本文深入剖析Dubbo服务端暴露流程，从Service注解处理到ServiceConfig构建，再到export()方法的调用。详细解释了如何通过反射设置配置，如何遍历不同协议暴露服务，尤其是Netty服务器的启动和Zookeeper注册过程。在NettyServer的doOpen()中开启服务端，接着通过RegistryProtocol与Zookeeper交互，完成服务注册和心跳监测。整个过程揭示了Dubbo服务从创建到上线的内部机制。
我们从AnnotationBean#postProcessAfterInitialization为入口分析
public Object postProcessAfterInitialization(Object bean, String beanName)
throws BeansException {
if (! isMatchPackage(bean)) {
return bean;
}
Service service = bean.getClass().getAnnotation(Service.class);
if (service != null) {
ServiceBean<Object> serviceConfig = new ServiceBean<Object>(service);
if (void.class.equals(service.interfaceClass())
&& "".equals(service.interfaceName())) {
if (bean.getClass().getInterfaces().length > 0) {
serviceConfig.setInterface(bean.getClass().getInterfaces()[0]);
} else {
throw new IllegalStateException("Failed to export remote service class " + bean.getClass().getName() + ", cause: The @Service undefined interfaceClass or interfaceName, and the service class unimplemented any interfaces.");
}
}
if (applicationContext != null) {
serviceConfig.setApplicationContext(applicationContext);
if (service.registry() != null && service.registry().length > 0) {
List<RegistryConfig> registryConfigs = new ArrayList<RegistryConfig>();
for (String registryId : service.registry()) {
if (registryId != null && registryId.length() > 0) {
registryConfigs.add((RegistryConfig)applicationContext.getBean(registryId, RegistryConfig.class));
}
}
serviceConfig.setRegistries(registryConfigs);
}
if (service.provider() != null && service.provider().length() > 0) {
serviceConfig.setProvider((ProviderConfig)applicationContext.getBean(service.provider(),ProviderConfig.class));
}
if (service.monitor() != null && service.monitor().length() > 0) {
serviceConfig.setMonitor((MonitorConfig)applicationContext.getBean(service.monitor(), MonitorConfig.class));
}
if (service.application() != null && service.application().length() > 0) {
serviceConfig.setApplication((ApplicationConfig)applicationContext.getBean(service.application(), ApplicationConfig.class));
}
if (service.module() != null && service.module().length() > 0) {
serviceConfig.setModule((ModuleConfig)applicationContext.getBean(service.module(), ModuleConfig.class));
}
if (service.provider() != null && service.provider().length() > 0) {
serviceConfig.setProvider((ProviderConfig)applicationContext.getBean(service.provider(), ProviderConfig.class));
} else {
}
if (service.protocol() != null && service.protocol().length > 0) {
List<ProtocolConfig> protocolConfigs = new ArrayList<ProtocolConfig>();
for (String protocolId : service.registry()) {
if (protocolId != null && protocolId.length() > 0) {
protocolConfigs.add((ProtocolConfig)applicationContext.getBean(protocolId, ProtocolConfig.class));
}
}
serviceConfig.setProtocols(protocolConfigs);
}
try {
serviceConfig.afterPropertiesSet();
} catch (RuntimeException e) {
throw (RuntimeException) e;
} catch (Exception e) {
throw new IllegalStateException(e.getMessage(), e);
}
}
serviceConfig.setRef(bean);
serviceConfigs.add(serviceConfig);
serviceConfig.export();
}
return bean;
}首先得到服务提供类的Service注解，再封装成ServiceConfig，再注入类的接口等一些配置信息，其实setRef(bean)就是把真正服务实现类的实例传入，再把ServiceConfig添加到本地的ServiceConfig集合中，最后再调用ServiceConfig的export()暴露服务。
我们先看下封装成serverConfig的过程。即ServiceBean<Object> serviceConfig = new ServiceBean<Object>(service);具体逻辑在父类ServerConfig的构造方法中。调用了appendAnnotation()方法。
