[dubbo 源码之 ]1. 服务提供方如何发布服务

服务发布

启动流程

`1.ServiceConfig#export`

服务提供方在启动部署时，dubbo会调用ServiceConfig#export来激活服务发布流程，如下所示：

Java API:

// 1. 创建ServiceConfig实例
ServiceConfig<IGreetingService> serviceConfig = new ServiceConfig<>();
// 2. 设置应用程序配置
serviceConfig.setApplication(new ApplicationConfig("deep-in-dubbo-first-provider"));
// 3. 设置注册中心
RegistryConfig registryConfig = new RegistryConfig("zookeeper://127.0.0.1:2181/");
serviceConfig.setRegistry(registryConfig);
// 4. 设置接口和实现类
// 5. 设置服务分组和版本
// dubbo中，服务接口+服务分组+服务版本唯一的确定一个服务，同一个接口可以有不同版本，方便维护升级
serviceConfig.setInterface(IGreetingService.class);
serviceConfig.setRef(new GreetingServiceImpl());
serviceConfig.setVersion("1.0.0");
serviceConfig.setGroup("dubbo-sxzhongf-group");
RpcContext.getContext().setAttachment("age","18");

        // 7. 导出服务，启动Netty监听链接请求，并将服务注册到注册中心
        serviceConfig.export();

