dubbo provider如何对invoker进行export

如何把provider的invoker export出去：1）为原始对象加wrapper，生成invoker；2）给invoker加各种filter，启动监听服务；3）注册服务地址

以HelloService为例：

public interface HelloService {
    String sayHello();
}

<dubbo:service interface="com.zhang.HelloService" ref="helloService" />

ServiceConfig和<dubbo:service>基本对应上了。

public interface ApplicationListener {
    public void onApplicationEvent(ApplicationEvent event);
}

public class ServiceBean<T> extends ServiceConfig<T> implements InitializingBean, ApplicationContextAware, ApplicationListener, BeanNameAware {
    public void onApplicationEvent(ApplicationEvent event) {
        if (ContextRefreshedEvent.class.getName().equals(event.getClass().getName())) {
            if (isDelay()) {
                if (logger.isInfoEnabled()) {
                    logger.info("The service ready on spring started. service: " + getInterface());
                }
                export();
            }
        }
    }
}

public class ServiceConfig<T> extends AbstractServiceConfig {
    private ProviderConfig provider;
    // 是否暴露
    protected Boolean             export;
    
    private String              interfaceName;
    private Class<?>            interfaceClass;
    //即<dubbo:service>的ref对象
    private T                   ref;
    
    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 {
            //关于export和delay的配置好像不怎么用，基本走else分支
            doExport();
        }
    }
    
    protected synchronized void doExport() {
        if (unexported) {
            throw new IllegalStateException("Already unexported!");
        }
        if (exported) {
            return;
        }
        if (interfaceName == null || interfaceName.length() == 0) {
            throw new IllegalStateException("<dubbo:service interface="" /> interface not allow null!");
        }
        checkDefault();
        if (provider != null) {
            if (application == null) {
                application = provider.getApplication();
            }
            if (registries == null) {
                registries = provider.getRegistries();
            }
            if (monitor == null) {
                monitor = provider.getMonitor();
            }
            if (protocols == null) {
                protocols = provider.getProtocols();
            }
        }
        if (application != null) {
            if (registries == null) {
                registries = application.getRegistries();
            }
            if (monitor == null) {
                monitor = application.getMonitor();
            }
        }
        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 = Class.forName(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 = Class.forName(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);
            }
        }
        checkApplication();
        checkRegistry();
        checkProtocol();
        checkStubAndMock(interfaceClass);
        if (path == null || path.length() == 0) {
            path = interfaceName;
        }
        doExportUrls();
        exported = true;
    }
}

一、生成invoker

ServiceConfig.doExportUrlsFor1Protocol 代码片段：

// ref就是原始对象
Invoker<?> invoker = proxyFactory.getInvoker(ref, (Class) interfaceClass,
                            registryURL.addParameterAndEncoded(Constants.EXPORT_KEY, url.toFullString()));
// protocol是Protocol$Adpative
Exporter<?> exporter = protocol.export(invoker);
exporters.add(exporter);

以javassist为例，默认从JavassistProxyFactory获取invoker，其实是生成wrapper。

// JavassistProxyFactory
public <T> Invoker<T> getInvoker(T proxy, Class<T> type, URL url) {
    // TODO Wrapper类不能正确处理带$的类名。这里的 T proxy 是原始对象
    final Wrapper wrapper = Wrapper.getWrapper(proxy.getClass().getName().indexOf('$') < 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);
        }
    };
}

com.alibaba.dubbo.common.bytecode.Wrapper.makeWrapper(Class<?> c) 方法中生成wrapper类，代码格式化后如下：

public class com.alibaba.dubbo.common.bytecode.Wrapper1 extends Wrapper {
    public static String[] pns = null;
    public static Map pts = null;
    public static String[] mns = { "sayHello" };
    public static String[] dmns = { "sayHello" };
    public static Class[] mts0 = null;

    public String[] getPropertyNames() {
        return pns;
    }

    public boolean hasProperty(String n) {
        return pts.containsKey($1);
    }

    public Class getPropertyType(String n) {
        return (Class) pts.get($1);
    }

    public String[] getMethodNames() {
        return mns;
    }

    public String[] getDeclaredMethodNames() {
        return dmns;
    }

    public void setPropertyValue(Object o, String n, Object v) {
        com.zhang.HelloServiceImpl w;
        try {
            w = ((com.zhang.HelloServiceImpl) $1);
        } catch (Throwable e) {
            throw new IllegalArgumentException(e);
        }
        throw new com.alibaba.dubbo.common.bytecode.NoSuchPropertyException(
                "Not found property ""
                        + $2
                        + "" filed or setter method in class com.zhang.HelloServiceImpl.");
    }

