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7.6 服务远程暴露

为了安全：服务启动的ip全部使用10.10.10.10

远程服务的暴露总体步骤：

将ref封装为invoker
将invoker转换为exporter
启动netty
注册服务到zookeeper
订阅
返回新的exporter实例

在7.4 服务远程暴露 - 创建Exporter与启动netty服务端中，实现了前三步，本节实现第四步：注册服务到zk。总体代码如下：RegistryProtocol.export(final Invoker<T> originInvoker)

1         final Registry registry = getRegistry(originInvoker);//创建ZookeeperRegistry实例：创建CuratorClient，并启动会话。
2         final URL registedProviderUrl = getRegistedProviderUrl(originInvoker);//获取真正要注册在zk上的url
3         registry.register(registedProviderUrl);//创建节点（即注册服务到zk上）

说明：

第一句代码用来创建ZookeeperRegistry实例：创建CuratorClient，并启动会话。
第二句代码获取真正要注册在zk上的url
第三句代码实现创建节点（即注册服务到zk上）

一创建ZookeeperRegistry实例

1 RegistryProtocol.getRegistry(final Invoker<?> originInvoker)

 1     /**
 2      * 根据invoker的地址获取registry实例
 3      */
 4     private Registry getRegistry(final Invoker<?> originInvoker) {
 5         URL registryUrl = originInvoker.getUrl();
 6         if (Constants.REGISTRY_PROTOCOL.equals(registryUrl.getProtocol())) {
 7             String protocol = registryUrl.getParameter(Constants.REGISTRY_KEY, Constants.DEFAULT_DIRECTORY);//zookeeper
 8             registryUrl = registryUrl.setProtocol(protocol).removeParameter(Constants.REGISTRY_KEY);
 9         }
10         return registryFactory.getRegistry(registryUrl);
11     }

首先对originInvoker中的url进行处理：

将协议换成zookeeper
去掉registry=zookeeper的参数

来看一下originInvoker的url：（解码后的）

registry://10.211.55.5:2181/com.alibaba.dubbo.registry.RegistryService?application=demo-provider&client=curator&dubbo=2.0.0&export=dubbo://10.10.10.10:20880/com.alibaba.dubbo.demo.DemoService?anyhost=true&application=demo-provider&dubbo=2.0.0&generic=false&interface=com.alibaba.dubbo.demo.DemoService&methods=sayHello&pid=2791&side=provider&timestamp=1507262031554&pid=2791&registry=zookeeper&timestamp=1507262031521

说明：

第一个红色部分代表协议：zookeeper
第二个红色部分是export参数
第三个红色部分是registry=zookeeper

经过处理之后的registryUrl为：

zookeeper://10.211.55.5:2181/com.alibaba.dubbo.registry.RegistryService?application=demo-provider&client=curator&dubbo=2.0.0&export=dubbo://10.10.10.10:20880/com.alibaba.dubbo.demo.DemoService?anyhost=true&application=demo-provider&dubbo=2.0.0&generic=false&interface=com.alibaba.dubbo.demo.DemoService&methods=sayHello&pid=2791&side=provider&timestamp=1507262031554&pid=2791&timestamp=1507262031521

之后使用注册工厂来创建注册中心。

2 RegistryFactory$Adaptive.getRegistry(com.alibaba.dubbo.common.URL registryUrl)

 1 public class RegistryFactory$Adaptive implements com.alibaba.dubbo.registry.RegistryFactory {
 2     public com.alibaba.dubbo.registry.Registry getRegistry(com.alibaba.dubbo.common.URL arg0) {
 3         if (arg0 == null)
 4             throw new IllegalArgumentException("url == null");
 5         com.alibaba.dubbo.common.URL url = arg0;
 6         String extName = ( url.getProtocol() == null ? "dubbo" : url.getProtocol() );//zookeeper
 7         if(extName == null)
 8             throw new IllegalStateException("Fail to get extension(com.alibaba.dubbo.registry.RegistryFactory) name from url(" + url.toString() + ") use keys([protocol])");
 9         com.alibaba.dubbo.registry.RegistryFactory extension = (com.alibaba.dubbo.registry.RegistryFactory)ExtensionLoader.getExtensionLoader(com.alibaba.dubbo.registry.RegistryFactory.class).getExtension(extName);
10         return extension.getRegistry(arg0);
11     }
12 }

这里获取到的extension是ZookeeperRegistryFactory，之后，使用ZookeeperRegistryFactory进行Registry的创建。首先来看一下ZookeeperRegistryFactory的继承图：

getRegistry方法在ZookeeperRegistryFactory的父类AbstractRegistryFactory中。

3 AbstractRegistryFactory.getRegistry(URL registryUrl)

 1     public Registry getRegistry(URL url) {
 2         url = url.setPath(RegistryService.class.getName())
 3                 .addParameter(Constants.INTERFACE_KEY, RegistryService.class.getName())
 4                 .removeParameters(Constants.EXPORT_KEY, Constants.REFER_KEY);
 5         String key = url.toServiceString();
 6         // 锁定注册中心获取过程，保证注册中心单一实例
 7         LOCK.lock();
 8         try {
 9             Registry registry = REGISTRIES.get(key);
10             if (registry != null) {
11                 return registry;
12             }
13             registry = createRegistry(url);
14             if (registry == null) {
15                 throw new IllegalStateException("Can not create registry " + url);
16             }
17             REGISTRIES.put(key, registry);
18             return registry;
19         } finally {
20             // 释放锁
21             LOCK.unlock();
22         }
23     }