        // 8. 挂起线程，避免服务停止
        System.out.println("api provider service is started...");
        System.in.read();
```

  <beans xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xmlns:dubbo="http://dubbo.apache.org/schema/dubbo"
         xmlns="http://www.springframework.org/schema/beans"
         xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-4.3.xsd
         http://dubbo.apache.org/schema/dubbo http://dubbo.apache.org/schema/dubbo/dubbo.xsd">
  
      <!-- provider's application name, used for tracing dependency relationship -->
      <dubbo:application name="first-xml-provider"/>
      <!-- use multicast registry center to export service -->
      <dubbo:registry address="zookeeper://127.0.0.1:2181/"/>
      <!-- use dubbo protocol to export service on port 20880 -->
      <dubbo:protocol name="dubbo" port="20880"/>
      <!-- service implementation, as same as regular local bean -->
      <bean id="demoService" class="com.sxzhongf.deep.in.dubbo.provider.service.impl.GreetingServiceImpl"/>
      <!-- declare the service interface to be exported -->
      <dubbo:service interface="com.sxzhongf.deep.in.dubbo.api.service.IGreetingService"
                     ref="demoService" version="1.0.0" group="dubbo-sxzhongf-group">
          <dubbo:method name="sayHello" async="false" timeout="0" retries="3"></dubbo:method>
          <dubbo:method name="testGeneric" async="false" timeout="10000" retries="3"></dubbo:method>
      </dubbo:service>
  </beans>

查看export源码可知，总共有三种服务导出选项：
java public synchronized void export() { //1. 是否导出 if (!shouldExport()) { return; } ... //2.延迟导出 if (shouldDelay()) { DELAY_EXPORT_EXECUTOR.schedule(this::doExport, getDelay(), TimeUnit.MILLISECONDS); } else { //3.立刻导出 doExport(); } }

`2.ServiceConfig#doExport`

此方法主要是根据设置的属性进行合法性检查，主要包含是否已被导出，doExportUrls();

`3.doExportUrls`

`4.ConfigValidationUtils#loadRegistries`

此方法用来加载所有的服务注册中心对象，在dubbo中,一个service可以被注册到多个注册中心。

通过doExportUrlsFor1Protocol(protocolConfig, registryURLs);

`5.doExportUrlsFor1Protocol`

在此方法中会将所有的参数封装成org.apache.dubbo.common.URL对象，然后执行具体的服务导出。

具体过程分为：

1.解析MethodConfig配置（单独的方法调用参数设置）
2.泛型调用类型设置
3.拼接URL参数

4.导出具体服务

导出又分为四种范围(scope)：

SCOPE_NONE = "none"，如果设定为none，表示该服务不导出。
SCOPE_LOCAL = "local" ，如果设定为local，表示该服务导出到本地（injvm--伪协议，实现类为：org.apache.dubbo.rpc.protocol.injvm.InjvmProtocol）
- SCOPE_REMOTE = "remote"，如果设定为remote,表示该服务导出到远程。
如果有注册中心，发布到注册中心
如果没有注册中心，则表示服务是直连方式
从dubbo-2.7.0开始，新增加了WritableMetadataService 来存储dubbo 服务的元数据，元数据可以存储在远端配置中心和本地，默认是存储在本地，通过设置：METADATA_KEY = "metadata"
- DEFAULT_METADATA_STORAGE_TYPE = "local"
- REMOTE_METADATA_STORAGE_TYPE = "remote"
```
    WritableMetadataService metadataService = WritableMetadataService.getExtension(url.getParameter(METADATA_KEY, DEFAULT_METADATA_STORAGE_TYPE));
    if (metadataService != null) { metadataService.publishServiceDefinition(url);
    }
```
- 不设置，导出到本地和远端

最终执行导出的代码如下

// 扩展适配类
private static final Protocol protocol = ExtensionLoader.getExtensionLoader(Protocol.class).getAdaptiveExtension();

// 扩展适配类
private static final ProxyFactory PROXY_FACTORY = ExtensionLoader.getExtensionLoader(ProxyFactory.class).getAdaptiveExtension();
...

Invoker<?> invoker = PROXY_FACTORY.getInvoker(ref, (Class) interfaceClass, registryURL.addParameterAndEncoded(EXPORT_KEY, url.toFullString()));
DelegateProviderMetaDataInvoker wrapperInvoker = new DelegateProviderMetaDataInvoker(invoker, this);

Exporter<?> exporter = protocol.export(wrapperInvoker);
exporters.add(exporter);

由于protocol和PROXY_FACTORY都是扩展适配类，跟踪代码我们可以发现：

执行PROXY_FACTORY.getInvoker的时候实际上首先执行扩展接口ProxyFactory的适配类ProxyFactory$Adaptive的getInvoker方法，根据URL中参数proxy的设置类型选择具体的代理工厂，默认使用的是javassist,,因此又调用了org.apache.dubbo.rpc.proxy.javassist.JavassistProxyFactory#getInvoker来获取代理实现类，代码如下：


public class JavassistProxyFactory extends AbstractProxyFactory {
    ...
    @Override
    public <T> Invoker<T> getInvoker(T proxy, Class<T> type, URL url) {
        // TODO Wrapper cannot handle this scenario correctly: the classname contains '$'
        // 这里使用javassist动态代理生成serviceImpl实现类的包装类`Wraaper...`
        final Wrapper wrapper = Wrapper.getWrapper(proxy.getClass().getName().indexOf('$') < 0 ? proxy.getClass() : type);
