dubbo源码分析-服务调用流程-笔记

消费端调用过程流程图

消费端的调用过程

消费端接口实例：

服务端接收消息处理过程

NettyHandler. messageReceived

• 接收消息的时候，通过NettyHandler.messageReceived作为入口

@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());
    }
}

handler.received

• 这个handler是什么呢？还记得在服务发布的时候，组装了一系列的handler吗？代码如下

HeaderExchanger.bind

public ExchangeServer bind(URL url, ExchangeHandler handler) throws RemotingException {
    return new HeaderExchangeServer(Transporters.bind(url, new DecodeHandler(new HeaderExchangeHandler(handler))));
}

NettyServer

• 接着又在Nettyserver中，wrap了多个handler

public NettyServer(URL url, ChannelHandler handler) throws RemotingException {
    super(url, ChannelHandlers.wrap(handler, ExecutorUtil.setThreadName(url, SERVER_THREAD_POOL_NAME)));
}
protected ChannelHandler wrapInternal(ChannelHandler handler, URL url) {
    return new MultiMessageHandler(new HeartbeatHandler(ExtensionLoader.getExtensionLoader(Dispatcher.class)
            .getAdaptiveExtension().dispatch(handler, url)));
}

所以服务端的handler处理链为

• MultiMessageHandler(HeartbeatHandler(AllChannelHandler(DecodeHandler)))
• MultiMessageHandler: 复合消息处理
• HeartbeatHandler：心跳消息处理，接收心跳并发送心跳响应
• AllChannelHandler：业务线程转化处理器，把接收到的消息封装成ChannelEventRunnable可执行任务给线程池处理
• DecodeHandler:业务解码处理器

HeaderExchangeHandler.received

• 交互层请求响应处理，有三种处理方式：
  1. handlerRequest，双向请求
  2. handler.received 单向请求
  3. handleResponse 响应消息

public void received(Channel channel, Object message) throws RemotingException {
    channel.setAttribute(KEY_READ_TIMESTAMP, System.currentTimeMillis());
    ExchangeChannel exchangeChannel = HeaderExchangeChannel.getOrAddChannel(channel);
    try {
        if (message instanceof Request) {
            // handle request.
            Request request = (Request) message;
            if (request.isEvent()) {
                handlerEvent(channel, request);
            } else {
                if (request.isTwoWay()) {
                    Response response = handleRequest(exchangeChannel, request);
                    channel.send(response);
                } else {
                    handler.received(exchangeChannel, request.getData());
                }
            }
        } else if (message instanceof Response) {
            handleResponse(channel, (Response) message);
        } else if (message instanceof String) {
            if (isClientSide(channel)) {
                Exception e = new Exception("Dubbo client can not supported string message: " + message + " in channel: " + channel + ", url: " + channel.getUrl());
                logger.error(e.getMessage(), e);
            } else {
                String echo = handler.telnet(channel, (String) message);
                if (echo != null && echo.length() > 0) {
                    channel.send(echo);
                }
            }
        } else {
            handler.received(exchangeChannel, message);
        }
    } finally {
        HeaderExchangeChannel.removeChannelIfDisconnected(channel);
    }
}

handleRequest

• 处理请求并返回response

Response handleRequest(ExchangeChannel channel, Request req) throws RemotingException {
    Response res = new Response(req.getId(), req.getVersion());
    if (req.isBroken()) {
        Object data = req.getData();
        String msg;
        if (data == null) msg = null;
        else if (data instanceof Throwable) msg = StringUtils.toString((Throwable) data);
        else msg = data.toString();
        res.setErrorMessage("Fail to decode request due to: " + msg);
        res.setStatus(Response.BAD_REQUEST);

        return res;
    }
    // find handler by message class.
    Object msg = req.getData();
    try {
        // handle data.
        Object result = handler.reply(channel, msg);
        res.setStatus(Response.OK);
        res.setResult(result);
    } catch (Throwable e) {
        res.setStatus(Response.SERVICE_ERROR);
        res.setErrorMessage(StringUtils.toString(e));
    }
    return res;
}

ExchangeHandlerAdaptive.replay(DubboProtocol)

• 调用DubboProtocol中定义的ExchangeHandlerAdaptive.replay方法处理消息

private ExchangeHandler requestHandler = new ExchangeHandlerAdapter() {
    
    public Object reply(ExchangeChannel channel, Object message) throws RemotingException {
     invoker.invoke(inv);
}

• 那接下来invoker.invoke会调用哪个类中的方法呢？
• 还记得在RegistryDirectory中发布本地方法的时候，对invoker做的包装吗？
• 通过InvokerDelegete对原本的invoker做了一层包装，而原本的invoker是什么呢？
• 是一个JavassistProxyFactory生成的动态代理吧。
• 所以此处的invoker应该是：

Filter(Listener(InvokerDelegete(AbstractProxyInvoker (Wrapper.invokeMethod)))

• RegistryDirectory生成invoker的代码如下:

private <T> ExporterChangeableWrapper<T>  doLocalExport(final Invoker<T> originInvoker){
    String key = getCacheKey(originInvoker);
    ExporterChangeableWrapper<T> exporter = (ExporterChangeableWrapper<T>) bounds.get(key);
    if (exporter == null) {
        synchronized (bounds) {
            exporter = (ExporterChangeableWrapper<T>) bounds.get(key);
            if (exporter == null) {
                final Invoker<?> invokerDelegete = new InvokerDelegete<T>(originInvoker, getProviderUrl(originInvoker));
                exporter = new ExporterChangeableWrapper<T>((Exporter<T>)protocol.export(invokerDelegete), originInvoker);
                bounds.put(key, exporter);
            }
        }
    }
    return (ExporterChangeableWrapper<T>) exporter;
}