dubbo源码学习(四)：暴露服务的过程

dubbo采用的nio异步的通信，通信协议默认为 netty,当然也可以选择 mina,grizzy。在服务端（provider）在启动时主要是开启netty监听，在zookeeper上注册服务节点，处理消费者请求，返回处理后的消息给消费者，消费者使用服务时主要是订阅服务的节点，监听zookeeper节点目录，服务端的变化时zookeeper会推送给消费者，消费者重新缓存服务地址等。服务者、消费者、zookeeper三者之间都是长连接。

下面看dubbo源码来看服务暴露的过程，服务暴露的入口为：com.alibaba.dubbo.config.ServiceConfig#export 方法，代码如下：

//是否延时暴露 
        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 { 
            //不延时暴露，则直接暴露 
            doExport(); 
        } 
上在代码无论是延时暴露或直接暴露调用的方法是：doExport（）,doExport会对解析完的配置再做一次检查，核心代码大家可以查看dubbo的源码，下面列出一小部分
/*
            检查默认设置,如果xml中没有配置<dubbo:provider
            主要是从系统环境变量中寻找是否有相应的provider的配置
*/ 
        checkDefault(); 
        //下面设置的内容如果没有配置<dubbo:provider时基本上都是Null 
        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) { 
            //registries一般都会配置 
            if (registries == null) { 
                registries = module.getRegistries(); 
            } 
            if (monitor == null) { 
                monitor = module.getMonitor(); 
            } 
        } 
        if (application != null) { 
            //application一般也会配置 
            if (registries == null) { 
                registries = application.getRegistries(); 
            } 
            if (monitor == null) { 
                monitor = application.getMonitor(); 
            } 
        } 
        //是否泛化调用 
        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); 
            } 
            /*
                检查即将暴露的接口的方法配置,检查方法是否在接口中存在
                一般不会配置所以一般情况下methods为null
                <dubbo:service  > <dubbo:method /> </dubbo:serivce>
             */ 
            checkInterfaceAndMethods(interfaceClass, methods); 
            /*
                检查接口的引用不为空,并且必须实现的是要暴露的接口
             */ 
            checkRef(); 
            generic = Boolean.FALSE.toString(); 
        } 