        return new AbstractProxyInvoker<T>(proxy, type, url) {
            @Override
            protected Object doInvoke(T proxy, String methodName,
                                      Class<?>[] parameterTypes,
                                      Object[] arguments) throws Throwable {
                return wrapper.invokeMethod(proxy, methodName, parameterTypes, arguments);
            }
        };
    }
    ...
}

上面代码有2个目的：

inal Wrapper wrapper = Wrapper.getWrapper(...);用来生成具体serviceImpl的包装类，减少反射的性能损耗；
return new AbstractProxyInvoker<T>... 返回了一个抽象的代理invoker，并且重写了doInvoker方法，重写之后使用包装类中的invokeMethod来调用方法。

经过上述2步，服务提供方就将具体的实现类转换为Invoker代理。

然后，当执行protocol.export(),实际上也是调用了Protocol$Adaptive#export()方法，同时也分为两种情况
如果为远程暴露，则执行RegistryProtocol#export
如果为本地暴露，则只需InjvmProtocol#export
由于dubbo的增强SPI特性支持，injectExtension((T) wrapperClass.getConstructor(type).newInstance(instance));,则在调用之前会一层一层调用，ProtocolFilterWrapper->ProtocolListenerWrapper->QosProtocolWrapper,最后会调用export方法，此方法会将Invoker转换为Exporter对象，在org.apache.dubbo.registry.integration.RegistryProtocol#export方法中,org.apache.dubbo.registry.integration.RegistryProtocol#doLocalExport方法启NettyServer来监听服务，org.apache.dubbo.registry.integration.RegistryProtocol#register将当前的服务注册到注册中心。
doLocalExport 是如何启动NettyServer呢？

                private <T> ExporterChangeableWrapper<T> doLocalExport(final Invoker<T> originInvoker, URL providerUrl) {
                    String key = getCacheKey(originInvoker);
            
                    return (ExporterChangeableWrapper<T>) bounds.computeIfAbsent(key, s -> {
                        Invoker<?> invokerDelegate = new InvokerDelegate<>(originInvoker, providerUrl);
                        return new ExporterChangeableWrapper<>((Exporter<T>) protocol.export(invokerDelegate), originInvoker);
                    });
                }

此时URL中的protocol类型为默认的dubbo，因此会执行DubboProtocol#export进行转换，如下:

            @Override
                public <T> Exporter<T> export(Invoker<T> invoker) throws RpcException {
                    URL url = invoker.getUrl();
            
                    // export service.
                    String key = serviceKey(url);
                    // invoker->exporter
                    DubboExporter<T> exporter = new DubboExporter<T>(invoker, key, exporterMap);
                    exporterMap.put(key, exporter);
            
                    //export an stub service for dispatching event
                    Boolean isStubSupportEvent = url.getParameter(STUB_EVENT_KEY, DEFAULT_STUB_EVENT);
                    Boolean isCallbackservice = url.getParameter(IS_CALLBACK_SERVICE, false);
                    if (isStubSupportEvent && !isCallbackservice) {
                        String stubServiceMethods = url.getParameter(STUB_EVENT_METHODS_KEY);
                        if (stubServiceMethods == null || stubServiceMethods.length() == 0) {
                            if (logger.isWarnEnabled()) {
                                logger.warn(new IllegalStateException("consumer [" + url.getParameter(INTERFACE_KEY) +
                                        "], has set stubproxy support event ,but no stub methods founded."));
                            }
            
                        } else {
                            stubServiceMethodsMap.put(url.getServiceKey(), stubServiceMethods);
                        }
                    }
                    //创建server
                    openServer(url);
                    //序列化提示
                    optimizeSerialization(url);
            
                    return exporter;
                }

可以看到代码执行到openServer,因为key=getAddress()=ip+port,因此，同一台机器只会开启一个NettyServer.

               private void openServer(URL url) {
                   // find server.
                   String key = url.getAddress();
                   //client can export a service which's only for server to invoke
                   boolean isServer = url.getParameter(IS_SERVER_KEY, true);
                   if (isServer) {
                       ProtocolServer server = serverMap.get(key);
                       if (server == null) {
