Java学习笔记——dubbo服务之底层通讯协议Protocol

我们先来找到通讯协议的入口点吧。通过Protocol接口查找通讯协议入口点，我们根据接口的export方法搜索发现入口了，在ServiceConfig的doExportUrlsFor1Protocol方法，如下图：

然后我们进入 protocol.export(invoker)方法发现有很多实现类，根据spi（不懂的请看之前写的容器篇）查看配置文件能找到如下

registry=com.alibaba.dubbo.registry.integration.RegistryProtocol

dubbo=com.alibaba.dubbo.rpc.protocol.dubbo.DubboProtocol   //这个是默认的，我们在Protocol接口上可以看到spi的注解

filter=com.alibaba.dubbo.rpc.protocol.ProtocolFilterWrapper

listener=com.alibaba.dubbo.rpc.protocol.ProtocolListenerWrapper

mock=com.alibaba.dubbo.rpc.support.MockProtocol

injvm=com.alibaba.dubbo.rpc.protocol.injvm.InjvmProtocol

rmi=com.alibaba.dubbo.rpc.protocol.rmi.RmiProtocol

hessian=com.alibaba.dubbo.rpc.protocol.hessian.HessianProtocol

com.alibaba.dubbo.rpc.protocol.http.HttpProtocol

com.alibaba.dubbo.rpc.protocol.webservice.WebServiceProtocol

thrift=com.alibaba.dubbo.rpc.protocol.thrift.ThriftProtocol

memcached=com.alibaba.dubbo.rpc.protocol.memcached.MemcachedProtocol

redis=com.alibaba.dubbo.rpc.protocol.redis.RedisProtocol

rest=com.alibaba.dubbo.rpc.protocol.rest.RestProtocol

进入DubboProtocol.export(Invoker<T> invoker)方法里面有个 openServer(url);

代码：

  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)); //createServer是创建服务

        } else {

        //server支持reset,配合override功能使用

        server.reset(url);

        }

        }

    }

继续进入createServer，上源码

    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;

    }

    dubbo从要暴漏的服务的URL中取得相关的配置（host，port等）进行服务端server的创建，同上面的server = Exchangers.bind(url, requestHandler) 正式创建服务。

    所以基本的创建步骤是

   export()  -->  openServer()  -->  createServer()  -->  server = Exchangers.bind(url, requestHandler);  

  我们进行来看 Exchangers.bind(url, requestHandler)

  源码：

public static ExchangeServer bind(URL url, ExchangeHandler handler) throws RemotingException {

      if (url == null) {

          throw new IllegalArgumentException("url == null");

      }

      if (handler == null) {

          throw new IllegalArgumentException("handler == null");

      }

      url = url.addParameterIfAbsent(Constants.CODEC_KEY, "exchange");

      return getExchanger(url).bind(url, handler);

  }

  然后通过getExchanger(url).bind(url, handler）的bing进入 HeaderExchanger类

  public ExchangeServer bind(URL url, ExchangeHandler handler) throws RemotingException {

        return new HeaderExchangeServer(Transporters.bind(url, new DecodeHandler(new HeaderExchangeHandler(handler))));

    }

    在进入Transporters类的bing的

  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);

     }

通过bing可以知道他讲调用:GrizzlyTransporter,MinaTransporter,NettyTransporter 通过spi默认是调用NettyTransporter

     到这里我们基本明白dubbo的通讯默认是交给了netty来处理，

     我们在看下doOPen方法

@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();

            // 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());//解码

                    pipeline.addLast("encoder", adapter.getEncoder());//编码

                    pipeline.addLast("handler", nettyHandler);

                    return pipeline;

                }

            });

            // bind

            channel = bootstrap.bind(getBindAddress());

        }

 了解netty的同学，肯定早已习惯这个方法的写法，就是创建了netty的server嘛，到这里dubbo的服务创建完毕了,这个时候控制台见打印：

 [DUBBO] Start NettyServer bind /0.0.0.0:20880, export /192.168.4.241:20880, dubbo version: 2.8.4, current host: 127.0.0.1