Dubbo是一款典型的高扩展、高性能、高可用的RPC微服务框架,用于解决微服务架构下的服务治理与通信问题。其核心模块包含【RPC通信】和【服务治理】,其中服务治理又分为服务注册与发现、服务容错、负载均衡、流量调度等。今天将重点介绍Dubbo的服务注册与发现。
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在介绍服务注册发现之前,先简单介绍一下贯穿整个Dubbo源码,也是Dubbo实现自适应扩展的核心--SPI机制,下图为Dubbo SPI实现的简单类图。
•1、Dubbo SPI原理:通过读取相应的配置文件找到具体实现类,然后通过以下两种方式实例化对象:(1)通过自适应的动态字节码编译技术,生成相应的动态代理类,(2)利用反射机制实现实例化。相较于Java SPI,Dubbo SPI实现了内部的IoC和Aop
•2、Dubbo SPI 优点:(1)高扩展:用户可以根据实际业务需求扩展相应的实现模块,包含字节码编译技术、rpc协议、通信方式、注册方式等,(2)解耦:通过封装SPI调用机制,架构上实现了上层应用与底层逻辑之间的解耦,为高扩展提供了支撑条件
•3、Dubbo SPI 常用样例(以getExtension和getAdaptiveExtension为例)
配置文件内容test1=com.dubbo.demo.service.TestServiceimpltest2=com.dubbo.demo.service.TestServiceImpl2一、通过getExtension方法生成实例 ExtensionLoaderextensionLoader = ExtensionLoader.getExtensionLoader(TestService.class); TestService t1 = extensionLoader.getExtension("test1"); TestService t2 = extensionLoader.getExtension("test2"); 二、通过getAdaptiveExtension生成实例(方法中需要@Adaptive注解,参数会对URL校验) TestService testService = ExtensionLoader.getExtensionLoader(TestService.class).getAdaptiveExtension(); URL url = new URL("test", "localhost", 8080, new String[]{"test.service", "test1"}); testService.sayHello("bbb", url);
调用getAdaptiveExtension方法最终会生成相应的代理类,最终生成的代理类会根据URL参数里面的protocol决定(以内部Protocol为例)
首先需要实例化ServiceConfig实例,声明“注册接口、接口实例、注册中心配置”,其中“ServiceBean”是实现Spring与Dubbo整合的桥梁。然后会由DubboBootstrap调用initialize方法实现configManager和Environment的初始化,其中就包括将ServiceConfig中的配置转换成内部封装的协议(ApplicationModel、ProviderModel等)
private static void startWithExport() throws InterruptedException { //初始化配置 ServiceConfigservice = new ServiceConfig<>(); service.setInterface(DemoService.class); service.setRef(new DemoServiceImpl()); service.setApplication(new ApplicationConfig("dubbo-demo-api-provider")); service.setRegistry(new RegistryConfig("zookeeper://127.0.0.1:2181")); //服务注册入口 service.export();}
public synchronized void export() { if (bootstrap == null) { bootstrap = DubboBootstrap.getInstance(); // compatible with api call. if (null != this.getRegistry()) { bootstrap.registries(this.getRegistries()); } //初始化配置() bootstrap.initialize(); } ...... if (shouldDelay()) { DELAY_EXPORT_EXECUTOR.schedule(this::doExport, getDelay(), TimeUnit.MILLISECONDS); } else { //服务注册 doExport(); } exported(); }
根据初始化配置组转注册接口服务的URL。其中URL也是Dubbo内部通过@Adaptive注解实现SPI的核心,通过修改URL的头部协议(如:register、dubbo、injvm等),在调用
private static final Protocol PROTOCOL = ExtensionLoader.getExtensionLoader(Protocol.class).getAdaptiveExtension();PROTOCOL.export(wrapperInvoker)
该方法的时候,会根据不同的协议切换不通的实现类,实现了Dubbo技术架构与业务逻辑的解耦。
private void doExportUrls() { //组装后的URL格式样例 //registry://127.0.0.1:2181/org.apache.dubbo.registry.RegistryService?application=dubbo-demo-api-provider&dubbo=2.0.2&pid=26212®istry=zookeeper×tamp=1663049763199 ListregistryURLs = ConfigValidationUtils.loadRegistries(this, true); int protocolConfigNum = protocols.size(); for (ProtocolConfig protocolConfig : protocols) { //组装pathKey : org.apache.dubbo.demo.DemoService String pathKey = URL.buildKey(getContextPath(protocolConfig) .map(p -> p + "/" + path) .orElse(path), group, version); //保存接口服务 repository.registerService(pathKey, interfaceClass); //服务注册 doExportUrlsFor1Protocol(protocolConfig, registryURLs, protocolConfigNum); }}
通过内置的动态字节码编译(默认javassist)生成Invoker代理类,然后通过反射机制生成Wrapper实例。其中Invoker是Dubbo的核心模型,Invoker是Dubbo中的实体域,也就是真实存在的。其他模型都向它靠拢或转换成它
private void doExportUrlsFor1Protocol(ProtocolConfig protocolConfig, ListregistryURLs, int protocolConfigNum) { ...... //组装新的URL //dubbo://2.0.0.1:20880/org.apache.dubbo.demo.DemoService?anyhost=true&application=dubbo-demo-api-provider&bind.ip=2.0.0.1&bind.port=20880&default=true&deprecated=false&dubbo=2.0.2&dynamic=true&generic=false&interface=org.apache.dubbo.demo.DemoService&methods=sayHello,sayHelloAsync&pid=46528&release=&service.name=ServiceBean:/org.apache.dubbo.demo.DemoService&side=provider×tamp=1663051456562 URL url = new URL(name, host, port, getContextPath(protocolConfig).map(p -> p + "/" + path).orElse(path), map); ...... //Invoker封装 Invoker> invoker = PROXY_FACTORY.getInvoker(ref, (Class) interfaceClass, registryURL.addParameterAndEncoded(EXPORT_KEY, url.toFullString())); //wrapper DelegateProviderMetaDataInvoker wrapperInvoker = new DelegateProviderMetaDataInvoker(invoker, this); //服务注册(此时URL头部协议变成了register,实际会调用RegistryProtocol) Exporter> exporter = PROTOCOL.export(wrapperInvoker); exporters.add(exporter);}# PROXY_FACTORYpublic Invoker getInvoker(T proxy, Class type, URL url) { // 动态代理类生成,反射生成实例 final Wrapper wrapper = Wrapper.getWrapper(proxy.getClass().getName().indexOf("$") < 0 ? proxy.getClass() : type); return new AbstractProxyInvoker (proxy, type, url) { @Override protected Object doInvoke(T proxy, String methodName, Class>[] parameterTypes, Object[] arguments) throws Throwable { return wrapper.invokeMethod(proxy, methodName, parameterTypes, arguments); } };}
此时会依次调用RegistryProtocol 、DubboProtocol 将Invoker封装成Exporter,并将封装后的Exporter存储到本地map中(类似于spring bean)。然后会调用底层通信服务(默认netty)进行端口监听,此时会通过责任链模式封装Exchanger与Transporter,用于处理网络传输消息的编码/解码。
# RegistryProtocol : exportpublicExporter export(final Invoker originInvoker) throws RpcException { ...... //此时URL头部协议已变成dubbo //dubbo://2.0.0.1:20880/org.apache.dubbo.demo.DemoService?anyhost=true&application=dubbo-demo-api-provider&bind.ip=2.0.0.1&bind.port=20880&default=true&deprecated=false&dubbo=2.0.2&dynamic=true&generic=false&interface=org.apache.dubbo.demo.DemoService&methods=sayHello,sayHelloAsync&pid=56036&release=&service.name=ServiceBean:/org.apache.dubbo.demo.DemoService&side=provider×tamp=1663052353098 providerUrl = overrideUrlWithConfig(providerUrl, overrideSubscribeListener); // export invoker final ExporterChangeableWrapper exporter = doLocalExport(originInvoker, providerUrl); // 此时Registry实例默认是ZookeeperRegistry final Registry registry = getRegistry(originInvoker); final URL registeredProviderUrl = getUrlToRegistry(providerUrl, registryUrl); // decide if we need to delay publish boolean register = providerUrl.getParameter(REGISTER_KEY, true); if (register) { //底层调用ZK,创建node节点 registry.register(registeredProviderUrl); } ....}# RegistryProtocol : doLocalExportprivate ExporterChangeableWrapper doLocalExport(final Invoker originInvoker, URL providerUrl) { String key = getCacheKey(originInvoker); return (ExporterChangeableWrapper ) bounds.computeIfAbsent(key, s -> { Invoker> invokerDelegate = new InvokerDelegate<>(originInvoker, providerUrl); //此时会调用DubboProtocol进行exporter封装 return new ExporterChangeableWrapper<>((Exporter ) protocol.export(invokerDelegate), originInvoker); });}
# DubboProtocol : exportpublicExporter export(Invoker invoker) throws RpcException { ...... // export service. String key = serviceKey(url); //exporter封装 DubboExporter exporter = new DubboExporter (invoker, key, exporterMap); exporterMap.put(key, exporter); ...... //开启服务监听 openServer(url); optimizeSerialization(url); return exporter;}
(5)步骤五:注册服务节点
封装Exporter并开启服务端口监听后,会调用注册中心(默认Zookeeper)注册服务节点信息
# RegistryProtocol : exportpublicExporter export(final Invoker originInvoker) throws RpcException { ...... //此时URL头部协议已变成dubbo //dubbo://2.0.0.1:20880/org.apache.dubbo.demo.DemoService?anyhost=true&application=dubbo-demo-api-provider&bind.ip=2.0.0.1&bind.port=20880&default=true&deprecated=false&dubbo=2.0.2&dynamic=true&generic=false&interface=org.apache.dubbo.demo.DemoService&methods=sayHello,sayHelloAsync&pid=56036&release=&service.name=ServiceBean:/org.apache.dubbo.demo.DemoService&side=provider×tamp=1663052353098 providerUrl = overrideUrlWithConfig(providerUrl, overrideSubscribeListener); // export invoker final ExporterChangeableWrapper exporter = doLocalExport(originInvoker, providerUrl); // 此时Registry实例默认是ZookeeperRegistry final Registry registry = getRegistry(originInvoker); final URL registeredProviderUrl = getUrlToRegistry(providerUrl, registryUrl); // decide if we need to delay publish boolean register = providerUrl.getParameter(REGISTER_KEY, true); if (register) { //底层调用ZK,创建node节点 registry.register(registeredProviderUrl); } ....}
至此,Dubbo服务注册的整体流程已大致结束,文中如有不当或者错误观点,欢迎大家评论区指出。感兴趣的同学,可以关注后续“Dubbo架构设计与源码解析”系列的文章。