完整流程图

Dubbo基础篇 服务调用完整流程.png

一句话总结流程

总结为一句话就是：客户端在发起远程调用时，具体的代理类会被InvokerInvacationHandler拦截，在这里面根据一些条件和负载均衡策略，选择出其中一个符合条件的Invoker，进行远程调用。提供者收到请求后，会从ExpoterMap中选择对应的Invoker（Wrapper包装），最终调用到具体的实现类。处理完请求后将结果返回。返回后客户端根据之前传过去的请求ID，找到之前的请求，然后再进行自己的业务处理

Consumer远程调用

• 调用对应的代理类
• 被InvokerInvocationHandler拦截
• ClusterInvoker经过路由过滤，负载均衡，选择其中一个Invoker，发起远程调用（带请求ID）

public class JavassistProxyFactory extends AbstractProxyFactory {

  @Override
  @SuppressWarnings("unchecked")
  public <T> T getProxy(Invoker<T> invoker, Class<?>[] interfaces) {
            // InvokerInvocationHandler （重点关注）
            // 远程调用时，调用的方法会被 InvokerInvocationHandler 拦截
      return (T) Proxy.getProxy(interfaces).newInstance(new InvokerInvocationHandler(invoker));
  }

  // ...
}

InvokerInvocationHandler处理

• 构建RpcInvocation
• 调用对应Invoker的invoke方法

@Override
public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
    if (method.getDeclaringClass() == Object.class) {
        return method.invoke(invoker, args);
    }
    // 获取调用的远程方法名
    String methodName = method.getName();
    // 获取参数
    Class<?>[] parameterTypes = method.getParameterTypes();
    if (parameterTypes.length == 0) {
        if ("toString".equals(methodName)) {
            return invoker.toString();
        } else if ("$destroy".equals(methodName)) {
            invoker.destroy();
            return null;
        } else if ("hashCode".equals(methodName)) {
            return invoker.hashCode();
        }
    } else if (parameterTypes.length == 1 && "equals".equals(methodName)) {
        return invoker.equals(args[0]);
    }
    // 构建一个dubbo rpc invocation
    RpcInvocation rpcInvocation = new RpcInvocation(method, invoker.getInterface().getName(), protocolServiceKey, args);
    String serviceKey = invoker.getUrl().getServiceKey();
    rpcInvocation.setTargetServiceUniqueName(serviceKey);

    // invoker.getUrl() returns consumer url.
    RpcContext.setRpcContext(invoker.getUrl());

    if (consumerModel != null) {
        rpcInvocation.put(Constants.CONSUMER_MODEL, consumerModel);
        rpcInvocation.put(Constants.METHOD_MODEL, consumerModel.getMethodModel(method));
    }

    // 远程调用
    return invoker.invoke(rpcInvocation).recreate();
}

Invoker#invoker方法

• 路由过滤
• 负载均衡

最终挑选出某一个invoker

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

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

    // 实际上就是directroy.list 通过方法名寻找invokers 里面回去做一些过滤 获取过滤后的invoke列表
    List<Invoker<T>> invokers = list(invocation);
    // 根据@SPI选择负载均衡的策略
    LoadBalance loadbalance = initLoadBalance(invokers, invocation);
    RpcUtils.attachInvocationIdIfAsync(getUrl(), invocation);
    return doInvoke(invocation, invokers, loadbalance); // 调用子类的方法
}

@Override
@SuppressWarnings({"unchecked", "rawtypes"})
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, RETRIES_KEY, 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);
        }
        // 根据负载均衡规则找出一个invoker
        Invoker<T> invoker = select(loadbalance, invocation, copyInvokers, invoked);
        invoked.add(invoker);
        RpcContext.getContext().setInvokers((List) invoked);
        try {
            // 远程调用(每次请求都有一个唯一的ID)
            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);
}

Provider处理请求

• 服务端的NettyServer处理请求，最终会调用到DubboProtcol#reply
• 根据客户端的请求，从ExportedMap中选择对应的Invoker （ExportedMap key:serviceKey()）
• 调用Invoker具体业务类的方法
  链式调用，入口 ProtocolFilterWrapper 会处理调用信息GenericFilter，上下文ContextFilter等
  
