說(shuō)明：本文以以下配置進(jìn)行服務(wù)發(fā)布流程分析：
注冊(cè)中心：zookeeper；
發(fā)布協(xié)議：dobbo

一、代理服務(wù)創(chuàng)建流程

代理服務(wù)創(chuàng)建流程圖：

dubbo服務(wù)調(diào)用流程.jpg

（1）、應(yīng)用使用<dubbo:service>配置

clipboard.png

（2）、DubboNamespaceHandler

模塊：dubbo-config -> dubbo-config-spring
包：org.apache.dubbo.config.spring.schema
主要方法：init()
主要源碼：

@Override
public void init() {
    registerBeanDefinitionParser("application", new DubboBeanDefinitionParser(ApplicationConfig.class, true));
    registerBeanDefinitionParser("module", new DubboBeanDefinitionParser(ModuleConfig.class, true));
    registerBeanDefinitionParser("registry", new DubboBeanDefinitionParser(RegistryConfig.class, true));
    registerBeanDefinitionParser("config-center", new DubboBeanDefinitionParser(ConfigCenterBean.class, true));
    registerBeanDefinitionParser("monitor", new DubboBeanDefinitionParser(MonitorConfig.class, true));
    registerBeanDefinitionParser("provider", new DubboBeanDefinitionParser(ProviderConfig.class, true));
    registerBeanDefinitionParser("consumer", new DubboBeanDefinitionParser(ConsumerConfig.class, true));
    registerBeanDefinitionParser("protocol", new DubboBeanDefinitionParser(ProtocolConfig.class, true));
    registerBeanDefinitionParser("service", new DubboBeanDefinitionParser(ServiceBean.class, true));
    registerBeanDefinitionParser("reference", new DubboBeanDefinitionParser(ReferenceBean.class, false));
    registerBeanDefinitionParser("annotation", new AnnotationBeanDefinitionParser());
}

本處主要定義dubbo的自定義標(biāo)簽的解析處理。

（3）、ReferenceBean.getObject()

模塊：dubbo-config -> dubbo-config-spring
包：org.apache.dubbo.config.spring.schema
主要方法：getObject()
主要源碼：

public Object getObject() {
    return get();
}

（4）、ReferenceBean.init()

模塊：dubbo-config -> dubbo-config-spring
包：org.apache.dubbo.config.spring.schema
主要方法：init()
主要源碼：

private void init() {
    if (initialized) {
        return;
    }
    initialized = true;
    checkStubAndLocal(interfaceClass);
    checkMock(interfaceClass);
    Map<String, String> map = new HashMap<String, String>();

    map.put(Constants.SIDE_KEY, Constants.CONSUMER_SIDE);
    appendRuntimeParameters(map);
    if (!isGeneric()) {
        String revision = Version.getVersion(interfaceClass, version);
        if (revision != null && revision.length() > 0) {
            map.put("revision", revision);
        }

        String[] methods = Wrapper.getWrapper(interfaceClass).getMethodNames();
        if (methods.length == 0) {
            logger.warn("No method found in service interface " + interfaceClass.getName());
            map.put("methods", Constants.ANY_VALUE);
        } else {
            map.put("methods", StringUtils.join(new HashSet<String>(Arrays.asList(methods)), ","));
        }
    }
    map.put(Constants.INTERFACE_KEY, interfaceName);
    appendParameters(map, application);
    appendParameters(map, module);
    appendParameters(map, consumer, Constants.DEFAULT_KEY);
    appendParameters(map, this);
    Map<String, Object> attributes = null;
    if (CollectionUtils.isNotEmpty(methods)) {
        attributes = new HashMap<String, Object>();
        for (MethodConfig methodConfig : methods) {
            appendParameters(map, methodConfig, methodConfig.getName());
            String retryKey = methodConfig.getName() + ".retry";
            if (map.containsKey(retryKey)) {
                String retryValue = map.remove(retryKey);
                if ("false".equals(retryValue)) {
                    map.put(methodConfig.getName() + ".retries", "0");
                }
            }
            attributes.put(methodConfig.getName(), convertMethodConfig2AyncInfo(methodConfig));
        }
    }