流程：

先处理url，之后获取Registry的key，然后根据该key从Map<String, Registry> REGISTRIES注册中心集合缓存中获取Registry，如果有，直接返回，如果没有，创建Registry，之后存入缓存，最后返回。

首先处理传入的registryUrl：

设置：path=com.alibaba.dubbo.registry.RegistryService
添加参数：interface=com.alibaba.dubbo.registry.RegistryService
去除export参数

最终得到的registryUrl如下：

zookeeper://10.211.55.5:2181/com.alibaba.dubbo.registry.RegistryService?application=demo-provider&client=curator&dubbo=2.0.0&interface=com.alibaba.dubbo.registry.RegistryService&pid=2791&timestamp=1507262031521

之后，很具上述的registryUrl创建Registry的key，该{ key : Registry }最终会被存储在Map<String, Registry> REGISTRIES注册中心集合（该属性是ZookeeperRegistryFactory父类AbstractRegistryFactory的一个属性）中。

根据registryUrl创建Registry的key：url.toServiceString()

 1     public String toServiceString() {
 2         return buildString(true, false, true, true);
 3     }
 4 
 5     private String buildString(boolean appendUser, boolean appendParameter, boolean useIP, boolean useService, String... parameters) {
 6         StringBuilder buf = new StringBuilder();
 7         if (protocol != null && protocol.length() > 0) {  //protocol://
 8             buf.append(protocol);
 9             buf.append("://");
10         }
11         if (appendUser && username != null && username.length() > 0) {  //protocol://username:password@host:port/group/interface{path}:version/parameters
12             buf.append(username);
13             if (password != null && password.length() > 0) {
14                 buf.append(":");
15                 buf.append(password);
16             }
17             buf.append("@");
18         }
19         String host;
20         if (useIP) {
21             host = getIp();
22         } else {
23             host = getHost();
24         }
25         if (host != null && host.length() > 0) {
26             buf.append(host);
27             if (port > 0) {
28                 buf.append(":");
29                 buf.append(port);
30             }
31         }
32         String path;
33         if (useService) {
34             path = getServiceKey();
35         } else {
36             path = getPath();
37         }
38         if (path != null && path.length() > 0) {
39             buf.append("/");
40             buf.append(path);
41         }
42         if (appendParameter) {
43             buildParameters(buf, true, parameters);
44         }
45         return buf.toString();
46     }
47 
48     public String getServiceKey() {
49         String inf = getServiceInterface();//先获取interface参数，如果没有的话，取path的值，这里都是com.alibaba.dubbo.registry.RegistryService
50         if (inf == null) return null;
51         StringBuilder buf = new StringBuilder();
52         String group = getParameter(Constants.GROUP_KEY);
53         if (group != null && group.length() > 0) {
54             buf.append(group).append("/"); //interfacegroup
55         }
56         buf.append(inf);
57         String version = getParameter(Constants.VERSION_KEY);
58         if (version != null && version.length() > 0) {
59             buf.append(":").append(version);
60         }
61         return buf.toString();
62     }

最终得到的应该是这样的形式：protocol://username:password@host:port/group/interface{path}:version?key1=value1&key2=value2...。

这里key=zookeeper://10.211.55.5:2181/com.alibaba.dubbo.registry.RegistryService

之后来到了真正创建Registry的地方。

 1 public class ZookeeperRegistryFactory extends AbstractRegistryFactory {
 2     private ZookeeperTransporter zookeeperTransporter;
 3 
 4     public void setZookeeperTransporter(ZookeeperTransporter zookeeperTransporter) {
 5         this.zookeeperTransporter = zookeeperTransporter;
 6     }
 7 
 8     public Registry createRegistry(URL url) {
 9         return new ZookeeperRegistry(url, zookeeperTransporter);
10     }
11 }

这里的zookeeperTransporter对象是一个com.alibaba.dubbo.remoting.zookeeper.ZookeeperTransporter$Adaptive对象。

在创建ZookeeperRegistry之前来看一下其继承图：

new ZookeeperRegistry(registryUrl, ZookeeperTransporter$Adaptive对象)

