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dubbo引用

dubbo引用

作者: 无聊之园 | 来源:发表于2021-11-21 10:39 被阅读0次

    dubbo引用

            registerBeanDefinitionParser("reference", new DubboBeanDefinitionParser(ReferenceBean.class, false));
    
    

    和导出一样,引用标签,最后会解析成ReferenceBean。

    看实现接口

    FactoryBean:所以是工厂方法,最终注入spring的对象是调用FactoryBean的getObject方法获得的对象。

    ApplicationContextAware:注入ApplicationContext对象。

    InitializingBean:初始化了spring之后调用afterPropertiesSet方法。

    DisposableBean:spring容器销毁会调用destory方法。这里什么没做。

    public class ReferenceBean<T> extends ReferenceConfig<T> implements FactoryBean, ApplicationContextAware, InitializingBean, DisposableBean {
    
    
    @Override
        @SuppressWarnings({"unchecked"})
        public void afterPropertiesSet() throws Exception {
            if (applicationContext != null) {
                // 从applicationContext中获取ConfigCenterBean类型的实例列表。这里什么也没做
                BeanFactoryUtils.beansOfTypeIncludingAncestors(applicationContext, ConfigCenterBean.class, false, false);
            }
    
          ...省略代码。从spring容器获取各种配置类set保存到成员方法中
          // 是否初始化。dubbo:reference可以配置init属性。
            if (shouldInit()) {
                // 真正获取对象
                getObject();
            }
        }
        
         @Override
        public Object getObject() {
            return get();
        }
    
    public synchronized T get() {
            //  检查和更新一下配置属性,导出服务也有这个方法,不看
            checkAndUpdateSubConfigs();
    
            if (destroyed) {
                throw new IllegalStateException("The invoker of ReferenceConfig(" + url + ") has already destroyed!");
            }
            if (ref == null) {
                init();
            }
            return ref;
        }
    
     private void init() {
            ...省略代码。各种拼装配置参数到map
            ref = createProxy(map);
    
            String serviceKey = URL.buildKey(interfaceName, group, version);
            ApplicationModel.initConsumerModel(serviceKey, buildConsumerModel(serviceKey, attributes));
            initialized = true;
        }
    
     private T createProxy(Map<String, String> map) {
            // 是否jvm内部就可以引用。根据url判定。false
            if (shouldJvmRefer(map)) {
                URL url = new URL(LOCAL_PROTOCOL, LOCALHOST_VALUE, 0, interfaceClass.getName()).addParameters(map);
                invoker = REF_PROTOCOL.refer(interfaceClass, url);
                if (logger.isInfoEnabled()) {
                    logger.info("Using injvm service " + interfaceClass.getName());
                }
            } else {
                urls.clear(); // reference retry init will add url to urls, lead to OOM
               // url不为空,则说明是dubbo:reference直接指定了url调用
                if (url != null && url.length() > 0) { // user specified URL, could be peer-to-peer address, or register center's address.
                    String[] us = SEMICOLON_SPLIT_PATTERN.split(url);
                    if (us != null && us.length > 0) {
                        for (String u : us) {
                            URL url = URL.valueOf(u);
                            if (StringUtils.isEmpty(url.getPath())) {
                                url = url.setPath(interfaceName);
                            }
                            // 是否是注册中心
                            if (REGISTRY_PROTOCOL.equals(url.getProtocol())) {
                                urls.add(url.addParameterAndEncoded(REFER_KEY, StringUtils.toQueryString(map)));
                            } else {
                                urls.add(ClusterUtils.mergeUrl(url, map));
                            }
                        }
                    }
                } else { // assemble URL from register center's configuration
                    // if protocols not injvm checkRegistry
                    // 不是本地协议引用,通过注册中心获取url,常用方式
                    if (!LOCAL_PROTOCOL.equalsIgnoreCase(getProtocol())){
                        checkRegistry();
                        // 加载注册中心url
                        List<URL> us = loadRegistries(false);
                        // 只有一个注册中心。us = registry://127.0.0.1:2181/org.apache.dubbo.registry.RegistryService?...
                        if (CollectionUtils.isNotEmpty(us)) {
                            for (URL u : us) {
                                URL monitorUrl = loadMonitor(u);
                                if (monitorUrl != null) {
                                    map.put(MONITOR_KEY, URL.encode(monitorUrl.toFullString()));
                                }
                                urls.add(u.addParameterAndEncoded(REFER_KEY, StringUtils.toQueryString(map)));
                            }
                        }
                        if (urls.isEmpty()) {
                            throw new IllegalStateException("No such any registry to reference " + interfaceName + " on the consumer " + NetUtils.getLocalHost() + " use dubbo version " + Version.getVersion() + ", please config <dubbo:registry address=\"...\" /> to your spring config.");
                        }
                    }
                }
                // urls添加的注册中心url:registry://。。。这里只有一个。
                if (urls.size() == 1) {
                    // REF_PROTOCOL自然是protocol扩展适配器类,因为url是registry协议,所以自然调用的是RegistryProtocol的refer方法
                    invoker = REF_PROTOCOL.refer(interfaceClass, urls.get(0));
                } else {
                    // 如果urls是多个注册中心,则便利各个url生成多个invoker,然后用cluster把多个invoker合并成一个invoker
                    。。。暂时不看
                  }
            // create service proxy
            return (T) PROXY_FACTORY.getProxy(invoker);
        }
    
