?dubbo服務(wù)暴露就是一個(gè)遠(yuǎn)程代理隧甚，打開網(wǎng)絡(luò)監(jiān)聽，接受服務(wù)調(diào)用請(qǐng)求渡冻，將服務(wù)接口名呻逆，IP，port發(fā)布到注冊(cè)中心的過程菩帝。通過《dubbo啟動(dòng)過程分析》可以了解到，在spring容器啟動(dòng)時(shí)會(huì)將容器中所有的bean初始化成單實(shí)例（默認(rèn)），如果bean繼承相應(yīng)的接口呼奢，在實(shí)例初始化完成后宜雀，會(huì)調(diào)用實(shí)現(xiàn)類中某些接口方法。dubbo的初始化也是通過這樣一個(gè)過程完成的握础。
ServiceConfig.export->doExport()-> doExportUrls()->doExportUrlsFor1Protocol()

//根據(jù)url暴露
 private void doExportUrlsFor1Protocol(ProtocolConfig protocolConfig, List<URL> registryURLs) {
        String name = protocolConfig.getName();//獲取服務(wù)提供者協(xié)議名稱
        if (name == null || name.length() == 0) {
            name = "dubbo";//默認(rèn)是dubbo
        }
        //獲取服務(wù)主機(jī)名辐董，為空則自動(dòng)查找本機(jī)IP
        if (NetUtils.isInvalidLocalHost(host)) {
            anyhost = true;
            try {
                host = InetAddress.getLocalHost().getHostAddress();
            } catch (UnknownHostException e) {
                logger.warn(e.getMessage(), e);
            }
        -----------------------------------------------
    }
 //SPI加載協(xié)議實(shí)現(xiàn)類中的默認(rèn)端口常量 
 final int defaultPort = ExtensionLoader.getExtensionLoader(Protocol.class).getExtension(name).getDefaultPort();
        if (port == null || port == 0) {//protocol沒有配置port
            port = defaultPort;
        }
        if (port == null || port <= 0) {
            port = getRandomPort(name);//使用本機(jī)隨機(jī)可用端口
            if (port == null || port < 0) {
                port = NetUtils.getAvailablePort(defaultPort);
                putRandomPort(name, port);
            }
            logger.warn("Use random available port(" + port + ") for protocol " + name);
        }
       //組織參數(shù)
       Map<String, String> map = new HashMap<String, String>();
       ..............................................................
       //形成類似dubbo://的統(tǒng)一URL
      URL url = new URL(name, host, port, (contextPath == null || contextPath.length() == 0 ? "" : contextPath + "/") + path, map);

        String scope = url.getParameter(Constants.SCOPE_KEY);//獲取是scope屬性
        //配置為none不暴露
        if (! Constants.SCOPE_NONE.toString().equalsIgnoreCase(scope)) {

            //配置不是remote的情況下做本地暴露 (配置為remote，則表示只暴露遠(yuǎn)程服務(wù))
            if (!Constants.SCOPE_REMOTE.toString().equalsIgnoreCase(scope)) {
                exportLocal(url);
            }
            //如果配置不是local則暴露為遠(yuǎn)程服務(wù).(配置為local禀综，則表示只暴露本地服務(wù))
            if (! Constants.SCOPE_LOCAL.toString().equalsIgnoreCase(scope) ){
                if (logger.isInfoEnabled()) {
                    logger.info("Export dubbo service " + interfaceClass.getName() + " to url " + url);
                }
                if (registryURLs != null && registryURLs.size() > 0
                        && url.getParameter("register", true)) {
                    for (URL registryURL : registryURLs) {
                        url = url.addParameterIfAbsent("dynamic", registryURL.getParameter("dynamic"));
                        //導(dǎo)入監(jiān)控中心信息
                        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);
                        }
                         //首先將URL中dubbo替換為registry简烘，創(chuàng)建遠(yuǎn)程代理Invoker
                        Invoker<?> invoker = proxyFactory.getInvoker(ref, (Class) interfaceClass, registryURL.addParameterAndEncoded(Constants.EXPORT_KEY, url.toFullString()));
                         //此處protocol為spi加載的適配類，會(huì)根據(jù)invoker中的protocol不同
                         //調(diào)用不同的具體實(shí)現(xiàn)類定枷，此處在SPI分析中已經(jīng)說明
                        //Protocol$Adaptor.export()-->dubbofilterwrapper.export()-->dubbolistenerwrapper.export()-->dubboprotocol.export()
                        Exporter<?> exporter = protocol.export(invoker);
                        exporters.add(exporter);
                    }
                } else {//本地服務(wù)
                    Invoker<?> invoker = proxyFactory.getInvoker(ref, (Class) interfaceClass, url);