 1     private final static int DEFAULT_ZOOKEEPER_PORT = 2181;
 2     private final static String DEFAULT_ROOT = "dubbo";
 3     private final String root;
 4     private final Set<String> anyServices = new ConcurrentHashSet<String>();
 5     private final ConcurrentMap<URL, ConcurrentMap<NotifyListener, ChildListener>> zkListeners = new ConcurrentHashMap<URL, ConcurrentMap<NotifyListener, ChildListener>>();
 6     private final ZookeeperClient zkClient;
 7 
 8     public ZookeeperRegistry(URL url, ZookeeperTransporter zookeeperTransporter) {
 9         super(url);
10         if (url.isAnyHost()) {
11             throw new IllegalStateException("registry address == null");
12         }
13         String group = url.getParameter(Constants.GROUP_KEY, DEFAULT_ROOT);//dubbo
14         if (!group.startsWith(Constants.PATH_SEPARATOR)) {
15             group = Constants.PATH_SEPARATOR + group;
16         }
17         this.root = group;// /dubbo
18         zkClient = zookeeperTransporter.connect(url);//创建zk客户端，启动会话
19         zkClient.addStateListener(new StateListener() {//监听重新连接成功事件，重新连接成功后，之前已经完成注册和订阅的url要重新进行注册和订阅（因为临时节点可能已经跪了）
20             public void stateChanged(int state) {
21                 if (state == RECONNECTED) {
22                     try {
23                         recover();
24                     } catch (Exception e) {
25                         logger.error(e.getMessage(), e);
26                     }
27                 }
28             }
29         });
30     }

new FailbackRegistry(registryUrl)

 1     private final ScheduledExecutorService retryExecutor = Executors.newScheduledThreadPool(1, new NamedThreadFactory("DubboRegistryFailedRetryTimer", true));
 2     // 失败重试定时器，定时检查是否有请求失败，如有，无限次重试
 3     private final ScheduledFuture<?> retryFuture;
 4     private final Set<URL> failedRegistered = new ConcurrentHashSet<URL>();
 5     private final Set<URL> failedUnregistered = new ConcurrentHashSet<URL>();
 6     private final ConcurrentMap<URL, Set<NotifyListener>> failedSubscribed = new ConcurrentHashMap<URL, Set<NotifyListener>>();
 7     private final ConcurrentMap<URL, Set<NotifyListener>> failedUnsubscribed = new ConcurrentHashMap<URL, Set<NotifyListener>>();
 8     private final ConcurrentMap<URL, Map<NotifyListener, List<URL>>> failedNotified = new ConcurrentHashMap<URL, Map<NotifyListener, List<URL>>>();
 9     private AtomicBoolean destroyed = new AtomicBoolean(false);
10 
11     public FailbackRegistry(URL url) {
12         super(url);
13         int retryPeriod = url.getParameter(Constants.REGISTRY_RETRY_PERIOD_KEY, Constants.DEFAULT_REGISTRY_RETRY_PERIOD);//5*1000
14         this.retryFuture = retryExecutor.scheduleWithFixedDelay(new Runnable() {
15             public void run() {
16                 // 检测并连接注册中心
17                 try {
18                     retry();
19                 } catch (Throwable t) { // 防御性容错
20                     logger.error("Unexpected error occur at failed retry, cause: " + t.getMessage(), t);
21                 }
22             }
23         }, retryPeriod, retryPeriod, TimeUnit.MILLISECONDS);
24     }

new AbstractRegistry(registryUrl)

 1     // URL地址分隔符，用于文件缓存中，服务提供者URL分隔
 2     private static final char URL_SEPARATOR = ' ';
 3     // URL地址分隔正则表达式，用于解析文件缓存中服务提供者URL列表
 4     private static final String URL_SPLIT = "\s+";
 5     // 本地磁盘缓存，其中特殊的key值.registies记录注册中心列表，其它均为notified服务提供者列表
 6     private final Properties properties = new Properties();
 7     // 文件缓存定时写入
 8     private final ExecutorService registryCacheExecutor = Executors.newFixedThreadPool(1, new NamedThreadFactory("DubboSaveRegistryCache", true));
 9     //是否是同步保存文件
10     private final boolean syncSaveFile;
11     // 本地磁盘缓存文件
12     private File file;
13     private final AtomicLong lastCacheChanged = new AtomicLong();
14     private final Set<URL> registered = new ConcurrentHashSet<URL>();//已经注册的url集合
15     private final ConcurrentMap<URL, Set<NotifyListener>> subscribed = new ConcurrentHashMap<URL, Set<NotifyListener>>();//已经订阅的<URL, Set<NotifyListener>>
16     private final ConcurrentMap<URL, Map<String, List<URL>>> notified = new ConcurrentHashMap<URL, Map<String, List<URL>>>();//已经通知的<URL, Map<String, List<URL>>>
17     private URL registryUrl;//注册url
18     private AtomicBoolean destroyed = new AtomicBoolean(false);
19 
20     public AbstractRegistry(URL url) {
21         setUrl(url);
22         // 启动文件保存定时器
23         syncSaveFile = url.getParameter(Constants.REGISTRY_FILESAVE_SYNC_KEY, false);
24         String filename = url.getParameter(Constants.FILE_KEY, System.getProperty("user.home") + "/.dubbo/dubbo-registry-" + url.getHost() + ".cache");
25         File file = null;
26         if (ConfigUtils.isNotEmpty(filename)) {
27             file = new File(filename);
28             if (!file.exists() && file.getParentFile() != null && !file.getParentFile().exists()) {
29                 if (!file.getParentFile().mkdirs()) {//创建文件所在的文件夹 /Users/jigangzhao/.dubbo/
30                     throw new IllegalArgumentException("Invalid registry store file " + file + ", cause: Failed to create directory " + file.getParentFile() + "!");
31                 }
32             }
33         }
34         this.file = file;
35         loadProperties();
36         notify(url.getBackupUrls());
37     }

