Dubbo源碼分析（一）啓動Provider

Dubbo是阿里巴巴開源的一個分佈式服務框架，在阿里內部和其他公司都有廣泛的應用，是目前比較成熟的一個服務框架。筆者將從源碼層面對Dubbo進行分析，學習其中優秀的設計。

經過數年的沉澱，Dubbo整體的設計和抽象已非常完善，這裏介紹的Provider啓動就涉及到了多個抽象模型。本文使用的版本爲2.5.3。

首先，當發佈一個服務的Server時，我們需要編寫一個Spring配置文件。

provider.xml

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<?xml version="1.0" encoding="UTF-8"?> <beans xmlns="...">     <dubbo:application name="hello-world-app" />     <dubbo:protocol name="dubbo" port="20880" />     <dubbo:service interface="net.beamlight.dubbo.service.DemoService" ref="demoService" registry="N/A" />     <bean id="demoService" class="net.beamlight.dubbo.provider.DemoServiceImpl" /> </beans>

其中關鍵的一行爲<dubbo:service …>，這裏使用了擴展的Spring Schema，相關定義在Dubbo jar包META-INF目錄下的spring.handlers、spring.schemas、dubbo.xsd中。指定的配置解析器爲com.alibaba.dubbo.config.spring.schema.DubboNamespaceHandler，所以它也就成了啓動provider的“應用程序入口”

DubboNamespaceHandler.java

Java

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publicvoidinit(){         ...         registerBeanDefinitionParser("service",newDubboBeanDefinitionParser(ServiceBean.class,true));         ...     }

DubboNamespaceHandler的邏輯很簡單，就是將xml文件中的配置信息轉換成對應的bean，繼續看關鍵的com.alibaba.dubbo.config.spring.ServiceBean

ServiceBean.java

Java

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@SuppressWarnings({ "unchecked", "deprecation" })     public void afterPropertiesSet() throws Exception {         ...         if (! isDelay()) {             export();         }     }

經過大段配置代碼後來到父類ServiceConfig的export()方法，它將啓動負責provider網絡通信的Server並將服務地址發佈出去。最終調用到doExportUrlsFor1Protocol()

ServiceConfig.java

Java

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privatestaticfinalProtocolprotocol=ExtensionLoader.getExtensionLoader(Protocol.class).getAdaptiveExtension();       privatevoiddoExportUrlsFor1Protocol(ProtocolConfigprotocolConfig,List<URL>registryURLs){         ...         Invoker<?>invoker=proxyFactory.getInvoker(ref,(Class)interfaceClass,url);         Exporter<?>exporter=protocol.export(invoker);         exporters.add(exporter);         ...     }

• Invoker – 執行具體的遠程調用
• Protocol – 服務地址的發佈和訂閱
• Exporter – 暴露服務的引用，或取消暴露

Protocol的具體實現類由配置指定，默認創建一個DubboProtocol，其export()方法轉到openServer()與createServer()

DubboProtocol.java

Java

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private ExchangeHandler requestHandler = new ExchangeHandlerAdapter() {         ...     };       private ExchangeServer createServer(URL url) {         ...         ExchangeServer server;         try {             server = Exchangers.bind(url, requestHandler);         } catch (RemotingException e) {             throw new RpcException("Fail to start server(url: " + url + ") " + e.getMessage(), e);         }         ...         return server;     }

requestHandler包含通信協議的主要處理邏輯，而server的創建來自Exchangers

Exchangers.java

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publicstaticExchangeServerbind(URLurl,ExchangeHandlerhandler)throwsRemotingException{         ...         returngetExchanger(url).bind(url,handler);     }

getExchanger()獲取的實例也來源於配置，默認返回HeaderExchanger

HeaderExchanger.java

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public class HeaderExchanger implements Exchanger {       public ExchangeClient connect(URL url, ExchangeHandler handler) throws RemotingException {         return new HeaderExchangeClient(Transporters.connect(url, new DecodeHandler(new HeaderExchangeHandler(handler))));     }       public ExchangeServer bind(URL url, ExchangeHandler handler) throws RemotingException {         return new HeaderExchangeServer(Transporters.bind(url, new DecodeHandler(new HeaderExchangeHandler(handler))));     } }

可以看到Server與Client實例均是在這裏創建的，HeaderExchangeServer需要一個Server類型的參數，來自Transporters.bind()

Transporters.java

Java

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publicstaticServerbind(URLurl,ChannelHandler...handlers)throwsRemotingException{         ...         returngetTransporter().bind(url,handler);     }

getTransporter()獲取的實例來源於配置，默認返回一個NettyTransporter

NettyTransporter.java

Java

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public class NettyTransporter implements Transporter {          public Server bind(URL url, ChannelHandler listener) throws RemotingException {         return new NettyServer(url, listener);     }       public Client connect(URL url, ChannelHandler listener) throws RemotingException {         return new NettyClient(url, listener);     } }

最終來到了NettyServer，在它的doOpen()方法中看到了我們熟悉的Netty Bootstrap

NettyServer.java

Java

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publicclassNettyServerextendsAbstractServerimplementsServer{       publicNettyServer(URLurl,ChannelHandlerhandler)throwsRemotingException{         super(url,ChannelHandlers.wrap(handler,ExecutorUtil.setThreadName(url,SERVER_THREAD_POOL_NAME)));     }       @Override     protectedvoiddoOpen()throwsThrowable{         NettyHelper.setNettyLoggerFactory();         ExecutorServiceboss=Executors.newCachedThreadPool(newNamedThreadFactory("NettyServerBoss",true));         ExecutorServiceworker=Executors.newCachedThreadPool(newNamedThreadFactory("NettyServerWorker",true));         ChannelFactorychannelFactory=newNioServerSocketChannelFactory(boss,worker,getUrl().getPositiveParameter(Constants.IO_THREADS_KEY,Constants.DEFAULT_IO_THREADS));         bootstrap=newServerBootstrap(channelFactory);                  finalNettyHandlernettyHandler=newNettyHandler(getUrl(),this);         channels=nettyHandler.getChannels();                  bootstrap.setPipelineFactory(newChannelPipelineFactory(){             publicChannelPipelinegetPipeline(){                 NettyCodecAdapteradapter=newNettyCodecAdapter(getCodec(),getUrl(),NettyServer.this);                 ChannelPipelinepipeline=Channels.pipeline();                   pipeline.addLast("decoder",adapter.getDecoder());                 pipeline.addLast("encoder",adapter.getEncoder());                 pipeline.addLast("handler",nettyHandler);                 returnpipeline;             }         });         // bind         channel=bootstrap.bind(getBindAddress());     } }

文中提到的核心類包括

1. DubboNamespaceHandler
2. ServiceBean
3. ServiceConfig
4. DubboProtocol
5. Exchangers
6. HeaderExchanger
7. HeaderExchangeServer
8. NettyTransporter
9. NettyServer

至此，所有Provider啓動的工作結束了，接下來就是接收請求並交給handler處理的過程，這些將在後面的文章予以介紹。