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

接下來將創(chuàng)建接口實(shí)現(xiàn)類的包裝類孤澎，也就是服務(wù)的包裝類，調(diào)用過程如下：
proxyfactory$adpative.getInvoker()--> StubProxyFactoryWrapper.getInvoker()->JavassistProxyFactory.getInvoker()
調(diào)用Javaassit創(chuàng)建服務(wù)包裝類欠窒，生成的類如下覆旭，重點(diǎn)看invokeMethod()這個(gè)方法，后面invoker.invoke()會(huì)掉到此方法去執(zhí)行業(yè)務(wù)邏輯岖妄。

package com.alibaba.dubbo.common.bytecode;

import com.alibaba.dubbo.demo.provider.DemoServiceImpl;
import java.lang.reflect.InvocationTargetException;
import java.util.Map;

public class Wrapper1
  extends Wrapper
  implements ClassGenerator.DC
{
  ...........................................................
  public Object invokeMethod(Object paramObject, String paramString, Class[] paramArrayOfClass, Object[] paramArrayOfObject)
    throws InvocationTargetException
  {
    DemoServiceImpl localDemoServiceImpl;
    try
    {
      localDemoServiceImpl = (DemoServiceImpl)paramObject;
    }
    catch (Throwable localThrowable1)
    {
      throw new IllegalArgumentException(localThrowable1);
    }
    try
    {
      if ((!"sayHello".equals(paramString)) || (paramArrayOfClass.length == 1)) {
        return localDemoServiceImpl.sayHello((String)paramArrayOfObject[0]);
      }
    }
    catch (Throwable localThrowable2)
    {
      throw new InvocationTargetException(localThrowable2);
    }
  }
}

最后返回AbstractProxyInvoker的實(shí)現(xiàn)型将，此實(shí)現(xiàn)類是一個(gè)非常重要的類，包含了服務(wù)實(shí)現(xiàn)類荐虐，服務(wù)接口七兜，url，還有剛才生成的服務(wù)包裝類的引用福扬。
然后執(zhí)行到如下的方法：
Exporter<?> exporter = protocol.export(invoker);
此處調(diào)用的過程為protocol$Adaptive.export()-->ProtocolFilterWrapper.export()--->ProtocolListenerWrapper.export()腕铸，兩個(gè)wrapper什么都沒有做，直接放行忧换，最終調(diào)到RegistryProtocol.export()
參數(shù)為剛才封裝好的AbstractProxyInvoker實(shí)現(xiàn)類恬惯，然后：
ExporterChangeableWrapper<T> exporter = doLocalExport(originInvoker);
下面來分析這個(gè)方法，這個(gè)方法非常重要亚茬，就在此方法中調(diào)用DubboProtocol完成服務(wù)的發(fā)布

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>
        //此處打開網(wǎng)絡(luò)監(jiān)聽
((Exporter<T>)protocol.export(invokerDelegete), originInvoker);
                    bounds.put(key, exporter);
                }
            }
        }
        return (ExporterChangeableWrapper<T>) exporter;
    }

在doLocalExport()中酪耳，將provider url與AbstractProxyInvoker實(shí)現(xiàn)類封裝到InvokerDelegete對(duì)象中，然后執(zhí)行protocol.export(invokerDelegete)方法刹缝，此處后面會(huì)重點(diǎn)分析碗暗，此方法返回一個(gè)DubboExporter對(duì)象，將此對(duì)象與AbstractProxyInvoker實(shí)現(xiàn)類封裝在ExporterChangeableWrapper對(duì)象中梢夯，并存儲(chǔ)在RegistryProtocol這個(gè)類的bounds屬性言疗，這個(gè)屬性是一個(gè)線程安全的map，以便以后服務(wù)調(diào)用使用颂砸。下面分析調(diào)用dubbo協(xié)議打開網(wǎng)絡(luò)監(jiān)聽的過程噪奄。依然是SPI機(jī)制死姚，經(jīng)過ProtocolFilterWrapper.export()，完成對(duì)Invoker的包裝勤篮，Invoker中加入了Filter調(diào)用鏈都毒。

private static <T> Invoker<T> buildInvokerChain(final Invoker<T> invoker, String key, String group) {
        Invoker<T> last = invoker;
         //SPI機(jī)制加載所有Filter擴(kuò)展
        List<Filter> filters = ExtensionLoader.getExtensionLoader(Filter.class).getActivateExtension(invoker.getUrl(), key, group);
        if (filters.size() > 0) {
         //加入Filter執(zhí)行鏈
            for (int i = filters.size() - 1; i >= 0; i --) {
                final Filter filter = filters.get(i);
                final Invoker<T> next = last;
                last = new Invoker<T>() {
                .......................................................
                    public Result invoke(Invocation invocation) throws RpcException {
                        return filter.invoke(next, invocation);
                    }
                .......................................................
                };
            }
        }
        return last;
    }

