Dubbo源码解析（六）Dubbo Protocol 以DubboProtocol为例
Protocol 包括两个功能，发布服务和引用服务，所以就可以想到，应该是在Service发布和Reference引用的时候调用了此接口。也就是在ServiceBean、ReferenceBean初始化的时候，这一层也不复杂
代码如下
@SPI("dubbo")
public interface Protocol {
/**
* Get default port when user doesn't config the port.
*
* @return default port
*/
int getDefaultPort();
/**
* Export service for remote invocation:
* 1. Protocol should record request source address after receive a request:
* RpcContext.getContext().setRemoteAddress();
* 2. export() must be idempotent, that is, there's no difference between invoking once and invoking twice when
* export the same URL
* 3. Invoker instance is passed in by the framework, protocol needs not to care
*
* @param Service type
* @param invoker Service invoker
* @return exporter reference for exported service, useful for unexport the service later
* @throws RpcException thrown when error occurs during export the service, for example: port is occupied
*/
@Adaptive
Exporter export(Invoker invoker) throws RpcException;
/**
* Refer a remote service:
* 1. When user calls `invoke()` method of `Invoker` object which's returned from `refer()` call, the protocol
* needs to correspondingly execute `invoke()` method of `Invoker` object
* 2. It's protocol's responsibility to implement `Invoker` which's returned from `refer()`. Generally speaking,
* protocol sends remote request in the `Invoker` implementation.
* 3. When there's check=false set in URL, the implementation must not throw exception but try to recover when
* connection fails.
*
* @param Service type
* @param type Service class
* @param url URL address for the remote service
* @return invoker service's local proxy
* @throws RpcException when there's any error while connecting to the service provider
*/
@Adaptive
Invoker refer(Class type, URL url) throws RpcException;
/**
* Destroy protocol:
* 1. Cancel all services this protocol exports and refers
* 2. Release all occupied resources, for example: connection, port, etc.
* 3. Protocol can continue to export and refer new service even after it's destroyed.
*/
void destroy();
} 如何发布服务的
ServiceBean初始化的时候发布服务
ServiceConfig.doExportUrlsFor1Protocol()
private void doExportUrlsFor1Protocol(ProtocolConfig protocolConfig, List registryURLs) {
// 省略 ....
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);
}
// 创建ServiceImpl的代理，默认是javassist、还有jdk
Invoker invoker = proxyFactory.getInvoker(ref, (Class) interfaceClass, registryURL.addParameterAndEncoded(Constants.EXPORT_KEY, url.toFullString()));
DelegateProviderMetaDataInvoker wrapperInvoker = new DelegateProviderMetaDataInvoker(invoker, this);
// 发布服务到协议上，这样说也不太合适，反正协议是发布的服务组的载体
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);
}
} 发布服务入口
public Exporter export(Invoker invoker) throws RpcException {
URL url = invoker.getUrl();
// export service.
String key = serviceKey(url);
DubboExporter exporter = new DubboExporter(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);
}
}
openServer(url);
optimizeSerialization(url);
return exporter;
} private void openServer(URL url) {
// 获取服务器地址.
String key = url.getAddress();
// 客户端可以导出仅用于服务器调用的服务
// client can export a service which's only for server to invoke
boolean isServer = url.getParameter(Constants.IS_SERVER_KEY, true);
if (isServer) {
// 从缓存中获取服务
ExchangeServer server = serverMap.get(key);
if (server == null) {
// 创建server
serverMap.put(key, createServer(url));
} else {
// 重置服务
// server supports reset, use together with override
server.reset(url);
}
}
} private ExchangeServer createServer(URL url) {
// send readonly event when server closes, it's enabled by default
url = url.addParameterIfAbsent(Constants.CHANNEL_READONLYEVENT_SENT_KEY, Boolean.TRUE.toString());
// enable heartbeat by default
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, DubboCodec.NAME);
ExchangeServer server;
try {
// 创建服务
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 supportedTypes = ExtensionLoader.getExtensionLoader(Transporter.class).getSupportedExtensions();
if (!supportedTypes.contains(str)) {
throw new RpcException("Unsupported client type: " + str);
}
}
return server;
} 如何引用服务的
引用服务入口
public Invoker refer(Class serviceType, URL url) throws RpcException {
// 优化序列化
optimizeSerialization(url);
// 创建Invoker
DubboInvoker invoker = new DubboInvoker(serviceType, url, getClients(url), invokers);
invokers.add(invoker);
return invoker;
}
获取此服务的连接
private ExchangeClient[] getClients(URL url) {
// 是否使用共享的connection
boolean service_share_connect = false;
// 获取connections
int connections = url.getParameter(Constants.CONNECTIONS_KEY, 0);
// 如果没有配置，将使用共享连接,否则一个服务一个连接
if (connections == 0) {
service_share_connect = true;
connections = 1;
}
ExchangeClient[] clients = new ExchangeClient[connections];
for (int i = 0; i < clients.length; i++) {
if (service_share_connect) {
clients[i] = getSharedClient(url);
} else {
clients[i] = initClient(url);
}
}
return clients;
} /**
* 获取共享的连接，多个服务公用同一个连接
*/
private ExchangeClient getSharedClient(URL url) {
// 获取ip地址
String key = url.getAddress();
ReferenceCountExchangeClient client = referenceClientMap.get(key);
if (client != null) {
// 如果client未关闭，引用加1
if (!client.isClosed()) {
client.incrementAndGetCount();
return client;
} else {
referenceClientMap.remove(key);
}
}
synchronized (key.intern()) {
ExchangeClient exchangeClient = initClient(url);
// 创建新的client
client = new ReferenceCountExchangeClient(exchangeClient, ghostClientMap);
referenceClientMap.put(key, client);
ghostClientMap.remove(key);
return client;
}
}
/**
* 创建新连接
*/
private ExchangeClient initClient(URL url) {
// 客户端类型，默认是netty3
String str = url.getParameter(Constants.CLIENT_KEY, url.getParameter(Constants.SERVER_KEY, Constants.DEFAULT_REMOTING_CLIENT));
// 添加解码器类型
url = url.addParameter(Constants.CODEC_KEY, DubboCodec.NAME);
// 设置与服务器的心跳，默认60s
url = url.addParameterIfAbsent(Constants.HEARTBEAT_KEY, String.valueOf(Constants.DEFAULT_HEARTBEAT));
// BIO is not allowed since it has severe performance issue.
//
if (str != null && str.length() > 0 && !ExtensionLoader.getExtensionLoader(Transporter.class).hasExtension(str)) {
throw new RpcException("Unsupported client type: " + str + "," +
" supported client type is " + StringUtils.join(ExtensionLoader.getExtensionLoader(Transporter.class).getSupportedExtensions(), " "));
}
ExchangeClient client;
try {
// 如果设置了延迟加载
if (url.getParameter(Constants.LAZY_CONNECT_KEY, false)) {
client = new LazyConnectExchangeClient(url, requestHandler);
} else {
// 立马连接客户端，后面分析Exchangers再说
client = Exchangers.connect(url, requestHandler);
}
} catch (RemotingException e) {
throw new RpcException("Fail to create remoting client for service(" + url + "): " + e.getMessage(), e);
}
return client;
}总结
Protocol 用于实现发布和引用服务。很简单，我觉得就是服务的载体。或许认识还不够吧。就像老大说的一样，我级别还不够，眼界还很低。所以这一层就是封装了封装 RPC 调用，即引用和发布服务