    String hostToRegistry = ConfigUtils.getSystemProperty(Constants.DUBBO_IP_TO_REGISTRY);
    if (StringUtils.isEmpty(hostToRegistry)) {
        hostToRegistry = NetUtils.getLocalHost();
    } else if (isInvalidLocalHost(hostToRegistry)) {
        throw new IllegalArgumentException("Specified invalid registry ip from property:" + Constants.DUBBO_IP_TO_REGISTRY + ", value:" + hostToRegistry);
    }
    map.put(Constants.REGISTER_IP_KEY, hostToRegistry);

    ref = createProxy(map);

    ConsumerModel consumerModel = new ConsumerModel(getUniqueServiceName(), interfaceClass, ref, interfaceClass.getMethods(), attributes);
    ApplicationModel.initConsumerModel(getUniqueServiceName(), consumerModel);
}

（5）、ReferenceBean.createProxy()

模塊：dubbo-config -> dubbo-config-spring
包：org.apache.dubbo.config.spring.schema
主要方法：createProxy()
主要源碼：

    if (urls.size() == 1) {
        invoker = refprotocol.refer(interfaceClass, urls.get(0));
    } else {
        List<Invoker<?>> invokers = new ArrayList<Invoker<?>>();
        URL registryURL = null;
        for (URL url : urls) {
            invokers.add(refprotocol.refer(interfaceClass, url));
            if (Constants.REGISTRY_PROTOCOL.equals(url.getProtocol())) {
                registryURL = url; // use last registry url
            }
        }
        if (registryURL != null) { // registry url is available
            // use RegistryAwareCluster only when register's cluster is available
            URL u = registryURL.addParameter(Constants.CLUSTER_KEY, RegistryAwareCluster.NAME);
            // The invoker wrap relation would be: RegistryAwareClusterInvoker(StaticDirectory) -> FailoverClusterInvoker(RegistryDirectory, will execute route) -> Invoker
            invoker = cluster.join(new StaticDirectory(u, invokers));
        } else { // not a registry url, must be direct invoke.
            invoker = cluster.join(new StaticDirectory(invokers));
        }
    }
}

Boolean c = check;
if (c == null && consumer != null) {
    c = consumer.isCheck();
}
if (c == null) {
    c = true; // default true
}
if (c && !invoker.isAvailable()) {
    // make it possible for consumer to retry later if provider is temporarily unavailable
    initialized = false;
    throw new IllegalStateException("Failed to check the status of the service " + interfaceName + ". No provider available for the service " + (group == null ? "" : group + "/") + interfaceName + (version == null ? "" : ":" + version) + " from the url " + invoker.getUrl() + " to the consumer " + NetUtils.getLocalHost() + " use dubbo version " + Version.getVersion());
}
if (logger.isInfoEnabled()) {
    logger.info("Refer dubbo service " + interfaceClass.getName() + " from url " + invoker.getUrl());
}
/**
 * @since 2.7.0
 * ServiceData Store
 */
MetadataReportService metadataReportService = null;
if ((metadataReportService = getMetadataReportService()) != null) {
    URL consumerURL = new URL(Constants.CONSUMER_PROTOCOL, map.remove(Constants.REGISTER_IP_KEY), 0, map.get(Constants.INTERFACE_KEY), map);
    metadataReportService.publishConsumer(consumerURL);
}
// create service proxy
return (T) proxyFactory.getProxy(invoker);

主要流程：

• refprotocol.refer()：主要?jiǎng)?chuàng)建客戶端的代理，其中封裝了consumer的注冊(cè)及訂閱操作，Directory、Router、Loadbalance以及傳輸層等；
• proxyFactory.getProxy()：利用JavassistProxy生成接口的動(dòng)態(tài)代理實(shí)現(xiàn)；

（6）、RegistryProtocol.java.refer()

模塊：dubbo-registry-> dubbo-registry-api
包：org.apache.dubbo.registry.integration
主要方法：refer()
主要源碼：

public <T> Invoker<T> refer(Class<T> type, URL url) throws RpcException {
    url = url.setProtocol(url.getParameter(REGISTRY_KEY, DEFAULT_REGISTRY)).removeParameter(REGISTRY_KEY);
    Registry registry = registryFactory.getRegistry(url);
    if (RegistryService.class.equals(type)) {
        return proxyFactory.getInvoker((T) registry, type, url);
    }