所有的检查通过之后，会调用 ：com.alibaba.dubbo.config.ServiceConfig#doExportUrls
/*
            将注册协议转化成url
            registry://45.119.68.23:2181/com.alibaba.dubbo.registry.RegistryService?
            application=test-dubbo&dubbo=2.5.3&pid=7648&registry=zookeeper×tamp=1462349748801
         */ 
        List<URL> registryURLs = loadRegistries(true); 
        //配置多通信协议时，都进行暴露 
        for (ProtocolConfig protocolConfig : protocols) { 
            doExportUrlsFor1Protocol(protocolConfig, registryURLs); 
        } 
doExportUrlsFor1Protocol中主要将所有的配置转化成map，然后将map转化成dubbo的统一URL，最终暴露的dubbo服务也就是这个统一的url，这个url也会注册到zookeeper的节点上，部分代码如下：
/*
    将不为null的配置对象中的属性设置到 map 中
    即将 xml 配置文件中的配置设置的值全转化成为map
    {side=provider, application=alijk-dubbo, accepts=1000,
        dubbo=2.5.3, threads=100, pid=7236, interface=cn.eoncloud.account.sdk.export.AccountService,
        threadpool=fixed, version=1.0.0, timeout=500, anyhost=true, timestamp=1462347843960}
*/ 
appendParameters(map, application); 
appendParameters(map, module); 
appendParameters(map, provider, Constants.DEFAULT_KEY); 
appendParameters(map, protocolConfig); 
appendParameters(map, this); 
......
/*
    将配置信息转化成 url ,主要根据之前map里的数据组装成url
    调用 URL#buildString方法
    dubbo://10.6.13.137:9998/cn.eoncloud.account.sdk.export.AccountService
    ?accepts=1000&anyhost=true&application=test-dubbo&dubbo=2.5.3
    &interface=cn.eoncloud.account.sdk.export.AccountService
    &methods=getAccountName,getAllTest&pid=7236&revision=1.0.0&side=provider
    &threadpool=fixed&threads=100&timeout=500×tamp=1462347843960&version=1.0.0
*/ 
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); 
} 
...... 
Invoker<?> invoker = proxyFactory.getInvoker(ref, (Class) interfaceClass, registryURL.addParameterAndEncoded(Constants.EXPORT_KEY, url.toFullString())); 
//com.alibaba.dubbo.registry.integration.RegistryProtocol#export 即将进行暴露 
Exporter<?> exporter = protocol.export(invoker); 
上面的代码核心暴露的一行代码为：protocol.export(invoker); 这个protocol的值为：RegistryProtocol，也就是暴露会跳到：RegistryProtocol.exprot中去处理，RegistryProtocol.exprot主要做两件事情：
1、开启netty服务端 。
2、创建zookeeper服务节点。
下面来看RegistryProtocol.export方法，代码如下：
public <T> Exporter<T> export(final Invoker<T> originInvoker) throws RpcException { 
        //export invoker doLocalExport调用dubboProtocol.export开启netty服务监听 
        final ExporterChangeableWrapper<T> exporter = doLocalExport(originInvoker); 
        //registry provider 
        final Registry registry = getRegistry(originInvoker); 
        final URL registedProviderUrl = getRegistedProviderUrl(originInvoker); 
        //调用zodoRegister的doRegister 创建zookeeper的服务节点 
        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); 
        //订阅 
        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); 
                } 
            } 
        }; 
    } 
上面的代码里有一段特别重要，关键性的代码在doLocalExport中：
final Invoker<?> invokerDelegete = new InvokerDelegete<T>(originInvoker, getProviderUrl(originInvoker)); 
//此处protol为dubboProtocol 
exporter = new ExporterChangeableWrapper<T>((Exporter<T>)protocol.export(invokerDelegete), originInvoker); 
从上面的代码中可以看到会调用dubboProtocol的export对服务进行暴露，这个export最终目的就是开启netty的监听，下面来看dubbo是如何一步一步开启netty的
private void openServer(URL url) { 
       // find server. ip:port 
       String key = url.getAddress(); 
       //client 也可以暴露一个只有server可以调用的服务。 
       boolean isServer = url.getParameter(Constants.IS_SERVER_KEY,true); 
       if (isServer) { 
        ExchangeServer server = serverMap.get(key); 
        if (server == null) { 
               //创建 Server 
            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) { 
       //默认开启server关闭时发送readonly事件 
       url = url.addParameterIfAbsent(Constants.CHANNEL_READONLYEVENT_SENT_KEY, Boolean.TRUE.toString()); 
       //默认开启heartbeat 
       url = url.addParameterIfAbsent(Constants.HEARTBEAT_KEY, String.valueOf(Constants.DEFAULT_HEARTBEAT)); 
       //默认使用netty 
       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); 
       //默认使用dubbo协议编码 
       url = url.addParameter(Constants.CODEC_KEY, Version.isCompatibleVersion() ? COMPATIBLE_CODEC_NAME : DubboCodec.NAME); 
       ExchangeServer server; 
       try { 
           //HeaderExchangeServer 在此处已经开启了Netty Server 进行监听 
           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; 
   } 
在上面的代码中：Exchangers.bind(url, requestHandler)  默认为：HeaderExchanger.bind()
public ExchangeServer bind(URL url, ExchangeHandler handler) throws RemotingException { 
        //Transporters默认为NettyTransporter 
        return new HeaderExchangeServer(Transporters.bind(url, new DecodeHandler(new HeaderExchangeHandler(handler)))); 
    } 
代码运行到这里可以看到传输方式了，dubbo默认采用的通信方式为 NettyTransporter ，再来看NettyTransporter.bind方法
public static final String NAME = "netty"; 
     
    public Server bind(URL url, ChannelHandler listener) throws RemotingException { 
        return new NettyServer(url, listener); 
    } 