protected void appendAnnotation(Class<?> annotationClass, Object annotation) {
Method[] methods = annotationClass.getMethods();
for (Method method : methods) {
if (method.getDeclaringClass() != Object.class
&& method.getReturnType() != void.class
&& method.getParameterTypes().length == 0
&& Modifier.isPublic(method.getModifiers())
&& ! Modifier.isStatic(method.getModifiers())) {
try {
String property = method.getName();
if ("interfaceClass".equals(property) || "interfaceName".equals(property)) {
property = "interface";
}
String setter = "set" + property.substring(0, 1).toUpperCase() + property.substring(1);
Object value = method.invoke(annotation, new Object[0]);
if (value != null && ! value.equals(method.getDefaultValue())) {
Class<?> parameterType = ReflectUtils.getBoxedClass(method.getReturnType());
if ("filter".equals(property) || "listener".equals(property)) {
parameterType = String.class;
value = StringUtils.join((String[]) value, ",");
} else if ("parameters".equals(property)) {
parameterType = Map.class;
value = CollectionUtils.toStringMap((String[]) value);
}
try {
Method setterMethod = getClass().getMethod(setter, new Class<?>[] { parameterType });
setterMethod.invoke(this, new Object[] { value });
} catch (NoSuchMethodException e) {
// ignore
}
}
} catch (Throwable e) {
logger.error(e.getMessage(), e);
}
}
}
}通过反射调用setter方法，将Service注解上的值注入到新生成的ServiceConfig实例中。(实现很巧妙，让人不禁多看几眼)
继续看ServiceConfig的export()方法。判断是否有export，并是否延迟暴露，最后调用doExport()；又是一堆的检查，在这最后调用doExportUrls()；
private void doExportUrls() {
//将注册的所有url匹配上对应的协议在服务端暴露出来
/**
* 将注册协议转化成url
* registry://45.119.68.23:2181/com.alibaba.dubbo.registry.RegistryService?
* application=test-dubbo&dubbo=2.5.3&pid=7648®istry=zookeeper×tamp=1462349748801
*/
List<URL> registryURLs = loadRegistries(true);
//配置多通信协议时，都进行暴露
for (ProtocolConfig protocolConfig : protocols) {
doExportUrlsFor1Protocol(protocolConfig, registryURLs);
}
}先调用loadRegistries()方法，对应每个注册中心生成匹配的URL的数据结构(URL即protocol+map形式)
registry://224.5.6.7:1234/com.alibaba.dubbo.registry.RegistryService?application=test-protocol-random-port&dubbo=2.0.0
&pid=4324®istry=dubbo×tamp=1527428955474
protected List<URL> loadRegistries(boolean provider) {
checkRegistry();
List<URL> registryList = new ArrayList<URL>();
if (registries != null && registries.size() > 0) {
for (RegistryConfig config : registries) {
String address = config.getAddress();
if (address == null || address.length() == 0) {
address = Constants.ANYHOST_VALUE;
}
String sysaddress = System.getProperty("dubbo.registry.address");
if (sysaddress != null && sysaddress.length() > 0) {
address = sysaddress;
}
if (address != null && address.length() > 0
&& ! RegistryConfig.NO_AVAILABLE.equalsIgnoreCase(address)) {
Map<String, String> map = new HashMap<String, String>();
appendParameters(map, application);
appendParameters(map, config);
map.put("path", RegistryService.class.getName());
map.put("dubbo", Version.getVersion());
map.put(Constants.TIMESTAMP_KEY, String.valueOf(System.currentTimeMillis()));
if (ConfigUtils.getPid() > 0) {
map.put(Constants.PID_KEY, 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);
for (URL url : urls) {
url = url.addParameter(Constants.REGISTRY_KEY, url.getProtocol());
url = url.setProtocol(Constants.REGISTRY_PROTOCOL);
if ((provider && url.getParameter(Constants.REGISTER_KEY, true))