    public <T> Invoker<T> refer(Class<T> type, URL url) throws RpcException {
            // 组成成zookeeper://..
            url = URLBuilder.from(url)
                    .setProtocol(url.getParameter(REGISTRY_KEY, DEFAULT_REGISTRY))
                    .removeParameter(REGISTRY_KEY)
                    .build();
            Registry registry = registryFactory.getRegistry(url);
            // type是引用的接口
            if (RegistryService.class.equals(type)) {
                return proxyFactory.getInvoker((T) registry, type, url);
            }
            // 如有有group分组,就从url参数中获取匹配。这里没有
            // group="a,b" or group="*"
            Map<String, String> qs = StringUtils.parseQueryString(url.getParameterAndDecoded(REFER_KEY));
            String group = qs.get(GROUP_KEY);
            if (group != null && group.length() > 0) {
                if ((COMMA_SPLIT_PATTERN.split(group)).length > 1 || "*".equals(group)) {
                    return doRefer(getMergeableCluster(), registry, type, url);
                }
            }
            return doRefer(cluster, registry, type, url);
        }
    
    private <T> Invoker<T> doRefer(Cluster cluster, Registry registry, Class<T> type, URL url) {
            // RegistryDirectory是比较重要的类,有订阅方法,订阅从注册中心获取远程服务地址就是这个类
            RegistryDirectory<T> directory = new RegistryDirectory<T>(type, url);
            directory.setRegistry(registry);
            directory.setProtocol(protocol);
            // all attributes of REFER_KEY
            Map<String, String> parameters = new HashMap<String, String>(directory.getUrl().getParameters());
           // 构建订阅url。consumer://。。。
           URL subscribeUrl = new URL(CONSUMER_PROTOCOL, parameters.remove(REGISTER_IP_KEY), 0, type.getName(), parameters);
           // 不是通用接口(interface=*),切需要注册。这里符合
            if (!ANY_VALUE.equals(url.getServiceInterface()) && url.getParameter(REGISTER_KEY, true)) {
                directory.setRegisteredConsumerUrl(getRegisteredConsumerUrl(subscribeUrl, url));
                // 往Zookeeper中注册consumer://,就是创建consumer节点。
                registry.register(directory.getRegisteredConsumerUrl());
            }
            directory.buildRouterChain(subscribeUrl);
            // 订阅consumer://。可以看到category有三个:providers、configurators、routes。后面会针对这三个节点添加订阅
            directory.subscribe(subscribeUrl.addParameter(CATEGORY_KEY,
                    PROVIDERS_CATEGORY + "," + CONFIGURATORS_CATEGORY + "," + ROUTERS_CATEGORY));
    
            Invoker invoker = cluster.join(directory);
            ProviderConsumerRegTable.registerConsumer(invoker, url, subscribeUrl, directory);
            return invoker;
        }
    
       public void subscribe(URL url) {
            setConsumerUrl(url);
            CONSUMER_CONFIGURATION_LISTENER.addNotifyListener(this);
            serviceConfigurationListener = new ReferenceConfigurationListener(this, url);
            // registry是zookeeperRegistry。这里真真添加订阅
            registry.subscribe(url, this);
        }
    

