消费端操作InvokerInvocationHandler代理发送请求，组装调用类

public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
    String methodName = method.getName();
    Class<?>[] parameterTypes = method.getParameterTypes();
    if (method.getDeclaringClass() == Object.class) {
        return method.invoke(invoker, args);
    }
    if ("toString".equals(methodName) && parameterTypes.length == 0) {
        return invoker.toString();
    }
    if ("hashCode".equals(methodName) && parameterTypes.length == 0) {
        return invoker.hashCode();
    }
    if ("equals".equals(methodName) && parameterTypes.length == 1) {
        return invoker.equals(args[0]);
    }

    return invoker.invoke(createInvocation(method, args)).recreate();
}

private RpcInvocation createInvocation(Method method, Object[] args) {
    RpcInvocation invocation = new RpcInvocation(method, args);
    if (RpcUtils.hasFutureReturnType(method)) {
        invocation.setAttachment(Constants.FUTURE_RETURNTYPE_KEY, "true");
        invocation.setAttachment(Constants.ASYNC_KEY, "true");
    }
    return invocation;
}

判断是否是mock调用

public Result invoke(Invocation invocation) throws RpcException {
    Result result = null;

    String value = directory.getUrl().getMethodParameter(invocation.getMethodName(), Constants.MOCK_KEY, Boolean.FALSE.toString()).trim();
    if (value.length() == 0 || value.equalsIgnoreCase("false")) {
        //no mock
        result = this.invoker.invoke(invocation);
    } else if (value.startsWith("force")) {
        if (logger.isWarnEnabled()) {
            logger.warn("force-mock: " + invocation.getMethodName() + " force-mock enabled , url : " + directory.getUrl());
        }
        //force:direct mock
        result = doMockInvoke(invocation, null);
    } else {
        //fail-mock
        try {
            result = this.invoker.invoke(invocation);
        } catch (RpcException e) {
            if (e.isBiz()) {
                throw e;
            }

            if (logger.isWarnEnabled()) {
                logger.warn("fail-mock: " + invocation.getMethodName() + " fail-mock enabled , url : " + directory.getUrl(), e);
            }
            result = doMockInvoke(invocation, e);
        }
    }
    return result;
}

检查集群invoker状态

public Result invoke(final Invocation invocation) throws RpcException {
    checkWhetherDestroyed();

    // binding attachments into invocation.
    Map<String, String> contextAttachments = RpcContext.getContext().getAttachments();
    if (contextAttachments != null && contextAttachments.size() != 0) {
        ((RpcInvocation) invocation).addAttachments(contextAttachments);
    }

    List<Invoker<T>> invokers = list(invocation);
    LoadBalance loadbalance = initLoadBalance(invokers, invocation);
    RpcUtils.attachInvocationIdIfAsync(getUrl(), invocation);
    return doInvoke(invocation, invokers, loadbalance);
}

从注册明细类中获取所有的invoker远程调用，经过路由链路挑选符合的invoker

protected List<Invoker<T>> list(Invocation invocation) throws RpcException {
    return directory.list(invocation);
}

 // Get invokers from cache, only runtime routers will be executed.
invokers = routerChain.route(getConsumerUrl(), invocation);

默认获取随机负载均衡

protected LoadBalance initLoadBalance(List<Invoker<T>> invokers, Invocation invocation) {
    if (CollectionUtils.isNotEmpty(invokers)) {
        return ExtensionLoader.getExtensionLoader(LoadBalance.class).getExtension(invokers.get(0).getUrl()
                .getMethodParameter(RpcUtils.getMethodName(invocation), Constants.LOADBALANCE_KEY, Constants.DEFAULT_LOADBALANCE));
    } else {
        return ExtensionLoader.getExtensionLoader(LoadBalance.class).getExtension(Constants.DEFAULT_LOADBALANCE);
    }
}

默认使用失败转移集群调用FailoverClusterInvoker，最多调用三次，从invoker集合中选择本次需要使用的invoker，尽量不使用上次调用失败的invoker。