|| (! provider && url.getParameter(Constants.SUBSCRIBE_KEY, true))) {
registryList.add(url);
}
}
}
}
}
return registryList;
}既然有多种通信协议，那么遍历所有不同的协议，都进行服务暴露(因为dubbo支持多通信协议时，都进行暴露)。
private void doExportUrlsFor1Protocol(ProtocolConfig protocolConfig, List<URL> registryURLs) {
//如果没配置protocol则默认使用dubbo协议
String name = protocolConfig.getName();
if (name == null || name.length() == 0) {
name = "dubbo";
}
//获取主机地址
String host = protocolConfig.getHost();
if (provider != null && (host == null || host.length() == 0)) {
host = provider.getHost();
}
boolean anyhost = false;
if (NetUtils.isInvalidLocalHost(host)) {
anyhost = true;
try {
host = InetAddress.getLocalHost().getHostAddress();
} catch (UnknownHostException e) {
logger.warn(e.getMessage(), e);
}
if (NetUtils.isInvalidLocalHost(host)) {
if (registryURLs != null && registryURLs.size() > 0) {
for (URL registryURL : registryURLs) {
try {
//创建socket，连接到注册中心
Socket socket = new Socket();
try {
SocketAddress addr = new InetSocketAddress(registryURL.getHost(), registryURL.getPort());
socket.connect(addr, 1000);
//获取服务所在主机地址
host = socket.getLocalAddress().getHostAddress();
break;
} finally {
try {
socket.close();
} catch (Throwable e) {}
}
} catch (Exception e) {
logger.warn(e.getMessage(), e);
}
}
}
if (NetUtils.isInvalidLocalHost(host)) {
host = NetUtils.getLocalHost();
}
}
}
//获取协议接口号
Integer port = protocolConfig.getPort();
if (provider != null && (port == null || port == 0)) {
port = provider.getPort();
}
final int defaultPort = ExtensionLoader.getExtensionLoader(Protocol.class).getExtension(name).getDefaultPort();
if (port == null || port == 0) {
port = defaultPort;
}
if (port == null || port <= 0) {
port = getRandomPort(name);
if (port == null || port < 0) {
port = NetUtils.getAvailablePort(defaultPort);
putRandomPort(name, port);
}
logger.warn("Use random available port(" + port + ") for protocol " + name);
}
//获取application、module、provider、protocol、exporter、registries、monitor所有属性
Map<String, String> map = new HashMap<String, String>();
if (anyhost) {
map.put(Constants.ANYHOST_KEY, "true");
}
map.put(Constants.SIDE_KEY, Constants.PROVIDER_SIDE);
map.put(Constants.DUBBO_VERSION_KEY, Version.getVersion());
map.put(Constants.TIMESTAMP_KEY, String.valueOf(System.currentTimeMillis()));
if (ConfigUtils.getPid() > 0) {
map.put(Constants.PID_KEY, String.valueOf(ConfigUtils.getPid()));
}
/**
* 将不为null的配置对象中的属性设置到 map 中
* 即将 xml 配置文件中的配置设置的值全转化成为map
* {side=provider, application=alijk-dubbo, accepts=1000,
* dubbo=2.5.3, threads=100, pid=7236, interface=cn.eoncloud.account.sdk.export.AccountService,
* threadpool=fixed, version=1.0.0, timeout=500, anyhost=true, timestamp=1462347843960}
*/
appendParameters(map, application);
appendParameters(map, module);
appendParameters(map, provider, Constants.DEFAULT_KEY);
appendParameters(map, protocolConfig);
appendParameters(map, this);
if (methods != null && methods.size() > 0) {
for (MethodConfig method : methods) {
appendParameters(map, method, method.getName());
String retryKey = method.getName() + ".retry";
if (map.containsKey(retryKey)) {
String retryValue = map.remove(retryKey);
if ("false".equals(retryValue)) {
map.put(method.getName() + ".retries", "0");
}
}
List<ArgumentConfig> arguments = method.getArguments();
if (arguments != null && arguments.size() > 0) {
for (ArgumentConfig argument : arguments) {
//类型自动转换.
