github新增仓库 "dubbo-read"（点此查看），集合所有《Dubbo原理和源码解析》系列文章，后续将继续补充该系列，同时将针对Dubbo所做的功能扩展也进行分享。不定期更新，欢迎Follow。
一、框架设计
在官方《Dubbo 用户指南》架构部分，给出了服务调用的整体架构和流程：
另外，在官方《Dubbo 开发指南》框架设计部分，给出了整体设计：
以及暴露服务时序图：
本文将根据以上几张图，分析服务暴露的实现原理，并进行详细的代码跟踪与解析。
二、原理和源码解析
2.1 标签解析
从文章《Dubbo原理和源码解析之标签解析》中我们知道，<dubbo:service> 标签会被解析成 ServiceBean。
ServiceBean 实现了 InitializingBean，在类加载完成之后会调用 afterPropertiesSet() 方法。在 afterPropertiesSet() 方法中，依次解析以下标签信息：
- <dubbo:provider>
- <dubbo:application>
- <dubbo:module>
- <dubbo:registry>
- <dubbo:monitor>
- <dubbo:protocol>
ServiceBean 还实现了 ApplicationListener，在 Spring 容器初始化的时候会调用 onApplicationEvent 方法。ServiceBean 重写了 onApplicationEvent 方法，实现了服务暴露的功能。
ServiceBean.java
public void onApplicationEvent(ApplicationEvent event) {
if (ContextRefreshedEvent.class.getName().equals(event.getClass().getName())) {
if (isDelay() && ! isExported() && ! isUnexported()) {
if (logger.isInfoEnabled()) {
logger.info("The service ready on spring started. service: " + getInterface());
}
export();
}
}
}
2.2 延迟暴露
ServiceBean 扩展了 ServiceConfig，调用 export() 方法时由 ServiceConfig 完成服务暴露的功能实现。
ServiceConfig.java
public synchronized void export() {
if (provider != null) {
if (export == null) {
export = provider.getExport();
}
if (delay == null) {
delay = provider.getDelay();
}
}
if (export != null && ! export.booleanValue()) {
return;
}
if (delay != null && delay > 0) {
Thread thread = new Thread(new Runnable() {
public void run() {
try {
Thread.sleep(delay);
} catch (Throwable e) {
}
doExport();
}
});
thread.setDaemon(true);
thread.setName("DelayExportServiceThread");
thread.start();
} else {
doExport();
}
}
由上面代码可知，如果设置了 delay 参数，Dubbo 的处理方式是启动一个守护线程在 sleep 指定时间后再 doExport。
2.3 参数检查
在 ServiceConfig 的 doExport() 方法中会进行参数检查和设置，包括：
- 泛化调用
- 本地实现
- 本地存根
- 本地伪装
- 配置（application、registry、protocol等）
ServiceConfig.java
protected synchronized void doExport() {
if (unexported) {
throw new IllegalStateException("Already unexported!");
}
if (exported) {
return;
}
exported = true;
if (interfaceName == null || interfaceName.length() == 0) {
throw new IllegalStateException("<dubbo:service interface=\"\" /> interface not allow null!");
}
checkDefault();
//省略
if (ref instanceof GenericService) {
interfaceClass = GenericService.class;
generic = true;
} else {
try {
interfaceClass = Class.forName(interfaceName, true, Thread.currentThread()
.getContextClassLoader());
} catch (ClassNotFoundException e) {
throw new IllegalStateException(e.getMessage(), e);
}
checkInterfaceAndMethods(interfaceClass, methods);
checkRef();
generic = false;
}
if(local !=null){
if(local=="true"){
local=interfaceName+"Local";
}
Class<?> localClass;
try {
localClass = ClassHelper.forNameWithThreadContextClassLoader(local);
} catch (ClassNotFoundException e) {
throw new IllegalStateException(e.getMessage(), e);
}
if(!interfaceClass.isAssignableFrom(localClass)){
throw new IllegalStateException("The local implemention class " + localClass.getName() + " not implement interface " + interfaceName);
}
}
if(stub !=null){
if(stub=="true"){
stub=interfaceName+"Stub";
}
Class<?> stubClass;
try {
stubClass = ClassHelper.forNameWithThreadContextClassLoader(stub);
} catch (ClassNotFoundException e) {