    ZookeeperRegistry继承于FailbackRegistry。跟服务导出,快速失败的逻辑是一样的。

    @Override
        public void doSubscribe(final URL url, final NotifyListener listener) {
            try {
                // 是否是通用接口。不看
                if (ANY_VALUE.equals(url.getServiceInterface())) {
                  ...省略
                } else {
                    List<URL> urls = new ArrayList<>();
                    // 前面看到category有三个。providers、configurators、routes。所以这里path有三个:/dubbo/**接口名/providers,/dubbo/**接口名/configurators、/dubbo/**接口名/routes。
                    for (String path : toCategoriesPath(url)) {
                        ConcurrentMap<NotifyListener, ChildListener> listeners = zkListeners.get(url);
                        if (listeners == null) {
                            zkListeners.putIfAbsent(url, new ConcurrentHashMap<>());
                            listeners = zkListeners.get(url);
                        }
                        ChildListener zkListener = listeners.get(listener);
                        if (zkListener == null) {
                        // 监听器是内部类,最终监听调用的是ZookeeperRegistry.this.notify方法
                            listeners.putIfAbsent(listener, (parentPath, currentChilds) -> ZookeeperRegistry.this.notify(url, listener, toUrlsWithEmpty(url, parentPath, currentChilds)));
                            zkListener = listeners.get(listener);
                        }
                        // zkClient内部逻辑会判定,如果没有这个节点就创建这个节点。
                        zkClient.create(path, false);
                        // zkClient跟服务导出一样是:CuratorZookeeperClient。
                        // 添加监听器,并且返回节点下的子节点。如果子节点为空,则通过consumer协议构建empty://协议返回。
                        // 所以providers节点下自然是服务地址方地址(可以登录zookeeper查看)
                        // configurators和routes没有子节点。所以返回empty://。
                        List<String> children = zkClient.addChildListener(path, zkListener);
                        if (children != null) {
                            urls.addAll(toUrlsWithEmpty(url, path, children));
                        }
                    }
                    // 添加完之后,手动调用唤醒方法。前面添加了三个节点的监听器。并返回了三个节点下的子节点。
                    // 一个是dubbo://...真正的服务地址地址。另外两个是empty://地址
                    notify(url, listener, urls);
                }
            } catch (Throwable e) {
                throw new RpcException("Failed to subscribe " + url + " to zookeeper " + getUrl() + ", cause: " + e.getMessage(), e);
            }
        }
    
     protected void notify(URL url, NotifyListener listener, List<URL> urls) {
            // keep every provider's category.
            Map<String, List<URL>> result = new HashMap<>();
            for (URL u : urls) {
                if (UrlUtils.isMatch(url, u)) {
                    // 获取url的category参数,有:providers、configurators、routes。
                    String category = u.getParameter(CATEGORY_KEY, DEFAULT_CATEGORY);
                    // 以category分组,保存在result
                    List<URL> categoryList = result.computeIfAbsent(category, k -> new ArrayList<>());
                    categoryList.add(u);
                }
            }
            if (result.size() == 0) {
                return;
            }
            Map<String, List<URL>> categoryNotified = notified.computeIfAbsent(url, u -> new ConcurrentHashMap<>());
            for (Map.Entry<String, List<URL>> entry : result.entrySet()) {
                String category = entry.getKey();
                List<URL> categoryList = entry.getValue();
                categoryNotified.put(category, categoryList);
                // listener是之前传入的RegistryDirectory。categoryList是result遍历:有dubbo://...,empty://,empty://
                listener.notify(categoryList);
                // We will update our cache file after each notification.
                // When our Registry has a subscribe failure due to network jitter, we can return at least the existing cache URL.
                saveProperties(url);
            }
        }
    
     @Override
        public synchronized void notify(List<URL> urls) {
        // 过滤,并按vonfigurator、route、provider分三组。
            Map<String, List<URL>> categoryUrls = urls.stream()
                    .filter(Objects::nonNull)
                    .filter(this::isValidCategory)
                    .filter(this::isNotCompatibleFor26x)
                    .collect(Collectors.groupingBy(url -> {
                        if (UrlUtils.isConfigurator(url)) {
                            return CONFIGURATORS_CATEGORY;
                        } else if (UrlUtils.isRoute(url)) {
                            return ROUTERS_CATEGORY;
                        } else if (UrlUtils.isProvider(url)) {
                            return PROVIDERS_CATEGORY;
                        }
                        return "";
                    }));
    // 如果是configurator协议则toConfigurators处理,否则不处理。toConfigurators方法内部会忽略empty://。
            List<URL> configuratorURLs = categoryUrls.getOrDefault(CONFIGURATORS_CATEGORY, Collections.emptyList());
            this.configurators = Configurator.toConfigurators(configuratorURLs).orElse(this.configurators);
    // 如果是route协议则toRoute处理,否则不处理。toRoute方法内部会忽略empty://。
            List<URL> routerURLs = categoryUrls.getOrDefault(ROUTERS_CATEGORY, Collections.emptyList());
            toRouters(routerURLs).ifPresent(this::addRouters);
            // providers协议则refreshOverrideAndInvoker处理。
            List<URL> providerURLs = categoryUrls.getOrDefault(PROVIDERS_CATEGORY, Collections.emptyList());
            refreshOverrideAndInvoker(providerURLs);
        }
    