  Dubbo基础篇 远程调用NettyService处理流程.png
  
  调用到AbstractProxyInvoker ，当前类调用通过Javaassist封装成Wrapper类最终调用到具体的实现类
• 返回处理结果

NettyServer的Handler处理请求

@Override
public void channelConnected(ChannelHandlerContext ctx, ChannelStateEvent e) throws Exception {
    NettyChannel channel = NettyChannel.getOrAddChannel(ctx.getChannel(), url, handler);
    try {
        if (channel != null) {
            channels.put(NetUtils.toAddressString((InetSocketAddress) ctx.getChannel().getRemoteAddress()), channel);
        }
        handler.connected(channel);
    } finally {
        NettyChannel.removeChannelIfDisconnected(ctx.getChannel());
    }

    if (logger.isInfoEnabled()) {
        logger.info("The connection between " + channel.getRemoteAddress() + " and " + channel.getLocalAddress() + " is established");
    }
}

@Override
public void connected(Channel channel) throws RemotingException {
  ExecutorService executor = getExecutorService();
  try {
        // 封装成ChannelEventRunnable，丢到线程中处理
    executor.execute(new ChannelEventRunnable(channel, handler, ChannelState.CONNECTED));
  } catch (Throwable t) {
    throw new ExecutionException("connect event", channel, getClass() + " error when process connected event .", t);
  }
}

void handleRequest(final ExchangeChannel channel, Request req) throws RemotingException {
    // 通过请求id，构建一个Response
    Response res = new Response(req.getId(), req.getVersion());
    if (req.isBroken()) {
        // 获取请求信息 方法名之类的
        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);

        channel.send(res);
        return;
    }
    // find handler by message class.
    Object msg = req.getData();
    try {
        // 最终调用 DubboProtocol reply
        CompletionStage<Object> future = handler.reply(channel, msg);
        future.whenComplete((appResult, t) -> {
            try {
                if (t == null) {
                    res.setStatus(Response.OK);
                    res.setResult(appResult);
                } else {
                    res.setStatus(Response.SERVICE_ERROR);
                    res.setErrorMessage(StringUtils.toString(t));
                }
                channel.send(res);
            } catch (RemotingException e) {
                logger.warn("Send result to consumer failed, channel is " + channel + ", msg is " + e);
            }
        });
    } catch (Throwable e) {
        res.setStatus(Response.SERVICE_ERROR);
        res.setErrorMessage(StringUtils.toString(e));
        channel.send(res);
    }
}

最终调用到 DubboProtocol

private ExchangeHandler requestHandler = new ExchangeHandlerAdapter() {

@Override
public CompletableFuture<Object> reply(ExchangeChannel channel, Object message) throws RemotingException {

    if (!(message instanceof Invocation)) {
        throw new RemotingException(channel, "Unsupported request: "
                + (message == null ? null : (message.getClass().getName() + ": " + message))
                + ", channel: consumer: " + channel.getRemoteAddress() + " --> provider: " + channel.getLocalAddress());
    }

    Invocation inv = (Invocation) message;
    // 根据inv获取Invoker   去exporterMap中找
    Invoker<?> invoker = getInvoker(channel, inv);
    // need to consider backward-compatibility if it's a callback
    if (Boolean.TRUE.toString().equals(inv.getObjectAttachments().get(IS_CALLBACK_SERVICE_INVOKE))) {
        String methodsStr = invoker.getUrl().getParameters().get("methods");
        boolean hasMethod = false;
        if (methodsStr == null || !methodsStr.contains(",")) {
            hasMethod = inv.getMethodName().equals(methodsStr);
        } else {
            String[] methods = methodsStr.split(",");
            for (String method : methods) {
                if (inv.getMethodName().equals(method)) {
                    hasMethod = true;
                    break;
                }
            }
        }
        if (!hasMethod) {
            logger.warn(new IllegalStateException("The methodName " + inv.getMethodName()
                    + " not found in callback service interface ,invoke will be ignored."
                    + " please update the api interface. url is:"
                    + invoker.getUrl()) + " ,invocation is :" + inv);
            return null;
        }
    }
    RpcContext.getContext().setRemoteAddress(channel.getRemoteAddress());
    // 调用对应的invoke方法（最终wrapper.invokeMethod，参考服务暴露文档）
    Result result = invoker.invoke(inv);
    return result.thenApply(Function.identity());
}