    public Object getPropertyValue(Object o, String n) {
        com.zhang.HelloServiceImpl w;
        try {
            w = ((com.zhang.HelloServiceImpl) $1);
        } catch (Throwable e) {
            throw new IllegalArgumentException(e);
        }
        throw new com.alibaba.dubbo.common.bytecode.NoSuchPropertyException(
                "Not found property ""
                        + $2
                        + "" filed or setter method in class com.zhang.HelloServiceImpl.");
    }

    public Object invokeMethod(Object o, String n, Class[] p, Object[] v)
            throws java.lang.reflect.InvocationTargetException {
        com.zhang.HelloServiceImpl w;
        try {
            w = ((com.zhang.HelloServiceImpl) $1);
        } catch (Throwable e) {
            throw new IllegalArgumentException(e);
        }
        try {
            if ("sayHello".equals($2) && $3.length == 0) {
                return ($w) w.sayHello();
            }
        } catch (Throwable e) {
            throw new java.lang.reflect.InvocationTargetException(e);
        }
        throw new com.alibaba.dubbo.common.bytecode.NoSuchMethodException(
                "Not found method "" + $2
                        + "" in class com.zhang.HelloServiceImpl.");
    }
}

二、开始export。贴出Protocol$Adpative的代码，重点关注export方法：

package com.alibaba.dubbo.rpc;
import com.alibaba.dubbo.common.extension.ExtensionLoader;
public class Protocol$Adpative implements com.alibaba.dubbo.rpc.Protocol {
    public void destroy() {
        throw new UnsupportedOperationException(
                "method public abstract void com.alibaba.dubbo.rpc.Protocol.destroy() of interface com.alibaba.dubbo.rpc.Protocol is not adaptive method!");
    }

    public int getDefaultPort() {
        throw new UnsupportedOperationException(
                "method public abstract int com.alibaba.dubbo.rpc.Protocol.getDefaultPort() of interface com.alibaba.dubbo.rpc.Protocol is not adaptive method!");
    }

    public com.alibaba.dubbo.rpc.Invoker refer(java.lang.Class arg0,
            com.alibaba.dubbo.common.URL arg1) throws java.lang.Class {
        if (arg1 == null)
            throw new IllegalArgumentException("url == null");
        com.alibaba.dubbo.common.URL url = arg1;
        String extName = (url.getProtocol() == null ? "dubbo" : url
                .getProtocol());
        if (extName == null)
            throw new IllegalStateException(
                    "Fail to get extension(com.alibaba.dubbo.rpc.Protocol) name from url("
                            + url.toString() + ") use keys([protocol])");
        com.alibaba.dubbo.rpc.Protocol extension = (com.alibaba.dubbo.rpc.Protocol) ExtensionLoader
                .getExtensionLoader(com.alibaba.dubbo.rpc.Protocol.class)
                .getExtension(extName);
        return extension.refer(arg0, arg1);
    }

    public com.alibaba.dubbo.rpc.Exporter export(
            com.alibaba.dubbo.rpc.Invoker arg0)
            throws com.alibaba.dubbo.rpc.Invoker {
        if (arg0 == null)
            throw new IllegalArgumentException(
                    "com.alibaba.dubbo.rpc.Invoker argument == null");
        if (arg0.getUrl() == null)
            throw new IllegalArgumentException(
                    "com.alibaba.dubbo.rpc.Invoker argument getUrl() == null");
        com.alibaba.dubbo.common.URL url = arg0.getUrl();
        // 根据invoker的url，获取扩展名
        String extName = (url.getProtocol() == null ? "dubbo" : url
                .getProtocol());
        if (extName == null)
            throw new IllegalStateException(
                    "Fail to get extension(com.alibaba.dubbo.rpc.Protocol) name from url("
                            + url.toString() + ") use keys([protocol])");
        com.alibaba.dubbo.rpc.Protocol extension = (com.alibaba.dubbo.rpc.Protocol) ExtensionLoader
                .getExtensionLoader(com.alibaba.dubbo.rpc.Protocol.class)
                .getExtension(extName);
        return extension.export(arg0);
    }
}