                           synchronized (this) {
                               server = serverMap.get(key);
                               if (server == null) {
                                   serverMap.put(key, createServer(url));
                               }
                           }
                       } else {
                           // server supports reset, use together with override
                           server.reset(url);
                       }
                   }
               }

对于org.apache.dubbo.remoting.Transporter 的适配类选择有三种：MinaTransporter、 NettyTransporter、GrizzlyTransporter，关于JavaNIO：Apache Mina、JBoss Netty、Sun Grizzly 框架对比：传送门

NettyServer启动之后，回到org.apache.dubbo.registry.integration.RegistryProtocol#export方法，继续执行将服务注册到注册中心，我们以Zookeeper为例：
1.首先查找所有注册中心

                final Registry registry = getRegistry(originInvoker);
                ...
                protected Registry getRegistry(final Invoker<?> originInvoker) {
                    URL registryUrl = getRegistryUrl(originInvoker);
                    return registryFactory.getRegistry(registryUrl);
                }

因为RegistryFactory是一个SPI扩展接口，代码中设置的为zookeeper，因此这里调用的是ZookeeperRegistryFactory，继承自：org.apache.dubbo.registry.support.AbstractRegistryFactory#getRegistry(org.apache.dubbo.common.URL),在此方法中调用了createRegistry，但是ZookeeperRegistryFactory重写了createRegistry,因此具体调用的是ZookeeperRegistryFactory#createRegistry，该方法返回了一个new ZookeeperRegistry(url, zookeeperTransporter)实例对象。

2.开始注册，RegistryProtocol#register方法执行注册动作，首先获取到我们在上一步找到的注册中心ZookeeperRegistry,ZookeeperRegistry 执行父类org.apache.dubbo.registry.support.FailbackRegistry#register，在该方法中会调用抽象方法：doRegister,ZookeeperRegistry 重写了改方法，则执行ZookeeperRegistry#doRegister ,如下：

                @Override
                public void doRegister(URL url) {
                    try {
                        zkClient.create(toUrlPath(url), url.getParameter(DYNAMIC_KEY, true));
                    } catch (Throwable e) {
                        throw new RpcException("Failed to register " + url + " to zookeeper " + getUrl() + ", cause: " + e.getMessage(), e);
                    }
                }

3.toUrlPath方法会把org.apache.dubbo.common.URL转换格式后存储到zookeeper,如下：

                dubbo://172.16.44.21:20880/com.sxzhongf.deep.in.dubbo.api.service.IGreetingService?anyhost=true&application=deep-in-dubbo-first-provider&default=true&deprecated=false&dubbo=2.0.2&dynamic=true&generic=false&group=dubbo-sxzhongf-group&interface=com.sxzhongf.deep.in.dubbo.api.service.IGreetingService&methods=sayHello,testGeneric&pid=8480&release=2.7.5&revision=1.0.0&side=provider&timestamp=1582872610313&version=1.0.0
                
                -----------------------转换------------------------
                
                /dubbo/com.sxzhongf.deep.in.dubbo.api.service.IGreetingService/providers/dubbo%3A%2F%2F172.16.44.21%3A20880%2Fcom.sxzhongf.deep.in.dubbo.api.service.IGreetingService%3Fanyhost%3Dtrue%26application%3Ddeep-in-dubbo-first-provider%26default%3Dtrue%26deprecated%3Dfalse%26dubbo%3D2.0.2%26dynamic%3Dtrue%26generic%3Dfalse%26group%3Ddubbo-sxzhongf-group%26interface%3Dcom.sxzhongf.deep.in.dubbo.api.service.IGreetingService%26methods%3DsayHello%2CtestGeneric%26pid%3D8480%26release%3D2.7.5%26revision%3D1.0.0%26side%3Dprovider%26timestamp%3D1582872610313%26version%3D1.0.0

转换之后的格式其实就是我们在zookeeper中看到的一样了，不过有几个目录：

dubbo
com.sxzhongf.deep.in.dubbo.api.service.IGreetingService
providers

               [zk: localhost:2181(CONNECTED) 2] ls  /dubbo/com.sxzhongf.deep.in.dubbo.api.service.IGreetingService/providers
               [dubbo%3A%2F%2F172.16.44.21%3A20880%2Fcom.sxzhongf.deep.in.dubbo.api.service.IGreetingService%3Fanyhost%3Dtrue%26application%3Ddeep-in-dubbo-first-provider%26default%3Dtrue%26deprecated%3Dfalse%26dubbo%3D2.0.2%26dynamic%3Dtrue%26generic%3Dfalse%26group%3Ddubbo-sxzhongf-group%26interface%3Dcom.sxzhongf.deep.in.dubbo.api.service.IGreetingService%26methods%3DsayHello%2CtestGeneric%26pid%3D15716%26release%3D2.7.5%26revision%3D1.0.0%26side%3Dprovider%26timestamp%3D1582872850187%26version%3D1.0.0]

至此，服务消费端就可以从注册中心获取服务提供service进行调用了，下节我们继续来分析，消费端是如何从注册中心拉取service进行处理的。