Dubbo源码手记-服务注册

今天来简单做一下Dubbo服务注册部分源码学习手记。

一、Dubbo配置解析

目前Dubbo最多的用法就是跟Spring集成,既然跟Spring集成,那么,Dubbo对象的实例化都将交由Spring统一处理。而Dubbo配置,对于Spring来说其实就是自定标签。这里Dubbo自定义标签解析类,在Dubbo配置模块(\dubbo-config\dubbo-config-spring\src\main\resources\META-INF/spring.handlers)进行了声明:

http\://dubbo.apache.org/schema/dubbo=org.apache.dubbo.config.spring.schema.DubboNamespaceHandler
http\://code.alibabatech.com/schema/dubbo=org.apache.dubbo.config.spring.schema.DubboNamespaceHandler
 1 public class DubboNamespaceHandler extends NamespaceHandlerSupport {
 2     static {
 3         Version.checkDuplicate(DubboNamespaceHandler.class);
 4     }
 5     @Override
 6     public void init() {
 7         registerBeanDefinitionParser("application", new DubboBeanDefinitionParser(ApplicationConfig.class, true));
 8         registerBeanDefinitionParser("module", new DubboBeanDefinitionParser(ModuleConfig.class, true));
 9         registerBeanDefinitionParser("registry", new DubboBeanDefinitionParser(RegistryConfig.class, true));
10         registerBeanDefinitionParser("config-center", new DubboBeanDefinitionParser(ConfigCenterBean.class, true));
11         registerBeanDefinitionParser("monitor", new DubboBeanDefinitionParser(MonitorConfig.class, true));
12         registerBeanDefinitionParser("provider", new DubboBeanDefinitionParser(ProviderConfig.class, true));
13         registerBeanDefinitionParser("consumer", new DubboBeanDefinitionParser(ConsumerConfig.class, true));
14         registerBeanDefinitionParser("protocol", new DubboBeanDefinitionParser(ProtocolConfig.class, true));
15         registerBeanDefinitionParser("service", new DubboBeanDefinitionParser(ServiceBean.class, true));
16         registerBeanDefinitionParser("reference", new DubboBeanDefinitionParser(ReferenceBean.class, false));
17         registerBeanDefinitionParser("annotation", new AnnotationBeanDefinitionParser());
18     }
19 }

对应一下Dubbo服务提供方的配置文件:

<dubbo:application name="demo-provider"/>
<dubbo:registry address="zookeeper://127.0.0.1:2181" />
<dubbo:protocol name="dubbo"/>
<bean id="demoService" class="org.apache.dubbo.demo.provider.DemoServiceImpl"/>
<dubbo:service interface="org.apache.dubbo.demo.DemoService" ref="demoService"/>

就是将这些标签解析成ApplicationConfig...ServiceBean等等对象。而服务注册部分最主要的桥梁就在于ServiceBean初始化解析完毕的时候。有Spring容器调用ServiceBean.afterPropertiesSet方法:

1 public void afterPropertiesSet() throws Exception {
2     // 此处省略配置检查
3     export();
4 }    

二、配置检查与缺省填充

进入export方法中,首先会对ServiceBean进行发布前的配置检查与填充。

1 public synchronized void export() {
2         checkAndUpdateSubConfigs(); // 加载并更新配置信息到Bean对象中,并检查
3 }

这里会有一系列的配置校验与配置填充的逻辑:

 1 public void checkAndUpdateSubConfigs() {
 2     checkDefault();
 3     if (provider != null) {
 4         inheritIfAbsentFromProvider();
 5     }
 6     if (module != null) {
 7         inheritIfAbsentFromModule();
 8     }
 9     if (application != null) {
10         inheritIfAbsentFromApplication();
11     }
12     checkApplication();
13     checkRegistry();
14     checkProtocol();
15     this.refresh();
16     checkMetadataReport();
17     checkRegistryDataConfig();
18     try {
19         interfaceClass = Class.forName(interfaceName, true, Thread.currentThread().getContextClassLoader());
20     } catch (ClassNotFoundException e) {
21         throw new IllegalStateException(e.getMessage(), e);
22     }
23     checkInterfaceAndMethods(interfaceClass, methods);
24     checkRef();
25     checkStubAndLocal(interfaceClass);
26     checkMock(interfaceClass);
27 }

这里只列了部分配置检查与填充。总体配置的区分是否配置中心优先,优先级为:

 1 public void refresh() {
 2     // getPrefix为对应配置类的前缀,ProviderConfig->Provider, ServiceBean->Service,
 3     // getId为beanId,
 4     CompositeConfiguration compositeConfiguration = Environment.getInstance().getConfiguration(getPrefix(), getId());
 5     InmemoryConfiguration config = new InmemoryConfiguration(getPrefix(), getId());
 6     config.addProperties(getMetaData()); // Bean对象的初始值
 7     if (Environment.getInstance().isConfigCenterFirst()) {
 8         // -D系统属性 > 配置中心应用配置 > 配置中心全局配置 > Bean对象的初始值 > 属性文件中的信息
 9         compositeConfiguration.addConfiguration(3, config);
10     } else {
11         // -D > Bean对象的初始值 > 配置中心应用配置 > 配置中心全局配置 > 属性文件中的信息
12         compositeConfiguration.addConfiguration(1, config);
13     }
14 }

