Dubbo源码分析----暴露服务

暴露服务的过程中,会涉及到两个Protocol

  1. DubboProtocol主要是做网络通信相关初始化
  2. RegistryProtocol主要是做zk的注册和订阅相关

在提供一个服务的时候,需要在配置文件里声明如下xml

    然后Spring会根据对应关系执行对应的BeanDefinitionParser,然后实例化对应的类,提供一个服务的时候会实例化ServiceBean(具体对应关系看DubboNamespaceHandler类;spring解析自定义标签可以看下spring源码关于标签的处理,这里就不说了)

    ServiceBean实现了InitializingBean和ApplicationContextAware接口,所以会执行afterPropertiesSet和onApplicationEvent方法,这里就是入口,然后就会执行export方法暴露服务

    一路跟下去,都是设置一下属性值,然后到了doExportUrls方法便开始主要的逻辑

    private void doExportUrls() {
        List registryURLs = loadRegistries(true);//获取注册中心的url
        for (ProtocolConfig protocolConfig : protocols) {
            doExportUrlsFor1Protocol(protocolConfig, registryURLs);
        }
    }

    在Zookeeper为注册中心的情况下,registryURLs值如下
[registry://127.0.0.1:2181/com.alibaba.dubbo.registry.RegistryService?application=test&dubbo=2.0.0&owner=william&pid=4444®istry=zookeeper×tamp=1488886235790]

    进入doExportUrlsFor1Protocol方法,看下暴露服务的主要逻辑

        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);
                }
            }
        }

1.本地暴露

    会先使用exportLocal暴露本地服务

    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");
        }
    }

    看了Dubbo的扩展机制会知道,ProxyFactory默认会使用接口上@Spi注解声明的服务,为了容易理解,我把注解上的@SPI设置成jdk,那么就会使用jdk对应的实现类,即JdkProxyFactory
    JdkProxyFactory的getInvoker方法如下:

    public  Invoker getInvoker(T proxy, Class type, URL url) {
        return new AbstractProxyInvoker(proxy, type, url) {
            @Override
            protected Object doInvoke(T proxy, String methodName, 
                                      Class[] parameterTypes, 
                                      Object[] arguments) throws Throwable {
                Method method = proxy.getClass().getMethod(methodName, parameterTypes);
                return method.invoke(proxy, arguments);
            }
        };
    }

    返回一个AbstractProxyInvoker类的对象,这个AbstractProxyInvoker主要是接收消费方的请求后,执行本地方法的一个Invoker,其中是使用了反射机制来调用了本地方法
    获取到Invoker之后,需要使用Protocol的export来暴露这个服务,在讲Dubbo扩展机制的时候,Protocol外面有两个装饰类,那么export会先调用ProtocolListenerWrapper

    public  Exporter export(Invoker invoker) throws RpcException {
        if (Constants.REGISTRY_PROTOCOL.equals(invoker.getUrl().getProtocol())) {
            return protocol.export(invoker);
        }
        return new ListenerExporterWrapper(protocol.export(invoker), 
                Collections.unmodifiableList(ExtensionLoader.getExtensionLoader(ExporterListener.class)
                        .getActivateExtension(invoker.getUrl(), Constants.EXPORTER_LISTENER_KEY)));
    }

    这时的url为
injvm://127.0.0.1/com.alibaba.dubbo.demo.DemoService?anyhost=true&application=test&dubbo=2.0.0&generic=false&interface=com.alibaba.dubbo.demo.DemoService&loadbalance=roundrobin&methods=sayHello&owner=william&pid=4444&side=provider×tamp=1488887324869
    对象为

Dubbo源码分析----暴露服务_第1张图片
image.png

    那么if条件不满足,将调用ProtocolFilterWrapper的export方法

    public  Invoker refer(Class type, URL url) throws RpcException {
        if (Constants.REGISTRY_PROTOCOL.equals(url.getProtocol())) {
            return protocol.refer(type, url);
        }
        return buildInvokerChain(protocol.refer(type, url), Constants.REFERENCE_FILTER_KEY, Constants.CONSUMER);
    }