然后經(jīng)過ProtocolListenerWrapper.export()調(diào)到DubboProtocol.export()，將結(jié)果封裝成ListenerExporterWrapper返回碰缔。

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

將前面?zhèn)鬟f過來的invoker,key账劲，exporterMap封裝到DubboExporter中，打開server此處是后續(xù)調(diào)用netty打開網(wǎng)絡(luò)監(jiān)聽,最終返回到DubboProtocol處的是HeaderExchangeServer金抡，此對(duì)象持有nettyserver瀑焦，在nettyserver構(gòu)造方法中，有兩個(gè)構(gòu)造參數(shù)一個(gè)是url梗肝，另一個(gè)是DecodeHandler榛瓮，此對(duì)象里又封裝了HeaderExchangeHandler，又封裝了ExchangeHandler统捶。初始化了nettyserver的基本參數(shù)如：ip,port,timeout等等榆芦。具體調(diào)用流程如下：
openServer(url)-->createServer(url)-->Exchangers.bind(url, requestHandler)-->HeaderExchanger.bind()-->NettyTransporter.bind()-->nettyserver.doopen()
在doopen()方法中，就是對(duì)netty的初始化操作喘鸟，設(shè)置線程池匆绣，綁定decoder、encoder什黑、handler崎淳，然后打開端口，進(jìn)行監(jiān)聽愕把。

  @Override
    protected void doOpen() throws Throwable {
        NettyHelper.setNettyLoggerFactory();
        ExecutorService boss = Executors.newCachedThreadPool(new NamedThreadFactory("NettyServerBoss", true));
        ExecutorService worker = Executors.newCachedThreadPool(new NamedThreadFactory("NettyServerWorker", true));
        ChannelFactory channelFactory = new NioServerSocketChannelFactory(boss, worker, getUrl().getPositiveParameter(Constants.IO_THREADS_KEY, Constants.DEFAULT_IO_THREADS));
        bootstrap = new ServerBootstrap(channelFactory);
        final NettyHandler nettyHandler = new NettyHandler(getUrl(), this);
        channels = nettyHandler.getChannels();
        bootstrap.setPipelineFactory(new ChannelPipelineFactory() {
            public ChannelPipeline getPipeline() {
                NettyCodecAdapter adapter = new NettyCodecAdapter(getCodec() ,getUrl(), NettyServer.this);
                ChannelPipeline pipeline = Channels.pipeline();
                pipeline.addLast("decoder", adapter.getDecoder());
                pipeline.addLast("encoder", adapter.getEncoder());
                pipeline.addLast("handler", nettyHandler);
                return pipeline;
            }
        });
        channel = bootstrap.bind(getBindAddress());
    }

打開網(wǎng)絡(luò)監(jiān)聽后拣凹，再次回到RegistryProtocol類中，下面就開始調(diào)用注冊(cè)中心進(jìn)行服務(wù)注冊(cè)和訂閱恨豁。首先調(diào)用getRegistry(originInvoker)嚣镜，spi機(jī)制，初始化時(shí)注入的是registryFactory適配類橘蜜，根據(jù)url中注冊(cè)中心參數(shù)獲取具體的實(shí)現(xiàn)類菊匿，此處是ZookeeperRegistryFactory

private Registry  getRegistry(final Invoker<?> originInvoker){
        URL registryUrl = originInvoker.getUrl();
        if (Constants.REGISTRY_PROTOCOL.equals(registryUrl.getProtocol())) {
            String protocol = registryUrl.getParameter(Constants.REGISTRY_KEY, Constants.DEFAULT_DIRECTORY);
            registryUrl = registryUrl.setProtocol(protocol).removeParameter(Constants.REGISTRY_KEY);
        }
        return registryFactory.getRegistry(registryUrl);
    }

調(diào)用到AbstractRegistryFactory.getRegistry()>ZookeeperRegistryFactory.createRegistry()，最終返回一個(gè) ZookeeperRegistry對(duì)象

public class ZookeeperRegistryFactory extends AbstractRegistryFactory {
    //此處是spi機(jī)制注入的適配類
    private ZookeeperTransporter zookeeperTransporter;
    public void setZookeeperTransporter(ZookeeperTransporter zookeeperTransporter) {
        this.zookeeperTransporter = zookeeperTransporter;
    }
    public Registry createRegistry(URL url) {
        return new ZookeeperRegistry(url, zookeeperTransporter);
    }
}

