dubbo框架揭秘之服务发布

通常情况下是通过Spring配置的方式去实现服务的发布，为了方便调试，我就不采用Spring配置的方式。

        DemoService demo = new DemoServiceImpl();
        ApplicationConfig config=new ApplicationConfig("hello-world-app");

        RegistryConfig reg=new RegistryConfig("127.0.0.1:2181");
        reg.setProtocol("zookeeper");

        ProtocolConfig protocol = new ProtocolConfig();
        protocol.setName("dubbo");
        protocol.setPort(20880);

        ServiceConfig<DemoService> service=new ServiceConfig<DemoService>();
        service.setApplication(config);
        service.setRegistry(reg);
        service.setProtocol(protocol);
        service.setInterface(DemoService.class);
        service.setRef(demo);
        service.setVersion("1.0");
        service.export();

        Thread.sleep(Integer.MAX_VALUE);

上面是服务发布的简短代码，其中最重要的就是export()方法。

public synchronized void export() {
           ...
            doExport()
    }
protected synchronized void doExport() {
       ...
        doExportUrls();
    }
private void doExportUrls() {
　　    //装配地址 registry://127.0.0.1:2181/com.alibaba.dubbo.registry.RegistryService?application=hello-world-app&dubbo=2.5.3&pid=5556&registry=zookeeper&timestamp=1484484518418　　
        List<URL> registryURLs = loadRegistries(true);
        for (ProtocolConfig protocolConfig : protocols) {
            doExportUrlsFor1Protocol(protocolConfig, registryURLs);
        }
    }

private void doExportUrlsFor1Protocol(ProtocolConfig protocolConfig, List<URL> registryURLs) {
        //配置为none不暴露
        if (! Constants.SCOPE_NONE.toString().equalsIgnoreCase(scope)) {

            //配置不是remote的情况下做本地暴露 (配置为remote，则表示只暴露远程服务)
            if (!Constants.SCOPE_REMOTE.toString().equalsIgnoreCase(scope)) {
                exportLocal(url);
            }
            //如果配置不是local则暴露为远程服务.(配置为local，则表示只暴露远程服务)
            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);
                }
            }
        }
        this.urls.add(url);
    }

最终调用的是protocol.export(invoker)方法，protocol是通过扩展点机制动态生成的类：

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

public class Protocol$Adpative implements com.alibaba.dubbo.rpc.Protocol {
        public void destroy() {
            throw new UnsupportedOperationException(
                    "method public abstract void com.alibaba.dubbo.rpc.Protocol.destroy() of interface com.alibaba.dubbo.rpc.Protocol is not adaptive method!");
        }

        public int getDefaultPort() {
            throw new UnsupportedOperationException(
                    "method public abstract int com.alibaba.dubbo.rpc.Protocol.getDefaultPort() of interface com.alibaba.dubbo.rpc.Protocol is not adaptive method!");
        }
　　　　 //调用该方法
        public com.alibaba.dubbo.rpc.Exporter export(com.alibaba.dubbo.rpc.Invoker arg0)
                throws com.alibaba.dubbo.rpc.Invoker {
            if (arg0 == null)
                throw new IllegalArgumentException("com.alibaba.dubbo.rpc.Invoker argument == null");
            if (arg0.getUrl() == null)
                throw new IllegalArgumentException("com.alibaba.dubbo.rpc.Invoker argument getUrl() == null");
            com.alibaba.dubbo.common.URL url = arg0.getUrl();
            String extName = (url.getProtocol() == null ? "dubbo" : url.getProtocol());
            if (extName == null)
                throw new IllegalStateException("Fail to get extension(com.alibaba.dubbo.rpc.Protocol) name from url("
                        + url.toString() + ") use keys([protocol])");
           //扩展点机制加载扩展类：
            com.alibaba.dubbo.rpc.Protocol extension = (com.alibaba.dubbo.rpc.Protocol) ExtensionLoader
                    .getExtensionLoader(com.alibaba.dubbo.rpc.Protocol.class).getExtension(extName);
            return extension.export(arg0);
        }

        public com.alibaba.dubbo.rpc.Invoker refer(java.lang.Class arg0, com.alibaba.dubbo.common.URL arg1)
                throws java.lang.Class {
            if (arg1 == null)
                throw new IllegalArgumentException("url == null");
            com.alibaba.dubbo.common.URL url = arg1;
            String extName = (url.getProtocol() == null ? "dubbo" : url.getProtocol());
            if (extName == null)
                throw new IllegalStateException("Fail to get extension(com.alibaba.dubbo.rpc.Protocol) name from url("
                        + url.toString() + ") use keys([protocol])");
            com.alibaba.dubbo.rpc.Protocol extension = (com.alibaba.dubbo.rpc.Protocol) ExtensionLoader
                    .getExtensionLoader(com.alibaba.dubbo.rpc.Protocol.class).getExtension(extName);
            return extension.refer(arg0, arg1);
        }
    }

加载扩展类的核心方法：

public T getExtension(String name) {
        ...
        Object instance = holder.get();
        if (instance == null) {
            synchronized (holder) {
                instance = holder.get();
                if (instance == null) {
                    instance = createExtension(name);
                    holder.set(instance);
                }
            }
        }
        return (T) instance;
    }
private T createExtension(String name) {
        try {
            T instance = (T) EXTENSION_INSTANCES.get(clazz);
            if (instance == null) {
                EXTENSION_INSTANCES.putIfAbsent(clazz, (T) clazz.newInstance());
                instance = (T) EXTENSION_INSTANCES.get(clazz);
            }
            injectExtension(instance);
            //cachedWrapperClasses在getAdaptiveExtension方法中被初始化，值为：ProtocolListenerWrapper、ProtocolFilterWrapper
            //这2个包装类通过装饰器模式，构造器实例化，最终返回ProtocolFilterWrapper(构造函数参数：ProtocolListenerWrapper(构造函数参数：RegistryProtocol))
            Set<Class<?>> wrapperClasses = cachedWrapperClasses;
            if (wrapperClasses != null && wrapperClasses.size() > 0) {
                for (Class<?> wrapperClass : wrapperClasses) {
                    instance = injectExtension((T) wrapperClass.getConstructor(type).newInstance(instance));
                }
            }
            return instance;
        } catch (Throwable t) {
            throw new IllegalStateException("Extension instance(name: " + name + ", class: " +
                    type + ")  could not be instantiated: " + t.getMessage(), t);
        }
    }    

所以，最终层层包装，调用RegistryProtocol的export(Invoker<T>)方法：

 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);
　　　　 //向注册中心注册地址：/dubbo/com.selrain.dubbodemo.DemoService/providers
        registry.register(registedProviderUrl);
        // 订阅override数据
        // FIXME 提供者订阅时，会影响同一JVM即暴露服务，又引用同一服务的的场景，因为subscribed以服务名为缓存的key，导致订阅信息覆盖。
        final URL overrideSubscribeUrl = getSubscribedOverrideUrl(registedProviderUrl);
        final OverrideListener overrideSubscribeListener = new OverrideListener(overrideSubscribeUrl);
        overrideListeners.put(overrideSubscribeUrl, overrideSubscribeListener);
        registry.subscribe(overrideSubscribeUrl, overrideSubscribeListener);
        //保证每次export都返回一个新的exporter实例
        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);
                }
            }
        };
    }

参考：

Dubbo原理解析-服务发布