     private void refreshInvoker(List<URL> invokerUrls) {
            Assert.notNull(invokerUrls, "invokerUrls should not be null");
            // 如果providers节点下已经空了,则说明服务提供没了,则这里invokerUrls则是empty://,这里就会调用destroyAllInvokers方法销毁所有invoke。
            if (invokerUrls.size() == 1
                    && invokerUrls.get(0) != null
                    && EMPTY_PROTOCOL.equals(invokerUrls.get(0).getProtocol())) {
                this.forbidden = true; // Forbid to access
                this.invokers = Collections.emptyList();
                routerChain.setInvokers(this.invokers);
                destroyAllInvokers(); // Close all invokers
            } else {
                this.forbidden = false; // Allow to access
                Map<String, Invoker<T>> oldUrlInvokerMap = this.urlInvokerMap; // local reference
                if (invokerUrls == Collections.<URL>emptyList()) {
                    invokerUrls = new ArrayList<>();
                }
                if (invokerUrls.isEmpty() && this.cachedInvokerUrls != null) {
                    invokerUrls.addAll(this.cachedInvokerUrls);
                } else {
                    this.cachedInvokerUrls = new HashSet<>();
                    this.cachedInvokerUrls.addAll(invokerUrls);//Cached invoker urls, convenient for comparison
                }
                if (invokerUrls.isEmpty()) {
                    return;
                }
                // 真正通过provider://,构建invoke类。key手机provider url。v
                Map<String, Invoker<T>> newUrlInvokerMap = toInvokers(invokerUrls);// Translate url list to Invoker map
             。。。省略代码
                try {
                // 新旧invokder对比,销毁不可用的旧的invoker。
                    destroyUnusedInvokers(oldUrlInvokerMap, newUrlInvokerMap); // Close the unused Invoker
                } catch (Exception e) {
                    logger.warn("destroyUnusedInvokers error. ", e);
                }
            }
        }
    
     private Map<String, Invoker<T>> toInvokers(List<URL> urls) {
           。。。省略代码
           // url是dubbo://,所以这里自然调用的是DubboProtocol.refer方法
               invoker = new InvokerDelegate<>(protocol.refer(serviceType, url), url, providerUrl);
                 return newUrlInvokerMap;
        }
        
         @Override
        public <T> Invoker<T> refer(Class<T> type, URL url) throws RpcException {
            return new AsyncToSyncInvoker<>(protocolBindingRefer(type, url));
        }
    
        @Override
        public <T> Invoker<T> protocolBindingRefer(Class<T> serviceType, URL url) throws RpcException {
           // 如果url有optimize参数,就会调用对应的接口方法,注册。这里没有不管
           optimizeSerialization(url);
    
            // create rpc invoker.
            //真正构建invoker。getClient猜都能猜到是建立远程服务提供者的服务连接
            DubboInvoker<T> invoker = new DubboInvoker<T>(serviceType, url, getClients(url), invokers);
            invokers.add(invoker);
            return invoker;
        }
    
    private ExchangeClient[] getClients(URL url) {
            // 是否使用共享连接。不同的远程接口,相同的远程应用应该会使用同一个连接
            boolean useShareConnect = false;
            int connections = url.getParameter(CONNECTIONS_KEY, 0);
            List<ReferenceCountExchangeClient> shareClients = null;
            // 下文的英文注释,也可以看出来,如果没有手动配置连接,则是共享连接,一个服务只有一个连接
            // if not configured, connection is shared, otherwise, one connection for one service
            if (connections == 0) {
                useShareConnect = true;
    
