目录

• dubbo版本
• No provider available from registry

dubbo版本

1. dubbo版本2.6.7

No provider available from registry

1. 如果没有服务提供者，消费者会抛出异常

   No provider available from registry dubbo-zookeeper:2181 for service group0/cn.jannal.dubbo.facade.DemoService:1.0.0 on consumer 172.16.117.33 use dubbo version 2.6.7, please check status of providers(disabled, not registered or in blacklist).
   

2. 上面的异常是在RegistryDirectory#doList方法中抛出。可以看到当forbidden=true才抛出异常

   public List<Invoker<T>> doList(Invocation invocation) {
       // 服务提供者关闭或禁用了服务，此时抛出 No provider 异常
       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).");
       }
   		...省略...
   }  
   

3. forbidden设置为true是在RegistryDirectory#refreshInvoker设置的。refreshInvoker是在RegistryDirectory#notify中被调用。 当某个服务的provider有变化时RegistryDirectory#notify就会被调用（例如zookeeper上某个服务的provider目录里的内容发生变化，则zk监听器会被触发）

   // URL的protocol是如何变为empty的？
   private void refreshInvoker(List<URL> invokerUrls) {
     if (invokerUrls != null && invokerUrls.size() == 1 && invokerUrls.get(0) != null
             && Constants.EMPTY_PROTOCOL.equals(invokerUrls.get(0).getProtocol())) {
         this.forbidden = true; // Forbid to access
         this.methodInvokerMap = null; // Set the method invoker map to null
         destroyAllInvokers(); // Close all invokers
     } 
     ...省略...
   }
   
    @Override
   public synchronized void notify(List<URL> urls) {
     List<URL> invokerUrls = new ArrayList<URL>();
     List<URL> routerUrls = new ArrayList<URL>();
     List<URL> configuratorUrls = new ArrayList<URL>();
     for (URL url : urls) {
         String protocol = url.getProtocol();
         String category = url.getParameter(Constants.CATEGORY_KEY, Constants.DEFAULT_CATEGORY);
         if (Constants.ROUTERS_CATEGORY.equals(category)
                 || Constants.ROUTE_PROTOCOL.equals(protocol)) {
             routerUrls.add(url);
         } else if (Constants.CONFIGURATORS_CATEGORY.equals(category)
                 || Constants.OVERRIDE_PROTOCOL.equals(protocol)) {
             configuratorUrls.add(url);
         } else if (Constants.PROVIDERS_CATEGORY.equals(category)) {
             invokerUrls.add(url);
         } else {
             logger.warn("Unsupported category " + category + " in notified url: " + url + " from registry " + getUrl().getAddress() + " to consumer " + NetUtils.getLocalHost());
         }
     }
     ...省略...
     // providers
     refreshInvoker(invokerUrls);
   }
   

4. 查看notify URL发现URL中的协议是empty。那URL的protocol是如何变为empty的？

   

5. 查看ZookeeperRegistry#doSubscribe,zookeeper初次订阅或者订阅的信息有变更时,都会触发ChildListener的childChanged方法，此方法调用前会调用toUrlsWithEmpty方法进行empty协议的设置。即如果consumer的URL与所有provider都不匹配，则将consumer的protocol设置为empty协议，从而最终导致forbidden=true

   protected void doSubscribe(final URL url, final NotifyListener listener){
     
     ...省略...
     ChildListener zkListener = listeners.get(listener);
     if (zkListener == null) {
         listeners.putIfAbsent(listener, new ChildListener() {
             @Override
             public void childChanged(String parentPath, List<String> currentChilds) {
                 ZookeeperRegistry.this.notify(url, listener, toUrlsWithEmpty(url, parentPath, currentChilds));
             }
         });
         zkListener = listeners.get(listener);
     }
     ...省略...
   }
   
   
   private List<URL> toUrlsWithEmpty(URL consumer, String path, List<String> providers) {
       List<URL> urls = toUrlsWithoutEmpty(consumer, providers);
     	//如果consumer的URL与所有provider都不匹配，则将consumer的protocol设置为empty协议
       if (urls == null || urls.isEmpty()) {
           int i = path.lastIndexOf('/');
           String category = i < 0 ? path : path.substring(i + 1);
           URL empty = consumer.setProtocol(Constants.EMPTY_PROTOCOL).addParameter(Constants.CATEGORY_KEY, category);
           urls.add(empty);
       }
       return urls;
   }
   
   private List<URL> toUrlsWithoutEmpty(URL consumer, List<String> providers) {
       List<URL> urls = new ArrayList<URL>();
       if (providers != null && !providers.isEmpty()) {
         	//遍历所有provider
           for (String provider : providers) {
               provider = URL.decode(provider);
               if (provider.contains("://")) {
                   URL url = URL.valueOf(provider);
                 	//如果与consumer的URL匹配，则添加url列表中
                   if (UrlUtils.isMatch(consumer, url)) {
                       urls.add(url);
                   }
               }
           }
       }
       return urls;
   }