throw new IllegalStateException(e.getMessage(), e);
}
if(!interfaceClass.isAssignableFrom(stubClass)){
throw new IllegalStateException("The stub implemention class " + stubClass.getName() + " not implement interface " + interfaceName);
}
}
//此处省略：检查并设置相关参数
doExportUrls();
}
2.4 多协议、多注册中心
在检查完参数之后，开始暴露服务。Dubbo 支持多协议和多注册中心：
ServiceConfig.java
private void doExportUrls() {
List<URL> registryURLs = loadRegistries(true);
for (ProtocolConfig protocolConfig : protocols) {
doExportUrlsFor1Protocol(protocolConfig, registryURLs);
}
}
2.5 组装URL
针对每个协议、每个注册中心，开始组装 URL。
ServiceConfig.java
private void doExportUrlsFor1Protocol(ProtocolConfig protocolConfig, List<URL> registryURLs) {
String name = protocolConfig.getName();
if (name == null || name.length() == 0) {
name = "dubbo";
}
//处理host
//处理port
Map<String, String> map = new HashMap<String, String>();
//设置参数到map
// 导出服务
String contextPath = protocolConfig.getContextpath();
if ((contextPath == null || contextPath.length() == 0) && provider != null) {
contextPath = provider.getContextpath();
}
URL url = new URL(name, host, port, (contextPath == null || contextPath.length() == 0 ? "" : contextPath + "/") + path, map);
if (ExtensionLoader.getExtensionLoader(ConfiguratorFactory.class)
.hasExtension(url.getProtocol())) {
url = ExtensionLoader.getExtensionLoader(ConfiguratorFactory.class)
.getExtension(url.getProtocol()).getConfigurator(url).configure(url);
}
//此处省略：服务暴露（详见 2.6 和 2.7）
this.urls.add(url);
}
2.6 本地暴露
如果配置 scope=none， 则不会进行服务暴露；如果没有配置 scope 或者 scope=local，则会进行本地暴露。
ServiceConfig.java
//public static final String LOCAL_PROTOCOL = "injvm";
//public static final String LOCALHOST = "127.0.0.1"; private void doExportUrlsFor1Protocol(ProtocolConfig protocolConfig, List<URL> registryURLs) {
//......
String scope = url.getParameter(Constants.SCOPE_KEY);
//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);
}
//......
}
//......
} private void exportLocal(URL url) {
if (!Constants.LOCAL_PROTOCOL.equalsIgnoreCase(url.getProtocol())) {
URL local = URL.valueOf(url.toFullString())
.setProtocol(Constants.LOCAL_PROTOCOL)
.setHost(NetUtils.LOCALHOST)
.setPort(0);
Exporter<?> exporter = protocol.export(
proxyFactory.getInvoker(ref, (Class) interfaceClass, local));
exporters.add(exporter);
logger.info("Export dubbo service " + interfaceClass.getName() +" to local registry");
}
}
1. 暴露服务的时候，会通过代理创建 Invoker；
2. 本地暴露时使用 injvm 协议，injvm 协议是一个伪协议，它不开启端口，不能被远程调用，只在 JVM 内直接关联，但执行 Dubbo 的 Filter 链。
2.7 远程暴露
如果没有配置 scope 或者 scope=remote，则会进行远程暴露。
ServiceConfig.java
private void doExportUrlsFor1Protocol(ProtocolConfig protocolConfig, List<URL> registryURLs) {
String scope = url.getParameter(Constants.SCOPE_KEY);
//配置为none不暴露
if (! Constants.SCOPE_NONE.toString().equalsIgnoreCase(scope)) {
//......
//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);
}
}
}
}
在服务暴露时，有两种情况：
- 不使用注册中心：直接暴露对应协议的服务，引用服务时只能通过直连方式引用
- 使用注册中心：暴露对应协议的服务后，会将服务节点注册到注册中心，引用服务时可以通过注册中心动态获取服务提供者列表，也可以通过直连方式引用
2.8 暴露服务
不使用注册中心时，直接调用对应协议（如 Dubbo 协议）的 export() 暴露服务。以 Dubbo 协议为例：
DubboProtocol.java
public <T> Exporter<T> export(Invoker<T> invoker) throws RpcException {
URL url = invoker.getUrl();
// export service.