package com.alibaba.dubbo.rpc.cluster;
import com.alibaba.dubbo.common.extension.ExtensionLoader;
public class Cluster$Adpative implements com.alibaba.dubbo.rpc.cluster.Cluster {
    public com.alibaba.dubbo.rpc.Invoker join(
            com.alibaba.dubbo.rpc.cluster.Directory arg0)
            throws com.alibaba.dubbo.rpc.cluster.Directory {
        if (arg0 == null)
            throw new IllegalArgumentException(
                    "com.alibaba.dubbo.rpc.cluster.Directory argument == null");
        if (arg0.getUrl() == null)
            throw new IllegalArgumentException(
                    "com.alibaba.dubbo.rpc.cluster.Directory argument getUrl() == null");
        com.alibaba.dubbo.common.URL url = arg0.getUrl();
        String extName = url.getParameter("cluster", "failover");
        if (extName == null)
            throw new IllegalStateException(
                    "Fail to get extension(com.alibaba.dubbo.rpc.cluster.Cluster) name from url("
                            + url.toString() + ") use keys([cluster])");
        com.alibaba.dubbo.rpc.cluster.Cluster extension = (com.alibaba.dubbo.rpc.cluster.Cluster) ExtensionLoader
                .getExtensionLoader(com.alibaba.dubbo.rpc.cluster.Cluster.class)
                .getExtension(extName);
        // extension是MockClusterWrapper
        return extension.join(arg0);
    }
}

从调用栈中能看出，Protocol$Adpative.export调用了两次，在Protocol$Adpative的export函数内部，
第一次获取的protocol是 ProtocolListenerWrapper/ProtocolFilterWrapper/RegistryProtocol，
第二次获取的protocol是 ProtocolListenerWrapper/ProtocolFilterWrapper/DubboProtocol。

第一次：ServiceConfig.doExportUrlsFor1Protocol代码片段：

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);
        }
        // 获取invoker
        Invoker<?> invoker = proxyFactory.getInvoker(ref, (Class) interfaceClass, registryURL.addParameterAndEncoded(Constants.EXPORT_KEY, url.toFullString()));
        // protocol是Protocol$Adpative
        // invoker的url：registry://127.0.0.1:2181/xxxxx
        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);
}

第二次 RegistryProtocol：

// RegistryProtocol
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));
                //protocol是com.alibaba.dubbo.rpc.Protocol$Adpative
                // invoker的url：dubbo://192.168.233.6:20880
                exporter = new ExporterChangeableWrapper<T>((Exporter<T>)protocol.export(invokerDelegete), originInvoker);
                bounds.put(key, exporter);
            }
        }
    }
    return (ExporterChangeableWrapper<T>) exporter;
}

暴露服务主要的步骤可能在这儿了：

// RegistryProtocol
public <T> Exporter<T> export(final Invoker<T> originInvoker) throws RpcException {
    //export invoker 开启服务
    final ExporterChangeableWrapper<T> exporter = doLocalExport(originInvoker);
    //registry provider 注册服务
    final Registry registry = getRegistry(originInvoker);
    final URL registedProviderUrl = getRegistedProviderUrl(originInvoker);
    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);
            }
        }
    };
}

在DubboProtocol中export，主要是启动服务：

// DubboProtocol
public <T> Exporter<T> export(Invoker<T> invoker) throws RpcException {
    URL url = invoker.getUrl();
    
    // export service.
    String key = serviceKey(url);
    //DubboExporter封装了invoker，invoker对象是RegistryProtocol$InvokerDelegete
    DubboExporter<T> exporter = new DubboExporter<T>(invoker, key, exporterMap);
    //把exporter放入map中
    //key: a/com.zhang.HelloService:20880
    //value: DubboExporter
    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));
    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 {
        //requestHandler是DubboProtocol的一个内部类（ExchangeHandlerAdapter）
        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;
}

绑定requestHandler

// Exchangers
public static ExchangeServer bind(URL url, ExchangeHandler handler) throws RemotingException {
    if (url == null) {
        throw new IllegalArgumentException("url == null");
    }
    if (handler == null) {
        throw new IllegalArgumentException("handler == null");
    }
    url = url.addParameterIfAbsent(Constants.CODEC_KEY, "exchange");
    return getExchanger(url).bind(url, handler);
}

// HeaderExchanger
public ExchangeServer bind(URL url, ExchangeHandler handler) throws RemotingException {
    return new HeaderExchangeServer(Transporters.bind(url, new DecodeHandler(new HeaderExchangeHandler(handler))));
}