链式调用点 ProtocolFilterWrapper

@Override
public Result invoke(Invocation invocation) throws RpcException {
    Result asyncResult;
    try {
        asyncResult = filter.invoke(next, invocation);
    } catch (Exception e) {
        if (filter instanceof ListenableFilter) {
            ListenableFilter listenableFilter = ((ListenableFilter) filter);
            try {
                Filter.Listener listener = listenableFilter.listener(invocation);
                if (listener != null) {
                    listener.onError(e, invoker, invocation);
                }
            } finally {
                listenableFilter.removeListener(invocation);
            }
        } else if (filter instanceof Filter.Listener) {
            Filter.Listener listener = (Filter.Listener) filter;
            listener.onError(e, invoker, invocation);
        }
        throw e;
    } finally {

    }
    return asyncResult.whenCompleteWithContext((r, t) -> {
        if (filter instanceof ListenableFilter) {
            ListenableFilter listenableFilter = ((ListenableFilter) filter);
            Filter.Listener listener = listenableFilter.listener(invocation);
            try {
                if (listener != null) {
                    if (t == null) {
                        listener.onResponse(r, invoker, invocation);
                    } else {
                        listener.onError(t, invoker, invocation);
                    }
                }
            } finally {
                listenableFilter.removeListener(invocation);
            }
        } else if (filter instanceof Filter.Listener) {
            Filter.Listener listener = (Filter.Listener) filter;
            if (t == null) {
                listener.onResponse(r, invoker, invocation);
            } else {
                listener.onError(t, invoker, invocation);
            }
        }
    });
}

最终调用到Wrapper#AbstractProxyInvoker

@Override
public Result invoke(Invocation invocation) throws RpcException {
    try {
        Object value = doInvoke(proxy, invocation.getMethodName(), invocation.getParameterTypes(), invocation.getArguments());
    CompletableFuture<Object> future = wrapWithFuture(value);
        CompletableFuture<AppResponse> appResponseFuture = future.handle((obj, t) -> {
            AppResponse result = new AppResponse();
            if (t != null) {
                if (t instanceof CompletionException) {
                    result.setException(t.getCause());
                } else {
                    result.setException(t);
                }
            } else {
                result.setValue(obj);
            }
            return result;
        });
        return new AsyncRpcResult(appResponseFuture, invocation);
    } catch (InvocationTargetException e) {
        if (RpcContext.getContext().isAsyncStarted() && !RpcContext.getContext().stopAsync()) {
            logger.error("Provider async started, but got an exception from the original method, cannot write the exception back to consumer because an async result may have returned the new thread.", e);
        }
        return AsyncRpcResult.newDefaultAsyncResult(null, e.getTargetException(), invocation);
    } catch (Throwable e) {
        throw new RpcException("Failed to invoke remote proxy method " + invocation.getMethodName() + " to " + getUrl() + ", cause: " + e.getMessage(), e);
    }
}

protected abstract Object doInvoke(T proxy, String methodName, Class<?>[] parameterTypes, Object[] arguments) throws Throwable;

Javassist动态代理

@Override
public <T> Invoker<T> getInvoker(T proxy, Class<T> type, URL url) {
    // TODO Wrapper cannot handle this scenario correctly: the classname contains '$'
    // 通过Javaassist封装成Wrapper类（Dubbo服务启动时生成，所以在运行时不会产生开销），减少反射的调用
    final Wrapper wrapper = Wrapper.getWrapper(proxy.getClass().getName().indexOf('$') < 0 ? proxy.getClass() : type);
    return new AbstractProxyInvoker<T>(proxy, type, url) {
        @Override
        // Wrapper最终调用最终调用服务提供者的接口实现类的方法
        protected Object doInvoke(T proxy, String methodName,
                                  Class<?>[] parameterTypes,
                                  Object[] arguments) throws Throwable {
            return wrapper.invokeMethod(proxy, methodName, parameterTypes, arguments);
        }
    };
}