先简单的总结一下：父子三代分别做的事情：

AbstractRegistry主要用来维护缓存文件。
FailbackRegistry主要用来做失败重试操作（包括：注册失败／反注册失败／订阅失败／反订阅失败／通知失败的重试）；也提供了供ZookeeperRegistry使用的zk重连后的恢复工作的方法。
ZookeeperRegistry创建zk客户端，启动会话；并且调用FailbackRegistry实现zk重连后的恢复工作。

先看AbstractRegistry

设置属性registryUrl=url：zookeeper://10.211.55.5:2181/com.alibaba.dubbo.registry.RegistryService?application=demo-provider&client=curator&dubbo=2.0.0&interface=com.alibaba.dubbo.registry.RegistryService&pid=4685&timestamp=1507286468150
创建文件/Users/jigangzhao/.dubbo/dubbo-registry-10.211.55.5.cache的文件夹/Users/jigangzhao/.dubbo
设置属性file：/Users/jigangzhao/.dubbo/dubbo-registry-10.211.55.5.cache文件，该文件存储信息将是这样的：
com.alibaba.dubbo.demo.DemoService=empty://10.10.10.10:20880/com.alibaba.dubbo.demo.DemoService?anyhost=true&application=demo-provider&category=configurators&check=false&dubbo=2.0.0&generic=false&interface=com.alibaba.dubbo.demo.DemoService&methods=sayHello&pid=5259&side=provider&timestamp=1507294508053
如果file存在，将file中的内容写入properties属性；既然有读file，那么是什么时候写入file的呢？AbstractRegistry创建了一个含有一个名字为DubboSaveRegistryCache的后台线程的FixedThreadPool，只在在notify(URL url, NotifyListener listener, List<URL> urls)方法中会被调用，我们此处由于ConcurrentMap<URL, Set<NotifyListener>> subscribed为空，所以AbstractRegistry(URL url)中的notify(url.getBackupUrls())不会执行，此处也不会创建文件。
最后是notify(url.getBackupUrls())（TODO 这里后续会写）

再来看FailbackRegistry：

只做了一件事，启动了一个含有一个名为DubboRegistryFailedRetryTimer的后台线程的ScheduledThreadPool，线程创建5s后开始第一次执行retry()，之后每隔5s执行一次。来看一下retry()