if(argument.getType() != null && argument.getType().length() >0){
Method[] methods = interfaceClass.getMethods();
//遍历所有方法
if(methods != null && methods.length > 0){
for (int i = 0; i < methods.length; i++) {
String methodName = methods[i].getName();
//匹配方法名称，获取方法签名.
if(methodName.equals(method.getName())){
Class<?>[] argtypes = methods[i].getParameterTypes();
//一个方法中单个callback
if (argument.getIndex() != -1 ){
if (argtypes[argument.getIndex()].getName().equals(argument.getType())){
appendParameters(map, argument, method.getName() + "." + argument.getIndex());
}else {
throw new IllegalArgumentException("argument config error : the index attribute and type attirbute not match :index :"+argument.getIndex() + ", type:" + argument.getType());
}
} else {
//一个方法中多个callback
for (int j = 0 ;j<argtypes.length ;j++) {
Class<?> argclazz = argtypes[j];
if (argclazz.getName().equals(argument.getType())){
appendParameters(map, argument, method.getName() + "." + j);
if (argument.getIndex() != -1 && argument.getIndex() != j){
throw new IllegalArgumentException("argument config error : the index attribute and type attirbute not match :index :"+argument.getIndex() + ", type:" + argument.getType());
}
}
}
}
}
}
}
}else if(argument.getIndex() != -1){
appendParameters(map, argument, method.getName() + "." + argument.getIndex());
}else {
throw new IllegalArgumentException("argument config must set index or type attribute.eg: <dubbo:argument index='0' .../> or <dubbo:argument type=xxx .../>");
}
}
}
} // end of methods for
}
if (ProtocolUtils.isGeneric(generic)) {
map.put("generic", generic);
map.put("methods", Constants.ANY_VALUE);
} else {
String revision = Version.getVersion(interfaceClass, version);
if (revision != null && revision.length() > 0) {
map.put("revision", revision);
}
String[] methods = Wrapper.getWrapper(interfaceClass).getMethodNames();
if(methods.length == 0) {
logger.warn("NO method found in service interface " + interfaceClass.getName());
map.put("methods", Constants.ANY_VALUE);
}
else {
map.put("methods", StringUtils.join(new HashSet<String>(Arrays.asList(methods)), ","));
}
}
if (! ConfigUtils.isEmpty(token)) {
if (ConfigUtils.isDefault(token)) {
map.put("token", UUID.randomUUID().toString());
} else {
map.put("token", token);
}
}
if ("injvm".equals(protocolConfig.getName())) {
protocolConfig.setRegister(false);
map.put("notify", "false");
}
// 导出服务
String contextPath = protocolConfig.getContextpath();
if ((contextPath == null || contextPath.length() == 0) && provider != null) {
contextPath = provider.getContextpath();
}
/**
* 将配置信息转化成 url ,主要根据之前map里的数据组装成url
* 调用 URL#buildString方法
* dubbo://10.6.13.137:9998/cn.eoncloud.account.sdk.export.AccountService
* ?accepts=1000&anyhost=true&application=test-dubbo&dubbo=2.5.3
* &interface=cn.eoncloud.account.sdk.export.AccountService
* &methods=getAccountName,getAllTest&pid=7236&revision=1.0.0&side=provider
* &threadpool=fixed&threads=100&timeout=500×tamp=1462347843960&version=1.0.0
*/
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);
}
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);