    // group="a,b" or group="*"
    Map<String, String> qs = StringUtils.parseQueryString(url.getParameterAndDecoded(REFER_KEY));
    String group = qs.get(Constants.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);
}

主要調(diào)用doRefer()進(jìn)行實(shí)際的工作；

（7）、RegistryProtocol.getRegistry()

模塊：dubbo-registry-> dubbo-registry-zookeeper
包：org.apache.dubbo.registry.zookeeper
主要方法：getRegistry()
主要源碼：

public Registry getRegistry(URL url) {
    url = url.setPath(RegistryService.class.getName())
            .addParameter(Constants.INTERFACE_KEY, RegistryService.class.getName())
            .removeParameters(Constants.EXPORT_KEY, Constants.REFER_KEY);
    String key = url.toServiceStringWithoutResolving();
    // Lock the registry access process to ensure a single instance of the registry
    LOCK.lock();
    try {
        Registry registry = REGISTRIES.get(key);
        if (registry != null) {
            return registry;
        }
        //create registry by spi/ioc
        registry = createRegistry(url);
        if (registry == null) {
            throw new IllegalStateException("Can not create registry " + url);
        }
        REGISTRIES.put(key, registry);
        return registry;
    } finally {
        // Release the lock
        LOCK.unlock();
    }
}

獲取注冊(cè)中心；

（8）、RegistryProtocol.doRefer()

模塊：dubbo-registry-> dubbo-registry-api
包：org.apache.dubbo.registry.integration
主要方法：doRefer()
主要源碼：

private <T> Invoker<T> doRefer(Cluster cluster, Registry registry, Class<T> type, URL url) {
    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());
    URL subscribeUrl = new URL(CONSUMER_PROTOCOL, parameters.remove(REGISTER_IP_KEY), 0, type.getName(), parameters);
    if (!ANY_VALUE.equals(url.getServiceInterface()) && url.getParameter(REGISTER_KEY, true)) {
        registry.register(getRegisteredConsumerUrl(subscribeUrl, url));
    }
    directory.buildRouterChain(subscribeUrl);
    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;
}

主要處理流程：

• 初始化RegistryDirectory：其對(duì)訂閱處理及服務(wù)提供者、路由、配置變更等進(jìn)行了處理，當(dāng)服務(wù)提供者變更時(shí)，此實(shí)例對(duì)應(yīng)的提供者列表跟隨變化。
• registry.register()：對(duì)Consumer進(jìn)行注冊(cè)；
• directory.subscribe()：訂閱服務(wù)提供者、路由規(guī)則、配置信息；當(dāng)有相關(guān)信息變更時(shí)，本地跟隨變更；
• cluster.join()：將集群策略、LoadBalance及RegistryDirectory等封裝成invoker；

（9）、ZookeeperRegistry.register()

模塊：dubbo-registry-> dubbo-registry-zookeeper
包：org.apache.dubbo.registry.zookeeper
主要方法：getRegistry()
主要源碼：

public void register(URL url) {
    super.register(url);
    removeFailedRegistered(url);
    removeFailedUnregistered(url);
    try {
        // Sending a registration request to the server side
        doRegister(url);
    } catch (Exception e) {
        Throwable t = e;

        // If the startup detection is opened, the Exception is thrown directly.
        boolean check = getUrl().getParameter(Constants.CHECK_KEY, true)
                && url.getParameter(Constants.CHECK_KEY, true)
                && !Constants.CONSUMER_PROTOCOL.equals(url.getProtocol());
        boolean skipFailback = t instanceof SkipFailbackWrapperException;
        if (check || skipFailback) {
            if (skipFailback) {
                t = t.getCause();
            }
            throw new IllegalStateException("Failed to register " + url + " to registry " + getUrl().getAddress() + ", cause: " + t.getMessage(), t);
        } else {
            logger.error("Failed to register " + url + ", waiting for retry, cause: " + t.getMessage(), t);
        }