                /**
                 * The xml configuration should have a higher priority than properties.
                 */
                String shareConnectionsStr = url.getParameter(SHARE_CONNECTIONS_KEY, (String) null);
                connections = Integer.parseInt(StringUtils.isBlank(shareConnectionsStr) ? ConfigUtils.getProperty(SHARE_CONNECTIONS_KEY,
                        DEFAULT_SHARE_CONNECTIONS) : shareConnectionsStr);
                // 
                shareClients = getSharedClient(url, connections);
            }
    
            ExchangeClient[] clients = new ExchangeClient[connections];
            for (int i = 0; i < clients.length; i++) {
                if (useShareConnect) {
                    clients[i] = shareClients.get(i);
    
                } else {
                    clients[i] = initClient(url);
                }
            }
    
            return clients;
        }
    
    private List<ReferenceCountExchangeClient> getSharedClient(URL url, int connectNum) {
            // 获得ip和端口:192.168.106.1:20880
            String key = url.getAddress();
            List<ReferenceCountExchangeClient> clients = referenceClientMap.get(key);
    
            if (checkClientCanUse(clients)) {
                batchClientRefIncr(clients);
                return clients;
            }
            // 这个锁的方式可以借鉴一下。我之前一直synchronized("".internal())。
            locks.putIfAbsent(key, new Object());
            synchronized (locks.get(key)) {
                clients = referenceClientMap.get(key);
                // dubbo check
                if (checkClientCanUse(clients)) {
                    batchClientRefIncr(clients);
                    return clients;
                }
                connectNum = Math.max(connectNum, 1);
                if (CollectionUtils.isEmpty(clients)) {
                // 这里建立连接
                    clients = buildReferenceCountExchangeClientList(url, connectNum);
                    referenceClientMap.put(key, clients);
    
                } 
                。。。省略代码
    
                return clients;
            }
        }
    
    
    private ReferenceCountExchangeClient buildReferenceCountExchangeClient(URL url) {
            ExchangeClient exchangeClient = initClient(url);
    
            return new ReferenceCountExchangeClient(exchangeClient);
        }
        
        private ExchangeClient initClient(URL url) {
    
            // 获取连接类型,默认是netty
            String str = url.getParameter(CLIENT_KEY, url.getParameter(SERVER_KEY, DEFAULT_REMOTING_CLIENT));
            // 添加编码方式
            url = url.addParameter(CODEC_KEY, DubboCodec.NAME);
            //设置心跳时间
            url = url.addParameterIfAbsent(HEARTBEAT_KEY, String.valueOf(DEFAULT_HEARTBEAT));
    
            // BIO is not allowed since it has severe performance issue.
            if (str != null && str.length() > 0 && !ExtensionLoader.getExtensionLoader(Transporter.class).hasExtension(str)) {
                throw new RpcException("Unsupported client type: " + str + "," +
                        " supported client type is " + StringUtils.join(ExtensionLoader.getExtensionLoader(Transporter.class).getSupportedExtensions(), " "));
            }
    
            ExchangeClient client;
            try {
                // connection should be lazy
                if (url.getParameter(LAZY_CONNECT_KEY, false)) {
                    client = new LazyConnectExchangeClient(url, requestHandler);
    
                } else {
                // 没有显示制定lasy连接,就进入这里。requestHandler是DubboProtol的内部类,之后处理消息就是这个类
                // 接下来的逻辑和服务导出差不多,不看了
                    client = Exchangers.connect(url, requestHandler);
                }
    
            } catch (RemotingException e) {
                throw new RpcException("Fail to create remoting client for service(" + url + "): " + e.getMessage(), e);
            }
    
            return client;
        }
    

    至此,从注册中心获取服务地址,构造invoker看完了。

       // // 订阅完之后,directory内部就维护了以远程服务有连接的invoker
       directory.subscribe(subscribeUrl.addParameter(CATEGORY_KEY,
                    PROVIDERS_CATEGORY + "," + CONFIGURATORS_CATEGORY + "," + ROUTERS_CATEGORY));
        //cluster是spi set注入的。spi注入的肯定是可适配扩展类。因为directory的url参数中没有指明cluster,所以默认的是FailoverCluster。外面还有一层MockClusterWrapper,这个不管。所以这个invoker可以看成是一个FailoverClusterInvoker。          
        Invoker invoker = cluster.join(directory);
    
    
    

