通常情况下是通过Spring配置的方式去实现服务的发布，为了方便调试，我就不采用Spring配置的方式。
DemoService demo = new DemoServiceImpl(); ApplicationConfig config=new ApplicationConfig("hello-world-app"); RegistryConfig reg=new RegistryConfig("127.0.0.1:2181"); reg.setProtocol("zookeeper"); ProtocolConfig protocol = new ProtocolConfig(); protocol.setName("dubbo"); protocol.setPort(20880); ServiceConfig<DemoService> service=new ServiceConfig<DemoService>(); service.setApplication(config); service.setRegistry(reg); service.setProtocol(protocol); service.setInterface(DemoService.class); service.setRef(demo); service.setVersion("1.0"); service.export(); Thread.sleep(Integer.MAX_VALUE);
上面是服务发布的简短代码，其中最重要的就是export()方法。
public synchronized void export() { ... doExport() } protected synchronized void doExport() { ... doExportUrls(); } private void doExportUrls() {
//装配地址 registry://127.0.0.1:2181/com.alibaba.dubbo.registry.RegistryService?application=hello-world-app&dubbo=2.5.3&pid=5556®istry=zookeeper×tamp=1484484518418 List<URL> registryURLs = loadRegistries(true); for (ProtocolConfig protocolConfig : protocols) { doExportUrlsFor1Protocol(protocolConfig, registryURLs); } } private void doExportUrlsFor1Protocol(ProtocolConfig protocolConfig, List<URL> registryURLs) { //配置为none不暴露 if (! Constants.SCOPE_NONE.toString().equalsIgnoreCase(scope)) { //配置不是remote的情况下做本地暴露 (配置为remote，则表示只暴露远程服务) if (!Constants.SCOPE_REMOTE.toString().equalsIgnoreCase(scope)) { exportLocal(url); } //如果配置不是local则暴露为远程服务.(配置为local，则表示只暴露远程服务) if (! Constants.SCOPE_LOCAL.toString().equalsIgnoreCase(scope) ){ if (logger.isInfoEnabled()) { logger.info("Export dubbo service " + interfaceClass.getName() + " to url " + url); } if (registryURLs != null && registryURLs.size() > 0 && url.getParameter("register", true)) { for (URL registryURL : registryURLs) { url = url.addParameterIfAbsent("dynamic", registryURL.getParameter("dynamic")); URL monitorUrl = loadMonitor(registryURL); if (monitorUrl != null) { url = url.addParameterAndEncoded(Constants.MONITOR_KEY, monitorUrl.toFullString()); } if (logger.isInfoEnabled()) { logger.info("Register dubbo service " + interfaceClass.getName() + " url " + url + " to registry " + registryURL); } Invoker<?> invoker = proxyFactory.getInvoker(ref, (Class) interfaceClass, registryURL.addParameterAndEncoded(Constants.EXPORT_KEY, url.toFullString())); Exporter<?> exporter = protocol.export(invoker); exporters.add(exporter); } } else { Invoker<?> invoker = proxyFactory.getInvoker(ref, (Class) interfaceClass, url); Exporter<?> exporter = protocol.export(invoker); exporters.add(exporter); } } } this.urls.add(url); }
最终调用的是protocol.export(invoker)方法，protocol是通过扩展点机制动态生成的类：
private static final Protocol protocol = ExtensionLoader.getExtensionLoader(Protocol.class).getAdaptiveExtension();
public class Protocol$Adpative implements com.alibaba.dubbo.rpc.Protocol {
public void destroy() {
throw new UnsupportedOperationException(
"method public abstract void com.alibaba.dubbo.rpc.Protocol.destroy() of interface com.alibaba.dubbo.rpc.Protocol is not adaptive method!");
}
public int getDefaultPort() {
throw new UnsupportedOperationException(
"method public abstract int com.alibaba.dubbo.rpc.Protocol.getDefaultPort() of interface com.alibaba.dubbo.rpc.Protocol is not adaptive method!");
}
//调用该方法
public com.alibaba.dubbo.rpc.Exporter export(com.alibaba.dubbo.rpc.Invoker arg0)
throws com.alibaba.dubbo.rpc.Invoker {
if (arg0 == null)
throw new IllegalArgumentException("com.alibaba.dubbo.rpc.Invoker argument == null");
if (arg0.getUrl() == null)
throw new IllegalArgumentException("com.alibaba.dubbo.rpc.Invoker argument getUrl() == null");
com.alibaba.dubbo.common.URL url = arg0.getUrl();
String extName = (url.getProtocol() == null ? "dubbo" : url.getProtocol());