  1     /**
  2      * 将所有注册失败的url（failedRegistered中的url）进行注册，之后从failedRegistered进行移除；
  3      * 将所有反注册失败的url（failedUnregistered中的url）进行反注册，之后从failedUnregistered进行移除；
  4      * 将所有订阅失败的url（failedSubscribed中的url）进行重新订阅，之后从failedSubscribed进行移除；
  5      * 将所有反订阅失败的url（failedUnsubscribed中的url）进行反订阅，之后从failedUnsubscribed进行移除；
  6      * 将所有通知失败的url（failedNotified中的url）进行通知，之后从failedNotified进行移除；
  7      */
  8     protected void retry() {
  9         if (!failedRegistered.isEmpty()) {
 10             Set<URL> failed = new HashSet<URL>(failedRegistered);
 11             if (failed.size() > 0) {
 12                 if (logger.isInfoEnabled()) {
 13                     logger.info("Retry register " + failed);
 14                 }
 15                 try {
 16                     for (URL url : failed) {
 17                         try {
 18                             doRegister(url);
 19                             failedRegistered.remove(url);
 20                         } catch (Throwable t) { // 忽略所有异常，等待下次重试
 21                             logger.warn("Failed to retry register " + failed + ", waiting for again, cause: " + t.getMessage(), t);
 22                         }
 23                     }
 24                 } catch (Throwable t) { // 忽略所有异常，等待下次重试
 25                     logger.warn("Failed to retry register " + failed + ", waiting for again, cause: " + t.getMessage(), t);
 26                 }
 27             }
 28         }
 29         if (!failedUnregistered.isEmpty()) {
 30             Set<URL> failed = new HashSet<URL>(failedUnregistered);
 31             if (failed.size() > 0) {
 32                 if (logger.isInfoEnabled()) {
 33                     logger.info("Retry unregister " + failed);
 34                 }
 35                 try {
 36                     for (URL url : failed) {
 37                         try {
 38                             doUnregister(url);
 39                             failedUnregistered.remove(url);
 40                         } catch (Throwable t) { // 忽略所有异常，等待下次重试
 41                             logger.warn("Failed to retry unregister  " + failed + ", waiting for again, cause: " + t.getMessage(), t);
 42                         }
 43                     }
 44                 } catch (Throwable t) { // 忽略所有异常，等待下次重试
 45                     logger.warn("Failed to retry unregister  " + failed + ", waiting for again, cause: " + t.getMessage(), t);
 46                 }
 47             }
 48         }
 49         if (!failedSubscribed.isEmpty()) {
 50             Map<URL, Set<NotifyListener>> failed = new HashMap<URL, Set<NotifyListener>>(failedSubscribed);
 51             for (Map.Entry<URL, Set<NotifyListener>> entry : new HashMap<URL, Set<NotifyListener>>(failed).entrySet()) {
 52                 if (entry.getValue() == null || entry.getValue().size() == 0) {
 53                     failed.remove(entry.getKey());
 54                 }
 55             }
 56             if (failed.size() > 0) {
 57                 if (logger.isInfoEnabled()) {
 58                     logger.info("Retry subscribe " + failed);
 59                 }
 60                 try {
 61                     for (Map.Entry<URL, Set<NotifyListener>> entry : failed.entrySet()) {
 62                         URL url = entry.getKey();
 63                         Set<NotifyListener> listeners = entry.getValue();
 64                         for (NotifyListener listener : listeners) {
 65                             try {
 66                                 doSubscribe(url, listener);//listener需要一个一个订阅，每订阅一个，就将该listener从当前的url监听列表中移除
 67                                 listeners.remove(listener);
 68                             } catch (Throwable t) { // 忽略所有异常，等待下次重试
 69                                 logger.warn("Failed to retry subscribe " + failed + ", waiting for again, cause: " + t.getMessage(), t);
 70                             }
 71                         }
 72                     }
 73                 } catch (Throwable t) { // 忽略所有异常，等待下次重试
 74                     logger.warn("Failed to retry subscribe " + failed + ", waiting for again, cause: " + t.getMessage(), t);
 75                 }
 76             }
 77         }
 78         if (!failedUnsubscribed.isEmpty()) {
 79             Map<URL, Set<NotifyListener>> failed = new HashMap<URL, Set<NotifyListener>>(failedUnsubscribed);
 80             for (Map.Entry<URL, Set<NotifyListener>> entry : new HashMap<URL, Set<NotifyListener>>(failed).entrySet()) {
 81                 if (entry.getValue() == null || entry.getValue().size() == 0) {
 82                     failed.remove(entry.getKey());
 83                 }
 84             }
 85             if (failed.size() > 0) {
 86                 if (logger.isInfoEnabled()) {
 87                     logger.info("Retry unsubscribe " + failed);
 88                 }
 89                 try {
 90                     for (Map.Entry<URL, Set<NotifyListener>> entry : failed.entrySet()) {
 91                         URL url = entry.getKey();
 92                         Set<NotifyListener> listeners = entry.getValue();
 93                         for (NotifyListener listener : listeners) {
 94                             try {
 95                                 doUnsubscribe(url, listener);//listener需要一个一个反订阅，每反订阅一个，就将该listener从当前的url监听列表中移除
 96                                 listeners.remove(listener);
 97                             } catch (Throwable t) { // 忽略所有异常，等待下次重试
 98                                 logger.warn("Failed to retry unsubscribe " + failed + ", waiting for again, cause: " + t.getMessage(), t);
 99                             }
100                         }
101                     }
102                 } catch (Throwable t) { // 忽略所有异常，等待下次重试
103                     logger.warn("Failed to retry unsubscribe " + failed + ", waiting for again, cause: " + t.getMessage(), t);
104                 }
105             }
106         }
107         if (!failedNotified.isEmpty()) {
108             Map<URL, Map<NotifyListener, List<URL>>> failed = new HashMap<URL, Map<NotifyListener, List<URL>>>(failedNotified);
109             for (Map.Entry<URL, Map<NotifyListener, List<URL>>> entry : new HashMap<URL, Map<NotifyListener, List<URL>>>(failed).entrySet()) {
110                 if (entry.getValue() == null || entry.getValue().size() == 0) {
111                     failed.remove(entry.getKey());
112                 }
113             }
114             if (failed.size() > 0) {
115                 if (logger.isInfoEnabled()) {
116                     logger.info("Retry notify " + failed);
117                 }
118                 try {
119                     for (Map<NotifyListener, List<URL>> values : failed.values()) {
120                         for (Map.Entry<NotifyListener, List<URL>> entry : values.entrySet()) {
121                             try {
122                                 NotifyListener listener = entry.getKey();
123                                 List<URL> urls = entry.getValue();
124                                 listener.notify(urls);
125                                 values.remove(listener);
126                             } catch (Throwable t) { // 忽略所有异常，等待下次重试
127                                 logger.warn("Failed to retry notify " + failed + ", waiting for again, cause: " + t.getMessage(), t);
128                             }
129                         }
130                     }
131                 } catch (Throwable t) { // 忽略所有异常，等待下次重试
132                     logger.warn("Failed to retry notify " + failed + ", waiting for again, cause: " + t.getMessage(), t);
133                 }
134             }
135         }
136     }