    接着看怎么进行服务调用的。注入到spring中的引用对象到底是怎样的

    回到createProxy方法。

         // ProxyFactory默认是javassist。
         return (T) PROXY_FACTORY.getProxy(invoker);
    
    
    public <T> T getProxy(Invoker<T> invoker, Class<?>[] interfaces) {
    // Proxy.getProxy(interfaces)会用javassist动态构建一个代理。看newInstance传参就知道,这个代理的构造方法接受一个InvokerInvocationHandler
    // 代理类的逻辑就是。代理类invoke,会调用构造方法传参过来的InvokerInvocationHandler的invoke方法
        return (T) Proxy.getProxy(interfaces).newInstance(new InvokerInvocationHandler(invoker));
    
    }
    
    

    至此,可以看到,最后返回给spring容器的是一个代理类。这个代理类调用的时候,其实最终调用的就是InvokerInvocationHandler的invoke方法。

    所以看一下InvokerInvocationHandler的invoke方法

     @Override
        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]);
            }
            // 最终调用的是构造方法里传过来的invoker的invoke方法。之前传过来的是MockClusterWrapper包装的FailoverClusterInvoker
            // 这里把method和args封装在RpcInvocation进行传输
            return invoker.invoke(new RpcInvocation(method, args)).recreate();
        }
    

    看FailoverClusterInvoker的invoke方法

     @Override
        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);
            }
            // 之前cluster维护了构造好的RegistryDirectly。而RegistryDirectly维护了已经和远程服务建立好链接的invoker。所以这里不用看逻辑都知道,是把那些invoker取出来。为什么是数组,因为可以存在多个连接调用。
            List<Invoker<T>> invokers = list(invocation);
            // 获取负载均衡策略
            LoadBalance loadbalance = initLoadBalance(invokers, invocation);
            RpcUtils.attachInvocationIdIfAsync(getUrl(), invocation);
            // 调用
            return doInvoke(invocation, invokers, loadbalance);
        }
    
    @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);
            // 获取重试次数
            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循环重试
            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);
                }
                ...省略代码
                Invoker<T> invoker = select(loadbalance, invocation, copyInvokers, invoked);
                invoked.add(invoker);
                RpcContext.getContext().setInvokers((List) invoked);
                try {
                    // 真正调用。这个invoker就是之前订阅zookeeper构建的RegistryDirectly的包装过的DubboInvoker
                    Result result = invoker.invoke(invocation);
                    
                    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);
        }
    

    dubboInvoker外面包装的Wrapper等不看

     @Override
        protected Result doInvoke(final Invocation invocation) throws Throwable {
            RpcInvocation inv = (RpcInvocation) invocation;
            final String methodName = RpcUtils.getMethodName(invocation);
            inv.setAttachment(PATH_KEY, getUrl().getPath());
            inv.setAttachment(VERSION_KEY, version);
            // dubboInvoker内部已经维护了跟远程服务建立了连接的client
            ExchangeClient currentClient;
            if (clients.length == 1) {
                currentClient = clients[0];
            } else {
                currentClient = clients[index.getAndIncrement() % clients.length];
            }
            try {
                // 方法是否有返回值
                boolean isOneway = RpcUtils.isOneway(getUrl(), invocation);
                int timeout = getUrl().getMethodParameter(methodName, TIMEOUT_KEY, DEFAULT_TIMEOUT);
                // 没有返回值
                if (isOneway) {
                    boolean isSent = getUrl().getMethodParameter(methodName, Constants.SENT_KEY, false);
                   // 发送接口调用
                    currentClient.send(inv, isSent);
                    RpcContext.getContext().setFuture(null);
                    return AsyncRpcResult.newDefaultAsyncResult(invocation);
                } else {
                    AsyncRpcResult asyncRpcResult = new AsyncRpcResult(inv);
                    // 发送接口调用
                    CompletableFuture<Object> responseFuture = currentClient.request(inv, timeout);
                    responseFuture.whenComplete((obj, t) -> {
                        if (t != null) {
                            asyncRpcResult.completeExceptionally(t);
                        } else {
                            asyncRpcResult.complete((AppResponse) obj);
                        }
                    });
                    RpcContext.getContext().setFuture(new FutureAdapter(asyncRpcResult));
                    return asyncRpcResult;
                }
            } 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);
            }
        }
    

    关于序列化和反序列化,就是netty的handler处理的(反序列化DecodeHandler),通过spi动态扩展选择哪种序列化方式。具体源码就不看了。

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