if (extName == null)
throw new IllegalStateException("Fail to get extension(com.alibaba.dubbo.rpc.Protocol) name from url("
+ url.toString() + ") use keys([protocol])");
//扩展点机制加载扩展类：
com.alibaba.dubbo.rpc.Protocol extension = (com.alibaba.dubbo.rpc.Protocol) ExtensionLoader
.getExtensionLoader(com.alibaba.dubbo.rpc.Protocol.class).getExtension(extName);
return extension.export(arg0);
}
public com.alibaba.dubbo.rpc.Invoker refer(java.lang.Class arg0, com.alibaba.dubbo.common.URL arg1)
throws java.lang.Class {
if (arg1 == null)
throw new IllegalArgumentException("url == null");
com.alibaba.dubbo.common.URL url = arg1;
String extName = (url.getProtocol() == null ? "dubbo" : url.getProtocol());
if (extName == null)
throw new IllegalStateException("Fail to get extension(com.alibaba.dubbo.rpc.Protocol) name from url("
+ url.toString() + ") use keys([protocol])");
com.alibaba.dubbo.rpc.Protocol extension = (com.alibaba.dubbo.rpc.Protocol) ExtensionLoader
.getExtensionLoader(com.alibaba.dubbo.rpc.Protocol.class).getExtension(extName);
return extension.refer(arg0, arg1);
}
}
加载扩展类的核心方法：
public T getExtension(String name) { ... Object instance = holder.get(); if (instance == null) { synchronized (holder) { instance = holder.get(); if (instance == null) { instance = createExtension(name); holder.set(instance); } } } return (T) instance; } private T createExtension(String name) { try { T instance = (T) EXTENSION_INSTANCES.get(clazz); if (instance == null) { EXTENSION_INSTANCES.putIfAbsent(clazz, (T) clazz.newInstance()); instance = (T) EXTENSION_INSTANCES.get(clazz); } injectExtension(instance);
//cachedWrapperClasses在getAdaptiveExtension方法中被初始化，值为：ProtocolListenerWrapper、ProtocolFilterWrapper
//这2个包装类通过装饰器模式，构造器实例化，最终返回ProtocolFilterWrapper(构造函数参数：ProtocolListenerWrapper(构造函数参数：RegistryProtocol))
Set<Class<?>> wrapperClasses = cachedWrapperClasses; if (wrapperClasses != null && wrapperClasses.size() > 0) { for (Class<?> wrapperClass : wrapperClasses) { instance = injectExtension((T) wrapperClass.getConstructor(type).newInstance(instance)); } } return instance; } catch (Throwable t) { throw new IllegalStateException("Extension instance(name: " + name + ", class: " + type + ") could not be instantiated: " + t.getMessage(), t); } }
所以，最终层层包装，调用RegistryProtocol的export(Invoker<T>)方法：
public <T> Exporter<T> export(final Invoker<T> originInvoker) throws RpcException { //export invoker final ExporterChangeableWrapper<T> exporter = doLocalExport(originInvoker); //registry provider final Registry registry = getRegistry(originInvoker); final URL registedProviderUrl = getRegistedProviderUrl(originInvoker);
//向注册中心注册地址：/dubbo/com.selrain.dubbodemo.DemoService/providers registry.register(registedProviderUrl); // 订阅override数据 // FIXME 提供者订阅时，会影响同一JVM即暴露服务，又引用同一服务的的场景，因为subscribed以服务名为缓存的key，导致订阅信息覆盖。 final URL overrideSubscribeUrl = getSubscribedOverrideUrl(registedProviderUrl); final OverrideListener overrideSubscribeListener = new OverrideListener(overrideSubscribeUrl); overrideListeners.put(overrideSubscribeUrl, overrideSubscribeListener); registry.subscribe(overrideSubscribeUrl, overrideSubscribeListener); //保证每次export都返回一个新的exporter实例 return new Exporter<T>() { public Invoker<T> getInvoker() { return exporter.getInvoker(); } public void unexport() { try { exporter.unexport(); } catch (Throwable t) { logger.warn(t.getMessage(), t); } try { registry.unregister(registedProviderUrl); } catch (Throwable t) { logger.warn(t.getMessage(), t); } try { overrideListeners.remove(overrideSubscribeUrl); registry.unsubscribe(overrideSubscribeUrl, overrideSubscribeListener); } catch (Throwable t) { logger.warn(t.getMessage(), t); } } }; }
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