dubbo源码分析二：服务发布

    本文将深入分析dubbo的服务发布涉及到的流程及主要类的代码。首先，我们先从类的关系图来看一下dubbo发布服务涉及到的相关类。

1.类图

   上图展示了部分服务发布过程中需要使用到的类和接口，其中：

    spring适配涉及到的类：DubboNamespaceHandler、DubboBeanDefinitionParser、ServiceBean;

    配置信息存储：ServicdConfig、RegistryConfig、MonitorConfig、ProtocolConfig、ProviderConfig等；

    应用协议：Protocol、DubboProtocol、HessianProtocol、ThriftProtocol、RmiProtocol、AbstractProxyProtocol、AbstractProtocol等；

    Server相关：Exchanger、HeaderExchanger、ExchangeServer、HeaderExchangeServer、Transporters、Transporter、NettyTransporter、NettyServer等；

2.时序图

    我们通过时序图来分析一下在发布服务的过程中，上面的类是如何串联在一起的：

    a.spring容器通过DubboBeanDefinitionParser类的对象来解析xml文件中的标签，生成ServiceConfig等配置对象；

    b.ServiceConfig的export()等发布服务的方法被调用；

    c.通过spi机制确定Protocol接口的实现对象为DubboProtocol的对象，调用它的openServer()等方法；

    d.通过spi机制确定Transporter接口的实现对象为NettyTransporter，调用它的bind()方法；

    e.调用NettyServer类，启动netty服务，绑定端口。

 3.核心代码解析

a.DubboProtocol

    public <T> Exporter<T> export(Invoker<T> invoker) throws RpcException {
        URL url = invoker.getUrl();//获取url信息
        
        // export service.
        String key = serviceKey(url);//产生与发布的接口映射的key ,格式例如：com.alibaba.dubbo.demo.DemoService:20882
        DubboExporter<T> exporter = new DubboExporter<T>(invoker, key, exporterMap);//创建DubboExporter对象
        exporterMap.put(key, exporter);//缓存此对象
        
        //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);//打开服务
        
        return exporter;
    }
    
    private void openServer(URL url) {
        // find server.
        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) {
        		serverMap.put(key, createServer(url));//创建新的服务
        	} 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));
        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;
    }

　　b.NettyServer

    protected void doOpen() throws Throwable {
        NettyHelper.setNettyLoggerFactory();
        ExecutorService boss = Executors.newCachedThreadPool(new NamedThreadFactory("NettyServerBoss", true));//boss线程池
        ExecutorService worker = Executors.newCachedThreadPool(new NamedThreadFactory("NettyServerWorker", true));//工作线程池
        ChannelFactory channelFactory = new NioServerSocketChannelFactory(boss, worker, getUrl().getPositiveParameter(Constants.IO_THREADS_KEY, Constants.DEFAULT_IO_THREADS));
        bootstrap = new ServerBootstrap(channelFactory);//服务启动类
        
        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());//增加解码器
                pipeline.addLast("encoder", adapter.getEncoder());//增加编码器
                pipeline.addLast("handler", nettyHandler);//业务处理类
                return pipeline;
            }
        });
        // bind
        channel = bootstrap.bind(getBindAddress());
    }