String key = serviceKey(url);
DubboExporter<T> exporter = new DubboExporter<T>(invoker, key, exporterMap);
exporterMap.put(key, exporter);
//export an stub service for dispaching event
Boolean isStubSupportEvent = url.getParameter(Constants.STUB_EVENT_KEY,Constants.DEFAULT_STUB_EVENT);
Boolean isCallbackservice = url.getParameter(Constants.IS_CALLBACK_SERVICE, false);
if (isStubSupportEvent && !isCallbackservice){
String stubServiceMethods = url.getParameter(Constants.STUB_EVENT_METHODS_KEY);
if (stubServiceMethods == null || stubServiceMethods.length() == 0 ){
if (logger.isWarnEnabled()){
logger.warn(new IllegalStateException("consumer [" +url.getParameter(Constants.INTERFACE_KEY) +
"], has set stubproxy support event ,but no stub methods founded."));
}
} else {
stubServiceMethodsMap.put(url.getServiceKey(), stubServiceMethods);
}
}
openServer(url);
return exporter;
}
调用 openServer() 方法创建并启动 Server：
DubboProtocol.java
private void openServer(URL url) {
// find server.
String key = url.getAddress();
//client 也可以暴露一个只有server可以调用的服务。
boolean isServer = url.getParameter(Constants.IS_SERVER_KEY,true);
if (isServer) {
ExchangeServer server = serverMap.get(key);
if (server == null) {
serverMap.put(key, createServer(url));
} else {
//server支持reset,配合override功能使用
server.reset(url);
}
}
}
private ExchangeServer createServer(URL url) {
//默认开启server关闭时发送readonly事件
url = url.addParameterIfAbsent(Constants.CHANNEL_READONLYEVENT_SENT_KEY, Boolean.TRUE.toString());
//默认开启heartbeat
url = url.addParameterIfAbsent(Constants.HEARTBEAT_KEY, String.valueOf(Constants.DEFAULT_HEARTBEAT));
String str = url.getParameter(Constants.SERVER_KEY, Constants.DEFAULT_REMOTING_SERVER);
if (str != null && str.length() > 0 && ! ExtensionLoader.getExtensionLoader(Transporter.class).hasExtension(str))
throw new RpcException("Unsupported server type: " + str + ", url: " + url);
url = url.addParameter(Constants.CODEC_KEY, Version.isCompatibleVersion() ? COMPATIBLE_CODEC_NAME : DubboCodec.NAME);
ExchangeServer server;
try {
server = Exchangers.bind(url, requestHandler);
} catch (RemotingException e) {
throw new RpcException("Fail to start server(url: " + url + ") " + e.getMessage(), e);
}
str = url.getParameter(Constants.CLIENT_KEY);
if (str != null && str.length() > 0) {
Set<String> supportedTypes = ExtensionLoader.getExtensionLoader(Transporter.class).getSupportedExtensions();
if (!supportedTypes.contains(str)) {
throw new RpcException("Unsupported client type: " + str);
}
}
return server;
}
Exchanger （默认 HeaderExchanger）封装请求响应模式，同步转异步，以 Request、Response 为中心:
HeaderExchager.java
public ExchangeServer bind(URL url, ExchangeHandler handler) throws RemotingException {
return new HeaderExchangeServer(Transporters.bind(url, new DecodeHandler(new HeaderExchangeHandler(handler))));
}
Transporters.java
public static Server bind(URL url, ChannelHandler... handlers) throws RemotingException {
if (url == null) {
throw new IllegalArgumentException("url == null");
}
if (handlers == null || handlers.length == 0) {
throw new IllegalArgumentException("handlers == null");
}
ChannelHandler handler;
if (handlers.length == 1) {
handler = handlers[0];
} else {
handler = new ChannelHandlerDispatcher(handlers);
}
return getTransporter().bind(url, handler);
}
底层传输默认使用 NettyTransporter，最终是创建 NettyServer：
NettyTransporter.java
public Server bind(URL url, ChannelHandler listener) throws RemotingException {
return new NettyServer(url, listener);
}
NettyServer.java
public class NettyServer extends AbstractServer implements Server {