}
//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)
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"));
// 配置的了monitor加载monitor，并给URL设置MONITOR_KEY
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);
}
//获取invoker;根据服务具体实现，实现接口以及regitryUrl从代理工厂ProxyFactory获取代理Invoker（继承于AbstractProxyInvoker）,它是对具体实现的一种代理
Invoker<?> invoker = proxyFactory.getInvoker(ref, (Class) interfaceClass, registryURL.addParameterAndEncoded(Constants.EXPORT_KEY, url.toFullString()));
//根据协议将invoker暴露成exporter，具体过程是创建一个ExchangeServer，它会绑定一个ServerSocket到配置端口
//protocol.export(invoker); 这个protocol的值为：RegistryProtocol，也就是暴露会跳到：RegistryProtocol.exprot中去处理
Exporter<?> exporter = protocol.export(invoker);
//将创建的exporter放进链表便于管理
exporters.add(exporter);
}
} else {
Invoker<?> invoker = proxyFactory.getInvoker(ref, (Class) interfaceClass, url);
Exporter<?> exporter = protocol.export(invoker);
exporters.add(exporter);
}
}
}
this.urls.add(url);
}这里主要将相关的配置转化成map，然后将map跟不同的protocol生成URL(上文介绍过，这是Dubbo特有的数据结构)。最终暴露的dubbo服务也就是这个统一的url，这个url也会注册到zookeeper的节点上。
dubbo://192.168.67.174:20880/com.alibaba.dubbo.config.api.DemoService?anyhost=true&application=test-protocol-random-port
&bind.ip=192.168.67.174&bind.port=20880&dubbo=2.0.0&generic=false&interface=com.alibaba.dubbo.config.api.DemoService
&methods=sayName,getUsers,echo,getBox,throwDemoException&pid=12732&side=provider×tamp=1527429609471//获取invoker;根据服务具体实现，实现接口以及regitryUrl从代理工厂ProxyFactory获取代理Invoker（继承于AbstractProxyInvoker）,它是对具体实现的一种代理
Invoker<?> invoker = proxyFactory.getInvoker(ref, (Class) interfaceClass, registryURL.addParameterAndEncoded(Constants.EXPORT_KEY, url.toFullString()));
//根据协议将invoker暴露成exporter，具体过程是创建一个ExchangeServer，它会绑定一个ServerSocket到配置端口
//protocol.export(invoker); 这个protocol的值为：RegistryProtocol，也就是暴露会跳到：RegistryProtocol.exprot中去处理
Exporter<?> exporter = protocol.export(invoker);
//将创建的exporter放进链表便于管理
exporters.add(exporter);然后根据不同的注册中心，不同的协议调用，先不同的protocol的export()；配置有filter或者listener的情况下，会在这里产生关于具体服务暴露操作的过滤与监听。值得一提的是，如果采用的是registry协议，那么并不会经过ProtocolListenerWrapper的监听，而是直接进入export()方法开始服务的暴露。这里protocol是registryProtocol，我们来看下RegistryProtocol.exprot()。注释强调了，主要做两件事：1、开启netty服务端 。2、创建zookeeper服务节点。
/**
* 主要做两件事情：1、开启netty服务端 。2、创建zookeeper服务节点
*/
public <T> Exporter<T> export(final Invoker<T> originInvoker) throws RpcException {
//export invoker doLocalExport调用dubboProtocol.export开启netty服务监听
final ExporterChangeableWrapper<T> exporter = doLocalExport(originInvoker);
//registry provider
final Registry registry = getRegistry(originInvoker);
final URL registedProviderUrl = getRegistedProviderUrl(originInvoker);
// 调用zodoRegister的doRegister 创建zookeeper的服务节点
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);
//订阅
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 <T> ExporterChangeableWrapper<T> doLocalExport(final Invoker<T> originInvoker){
String key = getCacheKey(originInvoker);
ExporterChangeableWrapper<T> exporter = (ExporterChangeableWrapper<T>) bounds.get(key);
if (exporter == null) {
synchronized (bounds) {
exporter = (ExporterChangeableWrapper<T>) bounds.get(key);