public Result doInvoke(Invocation invocation, final List<Invoker<T>> invokers, LoadBalance loadbalance) throws RpcException {
    List<Invoker<T>> copyInvokers = invokers;
    checkInvokers(copyInvokers, invocation);
    String methodName = RpcUtils.getMethodName(invocation);
    int len = getUrl().getMethodParameter(methodName, Constants.RETRIES_KEY, Constants.DEFAULT_RETRIES) + 1;
    if (len <= 0) {
        len = 1;
    }
    // retry loop.
    RpcException le = null; // last exception.
    List<Invoker<T>> invoked = new ArrayList<Invoker<T>>(copyInvokers.size()); // invoked invokers.
    Set<String> providers = new HashSet<String>(len);
    for (int i = 0; i < len; i++) {
        //Reselect before retry to avoid a change of candidate `invokers`.
        //NOTE: if `invokers` changed, then `invoked` also lose accuracy.
        if (i > 0) {
            checkWhetherDestroyed();
            copyInvokers = list(invocation);
            // check again
            checkInvokers(copyInvokers, invocation);
        }
        Invoker<T> invoker = select(loadbalance, invocation, copyInvokers, invoked);
        invoked.add(invoker);
        RpcContext.getContext().setInvokers((List) invoked);
        try {
            Result result = invoker.invoke(invocation);
            if (le != null && logger.isWarnEnabled()) {
                logger.warn("Although retry the method " + methodName
                        + " in the service " + getInterface().getName()
                        + " was successful by the provider " + invoker.getUrl().getAddress()
                        + ", but there have been failed providers " + providers
                        + " (" + providers.size() + "/" + copyInvokers.size()
                        + ") from the registry " + directory.getUrl().getAddress()
                        + " on the consumer " + NetUtils.getLocalHost()
                        + " using the dubbo version " + Version.getVersion() + ". Last error is: "
                        + le.getMessage(), le);
            }
            return result;
        } catch (RpcException e) {
            if (e.isBiz()) { // biz exception.
                throw e;
            }
            le = e;
        } catch (Throwable e) {
            le = new RpcException(e.getMessage(), e);
        } finally {
            providers.add(invoker.getUrl().getAddress());
        }
    }
    throw new RpcException(le.getCode(), "Failed to invoke the method "
            + methodName + " in the service " + getInterface().getName()
            + ". Tried " + len + " times of the providers " + providers
            + " (" + providers.size() + "/" + copyInvokers.size()
            + ") from the registry " + directory.getUrl().getAddress()
            + " on the consumer " + NetUtils.getLocalHost() + " using the dubbo version "
            + Version.getVersion() + ". Last error is: "
            + le.getMessage(), le.getCause() != null ? le.getCause() : le);
}

开始invoker代理包装类调用

class InvokerDelegate<T> extends InvokerWrapper<T>
public Result invoke(Invocation invocation) throws RpcException {
    return invoker.invoke(invocation);
}

监听器包装类

class ListenerInvokerWrapper<T>
public Result invoke(Invocation invocation) throws RpcException {
    return invoker.invoke(invocation);
}

过滤器ConsumerContextFilter，FutureFilter，MonitorFilter

class ProtocolFilterWrapper$1
public Result invoke(Invocation invocation) throws RpcException {
  Result result = filter.invoke(next, invocation);
  if (result instanceof AsyncRpcResult) {
      AsyncRpcResult asyncResult = (AsyncRpcResult) result;
      asyncResult.thenApplyWithContext(r -> filter.onResponse(r, invoker, invocation));
      return asyncResult;
  } else {
      return filter.onResponse(result, invoker, invocation);
  }
}

开始准备远程调用，选择一个客户端，判断同异步以及单双向方式，超时时间

class DubboInvoker<T> extends AbstractInvoker<T>
protected Result doInvoke(final Invocation invocation) throws Throwable {
    RpcInvocation inv = (RpcInvocation) invocation;
    final String methodName = RpcUtils.getMethodName(invocation);
    inv.setAttachment(Constants.PATH_KEY, getUrl().getPath());
    inv.setAttachment(Constants.VERSION_KEY, version);

    ExchangeClient currentClient;
    if (clients.length == 1) {
        currentClient = clients[0];
    } else {
        currentClient = clients[index.getAndIncrement() % clients.length];
    }
    try {
        boolean isAsync = RpcUtils.isAsync(getUrl(), invocation);
        boolean isAsyncFuture = RpcUtils.isReturnTypeFuture(inv);
        boolean isOneway = RpcUtils.isOneway(getUrl(), invocation);
        int timeout = getUrl().getMethodParameter(methodName, Constants.TIMEOUT_KEY, Constants.DEFAULT_TIMEOUT);
        if (isOneway) {
            boolean isSent = getUrl().getMethodParameter(methodName, Constants.SENT_KEY, false);
            currentClient.send(inv, isSent);
            RpcContext.getContext().setFuture(null);
            return new RpcResult();
        } else if (isAsync) {
            ResponseFuture future = currentClient.request(inv, timeout);
            // For compatibility
            FutureAdapter<Object> futureAdapter = new FutureAdapter<>(future);
            RpcContext.getContext().setFuture(futureAdapter);