三、获取和构建注册中心统一资源定位器

1 private void doExportUrls() {
2     // 获取注册中心统一资源列表,如果注册中心没有初始化,则先初始化
3     List registryURLs = loadRegistries(true);
4     // 将目标服务所有协议模式注册到每一个注册中心上
5     for (ProtocolConfig protocolConfig : protocols) {
6         doExportUrlsFor1Protocol(protocolConfig, registryURLs);
7     }
8 }

四、服务启动与服务注册

在doExportUrlsForProtocal方法里边其实就做了以下几件事:

 1 private void doExportUrlsFor1Protocol(ProtocolConfig protocolConfig, List registryURLs) {
 2      Map map = builderUrl();
 3      // 代表一个服务
 4      URL url = new URL(name, host, port, (StringUtils.isEmpty(contextPath) ? "" : contextPath + "/") + path, map);
 5      // 通过代理工厂将ref对象转化成invoker对象
 6      Invoker invoker = proxyFactory.getInvoker(ref, (Class) interfaceClass, url);
 7      //代理invoker对象
 8      DelegateProviderMetaDataInvoker wrapperInvoker = new DelegateProviderMetaDataInvoker(invoker, this);
 9      // 使用配置协议启动、暴露服务
10      Exporter exporter = protocol.export(wrapperInvoker);
11      //一个服务可能有多个提供者,保存在一起
12      exporters.add(exporter);
13 }

这里,我们着重看第10行服务暴露部分,这里调用export方法,如果是Dubbo协议的话,分别列举一下DubboProtocal、HttpProtocol的export:

 1 public class DubboProtocol extends AbstractProtocol {
 2     public  Exporter export(Invoker invoker) throws RpcException {
 3         URL url = invoker.getUrl();
 4         //忽略若干代码
 5         //打开服务
 6         openServer(url);
 7         optimizeSerialization(url);
 8         return exporter;
 9     }
10 }
1 public class HttpProtocol extends AbstractProxyProtocol {
2     protected  Runnable doExport(final T impl, Class type, URL url) throws RpcException {
3         String addr = getAddr(url);
4         HttpServer server = serverMap.get(addr);
5         server = httpBinder.bind(url, new InternalHandler());
6     }
7 }

其实这块就是,根据不同协议分别做了服务启动,如果是Dubbo协议则启动NettyServer,如果是Http协议则启动一个Tomcat。

那么现在服务启动了,但是在哪里注册了呢?其实我们要关注这个protocol对象的构建:

 1 /**
 2  * The {@link Protocol} implementation with adaptive functionality,it will be different in different scenarios.
 3  * A particular {@link Protocol} implementation is determined by the protocol attribute in the {@link URL}.
 4  * For example:
 5  *
 6  * 
  • when the url is registry://224.5.6.7:1234/org.apache.dubbo.registry.RegistryService?application=dubbo-sample, 7 * then the protocol is RegistryProtocol
  • 8 * 9 *
  • when the url is dubbo://224.5.6.7:1234/org.apache.dubbo.config.api.DemoService?application=dubbo-sample, then 10 * the protocol is DubboProtocol
  • 11 *

    12 * Actually,when the {@link ExtensionLoader} init the {@link Protocol} instants,it will automatically wraps two 13 * layers, and eventually will get a ProtocolFilterWrapper or ProtocolListenerWrapper 14 */ 15 private static final Protocol protocol = ExtensionLoader.getExtensionLoader(Protocol.class).getAdaptiveExtension();

    这段源码的意思是,在获取Protocol实例的时候,Dubbo框架自动给包装了两个切面,其实服务注册就是在这个切面里边完成的:

     1 public class ProtocolListenerWrapper implements Protocol {
     2     private final Protocol protocol;
     3     @Override
     4     public  Exporter export(Invoker invoker) throws RpcException {
     5         //如果是registerProtocol,则调用RegisterProtocol.export方法
     6         if (Constants.REGISTRY_PROTOCOL.equals(invoker.getUrl().getProtocol())) {
     7             return protocol.export(invoker);
     8         }
     9         return new ListenerExporterWrapper(protocol.export(invoker),
    10                 Collections.unmodifiableList(ExtensionLoader.getExtensionLoader(ExporterListener.class)
    11                         .getActivateExtension(invoker.getUrl(), Constants.EXPORTER_LISTENER_KEY)));
    12     }
    13 }

    再看看RegisterProtocol的export:

    1 public class RegistryProtocol implements Protocol {
    2     @Override
    3     public  Exporter export(final Invoker originInvoker) throws RpcException {
    4         register(registryUrl, registeredProviderUrl); // 服务注册
    5     }
    6 }

    如果注册中心是ZK的话其实就是给ZK写数据:

     1 @Override
     2 public void register(URL url) {
     3          //忽略很多代码
     4         doRegister(url);
     5         //忽略很多代码
     6 }
     7 protected void doRegister(URL url) {
     8     try {
     9         zkClient.create(toUrlPath(url), url.getParameter(Constants.DYNAMIC_KEY, true));
    10     } catch (Throwable e) {
    11         throw new RpcException("Failed to register " + url + " to zookeeper " + getUrl() + ", cause: " + e.getMessage(), e);
    12     }
    13 }
     
     

    相关文章:https://www.jianshu.com/p/7f3871492c71

     

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