    If条件还是不满足,执行下面的代码
    注意:这里的protocol就是InjvmProtocol了

    然后看下buildInvokerChain方法,这个方法建立了一个个的filter,使用了责任链模式,一个普通的Invoker调用也会经历这些filter,每个filter都有自己特殊的功能

    private static  Invoker buildInvokerChain(final Invoker invoker, String key, String group) {
        Invoker last = invoker;
        List filters = ExtensionLoader.getExtensionLoader(Filter.class).getActivateExtension(invoker.getUrl(), key, group);
        if (filters.size() > 0) {
            for (int i = filters.size() - 1; i >= 0; i --) {
                final Filter filter = filters.get(i);
                final Invoker next = last;
                last = new Invoker() {
                    public Class getInterface() {
                        return invoker.getInterface();
                    }
                    public URL getUrl() {
                        return invoker.getUrl();
                    }
                    public boolean isAvailable() {
                        return invoker.isAvailable();
                    }
                    public Result invoke(Invocation invocation) throws RpcException {
                        return filter.invoke(next, invocation);
                    }
                    public void destroy() {
                        invoker.destroy();
                    }
                    @Override
                    public String toString() {
                        return invoker.toString();
                    }
                };
            }
        }
        return last;
    }

    这里的group是provider,key是service.filter
    看下getActivateExtension方法实现

    public List getActivateExtension(URL url, String key, String group) {
        String value = url.getParameter(key);
        return getActivateExtension(url, value == null || value.length() == 0 ? null : Constants.COMMA_SPLIT_PATTERN.split(value), group);
    }

    public List getActivateExtension(URL url, String[] values, String group) {
        List exts = new ArrayList();
        List names = values == null ? new ArrayList(0) : Arrays.asList(values);
        if (! names.contains(Constants.REMOVE_VALUE_PREFIX + Constants.DEFAULT_KEY)) {
            getExtensionClasses();
            for (Map.Entry entry : cachedActivates.entrySet()) {
                String name = entry.getKey();
                Activate activate = entry.getValue();
                if (isMatchGroup(group, activate.group())) {
                    T ext = getExtension(name);
                    if (! names.contains(name)
                            && ! names.contains(Constants.REMOVE_VALUE_PREFIX + name) 
                            && isActive(activate, url)) {
                        exts.add(ext);
                    }
                }
            }
            Collections.sort(exts, ActivateComparator.COMPARATOR);
        }
        List usrs = new ArrayList();
        for (int i = 0; i < names.size(); i ++) {
            String name = names.get(i);
            if (! name.startsWith(Constants.REMOVE_VALUE_PREFIX)
                    && ! names.contains(Constants.REMOVE_VALUE_PREFIX + name)) {
                if (Constants.DEFAULT_KEY.equals(name)) {
                    if (usrs.size() > 0) {
                        exts.addAll(0, usrs);
                        usrs.clear();
                    }
                } else {
                    T ext = getExtension(name);
                    usrs.add(ext);
                }
            }
        }
        if (usrs.size() > 0) {
            exts.addAll(usrs);
        }
        return exts;
    }

    由于url中没有service.filter的key,所以values为[]
    cachedActivates记录了接口实现中带有Activate注解的类,需要筛选出group为provider的实现类,最后进行排序


Dubbo源码分析----暴露服务_第2张图片
filter.png

    过滤器调用的顺序和上图的顺序一样

    最后会调用InjvmProtocol的export方法,将invoker封装成InjvmExporter返回,得到Exporter之后,放到List里

    public  Exporter export(Invoker invoker) throws RpcException {
        return new InjvmExporter(invoker, invoker.getUrl().getServiceKey(), exporterMap);
    }

2.远程暴露

回到doExportUrlsFor1Protocol方法,暴露本地服务之后,根据注册中心的地址暴露远程服务

    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);
    }

获取Invoker的方式和之前一样
而实际调用的是哪个Protocol对象呢?根据Invoker中protocol属性的值(值为registry)和Dubbo扩展机制可以知道调用的是RegistryProtocol

    public  Exporter export(final Invoker originInvoker) throws RpcException {
        //export invoker
        final ExporterChangeableWrapper exporter = doLocalExport(originInvoker);
        //registry provider
        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() {
            public Invoker 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);
                }
            }
        };
    }