if (exporter == null) {
final Invoker<?> invokerDelegete = new InvokerDelegete<T>(originInvoker, getProviderUrl(originInvoker));
//此处protol为dubboProtocol
// dubboProtocol的export对服务进行暴露，这个export最终目的就是开启netty的监听
exporter = new ExporterChangeableWrapper<T>((Exporter<T>)protocol.export(invokerDelegete), originInvoker);
bounds.put(key, exporter);
}
}
}
return (ExporterChangeableWrapper<T>) exporter;
} 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;
} 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));
//默认使用netty
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);
//默认使用dubbo协议编码
url = url.addParameter(Constants.CODEC_KEY, Version.isCompatibleVersion() ? COMPATIBLE_CODEC_NAME : DubboCodec.NAME);
ExchangeServer server;
try {
//HeaderExchangeServer 在此处已经开启了Netty Server 进行监听
// Exchangers.bind(url, requestHandler) 默认为：HeaderExchanger.bind()
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;
}一些默认的处理，关键是Exchangers.bind()方法，返回了ExchangeServer(介个貌似已经是netty server的监听服务器，也就是说这里完成了对网络监听的配置与开启)我们来看下具体的流程。跟进去：
url = url.addParameterIfAbsent(Constants.CODEC_KEY, "exchange");
return getExchanger(url).bind(url, handler);
public static Exchanger getExchanger(URL url) {
String type = url.getParameter(Constants.EXCHANGER_KEY, Constants.DEFAULT_EXCHANGER);//header
return getExchanger(type);
}可以看到这里默认是headerExchange，那么继续去看它的bind方法
public ExchangeServer bind(URL url, ExchangeHandler handler) throws RemotingException {
//Transporters默认为NettyTransporter
return new HeaderExchangeServer(Transporters.bind(url,
new DecodeHandler(new HeaderExchangeHandler(handler))));
}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);
}
public static Transporter getTransporter() {
return ExtensionLoader.getExtensionLoader(Transporter.class).getAdaptiveExtension();
} public static final String NAME = "netty";
public Server bind(URL url, ChannelHandler listener) throws RemotingException {
return new NettyServer(url, listener);
}在这里我们看到其根据url建立NettyServer，并设置了回调listener，就是之前的requestHandler。
NettyServer的父类构造中调用了NettyServer的doOpen()
protected void doOpen() throws Throwable {
NettyHelper.setNettyLoggerFactory();
ExecutorService boss = Executors.newCachedThreadPool(new NamedThreadFactory("NettyServerBoss", true));
ExecutorService worker = Executors.newCachedThreadPool(new NamedThreadFactory("NettyServerWorker", true));
//最后一个参数为 NIO 最大工作线程数
ChannelFactory channelFactory = new NioServerSocketChannelFactory(boss, worker, getUrl().getPositiveParameter(Constants.IO_THREADS_KEY, Constants.DEFAULT_IO_THREADS));
//netty server 启动器
bootstrap = new ServerBootstrap(channelFactory);
final NettyHandler nettyHandler = new NettyHandler(getUrl(), this);
channels = nettyHandler.getChannels();
// https://issues.jboss.org/browse/NETTY-365
// https://issues.jboss.org/browse/NETTY-379
// 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 ; 创建一个绑定到指定地址的新通道，也就是绑定IP、端口供客户端连接
channel = bootstrap.bind(getBindAddress());
}这里就是很熟悉的netty服务端的开启，其中nettyHandler是处理业务逻辑层，它是处理客户端连接，消息收发等。
netty服务端开启后，我们回到HeaderExchangeServer的构造中，得到netty服务器后，开启心跳监测机制。
