Dubbo进阶（十三）：Directory的实现

港控/mmm° 2023-02-16 04:10 11阅读 0赞

首先我们依然再看一遍Dubbo调用的流程  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dhbmdjaGVuZ21pbmcx_size_16_color_FFFFFF_t_70]  
本文我们主要分析Directory。

首先通过UML来看下Directory的层级结构  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dhbmdjaGVuZ21pbmcx_size_16_color_FFFFFF_t_70 1]  
从这个UML图上可以看到，依然使用了模板模式。**AbstractDirectory**是一个抽象类，封装了通用逻辑，最重要的有`list`方法，用于返回所有可用的list，它会调用`doList`方法，`doList`是一个抽象方法，在不同的子类会有不同的实现。

public List<Invoker<T>> list(Invocation invocation) throws RpcException {
        if (destroyed) {
            throw new RpcException("Directory already destroyed .url: " + getUrl());
        }
    
        return doList(invocation);
    }
    
    protected abstract List<Invoker<T>> doList(Invocation invocation) throws RpcException;

**StaticDirectory**即静态服务目录，顾名思义，它内部存放的 Invoker 是不会变动的。通过`StaticDirectory`的构造函数可以看到将传入的invoker的list封装成静态的`Directory`对象，里面的列表不会变。

private final List<Invoker<T>> invokers;
    
    public StaticDirectory(List<Invoker<T>> invokers) {
        this(null, invokers, null);
    }
    
    public StaticDirectory(List<Invoker<T>> invokers, RouterChain<T> routerChain) {
        this(null, invokers, routerChain);
    }
    
    public StaticDirectory(URL url, List<Invoker<T>> invokers) {
        this(url, invokers, null);
    }
    
    public StaticDirectory(URL url, List<Invoker<T>> invokers, RouterChain<T> routerChain) {
        super(url == null && CollectionUtils.isNotEmpty(invokers) ? invokers.get(0).getUrl() : url, routerChain);
        if (CollectionUtils.isEmpty(invokers)) {
            throw new IllegalArgumentException("invokers == null");
        }
        this.invokers = invokers;
    }

**RegistryDirectory**是一种动态服务目录，实现了 NotifyListener 接口。当注册中心服务配置发生变化后，RegistryDirectory 可收到与当前服务相关的变化。收到变更通知后，RegistryDirectory 可根据配置变更信息刷新 Invoker 列表，接下来通过源码来分析一下RegistryDirectory。

*  列举invoker的list

public List<Invoker<T>> doList(Invocation invocation) {
        if (forbidden) {
            // 1. No service provider 2. Service providers are disabled
            throw new RpcException(RpcException.FORBIDDEN_EXCEPTION, "No provider available from registry " +
                    getUrl().getAddress() + " for service " + getConsumerUrl().getServiceKey() + " on consumer " +
                    NetUtils.getLocalHost() + " use dubbo version " + Version.getVersion() +
                    ", please check status of providers(disabled, not registered or in blacklist).");
        }
    
        if (multiGroup) {
            return this.invokers == null ? Collections.emptyList() : this.invokers;
        }
    
        List<Invoker<T>> invokers = null;
        try {
            // Get invokers from cache, only runtime routers will be executed.
            invokers = routerChain.route(getConsumerUrl(), invocation);
        } catch (Throwable t) {
            logger.error("Failed to execute router: " + getUrl() + ", cause: " + t.getMessage(), t);
        }
    
        return invokers == null ? Collections.emptyList() : invokers;
    }

*  接收服务变更通知，RegistryDirectory 是一个动态服务目录，它需要接受注册中心配置进行动态调整。因此 RegistryDirectory 实现了 NotifyListener 接口，通过这个接口获取注册中心变更通知，`notify`这个方法主要监听配置中心对应URL的变化，然后更新本地的参数配置并做provider list的整合。

public synchronized void notify(List<URL> urls) {
        Map<String, List<URL>> categoryUrls = urls.stream()
                .filter(Objects::nonNull)
                .filter(this::isValidCategory)
                .filter(this::isNotCompatibleFor26x)
                .collect(Collectors.groupingBy(this::judgeCategory));
    
        List<URL> configuratorURLs = categoryUrls.getOrDefault(CONFIGURATORS_CATEGORY, Collections.emptyList());
        this.configurators = Configurator.toConfigurators(configuratorURLs).orElse(this.configurators);
    
