Dubbo原理和源碼解析之服務暴露

github新增倉庫 "dubbo-read"（點此查看），集合所有《Dubbo原理和源碼解析》系列文章，后續將繼續補充該系列，同時將針對Dubbo所做的功能擴展也進行分享。不定期更新，歡迎Follow。

 

一、框架設計

在官方《Dubbo 用戶指南》架構部分，給出了服務調用的整體架構和流程：

 

另外，在官方《Dubbo 開發指南》框架設計部分，給出了整體設計：

以及暴露服務時序圖：

 

本文將根據以上幾張圖，分析服務暴露的實現原理，並進行詳細的代碼跟蹤與解析。

二、原理和源碼解析

2.1 標簽解析

從文章《Dubbo原理和源碼解析之標簽解析》中我們知道，<dubbo:service> 標簽會被解析成 ServiceBean。

ServiceBean 實現了 InitializingBean，在類加載完成之后會調用 afterPropertiesSet() 方法。在 afterPropertiesSet() 方法中，依次解析以下標簽信息：

• <dubbo:provider>
• <dubbo:application>
• <dubbo:module>
• <dubbo:registry>
• <dubbo:monitor>
• <dubbo:protocol>

ServiceBean 還實現了 ApplicationListener，在 Spring 容器初始化的時候會調用 onApplicationEvent 方法。ServiceBean 重寫了 onApplicationEvent 方法，實現了服務暴露的功能。

ServiceBean.java

public void onApplicationEvent(ApplicationEvent event) {
    if (ContextRefreshedEvent.class.getName().equals(event.getClass().getName())) {
        if (isDelay() && ! isExported() && ! isUnexported()) {
            if (logger.isInfoEnabled()) {
                logger.info("The service ready on spring started. service: " + getInterface());
            }
            export();
        }
    }
}

2.2 延遲暴露

ServiceBean 擴展了 ServiceConfig，調用 export() 方法時由 ServiceConfig 完成服務暴露的功能實現。

ServiceConfig.java

public synchronized void export() {
    if (provider != null) {
        if (export == null) {
            export = provider.getExport();
        }
        if (delay == null) {
            delay = provider.getDelay();
        }
    }
    if (export != null && ! export.booleanValue()) {
        return;
    }
    if (delay != null && delay > 0) {
        Thread thread = new Thread(new Runnable() {
            public void run() {
                try {
                    Thread.sleep(delay);
                } catch (Throwable e) {
                }
                doExport();
            }
        });
        thread.setDaemon(true);
        thread.setName("DelayExportServiceThread");
        thread.start();
    } else { doExport(); }
}

由上面代碼可知，如果設置了 delay 參數，Dubbo 的處理方式是啟動一個守護線程在 sleep 指定時間后再 doExport。

2.3 參數檢查

在 ServiceConfig 的 doExport() 方法中會進行參數檢查和設置，包括：

• 泛化調用
• 本地實現
• 本地存根
• 本地偽裝
• 配置（application、registry、protocol等）

ServiceConfig.java

protected synchronized void doExport() {
    if (unexported) {
        throw new IllegalStateException("Already unexported!");
    }
    if (exported) {
        return;
    }
    exported = true;
    if (interfaceName == null || interfaceName.length() == 0) {
        throw new IllegalStateException("<dubbo:service interface=\"\" /> interface not allow null!");
    }
    checkDefault();
    //省略
    if (ref instanceof GenericService) {
        interfaceClass = GenericService.class;
        generic = true;
    } else {
        try {
            interfaceClass = Class.forName(interfaceName, true, Thread.currentThread()
                    .getContextClassLoader());
        } catch (ClassNotFoundException e) {
            throw new IllegalStateException(e.getMessage(), e);
        }
        checkInterfaceAndMethods(interfaceClass, methods);
        checkRef();
        generic = false;
    }
    if(local !=null){
        if(local=="true"){
            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 implemention class " + localClass.getName() + " not implement interface " + interfaceName);
        }
    }
    if(stub !=null){
        if(stub=="true"){
            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 implemention class " + stubClass.getName() + " not implement interface " + interfaceName);
        }
    }
    //此處省略：檢查並設置相關參數
 doExportUrls();
}

2.4 多協議、多注冊中心

在檢查完參數之后，開始暴露服務。Dubbo 支持多協議和多注冊中心：

ServiceConfig.java

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

2.5 組裝URL

針對每個協議、每個注冊中心，開始組裝 URL。

ServiceConfig.java

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

    //處理host

    //處理port

    Map<String, String> map = new HashMap<String, String>();
    //設置參數到map

    // 導出服務
    String contextPath = protocolConfig.getContextpath();
    if ((contextPath == null || contextPath.length() == 0) && provider != null) {
        contextPath = provider.getContextpath();
    }
    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);
    }