最后回到我们的主角：ZookeeperRegistry

首先是为属性设置root=/dubbo，之后创建zk客户端，启动会话，最后创建了一个StateListener监听器，监听重新连接成功事件，重新连接成功后，之前已经完成注册和订阅的url要重新进行注册和订阅（因为临时节点可能已经跪了）。

来看创建zk客户端，启动会话的代码，这是此处最核心的部分：

ZookeeperTransporter$Adaptive.connect(com.alibaba.dubbo.common.URL registryUrl)

 1     public com.alibaba.dubbo.remoting.zookeeper.ZookeeperClient connect(com.alibaba.dubbo.common.URL arg0) {
 2         if (arg0 == null)
 3             throw new IllegalArgumentException("url == null");
 4         com.alibaba.dubbo.common.URL url = arg0;
 5         String extName = url.getParameter("client", url.getParameter("transporter", "zkclient"));//curator
 6         if(extName == null)
 7             throw new IllegalStateException("Fail to get extension(com.alibaba.dubbo.remoting.zookeeper.ZookeeperTransporter) name from url(" + url.toString() + ") use keys([client, transporter])");
 8         com.alibaba.dubbo.remoting.zookeeper.ZookeeperTransporter extension = (com.alibaba.dubbo.remoting.zookeeper.ZookeeperTransporter)ExtensionLoader.getExtensionLoader(com.alibaba.dubbo.remoting.zookeeper.ZookeeperTransporter.class).getExtension(extName);
 9         return extension.connect(arg0);
10     }

这里创建的extension是CuratorZookeeperTransporter实例。

1 public class CuratorZookeeperTransporter implements ZookeeperTransporter {
2     public ZookeeperClient connect(URL url) {
3         return new CuratorZookeeperClient(url);
4     }
5 }

new CuratorZookeeperClient(registryUrl)

 1     private final CuratorFramework client;
 2 
 3     public CuratorZookeeperClient(URL url) {
 4         super(url);
 5         try {
 6             CuratorFrameworkFactory.Builder builder = CuratorFrameworkFactory.builder()
 7                     .connectString(url.getBackupAddress())
 8                     .retryPolicy(new RetryNTimes(Integer.MAX_VALUE, 1000))
 9                     .connectionTimeoutMs(5000);
10             String authority = url.getAuthority();
11             if (authority != null && authority.length() > 0) {
12                 builder = builder.authorization("digest", authority.getBytes());
13             }
14             client = builder.build();
15             client.getConnectionStateListenable().addListener(new ConnectionStateListener() {
16                 public void stateChanged(CuratorFramework client, ConnectionState state) {
17                     if (state == ConnectionState.LOST) {
18                         CuratorZookeeperClient.this.stateChanged(StateListener.DISCONNECTED);
19                     } else if (state == ConnectionState.CONNECTED) {
20                         CuratorZookeeperClient.this.stateChanged(StateListener.CONNECTED);
21                     } else if (state == ConnectionState.RECONNECTED) {
22                         CuratorZookeeperClient.this.stateChanged(StateListener.RECONNECTED);
23                     }
24                 }
25             });
26             client.start();
27         } catch (Exception e) {
28             throw new IllegalStateException(e.getMessage(), e);
29         }
30     }

这里首先执行父类AbstractZookeeperClient的构造器来初始化一些参数，之后创建CuratorFramework客户端，然后添加了ConnectionStateListener监听器，监听连接断开／连接成功／重新连接成功事件，之后作出相应的操作（实际上这里只有重新连接成功事件会被处理，而处理器实际上就是ZookeeperRegistry构造器中的那个执行recover()的StateListener），

    protected void stateChanged(int state) {
        for (StateListener sessionListener : getSessionListeners()) {
            sessionListener.stateChanged(state);//此处查找实现类，只有ZookeeperRegistry构造器中的那个StateListener
        }
    }

最后阻塞，直到创建会话完成。

来看一下父类AbstractZookeeperClient：

1     private final URL url;
2     private final Set<StateListener> stateListeners = new CopyOnWriteArraySet<StateListener>();
3     private final ConcurrentMap<String, ConcurrentMap<ChildListener, TargetChildListener>> childListeners = new ConcurrentHashMap<String, ConcurrentMap<ChildListener, TargetChildListener>>();
4     private volatile boolean closed = false;
5 
6     public AbstractZookeeperClient(URL url) {
7         this.url = url;
8     }

说明：

设置属性url=registryUrl：zookeeper://10.211.55.5:2181/com.alibaba.dubbo.registry.RegistryService?application=demo-provider&client=curator&dubbo=2.0.0&interface=com.alibaba.dubbo.registry.RegistryService&pid=4685&timestamp=1507286468150
创建了一个Set<StateListener> stateListeners，ZookeeperRegistry构造器中的那个执行recover()的StateListener就将会放在这里