        List<URL> routerURLs = categoryUrls.getOrDefault(ROUTERS_CATEGORY, Collections.emptyList());
        toRouters(routerURLs).ifPresent(this::addRouters);
    
        // providers
        List<URL> providerURLs = categoryUrls.getOrDefault(PROVIDERS_CATEGORY, Collections.emptyList());
        /**
         * 3.x added for extend URL address
         */
        ExtensionLoader<AddressListener> addressListenerExtensionLoader = ExtensionLoader.getExtensionLoader(AddressListener.class);
        List<AddressListener> supportedListeners = addressListenerExtensionLoader.getActivateExtension(getUrl(), (String[]) null);
        if (supportedListeners != null && !supportedListeners.isEmpty()) {
            for (AddressListener addressListener : supportedListeners) {
                providerURLs = addressListener.notify(providerURLs, getConsumerUrl(),this);
            }
        }
        refreshOverrideAndInvoker(providerURLs);
    }

*  刷新Invoker列表

private void refreshInvoker(List<URL> invokerUrls) {
        Assert.notNull(invokerUrls, "invokerUrls should not be null");
    	//  invokerUrls的数量和协议头判断是否禁用所有的服务，如果禁用，则将 forbidden 设为 true，并销毁所有的 Invoker
        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 {
        	// 若不禁用，则将url转成Invoker
            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
    
            /**
             * If the calculation is wrong, it is not processed.
             *
             * 1. The protocol configured by the client is inconsistent with the protocol of the server.
             *    eg: consumer protocol = dubbo, provider only has other protocol services(rest).
             * 2. The registration center is not robust and pushes illegal specification data.
             *
             */
            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 {
            	// 销毁无用的Invoker，避免服务消费者调用已下线的服务的服务
                destroyUnusedInvokers(oldUrlInvokerMap, newUrlInvokerMap); // Close the unused Invoker
            } catch (Exception e) {
                logger.warn("destroyUnusedInvokers error. ", e);
            }
        }
    }

private Map<String, Invoker<T>> toInvokers(List<URL> urls) {
        Map<String, Invoker<T>> newUrlInvokerMap = new HashMap<>();
        if (urls == null || urls.isEmpty()) {
            return newUrlInvokerMap;
        }
        Set<String> keys = new HashSet<>();
        // 获取服务消费端配置的协议
        String queryProtocols = this.queryMap.get(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(",");
                // 检测服务提供者协议是否被服务消费者所支持
                for (String acceptProtocol : acceptProtocols) {
                    if (providerUrl.getProtocol().equals(acceptProtocol)) {
                        accept = true;
                        break;
                    }
                }
                if (!accept) {
                	// 若服务消费者协议头不被消费者所支持，则忽略当前 providerUrl
                    continue;
                }
            }
            // 忽略 empty 协议
            if (EMPTY_PROTOCOL.equals(providerUrl.getProtocol())) {
                continue;
            }
            // 通过 SPI 检测服务端协议是否被消费端支持
            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;
            }
            // 合并 url
            URL url = mergeUrl(providerUrl);
    
            String key = url.toFullString(); // The parameter urls are sorted
            if (keys.contains(key)) { // Repeated url
                continue;
            }
            keys.add(key);
            // 本地 Invoker 缓存列表
            Map<String, Invoker<T>> localUrlInvokerMap = this.urlInvokerMap; // local reference
            Invoker<T> invoker = localUrlInvokerMap == null ? null : localUrlInvokerMap.get(key);
           / / 缓存未命中
            if (invoker == null) { 
                try {
                    boolean enabled = true;
                    // 获取 disable 配置，并修改 enable 变量
                    if (url.hasParameter(DISABLED_KEY)) {
                        enabled = !url.getParameter(DISABLED_KEY, false);
                    } else {
                        enabled = url.getParameter(ENABLED_KEY, true);
                    }
                    if (enabled) {
                    	// 调用 refer 获取 Invoker
                        invoker = new InvokerDelegate<>(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) {
                	// 缓存 Invoker 实例
                    newUrlInvokerMap.put(key, invoker);
                }
            } else {
            	// 缓存命中，将 invoker 存储到 newUrlInvokerMap 中
                newUrlInvokerMap.put(key, invoker);
            }
        }
        keys.clear();
        return newUrlInvokerMap;
    }

也就是注册中心有变化，则更新`urlInvokerMap`和`cachedInvokerUrls`的值，这就是官网提到的它的值可能是动态变化的，比如注册中心推送变更的原因所在。

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