学习笔记---DUBBO的服务调用（服务端）

dubbo默认的是以netty为通讯框架，有了解过netty的清楚，不管是客户端还是服务端，在通讯过程中所产生的事件：连接断开，读/写，接受等事件，必定在：ChannelPipeline里面处理，而在：ChannelPipeline具体处理的就是：ChannelHandler了，据此，我们从学习笔记—DUBBO的服务暴露以及源码分析分析过，服务在暴露过程中，会建立NettyServer并且打开通道：

    @Override
    protected void doOpen() throws Throwable {
        bootstrap = new ServerBootstrap();

        bossGroup = new NioEventLoopGroup(1, new DefaultThreadFactory("NettyServerBoss", true));
        workerGroup = new NioEventLoopGroup(getUrl().getPositiveParameter(Constants.IO_THREADS_KEY, Constants.DEFAULT_IO_THREADS),
                new DefaultThreadFactory("NettyServerWorker", true));

        final NettyServerHandler nettyServerHandler = new NettyServerHandler(getUrl(), this);
        channels = nettyServerHandler.getChannels();

        bootstrap.group(bossGroup, workerGroup)
                .channel(NioServerSocketChannel.class)
                .childOption(ChannelOption.TCP_NODELAY, Boolean.TRUE)
                .childOption(ChannelOption.SO_REUSEADDR, Boolean.TRUE)
                .childOption(ChannelOption.ALLOCATOR, PooledByteBufAllocator.DEFAULT)
                .childHandler(new ChannelInitializer<NioSocketChannel>() {
                    @Override
                    protected void initChannel(NioSocketChannel ch) throws Exception {
                        NettyCodecAdapter adapter = new NettyCodecAdapter(getCodec(), getUrl(), NettyServer.this);
                        ch.pipeline()//.addLast("logging",new LoggingHandler(LogLevel.INFO))//for debug
                                .addLast("decoder", adapter.getDecoder())
                                .addLast("encoder", adapter.getEncoder())
                                .addLast("handler", nettyServerHandler);
                    }
                });
        // bind
        ChannelFuture channelFuture = bootstrap.bind(getBindAddress());
        channelFuture.syncUninterruptibly();
        channel = channelFuture.channel();

    }

由代码以及使用netty的api的分析，可以大胆的猜想：就是在：NettyServerHandler 处理：
断点可以确定这个猜想是对的，接着调用链：
NettyServer-》AbstractServer-》MultiMessageHandler-》HeartbeatHandler-》AllChannelHandler，断点：

可以看出来，这里开始利用线程池来创建新的现场来处理，这里实现了IO线程与业务线程的处理，将收到请求信息，信息类型，对应处理的nettyChannel（以便处理完成发送结果）等信息交给业务线程池来处理；
到：ChannelEventRunnable这个类了：

@Override
    public void run() {
        if (state == ChannelState.RECEIVED) {
            try {
                System.out.println(" ChannelEventRunnable.received(channel, message);"+handler.getClass().getName()+" "+message);
                handler.received(channel, message);
            } catch (Exception e) {
                logger.warn("ChannelEventRunnable handle " + state + " operation error, channel is " + channel
                        + ", message is " + message, e);
            }
        } else {
            switch (state) {
            case CONNECTED:
                try {
                    handler.connected(channel);
                } catch (Exception e) {
                    logger.warn("ChannelEventRunnable handle " + state + " operation error, channel is " + channel, e);
                }
                break;
            case DISCONNECTED:
                try {
                    handler.disconnected(channel);
                } catch (Exception e) {
                    logger.warn("ChannelEventRunnable handle " + state + " operation error, channel is " + channel, e);
                }
                break;
            case SENT:
                try {
                    handler.sent(channel, message);
                } catch (Exception e) {
                    logger.warn("ChannelEventRunnable handle " + state + " operation error, channel is " + channel
                            + ", message is " + message, e);
                }
            case CAUGHT:
                try {
                    handler.caught(channel, exception);
                } catch (Exception e) {
                    logger.warn("ChannelEventRunnable handle " + state + " operation error, channel is " + channel
                            + ", message is: " + message + ", exception is " + exception, e);
                }
                break;
            default:
                logger.warn("unknown state: " + state + ", message is " + message);
            }
        }
    }

可以看到这里处理不同的事件，我们关注读取事件，开始了 D
ecodeHandler-》HeaderExchangeHandler，断点：


接着调用了：DubboProtocol的方法来获取对应本地暴露的存根：Exporter：


这里获取：Exporter后便可以获取对应Invoker对象，接着就是责任链：filter了，

再通过责任链返回，调用： channel.send(response) 方法返回给消费端；