已经能看到NettyServer了，dubbo在暴露服务最终开启的netty服务监听，监听消费者发送的请求，通过反射调用方法得到结果通过 tcp/ip 网络传输返回给消费者。再进入到NettyServer中我们就能看到非常传统的开启Netty服务的代码了
protected void doOpen() throws Throwable { 
        NettyHelper.setNettyLoggerFactory(); 
        ExecutorService boss = Executors.newCachedThreadPool(new NamedThreadFactory("NettyServerBoss", true)); 
        ExecutorService worker = Executors.newCachedThreadPool(new NamedThreadFactory("NettyServerWorker", true)); 
        //最后一个参数为 NIO 最大工作线程数 
        ChannelFactory channelFactory = new NioServerSocketChannelFactory(boss, worker, getUrl().getPositiveParameter(Constants.IO_THREADS_KEY, Constants.DEFAULT_IO_THREADS)); 
        //netty server 启动器 
        bootstrap = new ServerBootstrap(channelFactory); 
         
        final NettyHandler nettyHandler = new NettyHandler(getUrl(), this); 
        channels = nettyHandler.getChannels(); 
        // https://issues.jboss.org/browse/NETTY-365 
        // https://issues.jboss.org/browse/NETTY-379 
        // 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; 
            } 
        }); 
        // 创建一个绑定到指定地址的新通道，也就是绑定IP、端口供客户端连接 
        channel = bootstrap.bind(getBindAddress()); 
    } 
上面的代码执行完成后，netty的服务端就已经开启了，可以接收客户端的连接了，但客户端连接上来要怎么处理呢？消息接收、发送怎么处理呢？所有的处理都在上面代码的 NettyHandler类中，Nettyhandler继承了Netty包中的的SimpleChannelHandler

NettyHandler extends SimpleChannelHandler  
重写了 channelConnected、channelDisconnected、messageReceived等方法，而我们比较关注的可能是messagereceived方法，在收到消息时如何处理，但今天暂时先不看dubbo如果处理消息，只看暴露，消息处理如何实现异步通信下一节再讲。

/** 
     * 收到消息时触发 
     * @param ctx 
     * @param e 
     * @throws Exception 
     */ 
    @Override 
    public void messageReceived(ChannelHandlerContext ctx, MessageEvent e) throws Exception { 
        NettyChannel channel = NettyChannel.getOrAddChannel(ctx.getChannel(), url, handler); 
        try { 
            handler.received(channel, e.getMessage()); 
        } finally { 
            NettyChannel.removeChannelIfDisconnected(ctx.getChannel()); 
        } 
    } 
从前面知道,开启netty服务是在RegistryProtocol.export 的 doLocalExport 中，在开启了netty服务后，就是在zookeeper上注册服务节点了，消费者在消费服务时会根据消费的接口名找到对应的zookeeper节点目录，对目录进行监听，接收推送

//registry provider 
final Registry registry = getRegistry(originInvoker); 
final URL registedProviderUrl = getRegistedProviderUrl(originInvoker); 
//调用zodoRegister的doRegister 创建zookeeper的服务节点 
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); 
//订阅 
registry.subscribe(overrideSubscribeUrl, overrideSubscribeListener); 
dubbo服务在zookeeper上的节点注册是：com.alibaba.dubbo.registry.support.FailbackRegistry#register

@Override 
    public void register(URL url) { 
        super.register(url); 
        failedRegistered.remove(url); 
        failedUnregistered.remove(url); 
        try { 
            // 向服务器端发送注册请求 
            doRegister(url); 
因为doRegister是一个抽象的方法，查看他的实现可以看到：




从上图可以看到doRegister实现有 dubbo、redis、zookeeper，这也是在我们配置时经常看到的 注册协议的配置 ，最为常用的就是 zookeeper了，所以再看ZookeeperRegistry的代码，看他的doRegistry干什么了如下
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); 
       } 
   } 
其实从上面已经可以看到 在zookeeper上面创建 节点了，默认不分组的情况下，服务结构如下：/dubbo/XXXXservice/consumers、providers



至此，dubbo的暴露基本上已经完成，开启了netty服务，注册了zookeeper的节点，就等着消费者连接上来使用了。下一节将介绍dubbo的消息发送和接收，NIO异步通讯的实现。

关注获取视频