本文详细探讨了Dubbo服务提供者如何通过ServiceBean暴露服务的过程，包括从@Service注解到服务注册、远程服务暴露、Netty服务器启动、Zookeeper连接和注册等步骤。分析了ServiceBean的生命周期方法及其实现，揭示了Dubbo服务从初始化到发布的内部机制。
Dubbo简介
项目中使用dubbo作为rpc框架，而且以前一直也是有过使用经验，但是没有深入学习过，近期项目进度不紧，就简单学习一下深入原理。
dubbo官方文档:http://dubbo.apache.org/zh-cn/docs/user/quick-start.html
开头开始一张众所周知的dubbo原理图：
节点角色说明
Provider 暴露服务的服务提供方
Consumer 调用远程服务的服务消费方
Registry 服务注册与发现的注册中心
Monitor 统计服务的调用次数和调用时间的监控中心
Container 服务运行容器
Provider
我们在写dubbo服务的时候，通常在实现类上面加上com.alibaba.dubbo.config.annotation的@Service注解，这就意味着是一个服务提供者，但是这个过程是怎样实现的呢？
早期的dubbo是通过spring的配置xml文件来实现，现在主要是使用注解，不过都是一个意思，标记为spring管理的bean。
标签的处理类dubbo中的定义写在META-INF/spring.handlers
http\://code.alibabatech.com/schema/dubbo=com.alibaba.dubbo.config.spring.schema.DubboNamespaceHandler
打开DubboNamespaceHandler可以看到：
可以看到dubbo自定义了一个DubboBeanDefinitionParser类去解析上面的标签,并且自定义了AnnotationBean，ServiceBean和ReferenceBean。
在服务提供方这节先研究一下ServiceBean，通过dubbo的启动日志，可以大概了解到服务发现的原理：
大概有如下操作：
第一个发布的动作：暴露本地服务
Export dubbo service com.alibaba.dubbo.demo.DemoService to local registry, dubbo version: 2.0.0, current host: 127.0.0.1
第二个发布动作：暴露远程服务
Export dubbo service com.alibaba.dubbo.demo.DemoService to url dubbo://192.168.100.38:20880/com.alibaba.dubbo.demo.DemoService?anyhost=true&application=demo-provider&dubbo=2.0.0&generic=false&interface=com.alibaba.dubbo.demo.DemoService&loadbalance=roundrobin&methods=sayHello&owner=william&pid=8484&side=provider×tamp=1473908495465, dubbo version: 2.0.0, current host: 127.0.0.1
Register dubbo service com.alibaba.dubbo.demo.DemoService url dubbo://192.168.100.38:20880/com.alibaba.dubbo.demo.DemoService?anyhost=true&application=demo-provider&dubbo=2.0.0&generic=false&interface=com.alibaba.dubbo.demo.DemoService&loadbalance=roundrobin&methods=sayHello&monitor=dubbo%3A%2F%2F192.168.48.117%3A2181%2Fcom.alibaba.dubbo.registry.RegistryService%3Fapplication%3Ddemo-provider%26backup%3D192.168.48.120%3A2181%2C192.168.48.123%3A2181%26dubbo%3D2.0.0%26owner%3Dwilliam%26pid%3D8484%26protocol%3Dregistry%26refer%3Ddubbo%253D2.0.0%2526interface%253Dcom.alibaba.dubbo.monitor.MonitorService%2526pid%253D8484%2526timestamp%253D1473908495729%26registry%3Dzookeeper%26timestamp%3D1473908495398&owner=william&pid=8484&side=provider×tamp=1473908495465 to registry registry://192.168.48.117:2181/com.alibaba.dubbo.registry.RegistryService?application=demo-provider&backup=192.168.48.120:2181,192.168.48.123:2181&dubbo=2.0.0&owner=william&pid=8484®istry=zookeeper×tamp=1473908495398, dubbo version: 2.0.0, current host: 127.0.0.1
第三个发布动作：启动netty
Start NettyServer bind /0.0.0.0:20880, export /192.168.100.38:20880, dubbo version: 2.0.0, current host: 127.0.0.1
第四个发布动作：打开连接zk
INFO zookeeper.ClientCnxn: Opening socket connection to server /192.168.48.117:2181
第五个发布动作：到zk注册
Register: dubbo://192.168.100.38:20880/com.alibaba.dubbo.demo.DemoService?anyhost=true&application=demo-provider&dubbo=2.0.0&generic=false&interface=com.alibaba.dubbo.demo.DemoService&loadbalance=roundrobin&methods=sayHello&owner=william&pid=8484&side=provider×tamp=1473908495465, dubbo version: 2.0.0, current host: 127.0.0.1
第六个发布动作；监听zk
Subscribe: provider://192.168.100.38:20880/com.alibaba.dubbo.demo.DemoService?anyhost=true&application=demo-provider&category=configurators&check=false&dubbo=2.0.0&generic=false&interface=com.alibaba.dubbo.demo.DemoService&loadbalance=roundrobin&methods=sayHello&owner=william&pid=8484&side=provider×tamp=1473908495465, dubbo version: 2.0.0, current host: 127.0.0.1
Notify urls for subscribe url provider://192.168.100.38:20880/com.alibaba.dubbo.d
那么，ServiceBean是何时暴露服务的呢？
查看ServiceBean源码可以发现：
public class ServiceBean<T> extends ServiceConfig<T> implements InitializingBean, DisposableBean, ApplicationContextAware, ApplicationListener, BeanNameAware {
private static final long serialVersionUID = 213195494150089726L;
private static transient ApplicationContext SPRING_CONTEXT;
private transient ApplicationContext applicationContext;
private transient String beanName;
private transient boolean supportedApplicationListener;
public ServiceBean() {
}
public ServiceBean(Service service) {
super(service);
}
//......