至此，一个完整的ZookeeperRegistry实例就创建完成了，来看一下属性：

ZookeeperClient zkClient = CuratorZookeeperClient实例
- CuratorFramework client：CuratorFrameworkImpl实例
- String url：zookeeper://10.211.55.5:2181/com.alibaba.dubbo.registry.RegistryService?application=demo-provider&client=curator&dubbo=2.0.0&interface=com.alibaba.dubbo.registry.RegistryService&pid=4685&timestamp=1507286468150
- Set<StateListener> stateListeners：{ 监听了重连成功事件的执行recover()的StateListener }
String root="/dubbo"
URL registryUrl = zookeeper://10.211.55.5:2181/com.alibaba.dubbo.registry.RegistryService?application=demo-provider&client=curator&dubbo=2.0.0&interface=com.alibaba.dubbo.registry.RegistryService&pid=4685&timestamp=1507286468150
Set<URL> registered：0//已经注册的url集合，此处为空
ConcurrentMap<URL, Set<NotifyListener>> subscribed：0//已经订阅的<URL, Set<NotifyListener>>
ConcurrentMap<URL, Map<String, List<URL>>> notified：0//已经通知的<URL, Map<String, List<URL>>>
Set<URL> failedRegistered：0//注册失败的url
Set<URL> failedUnregistered：0//反注册失败的url
ConcurrentMap<URL, Set<NotifyListener>> failedSubscribed：0//订阅失败的url
ConcurrentMap<URL, Set<NotifyListener>> failedUnsubscribed：0//反订阅失败的url
ConcurrentMap<URL, Map<NotifyListener, List<URL>>> failedNotified：0//通知失败的url
ConcurrentMap<URL, ConcurrentMap<NotifyListener, ChildListener>> zkListeners：0

还有一个定时线程：DubboRegistryFailedRetryTimer每隔5s执行一次retry()，进行失败重试。

最后，该ZookeeperRegistry会存储在ZookeeperRegistry的父类的static属性Map<String, Registry> REGISTRIES中：

Map<String, Registry> REGISTRIES：{ "zookeeper://10.211.55.5:2181/com.alibaba.dubbo.registry.RegistryService" : ZookeeperRegistry实例 }

二获取真正要注册到zk的节点url

1 final URL registedProviderUrl = getRegistedProviderUrl(originInvoker);

 1     /**
 2      * 1 获取originInvoker的export参数值：就是providerUrl
 3      * 2 去除providerUrl中所有参数名是"."开头的，然后去除参数monitor
 4      */
 5     private URL getRegistedProviderUrl(final Invoker<?> originInvoker) {
 6         URL providerUrl = getProviderUrl(originInvoker);
 7         //注册中心看到的地址
 8         final URL registedProviderUrl = providerUrl.removeParameters(getFilteredKeys(providerUrl)).removeParameter(Constants.MONITOR_KEY);
 9         return registedProviderUrl;
10     }
11 
12     /**
13      * 从invoker的URL中的Map<String, String> parameters中获取key为export的地址providerUrl：
14      */
15     private URL getProviderUrl(final Invoker<?> origininvoker) {
16         String export = origininvoker.getUrl().getParameterAndDecoded(Constants.EXPORT_KEY);
17         if (export == null || export.length() == 0) {
18             throw new IllegalArgumentException("The registry export url is null! registry: " + origininvoker.getUrl());
19         }
20         URL providerUrl = URL.valueOf(export);
21         return providerUrl;
22     }
23 
24     //过滤URL中不需要输出的参数(以点号开头的)
25     private static String[] getFilteredKeys(URL url) {
26         Map<String, String> params = url.getParameters();
27         if (params != null && !params.isEmpty()) {
28             List<String> filteredKeys = new ArrayList<String>();
29             for (Map.Entry<String, String> entry : params.entrySet()) {
30                 if (entry != null && entry.getKey() != null && entry.getKey().startsWith(Constants.HIDE_KEY_PREFIX)) {
31                     filteredKeys.add(entry.getKey());
32                 }
33             }
34             return filteredKeys.toArray(new String[filteredKeys.size()]);
35         } else {
36             return new String[]{};
37         }
38     }

最后得到的registedProviderUrl是：

dubbo://10.10.10.10:20880/com.alibaba.dubbo.demo.DemoService?anyhost=true&application=demo-provider&dubbo=2.0.0&generic=false&interface=com.alibaba.dubbo.demo.DemoService&methods=sayHello&pid=4758&side=provider&timestamp=1507289961588

三注册服务到zk

registry.register(registedProviderUrl);//创建节点（即注册服务到zk上）

这里的registry是ZookeeperRegistry。register(registedProviderUrl)方法在ZookeeperRegistry的父类FailbackRegistry中实现。