返回到RegistryProtocol.export(),獲得到了 ZookeeperRegistry计福，然后調(diào)用registry.register(registedProviderUrl)進(jìn)行注冊(cè)跌捆，進(jìn)一步跟蹤，調(diào)用鏈路為：FailbackRegistry.register()-->AbstractRegistry.register()-->ZookeeperRegistry.doRegister()象颖，在zk上創(chuàng)建一個(gè)臨時(shí)節(jié)點(diǎn)佩厚，注冊(cè)完成

protected void doRegister(URL url) {
        try {
             //在zk上創(chuàng)建一個(gè)臨時(shí)節(jié)點(diǎn)
            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);
        }
    }

回到RegistryProtocol，注冊(cè)完成之后说订，下面開始訂閱抄瓦，需要感知zk node的變化潮瓶，此處使用的zk的watcher機(jī)制，首先初始化一個(gè)NotifyListener闺鲸，后面監(jiān)聽變化調(diào)用到此對(duì)象中的notify方法筋讨。

 final URL overrideSubscribeUrl = getSubscribedOverrideUrl(registedProviderUrl);
 final OverrideListener overrideSubscribeListener = new OverrideListener(overrideSubscribeUrl);
 overrideListeners.put(overrideSubscribeUrl, overrideSubscribeListener);
 registry.subscribe(overrideSubscribeUrl, overrideSubscribeListener);

調(diào)用鏈路：FailbackRegistry.subscribe()-->AbstractRegistry.subscribe()-->ZookeeperRegistry.doSubscribe(),主要是注冊(cè)主節(jié)點(diǎn)和子節(jié)點(diǎn)監(jiān)聽

protected void doSubscribe(final URL url, final NotifyListener listener) {
 .......................
   List<URL> urls = new ArrayList<URL>();
                for (String path : toCategoriesPath(url)) {
                   //zkListeners根據(jù)key存儲(chǔ)了主節(jié)點(diǎn)和子節(jié)點(diǎn)監(jiān)聽
                    ConcurrentMap<NotifyListener, ChildListener> listeners = zkListeners.get(url);
                    if (listeners == null) {//沒有 初始化
                        zkListeners.putIfAbsent(url, new ConcurrentHashMap<NotifyListener, ChildListener>());
                        listeners = zkListeners.get(url);
                    }
                   //根據(jù)主節(jié)點(diǎn)監(jiān)聽獲取子節(jié)點(diǎn)監(jiān)聽
                    ChildListener zkListener = listeners.get(listener);
                    if (zkListener == null) {//沒有，new一個(gè)
                        listeners.putIfAbsent(listener, new ChildListener() {
                            public void childChanged(String parentPath, List<String> currentChilds) {
                                //節(jié)點(diǎn)刪除摸恍，更新會(huì)觸發(fā)notify方法
                                ZookeeperRegistry.this.notify(url, listener, toUrlsWithEmpty(url, parentPath, currentChilds));
                            }
                        });
                        zkListener = listeners.get(listener);
                    }
                    zkClient.create(path, false);//創(chuàng)造一個(gè)永久節(jié)點(diǎn)？赤屋？
                   //添加子節(jié)點(diǎn)監(jiān)聽器
                    List<String> children = zkClient.addChildListener(path, zkListener);
                    if (children != null) {
                        urls.addAll(toUrlsWithEmpty(url, path, children));
                    }
                }
                notify(url, listener, urls);
            }
 .......................
}

notify(url, listener, urls)調(diào)用鏈比較復(fù)雜立镶，鏈路為：
FailbackRegistry.notify()-->FailbackRegistry.doNotify()-->AbstractRegistry.notify()-->listener.notify()，此處的listener為剛才registryProtocol傳遞過來的OverrideListener,然后調(diào)用OverrideListener.notify()-->RegistryProtocol.doChangeLocalExport(),對(duì)修改了url的invoker重新export,至此整個(gè)發(fā)布過程全部完成类早。

private <T> void doChangeLocalExport(final Invoker<T> originInvoker, URL newInvokerUrl){
        String key = getCacheKey(originInvoker);
        final ExporterChangeableWrapper<T> exporter = (ExporterChangeableWrapper<T>) bounds.get(key);
        if (exporter == null){
            logger.warn(new IllegalStateException("error state, exporter should not be null"));
            return ;//不存在是異常場景 直接返回 
        } else {
            final Invoker<T> invokerDelegete = new InvokerDelegete<T>(originInvoker, newInvokerUrl);
            //調(diào)用dubboprotocol.export()重新發(fā)布
            exporter.setExporter(protocol.export(invokerDelegete));
        }
    }