    //此處省略：服務暴露（詳見 2.6 和 2.7）
    
    this.urls.add(url);
}

2.6 本地暴露

如果配置 scope=none， 則不會進行服務暴露；如果沒有配置 scope 或者 scope=local，則會進行本地暴露。

ServiceConfig.java

//public static final String LOCAL_PROTOCOL = "injvm";
//public static final String LOCALHOST = "127.0.0.1";

private void doExportUrlsFor1Protocol(ProtocolConfig protocolConfig, List<URL> registryURLs) {
    //......
    String scope = url.getParameter(Constants.SCOPE_KEY);
    //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，則表示只暴露遠程服務)
        if (!Constants.SCOPE_REMOTE.toString().equalsIgnoreCase(scope)) {
            exportLocal(url);
        }
        //......
    }
    //......
}

private void exportLocal(URL url) {
    if (!Constants.LOCAL_PROTOCOL.equalsIgnoreCase(url.getProtocol())) {
        URL local = URL.valueOf(url.toFullString())
                .setProtocol(Constants.LOCAL_PROTOCOL)
                .setHost(NetUtils.LOCALHOST)
                .setPort(0);
        Exporter<?> exporter = protocol.export( proxyFactory.getInvoker(ref, (Class) interfaceClass, local)); exporters.add(exporter);
        logger.info("Export dubbo service " + interfaceClass.getName() +" to local registry");
    }
}

1. 暴露服務的時候，會通過代理創建 Invoker；

2. 本地暴露時使用 injvm 協議，injvm 協議是一個偽協議，它不開啟端口，不能被遠程調用，只在 JVM 內直接關聯，但執行 Dubbo 的 Filter 鏈。

2.7 遠程暴露

如果沒有配置 scope 或者 scope=remote，則會進行遠程暴露。

ServiceConfig.java

private void doExportUrlsFor1Protocol(ProtocolConfig protocolConfig, List<URL> registryURLs) {
    String scope = url.getParameter(Constants.SCOPE_KEY);
    //配置為none不暴露
    if (! Constants.SCOPE_NONE.toString().equalsIgnoreCase(scope)) {
        //......
        //如果配置不是local則暴露為遠程服務.(配置為local，則表示只暴露遠程服務)
        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"));
                    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);
                    }
                    Invoker<?> invoker = proxyFactory.getInvoker(ref, (Class) interfaceClass, registryURL.addParameterAndEncoded(Constants.EXPORT_KEY, url.toFullString()));
    
                    Exporter<?> exporter = protocol.export(invoker);
                    exporters.add(exporter);
                }
            } else {
                Invoker<?> invoker = proxyFactory.getInvoker(ref, (Class) interfaceClass, url);
    
                Exporter<?> exporter = protocol.export(invoker); exporters.add(exporter); } }
    }
}

在服務暴露時，有兩種情況：

• 不使用注冊中心：直接暴露對應協議的服務，引用服務時只能通過直連方式引用
• 使用注冊中心：暴露對應協議的服務后，會將服務節點注冊到注冊中心，引用服務時可以通過注冊中心動態獲取服務提供者列表，也可以通過直連方式引用

2.8 暴露服務

不使用注冊中心時，直接調用對應協議（如 Dubbo 協議）的 export() 暴露服務。以 Dubbo 協議為例：

DubboProtocol.java

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 dispaching 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); return exporter;
}

調用 openServer() 方法創建並啟動 Server：

DubboProtocol.java

private void openServer(URL url) {
    // find server.
    String key = url.getAddress();
    //client 也可以暴露一個只有server可以調用的服務。
    boolean isServer = url.getParameter(Constants.IS_SERVER_KEY,true);
    if (isServer) {
        ExchangeServer server = serverMap.get(key);
        if (server == null) {
            serverMap.put(key, createServer(url));
        } else {
            //server支持reset,配合override功能使用
            server.reset(url);
        }
    }
}

private ExchangeServer createServer(URL url) {
    //默認開啟server關閉時發送readonly事件
    url = url.addParameterIfAbsent(Constants.CHANNEL_READONLYEVENT_SENT_KEY, Boolean.TRUE.toString());
    //默認開啟heartbeat
    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, Version.isCompatibleVersion() ? COMPATIBLE_CODEC_NAME : 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;
}

Exchanger （默認 HeaderExchanger）封裝請求響應模式，同步轉異步，以 Request、Response 為中心:

HeaderExchager.java

public ExchangeServer bind(URL url, ExchangeHandler handler) throws RemotingException {
    return new HeaderExchangeServer(Transporters.bind(url, new DecodeHandler(new HeaderExchangeHandler(handler))));
}

Transporters.java

public static Server bind(URL url, ChannelHandler... handlers) throws RemotingException {
    if (url == null) {
        throw new IllegalArgumentException("url == null");
    }
    if (handlers == null || handlers.length == 0) {
        throw new IllegalArgumentException("handlers == null");
    }
    ChannelHandler handler;
    if (handlers.length == 1) {
        handler = handlers[0];
    } else {
        handler = new ChannelHandlerDispatcher(handlers);
    }
    return getTransporter().bind(url, handler);
}

底層傳輸默認使用 NettyTransporter，最終是創建 NettyServer：

NettyTransporter.java

public Server bind(URL url, ChannelHandler listener) throws RemotingException {
    return new NettyServer(url, listener);
}

