(arg0);
  }
  
  public void destroy() {
    throw new UnsupportedOperationException("method public abstract void Protocol.destroy() of interface Protocol is not adaptive method!");
  }

根据ExtensionLoader.getExtensionLoader(Protocol.class).getAdaptiveExtension();生成适配类，@Adaptive，export方法使用适配类从一开始url参数获取name值

 

dubbo服务初始化与暴露服务总结
spring容器启动时会解析dubbo的自定义标签，解析的最终目的是返回 RootBeanDefinition 
对象，RootBeanDefinition包含了解析出来的关于bean的所有信息，注意，在bean的解析完后其实只是spring将其转化成spring内部的一种抽象的数据对象结构，bean的创建（实例化）是第一次调用 getBean 时创建的。

例如dubbo:service标签被解析成一个ServiceBean，ServiceBean实现了ApplicationListener和InitializingBean接口，ServiceBean有个核心方法export，在这个方法中初始化服务提供者并且暴露远程服务。这个方法在bean初始化或容器中所有bean刷新完毕时被调用，根据provider的延迟设置决定，如果设置了延迟（delay属性）在bean初始化结束之后调用否则容易刷新事件中被调用，默认会延迟export，即在所有bean的刷新结束时间中被调用。

生成url， 
a.注册中心的url：在服务初始化时需要对注册中心进行访问，所以需要一个URL来跟注册中心通信，根据应用的注册中心配置来生成这个URL，URL协议是registry，包含了注册中心地址、端口，path部分是com.alibaba.dubbo.registry.RegistryService类名，其中还有dubbo版本、应用名称等信息放在URL的参数中，格式化之后是这种形式：registry://10.165.124.205:2181/com.alibaba.dubbo.registry.RegistryService?application=… 
b.服务本身的url:还需要生成一个URL来携带服务本身的信息，协议由应用侧指定，在我们的示例配置中是dubbo协议，host是本机ip，端口是上面选中的随机或配置中指定的端口，path是服务对应的接口class全名（含包路径），添加side参数provider，dubbo版本号、服务方法名称、group等等，格式化之后是这种形式：

dubbo://10.240.176.159:20880/com.netease.haitao.mykaola.generic.api.InternalStaffServiceFacade?…&createInternalStaffOperDetail.timeout=10000&…&default.group=hzchenyunyun1&…&dubbo=3.0.0&…&methods=…&…&side=provider&… 

生成远程服务代理,生成代理的目的是你调用 invoker 的相关函数后，就会等于是调用 DubboInvoker 中的相关函数；也就是将本地调用转为网络调用并获得结果；

启动服务监听，框架默认使用Netty，打开端口监听， 
并添加三个IO事件处理器，NettyCodecAdapter负责请求解码、响应编码，nettyHandler处理请求。

暴露服务（将服务注册到注册中心），提供者会在zookeeper注册中心生成一个节点，此节点存储了服务提供方ip、端口、group、接口名称、版本、应用名称（redis注册中心通过set命令把这些信息缓存到redis服务器）。

为了感知注册中心的一些配置变化，提供者会监听注册中心路径/dubbo/${interfaceClass}/configurators的节点，监听该节点在注册中心的一些配置信息变更。zookeeper注册中心通过zookeeper框架的监听回调接口进行监听（redis注册中心通过订阅命令（subscribe）监听），服务器缓存注册中心的配置，当配置发生变更时，服务会刷新本地缓存，代码在ZookeeperRegistry的doSubscribe方法。