public NettyServer(URL url, ChannelHandler handler) throws RemotingException{
super(url, ChannelHandlers.wrap(handler, ExecutorUtil.setThreadName(url, SERVER_THREAD_POOL_NAME)));
}
}
AbstractServer.java
public abstract class AbstractServer extends AbstractEndpoint implements Server {
public AbstractServer(URL url, ChannelHandler handler) throws RemotingException {
super(url, handler);
localAddress = getUrl().toInetSocketAddress();
String host = url.getParameter(Constants.ANYHOST_KEY, false)
|| NetUtils.isInvalidLocalHost(getUrl().getHost())
? NetUtils.ANYHOST : getUrl().getHost();
bindAddress = new InetSocketAddress(host, getUrl().getPort());
this.accepts = url.getParameter(Constants.ACCEPTS_KEY, Constants.DEFAULT_ACCEPTS);
this.idleTimeout = url.getParameter(Constants.IDLE_TIMEOUT_KEY, Constants.DEFAULT_IDLE_TIMEOUT);
try {
doOpen();
if (logger.isInfoEnabled()) {
logger.info("Start " + getClass().getSimpleName() + " bind " + getBindAddress() + ", export " + getLocalAddress());
}
} catch (Throwable t) {
throw new RemotingException(url.toInetSocketAddress(), null, "Failed to bind " + getClass().getSimpleName()
+ " on " + getLocalAddress() + ", cause: " + t.getMessage(), t);
}
if (handler instanceof WrappedChannelHandler ){
executor = ((WrappedChannelHandler)handler).getExecutor();
}
}
}
NettyServer.java
public class NettyServer extends AbstractServer implements Server {
protected void doOpen() throws Throwable {
NettyHelper.setNettyLoggerFactory();
ExecutorService boss = Executors.newCachedThreadPool(new NamedThreadFactory("NettyServerBoss", true));
ExecutorService worker = Executors.newCachedThreadPool(new NamedThreadFactory("NettyServerWorker", true));
ChannelFactory channelFactory = new NioServerSocketChannelFactory(boss, worker, getUrl().getPositiveParameter(Constants.IO_THREADS_KEY, Constants.DEFAULT_IO_THREADS));
bootstrap = new ServerBootstrap(channelFactory);
final NettyHandler nettyHandler = new NettyHandler(getUrl(), this);
channels = nettyHandler.getChannels();
// final Timer timer = new HashedWheelTimer(new NamedThreadFactory("NettyIdleTimer", true));
bootstrap.setPipelineFactory(new ChannelPipelineFactory() {
public ChannelPipeline getPipeline() {
NettyCodecAdapter adapter = new NettyCodecAdapter(getCodec() ,getUrl(), NettyServer.this);
ChannelPipeline pipeline = Channels.pipeline();
/*int idleTimeout = getIdleTimeout();
if (idleTimeout > 10000) {
pipeline.addLast("timer", new IdleStateHandler(timer, idleTimeout / 1000, 0, 0));
}*/
pipeline.addLast("decoder", adapter.getDecoder());
pipeline.addLast("encoder", adapter.getEncoder());
pipeline.addLast("handler", nettyHandler);
return pipeline;
}
});
// bind
channel = bootstrap.bind(getBindAddress());
}
}
2.9 服务注册
如果使用了注册中心，则在通过具体协议（如 Dubbo 协议）暴露服务之后（即在 2.8 基础之上）进入服务注册流程，将服务节点注册到注册中心。
RegistryProtocol.java
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Zookeeper注册节点
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);
}
}
};
}
private Registry getRegistry(final Invoker<?> originInvoker){
URL registryUrl = originInvoker.getUrl();
if (Constants.REGISTRY_PROTOCOL.equals(registryUrl.getProtocol())) {
String protocol = registryUrl.getParameter(Constants.REGISTRY_KEY, Constants.DEFAULT_DIRECTORY);
registryUrl = registryUrl.setProtocol(protocol).removeParameter(Constants.REGISTRY_KEY);
}
return registryFactory.getRegistry(registryUrl);
}
getRegistry() 方法根据注册中心类型（默认 Zookeeper）获取注册中心客户端，由注册中心客户端实例来进行真正的服务注册。
注册中心客户端将节点注册到注册中心，同时订阅对应的 override 数据，实时监听服务的属性变动实现动态配置功能。
最终返回的 Exporter 实现了 unexport() 方法，这样在服务下线时清理相关资源。
至此，服务暴露流程结束。