final Registry registry = getRegistry(originInvoker);
final URL registedProviderUrl = getRegistedProviderUrl(originInvoker);
// 调用zodoRegister的doRegister 创建zookeeper的服务节点
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);
//订阅
registry.subscribe(overrideSubscribeUrl, overrideSubscribeListener);回到RegistryProtocol.exprot()中继续，通过getRegistry()获得注册中心的实例，会根据配置的registryFactory生成对应的registry实例(这里是zookeeperRegister)。得到zookeeper注册中心的URL，通过register()的方式向注册创建zk节点，之后，向注册中心订阅这一服务，以保证注册数据变动时的自动推送。
getRegistry()使用RegistryFactory的getRegistry()，实际上是调用Zookeeper的ceateRegistry()方法(根据配置，使用zookeeper注册中心为例子)。
public Registry createRegistry(URL url) {
return new ZookeeperRegistry(url, zookeeperTransporter);
}我们继续来看
public ZookeeperRegistry(URL url, ZookeeperTransporter zookeeperTransporter) {
super(url);
if (url.isAnyHost()) {
throw new IllegalStateException("registry address == null");
}
String group = url.getParameter(Constants.GROUP_KEY, DEFAULT_ROOT);
if (! group.startsWith(Constants.PATH_SEPARATOR)) {
group = Constants.PATH_SEPARATOR + group;
}
this.root = group;
zkClient = zookeeperTransporter.connect(url);
zkClient.addStateListener(new StateListener() {
public void stateChanged(int state) {
if (state == RECONNECTED) {
try {
recover();
} catch (Exception e) {
logger.error(e.getMessage(), e);
}
}
}
});
}建立了zkClient。
我们再来看registry.register()方法的具体逻辑
@Override
public void register(URL url) {
super.register(url);
failedRegistered.remove(url);
failedUnregistered.remove(url);
try {
// 向服务器端发送注册请求
doRegister(url);
} catch (Exception e) {
Throwable t = e;
// 如果开启了启动时检测，则直接抛出异常
boolean check = getUrl().getParameter(Constants.CHECK_KEY, true)
&& url.getParameter(Constants.CHECK_KEY, true)
&& ! Constants.CONSUMER_PROTOCOL.equals(url.getProtocol());
boolean skipFailback = t instanceof SkipFailbackWrapperException;
if (check || skipFailback) {
if(skipFailback) {
t = t.getCause();
}
throw new IllegalStateException("Failed to register " + url + " to registry " + getUrl().getAddress() + ", cause: " + t.getMessage(), t);
} else {
logger.error("Failed to register " + url + ", waiting for retry, cause: " + t.getMessage(), t);
}
// 将失败的注册请求记录到失败列表，定时重试
failedRegistered.add(url);
}
}
//zookeeper类
protected void doRegister(URL url) {
try {
zkClient.create(toUrlPath(url), url.getParameter(Constants.DYNAMIC_KEY, true));
} catch (Throwable e) {
throw new RpcException("Failed to register " + url + " to zookeeper " + getUrl() + ", cause: " + e.getMessage(), e);
}
}可以看到这里创建了zk节点。
我们继续回到前面的doExportUrlsFor1Protocol中
//获取invoker;根据服务具体实现，实现接口以及regitryUrl从代理工厂ProxyFactory获取代理Invoker（继承于AbstractProxyInvoker）,它是对具体实现的一种代理
Invoker<?> invoker = proxyFactory.getInvoker(ref, (Class) interfaceClass, registryURL.addParameterAndEncoded(Constants.EXPORT_KEY, url.toFullString()));
//根据协议将invoker暴露成exporter，具体过程是创建一个ExchangeServer，它会绑定一个ServerSocket到配置端口
//protocol.export(invoker); 这个protocol的值为：RegistryProtocol，也就是暴露会跳到：RegistryProtocol.exprot中去处理
Exporter<?> exporter = protocol.export(invoker);
//将创建的exporter放进链表便于管理