        // Record a failed registration request to a failed list, retry regularly
        addFailedRegistered(url);
    }
}

（10）、RegistryDirectory.buildRouterChain()

模塊：dubbo-registry-> dubbo-registry-api
包：org.apache.dubbo.registry.integration
主要方法：buildRouterChain()
主要源碼：

（11）、RegistryDirectory.subscribe()

模塊：dubbo-registry-> dubbo-registry-api
包：org.apache.dubbo.registry.integration
主要方法：subscribe()
主要源碼：

public void subscribe(URL url) {
    setConsumerUrl(url);
    consumerConfigurationListener.addNotifyListener(this);
    serviceConfigurationListener = new ReferenceConfigurationListener(this, url);
    registry.subscribe(url, this);
}

主要地調(diào)用ZookeeperRegistry對(duì)服務(wù)提供者等進(jìn)行訂閱處理；

（12）、ZookeeperRegistry.subscribe()

模塊：dubbo-registry->dubbo-registry-api
包：org.apache.dubbo.registry.zookeeper
主要方法：subscribe()
主要源碼：

public void subscribe(URL url, NotifyListener listener) {
    super.subscribe(url, listener);
    removeFailedSubscribed(url, listener);
    try {
        // Sending a subscription request to the server side
        doSubscribe(url, listener);
    } catch (Exception e) {
        Throwable t = e;

        List<URL> urls = getCacheUrls(url);
        if (CollectionUtils.isNotEmpty(urls)) {
            notify(url, listener, urls);
            logger.error("Failed to subscribe " + url + ", Using cached list: " + urls + " from cache file: " + getUrl().getParameter(Constants.FILE_KEY, System.getProperty("user.home") + "/dubbo-registry-" + url.getHost() + ".cache") + ", cause: " + t.getMessage(), t);
        } else {
            // If the startup detection is opened, the Exception is thrown directly.
            boolean check = getUrl().getParameter(Constants.CHECK_KEY, true)
                    && url.getParameter(Constants.CHECK_KEY, true);
            boolean skipFailback = t instanceof SkipFailbackWrapperException;
            if (check || skipFailback) {
                if (skipFailback) {
                    t = t.getCause();
                }
                throw new IllegalStateException("Failed to subscribe " + url + ", cause: " + t.getMessage(), t);
            } else {
                logger.error("Failed to subscribe " + url + ", waiting for retry, cause: " + t.getMessage(), t);
            }
        }

        // Record a failed registration request to a failed list, retry regularly
        addFailedSubscribed(url, listener);
    }
}

主要處理流程：

• 將服務(wù)提供者的url及監(jiān)聽(tīng)器放入訂閱隊(duì)列中；
• 從訂閱失敗隊(duì)列中移除本url；
• 創(chuàng)建對(duì)當(dāng)前url的監(jiān)聽(tīng)器；
• 若訂閱失敗，則將當(dāng)前url及監(jiān)聽(tīng)器添加到訂閱失敗隊(duì)列中；

（13）、RegistryDirectory.notify()

模塊：dubbo-registry-> dubbo-registry-api
包：org.apache.dubbo.registry.integration
主要方法：notify()
主要源碼：

public synchronized void notify(List<URL> urls) {
    List<URL> categoryUrls = urls.stream()
            .filter(this::isValidCategory)
            .filter(this::isNotCompatibleFor26x)
            .collect(Collectors.toList());

    /**
     * TODO Try to refactor the processing of these three type of urls using Collectors.groupBy()?
     */
    this.configurators = Configurator.toConfigurators(classifyUrls(categoryUrls, UrlUtils::isConfigurator))
            .orElse(configurators);

    toRouters(classifyUrls(categoryUrls, UrlUtils::isRoute)).ifPresent(this::addRouters);

    // providers
    refreshOverrideAndInvoker(classifyUrls(categoryUrls, UrlUtils::isProvider));
}

當(dāng)初次訂閱或訂閱的信息變更時(shí)。

主要流程流程為：更新配置、更新路由信息、更新提供者信息；

（14）、RegistryDirectory.refreshOverrideAndInvoker()

