搜云库技术团队
Spring在启动Dubbo服务端应用时，会实例化ServiceBean
@SuppressWarnings({"unchecked", "deprecation"})
public void afterPropertiesSet() throws Exception {
// 设置一揽子provider属性
......
if (!isDelay()) {
export();
}
}
此后调用的是ServiceConfig中的doExportUrls方法：
@SuppressWarnings({"unchecked", "rawtypes"})
private void doExportUrls() {
// 获取注册中心地址
List<URL> registryURLs = loadRegistries(true);
for (ProtocolConfig protocolConfig : protocols) {
doExportUrlsFor1Protocol(protocolConfig, registryURLs);
}
}
最终实现的是如下逻辑：
private void doExportUrlsFor1Protocol(ProtocolConfig protocolConfig, List<URL> registryURLs) {
// 省略...
......
String scope = url.getParameter(Constants.SCOPE_KEY);
// don't export when none is configured
if (!Constants.SCOPE_NONE.toString().equalsIgnoreCase(scope)) {
// export to local if the config is not remote (export to remote only when config is remote)
if (!Constants.SCOPE_REMOTE.toString().equalsIgnoreCase(scope)) {
// 暴露到本地，使用injvm协议，本地调用服务时会采用此协议
exportLocal(url);
}
// export to remote if the config is not local (export to local only when config is local)
if (!Constants.SCOPE_LOCAL.toString().equalsIgnoreCase(scope)) {
// 暴露到服务注册中心
if (logger.isInfoEnabled()) {
logger.info("Export dubbo service " + interfaceClass.getName() + " to url " + url);
}
if (registryURLs != null && !registryURLs.isEmpty()) {
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()));
DelegateProviderMetaDataInvoker wrapperInvoker = new DelegateProviderMetaDataInvoker(invoker, this);
// 暴露服务，protocol实例为ProtocolListenerWrapper，ProtocolListenerWrapper使用装饰器模式，会不断的调用Protocol接口的子类实例
Exporter<?> exporter = protocol.export(wrapperInvoker);
exporters.add(exporter);
}
} else {
Invoker<?> invoker = proxyFactory.getInvoker(ref, (Class) interfaceClass, url);
DelegateProviderMetaDataInvoker wrapperInvoker = new DelegateProviderMetaDataInvoker(invoker, this);
Exporter<?> exporter = protocol.export(wrapperInvoker);
exporters.add(exporter);
}
}
}
this.urls.add(url);
}
代码 Exporter<?> exporter = protocol.export(wrapperInvoker); protocol实例为ProtocolListenerWrapper，ProtocolListenerWrapper使用了装饰器模式，依次包装了Protocol接口的子类，其中最重要的两个子类是DubboProtocol和RegistryProtocol。DubboProtocol的主要功能是启动NettyServer和重置服务URL的部分参数，RegistryProtocol的主要功能是暴露服务到注册中心，例如zookeeper。
接下来先看DubboProtocol的export方法：
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 dispatching 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);
}
}
// 启动NettyServer和重置服务URL的部分参数
openServer(url);
optimizeSerialization(url);
return exporter;
}
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(Constants.IS_SERVER_KEY, true);
if (isServer) {
ExchangeServer server = serverMap.get(key);
if (server == null) {
// 启动NettyServer并放入serverMap
serverMap.put(key, createServer(url));
} else {
// server supports reset, use together with override
// 重置服务URL的部分参数
server.reset(url);
}
}
}
private ExchangeServer createServer(URL url) {
......
url = url.addParameter(Constants.CODEC_KEY, DubboCodec.NAME);
ExchangeServer server;
try {
// 启动NettyServer
server = Exchangers.bind(url, requestHandler);
} catch (RemotingException e) {
throw new RpcException("Fail to start server(url: " + url + ") " + e.getMessage(), e);
}
......
return server;
}
最终会调用HeaderExchanger的bind方法：
public ExchangeServer bind(URL url, ExchangeHandler handler) throws RemotingException {
return new HeaderExchangeServer(Transporters.bind(url, new DecodeHandler(new HeaderExchangeHandler(handler))));
}
剩下就是实例化NettyServer了，这里不再贴出该部分代码，若感兴趣可自行跟踪源码啦。
这里注意到NettyServer中有一个属性channels，这里维护了所有客户端的连接。