2.1 doLocalExport

先看下doLocalExport方法

    private  ExporterChangeableWrapper  doLocalExport(final Invoker originInvoker){
        String key = getCacheKey(originInvoker);
        ExporterChangeableWrapper exporter = (ExporterChangeableWrapper) bounds.get(key);
        if (exporter == null) {
            synchronized (bounds) {
                exporter = (ExporterChangeableWrapper) bounds.get(key);
                if (exporter == null) {
                    final Invoker invokerDelegete = new InvokerDelegete(originInvoker, getProviderUrl(originInvoker));
                    exporter = new ExporterChangeableWrapper((Exporter)protocol.export(invokerDelegete), originInvoker);
                    bounds.put(key, exporter);
                }
            }
        }
        return (ExporterChangeableWrapper) exporter;
    }

originInvoker的url值为:
registry://127.0.0.1:2181/com.alibaba.dubbo.registry.RegistryService?application=test&dubbo=2.0.0&export=dubbo%3A%2F%2F10.1.87.36%3A20888%2Fcom.alibaba.dubbo.demo.DemoService%3Fanyhost%3Dtrue%26application%3Dtest%26dubbo%3D2.0.0%26generic%3Dfalse%26interface%3Dcom.alibaba.dubbo.demo.DemoService%26loadbalance%3Droundrobin%26methods%3DsayHello%26owner%3Dwilliam%26pid%3D14204%26side%3Dprovider%26threads%3D1%26timestamp%3D1518580683573&owner=william&pid=14204®istry=zookeeper×tamp=1518580683551
url是代表注册中心相关信息,getCacheKey是获取url中的provider属性,即provider的url:
dubbo://10.1.87.36:20888/com.alibaba.dubbo.demo.DemoService?anyhost=true&application=test&dubbo=2.0.0&generic=false&interface=com.alibaba.dubbo.demo.DemoService&loadbalance=roundrobin&methods=sayHello&owner=william&pid=14204&side=provider&threads=1×tamp=1518580683573
第一次进来的时候,bounds中该key对应的值为空,所以根据provider的url和originInvoker封装成新的Invoker,此时Invoker的url就是provider的url,其中protocol的值为dubbo,那么将调用DubboProtocol的export方法,一开始已经介绍,DubboProtocol主要是做网络通信相关初始化
DubboProtocol的export方法如下:

    public  Exporter export(Invoker invoker) throws RpcException {
        URL url = invoker.getUrl();
        
        String key = serviceKey(url);
        DubboExporter exporter = new DubboExporter(invoker, key, exporterMap);
        exporterMap.put(key, exporter);
        
        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;
    }

key=全类名+dubbo监听端口号
然后将Invoker封装成Export,然后放到map中
所以看下来,Export和invoker是一对一的关系
exporterMap主要是将服务名和export进行关联,看到这里其实已经差不多结束了,Dubbo接收到consumer的请求时,会在exporterMap中找到对应的exporter,然后找到对应的Invoker,有了invoker就可以调用本地的服务

2.2 getRegistry

再回到RegistryProtocol的exprot方法中,接下来就是执行getRegistry(originInvoker)这句代码了,主要是做注册中心的初始化

    /**
     * 根据invoker的地址获取registry实例
     * @param originInvoker
     * @return
     */
    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);
    }

在上面我们看到invoker的url中,registry属性是zookeeper,根据spi机制,该RegistryFactory为ZookeeperRegistryFactory,getRegistry会调用到父类AbstractRegistryFactory的方法

    public Registry getRegistry(URL url) {
        url = url.setPath(RegistryService.class.getName())
                .addParameter(Constants.INTERFACE_KEY, RegistryService.class.getName())
                .removeParameters(Constants.EXPORT_KEY, Constants.REFER_KEY);
        String key = url.toServiceString();
        // 锁定注册中心获取过程,保证注册中心单一实例
        LOCK.lock();
        try {
            Registry registry = REGISTRIES.get(key);
            if (registry != null) {
                return registry;
            }
            registry = createRegistry(url);
            if (registry == null) {
                throw new IllegalStateException("Can not create registry " + url);
            }
            REGISTRIES.put(key, registry);
            return registry;
        } finally {
            // 释放锁
            LOCK.unlock();
        }
    }

createRegistry在父类中没有实现,调用到ZookeeperRegistryFactory中

    public Registry createRegistry(URL url) {
        return new ZookeeperRegistry(url, zookeeperTransporter);
    }

先看下Registry的继承结构


Dubbo源码分析----暴露服务_第3张图片
image.png

可以看到ZookeeperRegistry有两个父类,所以ZookeeperRegistry会先调用父类的构造方法,这个过程主要做了几件事:

  1. 加载服务缓存文件(AbstractRegistry)
  2. 异步(默认)更新缓存文件(AbstractRegistry)
  3. 定时重试失败的动作:注册失败,取消注册失败,订阅失败,取消订阅失败,通知失败(FailbackRegistry)
  4. 初始化zk通信相关(ZookeeperRegistry)
加载服务缓存文件:
    public AbstractRegistry(URL url) {
        setUrl(url);
        // 启动文件保存定时器
        syncSaveFile = url.getParameter(Constants.REGISTRY_FILESAVE_SYNC_KEY, false);
        String filename = url.getParameter(Constants.FILE_KEY, System.getProperty("user.home") + "/.dubbo/dubbo-registry-" + url.getHost() + ".cache");
        File file = null;
        if (ConfigUtils.isNotEmpty(filename)) {
            file = new File(filename);
            if(! file.exists() && file.getParentFile() != null && ! file.getParentFile().exists()){
                if(! file.getParentFile().mkdirs()){
                    throw new IllegalArgumentException("Invalid registry store file " + file + ", cause: Failed to create directory " + file.getParentFile() + "!");
                }
            }
        }
        this.file = file;
        loadProperties();
        notify(url.getBackupUrls());
    }

loadProperties主要是将dubbo的服务缓存文件加载进来,转换成Properties对象
Key=服务名 Value=url

更新缓存文件:

AbstractRegistry类中还有一个doSaveProperties方法,主要用来更新缓存文件,在更新前会先把本地文件的内容先更新到properties对象中,然后再进行更新操作

    public void doSaveProperties(long version) {
        if(version < lastCacheChanged.get()){
            return;
        }
        if (file == null) {
            return;
        }
        Properties newProperties = new Properties();
        // 保存之前先读取一遍,防止多个注册中心之间冲突
        InputStream in = null;
        try {
            if (file.exists()) {
                in = new FileInputStream(file);
                newProperties.load(in);
            }
        } catch (Throwable e) {
        } finally {
            ....
        }     
     // 保存
        try {
            newProperties.putAll(properties);
            File lockfile = new File(file.getAbsolutePath() + ".lock");
            if (!lockfile.exists()) {
                lockfile.createNewFile();
            }
            RandomAccessFile raf = new RandomAccessFile(lockfile, "rw");
            try {
                FileChannel channel = raf.getChannel();
                try {
                    FileLock lock = channel.tryLock();
                    if (lock == null) {
                        throw new IOException("Can not lock the registry cache file " + file.getAbsolutePath() + ", ignore and retry later, maybe multi java process use the file, please config: dubbo.registry.file=xxx.properties");
                    }
                    // 保存
                    try {
                        if (! file.exists()) {
                            file.createNewFile();
                        }
                        FileOutputStream outputFile = new FileOutputStream(file);  
                        try {
                            newProperties.store(outputFile, "Dubbo Registry Cache");
                        } finally {
                            outputFile.close();
                        }
                    } finally {
                        lock.release();
                    }
                } finally {
                    channel.close();
                }
            } finally {,
            }
        } catch (Throwable e) {
            if (version < lastCacheChanged.get()) {
                return;
            } else {
                registryCacheExecutor.execute(new SaveProperties(lastCacheChanged.incrementAndGet()));
            }
        }
    }

更新的时候会对.lock文件进行加锁,这样其他线程/进程就无法修改缓存文件,如果tryLock返回空,证明该文件正在被修改,那么增加版本号进行重试
doSaveProperties方法开头的时候有句代码:

if(version < lastCacheChanged.get()){return;}

可以看到保存的时候有版本号的判断,lastCacheChanged这个是在saveProperties方法中增加的,如果当条件满足,那么证明在这个线程执行saveProperties方法之后还没执行doSaveProperties操作的时候,又有线程执行了saveProperties操作,把version+1了,那么当前线程直接return,让后续线程继续

定时重试失败的动作

构造方法里起了一个定时器,定时进行重试操作,代码简化如下:

    // 重试失败的动作
    protected void retry() {
        if (! failedRegistered.isEmpty()) {
            Set failed = new HashSet(failedRegistered);
            for (URL url : failed) {
                    doRegister(url);
                    failedRegistered.remove(url);
            }
        }
        if (! failedUnregistered.isEmpty()) {
            Set failed = new HashSet(failedUnregistered);
            if (logger.isInfoEnabled()) {
                logger.info("Retry unregister " + failed);
            }
            for (URL url : failed) {
                    doUnregister(url);
                    failedUnregistered.remove(url);
            }
        }
        if (! failedSubscribed.isEmpty()) {
            Map> failed = new HashMap>(failedSubscribed);
            for (Map.Entry> entry : failed.entrySet()) {
                URL url = entry.getKey();
                Set listeners = entry.getValue();
                for (NotifyListener listener : listeners) {
                    doSubscribe(url, listener);
                    listeners.remove(listener);
                }
            }
        }
        if (! failedUnsubscribed.isEmpty()) {
            Map> failed = new HashMap>(failedUnsubscribed);
            for (Map.Entry> entry : failed.entrySet()) {
                URL url = entry.getKey();
                Set listeners = entry.getValue();
                for (NotifyListener listener : listeners) {
                    try {
                        doUnsubscribe(url, listener);
                        listeners.remove(listener);
                    } catch (Throwable t) { // 忽略所有异常,等待下次重试
                        logger.warn("Failed to retry unsubscribe " + failed + ", waiting for again, cause: " + t.getMessage(), t);
                    }
                }
            }
        }
        if (! failedNotified.isEmpty()) {
            Map>> failed = new HashMap>>(failedNotified);
            for (Map> values : failed.values()) {
                for (Map.Entry> entry : values.entrySet()) {
                    NotifyListener listener = entry.getKey();
                    List urls = entry.getValue();
                    listener.notify(urls);
                    values.remove(listener);
                }
            }
        }
    }

从对面失败的集合从取数据执行相应的重试

初始化zk通信相关

这里会连接zk,然后增加监听器

2.3 register

再回到RegistryProtocol的export方法,registry初始化完成之后,接下来会调用register方法,仍然是先调用父类的方法
AbstractRegistry.register:将url加入到registered集合中
FailbackRegistry.register:

    @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);
        }
    }

从代码上看到,可以分为几步

  1. failedRegistered和failedUnregistered中移除该url
  2. 发送注册请求

可以看到注册会失败,如果设置了check为false,那么放到重试队列中重试

doRegister方法是在ZookeeperRegistry中实现的,主要是在zk上创建节点,创建逻辑如下:

    public void create(String path, boolean ephemeral) {
        int i = path.lastIndexOf('/');
        if (i > 0) {
            create(path.substring(0, i), false);
        }
        if (ephemeral) {
            createEphemeral(path);
        } else {
            createPersistent(path);
        }
    }

Path格式为:
/dubbo/服务名/providers(可能是configurators或者router节点)/url
该方法会递归把每个父节点都创建完毕,可以看到除了dubbo这个节点是持久化节点,其他都是临时节点,那么当服务与zk断开连接一段时间后,zk会删除该节点,服务消费方就会得到通知,知道该提供者下线,做相应操作

2.4 subscribe

接下来看订阅方法subscribe,同理会先调用父类的方法
AbstractRegistry.subscribe:将listener保存到subscribed中
FailbackRegistry.subscribe:

    @Override
    public void subscribe(URL url, NotifyListener listener) {
        super.subscribe(url, listener);
        removeFailedSubscribed(url, listener);
        try {
            // 向服务器端发送订阅请求
            doSubscribe(url, listener);
        } catch (Exception e) {
            Throwable t = e;

            List urls = getCacheUrls(url);
            if (urls != null && urls.size() > 0) {
                notify(url, listener, urls);
                logger.error("Failed to subscribe " + url + ", Using cached list: " + urls + " from cache file: " + getUrl().getParameter(Constants.FILE_KEY, System.getProperty("user.home") + "/dubbo-registry-" + url.getHost() + ".cache") + ", cause: " + t.getMessage(), t);
            } else {
                // 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);
                boolean skipFailback = t instanceof SkipFailbackWrapperException;
                if (check || skipFailback) {
                    if(skipFailback) {
                        t = t.getCause();
                    }
                    throw new IllegalStateException("Failed to subscribe " + url + ", cause: " + t.getMessage(), t);
                } else {
                    logger.error("Failed to subscribe " + url + ", waiting for retry, cause: " + t.getMessage(), t);
                }
            }

            // 将失败的订阅请求记录到失败列表,定时重试
            addFailedSubscribed(url, listener);
        }
    }