}
ServiceBean里面实现了ApplicationListener,ApplicationContextAware,InitializingBean接口，这3个接口分别会在spring启动的不同时机依次调用:
自己写了一个简单的方法验证一下顺序：
所以依次去看一下里面都进行了哪些操作：
public void setApplicationContext(ApplicationContext applicationContext) {
this.applicationContext = applicationContext;
SpringExtensionFactory.addApplicationContext(applicationContext);
if (applicationContext != null) {
SPRING_CONTEXT = applicationContext;
try {
Method method = applicationContext.getClass().getMethod("addApplicationListener", ApplicationListener.class);
method.invoke(applicationContext, this);
this.supportedApplicationListener = true;
} catch (Throwable var5) {
if (applicationContext instanceof AbstractApplicationContext) {
try {
Method method = AbstractApplicationContext.class.getDeclaredMethod("addListener", ApplicationListener.class);
if (!method.isAccessible()) {
method.setAccessible(true);
}
method.invoke(applicationContext, this);
this.supportedApplicationListener = true;
} catch (Throwable var4) {
}
}
}
}
}
//......
public void afterPropertiesSet() throws Exception {
this.setPosition(PriorityGroupUtil.getInnerPosition());
Map protocolConfigMap;
if (this.getProvider() == null) {
protocolConfigMap = this.applicationContext == null ? null : BeanFactoryUtils.beansOfTypeIncludingAncestors(this.applicationContext, ProviderConfig.class, false, false);
if (protocolConfigMap != null && protocolConfigMap.size() > 0) {
Map<String, ProtocolConfig> protocolConfigMap = this.applicationContext == null ? null : BeanFactoryUtils.beansOfTypeIncludingAncestors(this.applicationContext, ProtocolConfig.class, false, false);
Iterator i$;
ProviderConfig config;
if ((protocolConfigMap == null || protocolConfigMap.size() == 0) && protocolConfigMap.size() > 1) {
List<ProviderConfig> providerConfigs = new ArrayList();
i$ = protocolConfigMap.values().iterator();
while(i$.hasNext()) {
config = (ProviderConfig)i$.next();
if (config.isDefault() != null && config.isDefault()) {
providerConfigs.add(config);
}
}
if (providerConfigs.size() > 0) {
this.setProviders(providerConfigs);
}
} else {
ProviderConfig providerConfig = null;
i$ = protocolConfigMap.values().iterator();
label318:
while(true) {
do {
if (!i$.hasNext()) {
if (providerConfig != null) {
this.setProvider(providerConfig);
}
break label318;
}
}
//.....