exporters.add(exporter);我们分析了Protocol.export这个方法，现在本地建立netty server监听，再将invoker服务以URL的数据格式，在zookeeper注册中心新建一个zk节点，记录其中。
那么具体的服务是如何封装在invoker中？我们从Invoker<?> invoker = proxyFactory.getInvoker();中入手。默认的是javassistProxyFactory
public <T> Invoker<T> getInvoker(T proxy, Class<T> type, URL url) {
// TODO Wrapper类不能正确处理带$的类名
final Wrapper wrapper = Wrapper.getWrapper(proxy.getClass().getName().indexOf('$') < 0 ? proxy.getClass() : type);
return new AbstractProxyInvoker<T>(proxy, type, url) {
@Override
protected Object doInvoke(T proxy, String methodName,
Class<?>[] parameterTypes,
Object[] arguments) throws Throwable {
return wrapper.invokeMethod(proxy, methodName, parameterTypes, arguments);
}
};
} 在getWrapper方法中，根据需要包装的类来WRAPPER_MAP中寻找，如果没有，则调用makeWrapper，并以需要包装的类为key，得到的wrapper为value存入WRAPPER_MAP中。
makeWrapper()方法根据传入所要包装的类动态生成新的包装类。之后调用了该包装类的invokerMethod方法。我们来重点看下makeWrapper()的关于invokeMethod()方法的生成部分。
if( hasMethod ){
c3.append(" try{");
}
for( Method m : methods )
{
if( m.getDeclaringClass() == Object.class ) //ignore Object's method.
continue;
String mn = m.getName();
c3.append(" if( \"").append(mn).append("\".equals( $2 ) ");
int len = m.getParameterTypes().length;
c3.append(" && ").append(" $3.length == ").append(len);
boolean override = false;
for( Method m2 : methods ) {
if (m != m2 && m.getName().equals(m2.getName())) {
override = true;
break;
}
}
if (override) {
if (len > 0) {
for (int l = 0; l < len; l ++) {
c3.append(" && ").append(" $3[").append(l).append("].getName().equals(\"")
.append(m.getParameterTypes()[l].getName()).append("\")");
}
}
}
c3.append(" ) { ");
if( m.getReturnType() == Void.TYPE )
c3.append(" w.").append(mn).append('(').append(args(m.getParameterTypes(), "$4")).append(");")
.append(" return null;");
else
c3.append(" return ($w)w.").append(mn).append('(').append(args(m.getParameterTypes(), "$4")).append(");");
c3.append(" }");
mns.add(mn);
if( m.getDeclaringClass() == c )
dmns.add(mn);
ms.put(ReflectUtils.getDesc(m), m);
}
if( hasMethod ){
c3.append(" } catch(Throwable e) { " );
c3.append(" throw new java.lang.reflect.InvocationTargetException(e); " );
c3.append(" }");
}
c3.append(" throw new " + NoSuchMethodException.class.getName() + "(\"Not found method \\\"\"+$2+\"\\\" in class "
+ c.getName() + ".\"); }"); public Object invokeMethod(Object o, String n, Class[] p, Object[] v) throws java.lang.reflect.InvocationTargetException {
dubbo.provider.hello.service.impl.HelloWorld w;
try {
w = ((dubbo.provider.hello.service.impl.HelloServiceImpl) $1);
} catch (Throwable e) {
throw new IllegalArgumentException(e);
}
try {
if ("helloWorld".equals($2) && $3.length == 0) {
w. helloWorld ();
return null;
}
if ("getName".equals($2) && $3.length == 0) {
return ($w)w. getNanme ();
}
if ("setName".equals($2) && $3.length == 1) {
return ($w)w. setNanme ($4);
}
} catch (Throwable e) {
throw new java.lang.reflect.InvocationTargetException(e);
}
throw new com.alibaba.dubbo.common.bytecode.NoSuchMethodException("Not found method \""
+ $2 + "\" in class dubbo.provider.hello.service.impl.HelloServiceImpl.");
} 
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