模塊：dubbo-registry-> dubbo-registry-api
包：org.apache.dubbo.registry.integration
主要方法：refreshOverrideAndInvoker()
主要源碼：

private void refreshOverrideAndInvoker(List<URL> urls) {
    // mock zookeeper://xxx?mock=return null
    overrideDirectoryUrl();
    refreshInvoker(urls);
}

（15）、RegistryDirectory.refreshInvoker()

模塊：dubbo-registry-> dubbo-registry-api
包：org.apache.dubbo.registry.integration
主要方法：refreshInvoker()
主要源碼：

private void refreshInvoker(List<URL> invokerUrls) {
    Assert.notNull(invokerUrls, "invokerUrls should not be null");

    if (invokerUrls.size() == 1 && invokerUrls.get(0) != null && Constants.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;
        }
        Map<String, Invoker<T>> newUrlInvokerMap = toInvokers(invokerUrls);// Translate url list to Invoker map

        // state change
        // If the calculation is wrong, it is not processed.
        if (CollectionUtils.isEmptyMap(newUrlInvokerMap)) {
            logger.error(new IllegalStateException("urls to invokers error .invokerUrls.size :" + invokerUrls.size() + ", invoker.size :0. urls :" + invokerUrls
                    .toString()));
            return;
        }

        List<Invoker<T>> newInvokers = Collections.unmodifiableList(new ArrayList<>(newUrlInvokerMap.values()));
        // pre-route and build cache, notice that route cache should build on original Invoker list.
        // toMergeMethodInvokerMap() will wrap some invokers having different groups, those wrapped invokers not should be routed.
        routerChain.setInvokers(newInvokers);
        this.invokers = multiGroup ? toMergeInvokerList(newInvokers) : newInvokers;
        this.urlInvokerMap = newUrlInvokerMap;

        try {
            destroyUnusedInvokers(oldUrlInvokerMap, newUrlInvokerMap); // Close the unused Invoker
        } catch (Exception e) {
            logger.warn("destroyUnusedInvokers error. ", e);
        }
    }
}

（16）、RegistryDirectory.toInvokers()

模塊：dubbo-registry-> dubbo-registry-api
包：org.apache.dubbo.registry.integration
主要方法：toInvokers()
主要源碼：

private Map<String, Invoker<T>> toInvokers(List<URL> urls) {
    Map<String, Invoker<T>> newUrlInvokerMap = new HashMap<String, Invoker<T>>();
    if (urls == null || urls.isEmpty()) {
        return newUrlInvokerMap;
    }
    Set<String> keys = new HashSet<String>();
    String queryProtocols = this.queryMap.get(Constants.PROTOCOL_KEY);
    for (URL providerUrl : urls) {
        // If protocol is configured at the reference side, only the matching protocol is selected
        if (queryProtocols != null && queryProtocols.length() > 0) {
            boolean accept = false;
            String[] acceptProtocols = queryProtocols.split(",");
            for (String acceptProtocol : acceptProtocols) {
                if (providerUrl.getProtocol().equals(acceptProtocol)) {
                    accept = true;
                    break;
                }
            }
            if (!accept) {
                continue;
            }
        }
        if (Constants.EMPTY_PROTOCOL.equals(providerUrl.getProtocol())) {
            continue;
        }
        if (!ExtensionLoader.getExtensionLoader(Protocol.class).hasExtension(providerUrl.getProtocol())) {
            logger.error(new IllegalStateException("Unsupported protocol " + providerUrl.getProtocol() +
                    " in notified url: " + providerUrl + " from registry " + getUrl().getAddress() +
                    " to consumer " + NetUtils.getLocalHost() + ", supported protocol: " +
                    ExtensionLoader.getExtensionLoader(Protocol.class).getSupportedExtensions()));
            continue;
        }
        URL url = mergeUrl(providerUrl);