public void onApplicationEvent(ApplicationEvent event) {
if (ContextRefreshedEvent.class.getName().equals(event.getClass().getName()) && this.isDelay() && !this.isExported() && !this.isUnexported()) {
if (logger.isInfoEnabled()) {
logger.info("The service ready on spring started. service: " + this.getInterface());
}
this.export();
}
}
前面基本上都是一些初始化操作，只有在最后的地方，调用了一个export方法。
跟进查看：
还是在不断的初始化一些配置，还有一些校验操作。在后面可以看到一个doExportUrls方法：
private void doExportUrls() {
List<URL> registryURLs = this.loadRegistries(true);
Iterator i$ = this.protocols.iterator();
while(i$.hasNext()) {
ProtocolConfig protocolConfig = (ProtocolConfig)i$.next();
this.doExportUrlsFor1Protocol(protocolConfig, registryURLs);
}
}
loadRegistries（）：这里主要是注册url的一个拼接
URL格式类似于：registry://192.123.1.101:2181/com.alibaba.dubbo.registry.。。。
protected List<URL> loadRegistries(boolean provider) {
this.checkRegistry();
List<URL> registryList = new ArrayList();
if (this.registries != null && this.registries.size() > 0) {
Iterator i$ = this.registries.iterator();
label75:
while(true) {
RegistryConfig config;
String address;
do {
do {
do {
if (!i$.hasNext()) {
return registryList;
}
config = (RegistryConfig)i$.next();
address = config.getAddress();
if (address == null || address.length() == 0) {
address = "0.0.0.0";
}
String sysaddress = System.getProperty("dubbo.registry.address");
if (sysaddress != null && sysaddress.length() > 0) {
address = sysaddress;
}
} while(address == null);
} while(address.length() <= 0);
} while("N/A".equalsIgnoreCase(address));
Map<String, String> map = new HashMap();
appendParameters(map, this.application);
appendParameters(map, config);
map.put("path", RegistryService.class.getName());
map.put("dubbo", Version.getVersion());
map.put("timestamp", String.valueOf(System.currentTimeMillis()));
if (ConfigUtils.getPid() > 0) {
map.put("pid", String.valueOf(ConfigUtils.getPid()));
}
if (!map.containsKey("protocol")) {
if (ExtensionLoader.getExtensionLoader(RegistryFactory.class).hasExtension("remote")) {
map.put("protocol", "remote");
} else {
map.put("protocol", "dubbo");
}
}
List<URL> urls = UrlUtils.parseURLs(address, map);
Iterator i$ = urls.iterator();
while(true) {
URL url;
do {
if (!i$.hasNext()) {
continue label75;
}
url = (URL)i$.next();
url = url.addParameter("registry", url.getProtocol());
url = url.setProtocol("registry");
} while((!provider || !url.getParameter("register", true)) && (provider || !url.getParameter("subscribe", true)));
registryList.add(url);
}
}
} else {
return registryList;
}
}
然后再遍历protocols变量，将protocols列表中的每个protocol根据url暴露出去,主要是doExportUrlsFor1Protocol方法。
这个方法是把上面的URL转成dubbo协议的URL：
url地址包含了版本号，接口名，方法列表，序列化方法，过期时间等这个接口bean所有需要用到的上下文信息，并且地址头也由registry改成了dubbo。
接下来就可以暴露本地接口：
private void exportLocal(URL url) {
if (!"injvm".equalsIgnoreCase(url.getProtocol())) {
URL local = URL.valueOf(url.toFullString()).setProtocol("injvm").setHost("127.0.0.1").setPort(0);
ServiceClassHolder.getInstance().pushServiceClass(this.getServiceClass(this.ref));
Exporter<?> exporter = protocol.export(proxyFactory.getInvoker(this.ref, this.interfaceClass, local));
this.exporters.add(exporter);
logger.info("Export dubbo service " + this.interfaceClass.getName() + " to local registry");
}
}
此时可以看到：
Exporter<?> exporter = protocol.export(proxyFactory.getInvoker(this.ref, this.interfaceClass, local));
默认使用的是javassistProxyFactory，所以跟进去看一下：
public <T> Invoker<T> getInvoker(T proxy, Class<T> type, URL url) {
final Wrapper wrapper = Wrapper.getWrapper(proxy.getClass().getName().indexOf(36) < 0 ? proxy.getClass() : type);
return new AbstractProxyInvoker<T>(proxy, type, url) {
protected Object doInvoke(T proxy, String methodName, Class<?>[] parameterTypes, Object[] arguments) throws Throwable {