和注册类似,区别是订阅失败的时候,首先会调用getCacheUrls获取url,这个方法就是从缓存的properties对象里获取服务的url,如果没有数据才执行和注册一样的操作,有则调用notify方法,这个后面会说到

看下核心的ZookeeperRegistry的doSubscribe方法

    List urls = new ArrayList();
    for (String path : toCategoriesPath(url)) {
        ConcurrentMap listeners = zkListeners.get(url);
        if (listeners == null) {
            zkListeners.putIfAbsent(url, new ConcurrentHashMap());
            listeners = zkListeners.get(url);
        }
        ChildListener zkListener = listeners.get(listener);
        if (zkListener == null) {
            listeners.putIfAbsent(listener, new ChildListener() {
                public void childChanged(String parentPath, List currentChilds) {
                    ZookeeperRegistry.this.notify(url, listener, toUrlsWithEmpty(url, parentPath, currentChilds));
                }
            });
            zkListener = listeners.get(listener);
        }
        zkClient.create(path, false);
        List children = zkClient.addChildListener(path, zkListener);
        if (children != null) {
            urls.addAll(toUrlsWithEmpty(url, path, children));
        }
    }
    notify(url, listener, urls);

toCategoriesPath方法是从url中获取category属性的值,转换成zk上路径的形式,由于provider只有一个configurators,所以path如下
/dubbo/服务名/configurators,接下来就是为该节点添加监听回调,然后返回子节点
如果子节点为空,那么toUrlsWithEmpty方法会返回empty://....格式的url,即protocol为empty,这个协议后面会用到
接下来notify一路会调用到AbstractRegistry的notify方法

    protected void notify(URL url, NotifyListener listener, List urls) {
       ....
        Map> result = new HashMap>();
        for (URL u : urls) {
            if (UrlUtils.isMatch(url, u)) {
                String category = u.getParameter(Constants.CATEGORY_KEY, Constants.DEFAULT_CATEGORY);
                List categoryList = result.get(category);
                if (categoryList == null) {
                    categoryList = new ArrayList();
                    result.put(category, categoryList);
                }
                categoryList.add(u);
            }
        }
        if (result.size() == 0) {
            return;
        }
        Map> categoryNotified = notified.get(url);
        if (categoryNotified == null) {
            notified.putIfAbsent(url, new ConcurrentHashMap>());
            categoryNotified = notified.get(url);
        }
        for (Map.Entry> entry : result.entrySet()) {
            String category = entry.getKey();
            List categoryList = entry.getValue();
            categoryNotified.put(category, categoryList);
            saveProperties(url);
            listener.notify(categoryList);
        }
    }

主要看下最下面的循环,即遍历每个类目下的url,执行一遍saveProperties方法(把服务信息保存到文件),调用监听器的notify方法,listener最初初始化为OverrideListener

       public void notify(List urls) {
            List result = null;
            for (URL url : urls) {
                URL overrideUrl = url;
                if (url.getParameter(Constants.CATEGORY_KEY) == null
                        && Constants.OVERRIDE_PROTOCOL.equals(url.getProtocol())) {
                    // 兼容旧版本
                    overrideUrl = url.addParameter(Constants.CATEGORY_KEY, Constants.CONFIGURATORS_CATEGORY);
                }
                if (! UrlUtils.isMatch(subscribeUrl, overrideUrl)) {
                    if (result == null) {
                        result = new ArrayList(urls);
                    }
                    result.remove(url);
                }
            }
            if (result != null) {
                urls = result;
            }
            this.configurators = RegistryDirectory.toConfigurators(urls);
            List> exporters = new ArrayList>(bounds.values());
            for (ExporterChangeableWrapper exporter : exporters){
                Invoker invoker = exporter.getOriginInvoker();
                final Invoker originInvoker ;
                if (invoker instanceof InvokerDelegete){
                    originInvoker = ((InvokerDelegete)invoker).getInvoker();
                }else {
                    originInvoker = invoker;
                }
                
                URL originUrl = RegistryProtocol.this.getProviderUrl(originInvoker);
                URL newUrl = getNewInvokerUrl(originUrl, urls);
                
                if (! originUrl.equals(newUrl)){
                    RegistryProtocol.this.doChangeLocalExport(originInvoker, newUrl);
                }
            }
        }

主要看下最下面的循环,会比对invoker的url是新的url是否是一样,如果不一样,那么更新invoker的url

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