            Result result;
            if (isAsyncFuture) {
                // register resultCallback, sometimes we need the async result being processed by the filter chain.
                result = new AsyncRpcResult(futureAdapter, futureAdapter.getResultFuture(), false);
            } else {
                result = new SimpleAsyncRpcResult(futureAdapter, futureAdapter.getResultFuture(), false);
            }
            return result;
        } else {
            RpcContext.getContext().setFuture(null);
            return (Result) currentClient.request(inv, timeout).get();
        }
    } catch (TimeoutException e) {
        throw new RpcException(RpcException.TIMEOUT_EXCEPTION, "Invoke remote method timeout. method: " + invocation.getMethodName() + ", provider: " + getUrl() + ", cause: " + e.getMessage(), e);
    } catch (RemotingException e) {
        throw new RpcException(RpcException.NETWORK_EXCEPTION, "Failed to invoke remote method: " + invocation.getMethodName() + ", provider: " + getUrl() + ", cause: " + e.getMessage(), e);
    }
}

同步进行请求

class ReferenceCountExchangeClient implements ExchangeClient
public ResponseFuture request(Object request, int timeout) throws RemotingException {
    return client.request(request, timeout);
}

class HeaderExchangeClient implements ExchangeClient
public ResponseFuture request(Object request, int timeout) throws RemotingException {
    return channel.request(request, timeout);
}

把请求数据包装为请求Request

class HeaderExchangeChannel implements ExchangeChannel
public ResponseFuture request(Object request, int timeout) throws RemotingException {
    if (closed) {
        throw new RemotingException(this.getLocalAddress(), null, "Failed to send request " + request + ", cause: The channel " + this + " is closed!");
    }
    // create request.
    Request req = new Request();
    req.setVersion(Version.getProtocolVersion());
    req.setTwoWay(true);
    req.setData(request);
    DefaultFuture future = DefaultFuture.newFuture(channel, req, timeout);
    try {
        channel.send(req);
    } catch (RemotingException e) {
        future.cancel();
        throw e;
    }
    return future;
}

通过netty开始进行发送请求

class AbstractPeer implements Endpoint, ChannelHandler
public void send(Object message) throws RemotingException {
    send(message, url.getParameter(Constants.SENT_KEY, false));
}

class AbstractChannel extends AbstractPeer implements Channel
public void send(Object message, boolean sent) throws RemotingException {
    if (isClosed()) {
        throw new RemotingException(this, "Failed to send message "
                + (message == null ? "" : message.getClass().getName()) + ":" + message
                + ", cause: Channel closed. channel: " + getLocalAddress() + " -> " + getRemoteAddress());
    }
}

把请求写入通道，后续会进行编码发送

class NettyChannel extends AbstractChannel
public void send(Object message, boolean sent) throws RemotingException {
    super.send(message, sent);

    boolean success = true;
    int timeout = 0;
    try {
        ChannelFuture future = channel.writeAndFlush(message);
        if (sent) {
            timeout = getUrl().getPositiveParameter(Constants.TIMEOUT_KEY, Constants.DEFAULT_TIMEOUT);
            success = future.await(timeout);
        }
        Throwable cause = future.cause();
        if (cause != null) {
            throw cause;
        }
    } catch (Throwable e) {
        throw new RemotingException(this, "Failed to send message " + message + " to " + getRemoteAddress() + ", cause: " + e.getMessage(), e);
    }

    if (!success) {
        throw new RemotingException(this, "Failed to send message " + message + " to " + getRemoteAddress()
                + "in timeout(" + timeout + "ms) limit");
    }
}

对写事件进行处理，我们添加监听器以确保我们的写事件是正确的。如果我们的写事件有错误（在大多数情况下编码器失败），我们需要直接返回请求，而不是阻塞调用进程，依次经过各个处理器对发送事件做处理。

class NettyClientHandler extends ChannelDuplexHandler
public void write(ChannelHandlerContext ctx, Object msg, ChannelPromise promise) throws Exception {
    super.write(ctx, msg, promise);
    final NettyChannel channel = NettyChannel.getOrAddChannel(ctx.channel(), url, handler);
    final boolean isRequest = msg instanceof Request;

    // We add listeners to make sure our out bound event is correct.
    // If our out bound event has an error (in most cases the encoder fails),
    // we need to have the request return directly instead of blocking the invoke process.
    promise.addListener(future -> {
        try {
            if (future.isSuccess()) {
                // if our future is success, mark the future to sent.
                handler.sent(channel, msg);
                return;
            }

            Throwable t = future.cause();
            if (t != null && isRequest) {
                Request request = (Request) msg;
                Response response = buildErrorResponse(request, t);
                handler.received(channel, response);
            }
        } finally {
            NettyChannel.removeChannelIfDisconnected(ctx.channel());
        }
    });
}