return wrapper.invokeMethod(proxy, methodName, parameterTypes, arguments);
}
};
}
目前自己学习只有到这里，后续还有待深入学习。
参考：
https://blog.youkuaiyun.com/jyxmust/article/details/82669722
ServiceBean.onApplicationEvent
-->export()
-->ServiceConfig.export()
-->doExport()
-->doExportUrls()//里面有一个for循环，代表了一个服务可以有多个通信协议，例如 tcp协议 http协议，默认是tcp协议
-->loadRegistries(true)//从dubbo.properties里面组装registry的url信息
-->doExportUrlsFor1Protocol(ProtocolConfig protocolConfig, List<URL> registryURLs)
//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)
-->exportLocal(URL url)
-->proxyFactory.getInvoker(ref, (Class) interfaceClass, local)
-->ExtensionLoader.getExtensionLoader(com.alibaba.dubbo.rpc.ProxyFactory.class).getExtension("javassist");
-->extension.getInvoker(arg0, arg1, arg2)
-->StubProxyFactoryWrapper.getInvoker(T proxy, Class<T> type, URL url)
-->proxyFactory.getInvoker(proxy, type, url)
-->JavassistProxyFactory.getInvoker(T proxy, Class<T> type, URL url)
-->Wrapper.getWrapper(com.alibaba.dubbo.demo.provider.DemoServiceImpl)
-->makeWrapper(Class<?> c)
-->return new AbstractProxyInvoker<T>(proxy, type, url)
-->protocol.export
-->Protocol$Adpative.export
-->ExtensionLoader.getExtensionLoader(com.alibaba.dubbo.rpc.Protocol.class).getExtension("injvm");
-->extension.export(arg0)
-->ProtocolFilterWrapper.export
-->buildInvokerChain //创建8个filter
-->ProtocolListenerWrapper.export
-->InjvmProtocol.export
-->return new InjvmExporter<T>(invoker, invoker.getUrl().getServiceKey(), exporterMap)
-->目的：exporterMap.put(key, this)//key=com.alibaba.dubbo.demo.DemoService, this=InjvmExporter
//如果配置不是local则暴露为远程服务.(配置为local，则表示只暴露本地服务)
-->proxyFactory.getInvoker//原理和本地暴露一样都是为了获取一个Invoker对象
-->protocol.export(invoker)
-->Protocol$Adpative.export
-->ExtensionLoader.getExtensionLoader(com.alibaba.dubbo.rpc.Protocol.class).getExtension("registry");
-->extension.export(arg0)
-->ProtocolFilterWrapper.export
-->ProtocolListenerWrapper.export
-->RegistryProtocol.export
-->doLocalExport(originInvoker)
-->getCacheKey(originInvoker);//读取 dubbo://192.168.100.51:20880/
-->rotocol.export
-->Protocol$Adpative.export
-->ExtensionLoader.getExtensionLoader(com.alibaba.dubbo.rpc.Protocol.class).getExtension("dubbo");
-->extension.export(arg0)
-->ProtocolFilterWrapper.export
-->buildInvokerChain//创建8个filter
-->ProtocolListenerWrapper.export
---------1.netty服务暴露的开始------- -->DubboProtocol.export
-->serviceKey(url)//组装key=com.alibaba.dubbo.demo.DemoService:20880
-->目的：exporterMap.put(key, this)//key=com.alibaba.dubbo.demo.DemoService:20880, this=DubboExporter
-->openServer(url)
-->createServer(url)
--------2.信息交换层 exchanger 开始-------------->Exchangers.bind(url, requestHandler)//exchaanger是一个信息交换层
-->getExchanger(url)
-->getExchanger(type)
-->ExtensionLoader.getExtensionLoader(Exchanger.class).getExtension("header")
-->HeaderExchanger.bind
-->Transporters.bind(url, new DecodeHandler(new HeaderExchangeHandler(handler)))
-->new HeaderExchangeHandler(handler)//this.handler = handler
-->new DecodeHandler
-->new AbstractChannelHandlerDelegate//this.handler = handler;
---------3.网络传输层 transporter--------------------->Transporters.bind
-->getTransporter()
-->ExtensionLoader.getExtensionLoader(Transporter.class).getAdaptiveExtension()
-->Transporter$Adpative.bind
-->ExtensionLoader.getExtensionLoader(com.alibaba.dubbo.remoting.Transporter.class).getExtension("netty");
-->extension.bind(arg0, arg1)
-->NettyTransporter.bind
--new NettyServer(url, listener)
-->AbstractPeer //this.url = url; this.handler = handler;
-->AbstractEndpoint//codec timeout=1000 connectTimeout=3000
-->AbstractServer //bindAddress accepts=0 idleTimeout=600000
---------4.打开断开，暴露netty服务-------------------------------->doOpen()
-->设置 NioServerSocketChannelFactory boss worker的线程池 线程个数为3