NettyServer.java

public class NettyServer extends AbstractServer implements Server {
    public NettyServer(URL url, ChannelHandler handler) throws RemotingException{
        super(url, ChannelHandlers.wrap(handler, ExecutorUtil.setThreadName(url, SERVER_THREAD_POOL_NAME))); }
}

AbstractServer.java

public abstract class AbstractServer extends AbstractEndpoint implements Server {
    public AbstractServer(URL url, ChannelHandler handler) throws RemotingException {
        super(url, handler);
        localAddress = getUrl().toInetSocketAddress();
        String host = url.getParameter(Constants.ANYHOST_KEY, false) 
                        || NetUtils.isInvalidLocalHost(getUrl().getHost()) 
                        ? NetUtils.ANYHOST : getUrl().getHost();
        bindAddress = new InetSocketAddress(host, getUrl().getPort());
        this.accepts = url.getParameter(Constants.ACCEPTS_KEY, Constants.DEFAULT_ACCEPTS);
        this.idleTimeout = url.getParameter(Constants.IDLE_TIMEOUT_KEY, Constants.DEFAULT_IDLE_TIMEOUT);
        try {
            doOpen(); if (logger.isInfoEnabled()) {
                logger.info("Start " + getClass().getSimpleName() + " bind " + getBindAddress() + ", export " + getLocalAddress());
            }
        } catch (Throwable t) {
            throw new RemotingException(url.toInetSocketAddress(), null, "Failed to bind " + getClass().getSimpleName() 
                                        + " on " + getLocalAddress() + ", cause: " + t.getMessage(), t);
        }
        if (handler instanceof WrappedChannelHandler ){
            executor = ((WrappedChannelHandler)handler).getExecutor();
        }
    }
}

NettyServer.java

public class NettyServer extends AbstractServer implements Server {
    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();
        // final Timer timer = new HashedWheelTimer(new NamedThreadFactory("NettyIdleTimer", true));
        bootstrap.setPipelineFactory(new ChannelPipelineFactory() {
            public ChannelPipeline getPipeline() {
                NettyCodecAdapter adapter = new NettyCodecAdapter(getCodec() ,getUrl(), NettyServer.this);
                ChannelPipeline pipeline = Channels.pipeline();
                /*int idleTimeout = getIdleTimeout();
                if (idleTimeout > 10000) {
                    pipeline.addLast("timer", new IdleStateHandler(timer, idleTimeout / 1000, 0, 0));
                }*/
                pipeline.addLast("decoder", adapter.getDecoder());
                pipeline.addLast("encoder", adapter.getEncoder());
                pipeline.addLast("handler", nettyHandler);
                return pipeline;
            }
        });
        // bind
        channel = bootstrap.bind(getBindAddress()); }
}

2.9 服務注冊

如果使用了注冊中心，則在通過具體協議（如 Dubbo 協議）暴露服務之后（即在 2.8 基礎之上）進入服務注冊流程，將服務節點注冊到注冊中心。

RegistryProtocol.java

public <T> Exporter<T> export(final Invoker<T> originInvoker) throws RpcException {
    //export invoker
    final ExporterChangeableWrapper<T> exporter = doLocalExport(originInvoker);
    //registry provider
    final Registry registry = getRegistry(originInvoker);
    final URL registedProviderUrl = getRegistedProviderUrl(originInvoker);
    //向Zookeeper注冊節點
    registry.register(registedProviderUrl);
    // 訂閱override數據
    // FIXME 提供者訂閱時，會影響同一JVM即暴露服務，又引用同一服務的的場景，因為subscribed以服務名為緩存的key，導致訂閱信息覆蓋。
    final URL overrideSubscribeUrl = getSubscribedOverrideUrl(registedProviderUrl);
    final OverrideListener overrideSubscribeListener = new OverrideListener(overrideSubscribeUrl);
    overrideListeners.put(overrideSubscribeUrl, overrideSubscribeListener);
    registry.subscribe(overrideSubscribeUrl, overrideSubscribeListener); //保證每次export都返回一個新的exporter實例
    return new Exporter<T>() {
        public Invoker<T> getInvoker() {
            return exporter.getInvoker();
        }
        public void unexport() {
            try {
                exporter.unexport();
            } catch (Throwable t) {
                logger.warn(t.getMessage(), t);
            }
            try {
                registry.unregister(registedProviderUrl);
            } catch (Throwable t) {
                logger.warn(t.getMessage(), t);
            }
            try {
                overrideListeners.remove(overrideSubscribeUrl);
                registry.unsubscribe(overrideSubscribeUrl, overrideSubscribeListener);
            } catch (Throwable t) {
                logger.warn(t.getMessage(), t);
            }
        }
    };
}

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);
}

getRegistry() 方法根據注冊中心類型（默認 Zookeeper）獲取注冊中心客戶端，由注冊中心客戶端實例來進行真正的服務注冊。

注冊中心客戶端將節點注冊到注冊中心，同時訂閱對應的 override 數據，實時監聽服務的屬性變動實現動態配置功能。

最終返回的 Exporter 實現了 unexport() 方法，這樣在服務下線時清理相關資源。

 

至此，服務暴露流程結束。