        String key = url.toFullString(); // The parameter urls are sorted
        if (keys.contains(key)) { // Repeated url
            continue;
        }
        keys.add(key);
        // Cache key is url that does not merge with consumer side parameters, regardless of how the consumer combines parameters, if the server url changes, then refer again
        Map<String, Invoker<T>> localUrlInvokerMap = this.urlInvokerMap; // local reference
        Invoker<T> invoker = localUrlInvokerMap == null ? null : localUrlInvokerMap.get(key);
        if (invoker == null) { // Not in the cache, refer again
            try {
                boolean enabled = true;
                if (url.hasParameter(Constants.DISABLED_KEY)) {
                    enabled = !url.getParameter(Constants.DISABLED_KEY, false);
                } else {
                    enabled = url.getParameter(Constants.ENABLED_KEY, true);
                }
                if (enabled) {
                    invoker = new InvokerDelegate<T>(protocol.refer(serviceType, url), url, providerUrl);
                }
            } catch (Throwable t) {
                logger.error("Failed to refer invoker for interface:" + serviceType + ",url:(" + url + ")" + t.getMessage(), t);
            }
            if (invoker != null) { // Put new invoker in cache
                newUrlInvokerMap.put(key, invoker);
            }
        } else {
            newUrlInvokerMap.put(key, invoker);
        }
    }
    keys.clear();
    return newUrlInvokerMap;
}

將服務(wù)提供者轉(zhuǎn)換為Invoker；

（17）、DubboProtocol.refer()

模塊：dubbo-rpc->dubbo-rpc-dubbo
包：org.apache.dubbo.rpc.protocol.dubbo
主要方法：refer()
主要源碼：

public <T> Invoker<T> refer(Class<T> serviceType, URL url) throws RpcException {
    optimizeSerialization(url);
    // create rpc invoker.
    DubboInvoker<T> invoker = new DubboInvoker<T>(serviceType, url, getClients(url), invokers);
    invokers.add(invoker);
    return invoker;
}

（18）、DubboProtocol.getClients()

模塊：dubbo-rpc->dubbo-rpc-dubbo
包：org.apache.dubbo.rpc.protocol.dubbo
主要方法：getClients()
主要源碼：

private ExchangeClient[] getClients(URL url) {
    // whether to share connection
    boolean serviceShareConnect = false;
    int connections = url.getParameter(Constants.CONNECTIONS_KEY, 0);
    // if not configured, connection is shared, otherwise, one connection for one service
    if (connections == 0) {
        serviceShareConnect = true;
        connections = 1;
    }

    ExchangeClient[] clients = new ExchangeClient[connections];
    for (int i = 0; i < clients.length; i++) {
        if (serviceShareConnect) {
            clients[i] = getSharedClient(url);
        } else {
            clients[i] = initClient(url);
        }
    }
    return clients;
}

（19）、DubboProtocol.initClient()

模塊：dubbo-rpc->dubbo-rpc-dubbo
包：org.apache.dubbo.rpc.protocol.dubbo
主要方法：initClient()
主要源碼：

private ExchangeClient initClient(URL url) {

    // client type setting.
    String str = url.getParameter(Constants.CLIENT_KEY, url.getParameter(Constants.SERVER_KEY, Constants.DEFAULT_REMOTING_CLIENT));

    url = url.addParameter(Constants.CODEC_KEY, DubboCodec.NAME);
    // enable heartbeat by default
    url = url.addParameterIfAbsent(Constants.HEARTBEAT_KEY, String.valueOf(Constants.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(Constants.LAZY_CONNECT_KEY, false)) {
            client = new LazyConnectExchangeClient(url, requestHandler);
        } else {
            client = Exchangers.connect(url, requestHandler);
        }
    } catch (RemotingException e) {
        throw new RpcException("Fail to create remoting client for service(" + url + "): " + e.getMessage(), e);
    }
    return client;
}

（20）、FailoverCluster.join()

模塊：dubbo-cluster
包：org.apache.dubbo.rpc.cluster.support
主要方法：join()
主要源碼：

public <T> Invoker<T> join(Directory<T> directory) throws RpcException {
    return new FailoverClusterInvoker<T>(directory);
}

（21）、JavassistProxyFactory.getProxy()

模塊：dubbo-rpc-> dubbo-rpc-api
包：org.apache.dubbo.rpc.proxy.javassist
主要方法：getProxy()
主要源碼：

public <T> T getProxy(Invoker<T> invoker, Class<?>[] interfaces) {
    return (T) Proxy.getProxy(interfaces).newInstance(new InvokerInvocationHandler(invoker));
}