-->设置编解码 hander
-->bootstrap.bind(getBindAddress())
-->new HeaderExchangeServer
-->this.server=NettyServer
-->heartbeat=60000
-->heartbeatTimeout=180000
-->startHeatbeatTimer()//这是一个心跳定时器，采用了线程池，如果断开就心跳重连。
-->getRegistry(originInvoker)//zk 连接
-->registryFactory.getRegistry(registryUrl)
-->ExtensionLoader.getExtensionLoader(RegistryFactory.class).getExtension("zookeeper");
-->extension.getRegistry(arg0)
-->AbstractRegistryFactory.getRegistry//创建一个注册中心，存储在REGISTRIES
-->createRegistry(url)
-->new ZookeeperRegistry(url, zookeeperTransporter)
-->AbstractRegistry
-->loadProperties()//目的：把C:\Users\bobo\.dubbo\dubbo-registry-192.168.48.117.cache
文件中的内容加载为properties
-->notify(url.getBackupUrls())//不做任何事
-->FailbackRegistry
-->retryExecutor.scheduleWithFixedDelay(new Runnable()//建立线程池，检测并连接注册中心,如果失败了就重连
-->ZookeeperRegistry
-->zookeeperTransporter.connect(url)
-->ZookeeperTransporter$Adpative.connect(url)
-->ExtensionLoader.getExtensionLoader(ZookeeperTransporter.class).getExtension("zkclient");
-->extension.connect(arg0)
-->ZkclientZookeeperTransporter.connect
-->new ZkclientZookeeperClient(url)
-->AbstractZookeeperClient
-->ZkclientZookeeperClient
-->new ZkClient(url.getBackupAddress());//连接ZK
-->client.subscribeStateChanges(new IZkStateListener()//订阅的目标：连接断开，重连
-->zkClient.addStateListener(new StateListener()
-->recover //连接失败 重连
-->registry.register(registedProviderUrl)//创建节点
-->AbstractRegistry.register
-->FailbackRegistry.register
-->doRegister(url)//向zk服务器端发送注册请求
-->ZookeeperRegistry.doRegister
-->zkClient.create
-->AbstractZookeeperClient.create//dubbo/com.alibaba.dubbo.demo.DemoService/providers/
dubbo%3A%2F%2F192.168.100.52%3A20880%2Fcom.alibaba.dubbo.demo.DemoService%3Fanyhost%3Dtrue%26
application%3Ddemo-provider%26dubbo%3D2.0.0%26generic%3Dfalse%26interface%3D
com.alibaba.dubbo.demo.DemoService%26loadbalance%3Droundrobin%26methods%3DsayHello%26owner%3
Dwilliam%26pid%3D2416%26side%3Dprovider%26timestamp%3D1474276306353
-->createEphemeral(path);//临时节点 dubbo%3A%2F%2F192.168.100.52%3A20880%2F.............
-->createPersistent(path);//持久化节点 dubbo/com.alibaba.dubbo.demo.DemoService/providers
-->registry.subscribe//订阅ZK
-->AbstractRegistry.subscribe
-->FailbackRegistry.subscribe
-->doSubscribe(url, listener)// 向服务器端发送订阅请求
-->ZookeeperRegistry.doSubscribe
-->new ChildListener()
-->实现了 childChanged
-->实现并执行 ZookeeperRegistry.this.notify(url, listener, toUrlsWithEmpty(url, parentPath, currentChilds));
//A
-->zkClient.create(path, false);//第一步：先创建持久化节点/dubbo/com.alibaba.dubbo.demo.DemoService/configurators
-->zkClient.addChildListener(path, zkListener)
-->AbstractZookeeperClient.addChildListener
//C
-->createTargetChildListener(path, listener)//第三步：收到订阅后的处理，交给FailbackRegistry.notify处理
-->ZkclientZookeeperClient.createTargetChildListener
-->new IZkChildListener()
-->实现了 handleChildChange //收到订阅后的处理
-->listener.childChanged(parentPath, currentChilds);
-->实现并执行ZookeeperRegistry.this.notify(url, listener, toUrlsWithEmpty(url, parentPath, currentChilds));
-->收到订阅后处理 FailbackRegistry.notify
//B
-->addTargetChildListener(path, targetListener)第二步
-->ZkclientZookeeperClient.addTargetChildListener
-->client.subscribeChildChanges(path, listener)//第二步：启动加入订阅/dubbo/com.alibaba.dubbo.demo.DemoService/configurators
-->notify(url, listener, urls)
-->FailbackRegistry.notify
-->doNotify(url, listener, urls);
-->AbstractRegistry.notify
-->saveProperties(url);//把服务端的注册url信息更新到C:\Users\bobo\.dubbo\dubbo-registry-192.168.48.117.cache
-->registryCacheExecutor.execute(new SaveProperties(version));//采用线程池来处理
-->listener.notify(categoryList)
-->RegistryProtocol.notify
-->RegistryProtocol.this.getProviderUrl(originInvoker)//通过invoker的url 获取 providerUrl的地址
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