1 FailbackRegistry.register(registedProviderUrl)

 1     @Override
 2     public void register(URL url) {
 3         if (destroyed.get()){
 4             return;
 5         }
 6         super.register(url);
 7         failedRegistered.remove(url);
 8         failedUnregistered.remove(url);
 9         try {
10             // 向服务器端发送注册请求
11             doRegister(url);
12         } catch (Exception e) {
13             Throwable t = e;
14             // 如果开启了启动时检测check=true，则直接抛出异常，不会加入到failedRegistered中
15             boolean check = getUrl().getParameter(Constants.CHECK_KEY, true)
16                     && url.getParameter(Constants.CHECK_KEY, true)
17                     && !Constants.CONSUMER_PROTOCOL.equals(url.getProtocol());
18             boolean skipFailback = t instanceof SkipFailbackWrapperException;
19             if (check || skipFailback) {
20                 if (skipFailback) {
21                     t = t.getCause();
22                 }
23                 throw new IllegalStateException("Failed to register " + url + " to registry " + getUrl().getAddress() + ", cause: " + t.getMessage(), t);
24             } else {
25                 logger.error("Failed to register " + url + ", waiting for retry, cause: " + t.getMessage(), t);
26             }
27             // 将失败的注册请求记录到失败列表，定时重试
28             failedRegistered.add(url);
29         }
30     }

首先调用父类AbstractRegistry的register(registedProviderUrl)将当前的registeredProviderUrl放到Set<URL> registered属性中，如下：

1     public void register(URL url) {
2         if (url == null) {
3             throw new IllegalArgumentException("register url == null");
4         }
5         if (logger.isInfoEnabled()) {
6             logger.info("Register: " + url);
7         }
8         registered.add(url);
9     }

之后，从failedRegistered和failedUnregistered两个url集合中删除该url。然后执行真正的服务注册（创建节点，doRegister(url)），如果在创建过程中抛出异常，如果url的协议不是consumer并且开启了check=true的属性并且当前存储的URL registryUrl也有check=true的话，那么直接抛出异常，不会将该url加入到failedRegistered集合；当然抛出的异常如果是SkipFailbackWrapperException，那么也会直接抛出异常，不会将该url加入到failedRegistered集合。否则，会将该url加入到failedRegistered集合，然后DubboRegistryFailedRetryTimer线程会每隔5s执行一次doRegister(url)。

我们来看真正doRegister(url)。

2 ZookeeperRegistry.doRegister(registedProviderUrl)

1     protected void doRegister(URL url) {
2         try {
3             zkClient.create(toUrlPath(url), url.getParameter(Constants.DYNAMIC_KEY, true));
4         } catch (Throwable e) {
5             throw new RpcException("Failed to register " + url + " to zookeeper " + getUrl() + ", cause: " + e.getMessage(), e);
6         }
7     }

首先是对入参registedProviderUrl进行一顿处理，

 1     private String toUrlPath(URL url) {
 2         return toCategoryPath(url) + Constants.PATH_SEPARATOR + URL.encode(url.toFullString());
 3     }
 4 
 5     private String toCategoryPath(URL url) {
 6         return toServicePath(url) + Constants.PATH_SEPARATOR + url.getParameter(Constants.CATEGORY_KEY, Constants.DEFAULT_CATEGORY);
 7     }
 8 
 9     private String toServicePath(URL url) {
10         String name = url.getServiceInterface();
11         if (Constants.ANY_VALUE.equals(name)) {
12             return toRootPath();
13         }
14         return toRootDir() + URL.encode(name);// /dubbo/com.alibaba.dubbo.demo.DemoService
15     }
16 
17     private String toRootDir() {
18         if (root.equals(Constants.PATH_SEPARATOR)) {
19             return root;
20         }
21         return root + Constants.PATH_SEPARATOR;// /dubbo/
22     }
23 
24     private String toRootPath() {
25         return root;
26     }

这里就体现了上边的ZookeeperRegistry的root属性的作用。最终实际上得到的是：/dubbo/interface/category/encode过的export，该节点也将是创建在zk上的节点。

/dubbo是根节点
/interface是服务接口
/category是providers／consumers／routers／configurators等

最终得到的url是：

/dubbo/com.alibaba.dubbo.demo.DemoService/providers/dubbo%3A%2F%2F10.10.10.10%3A20880%2Fcom.alibaba.dubbo.demo.DemoService%3Fanyhost%3Dtrue%26application%3Ddemo-provider%26dubbo%3D2.0.0%26generic%3Dfalse%26interface%3Dcom.alibaba.dubbo.demo.DemoService%26methods%3DsayHello%26pid%3D5148%26side%3Dprovider%26timestamp%3D1507291294629
解码后：/dubbo/com.alibaba.dubbo.demo.DemoService/providers/dubbo://10.10.10.10:20880/com.alibaba.dubbo.demo.DemoService?anyhost=true&application=demo-provider&dubbo=2.0.0&generic=false&interface=com.alibaba.dubbo.demo.DemoService&methods=sayHello&pid=5148&side=provider&timestamp=1507291294629

最后执行zkClient.create(toUrlPath(url), url.getParameter(Constants.DYNAMIC_KEY, true))来创建节点，该方法由CuratorZookeeperClient的父类AbstractZookeeperClient来执行：

 1     public void create(String path, boolean ephemeral) {
 2         int i = path.lastIndexOf('/');
 3         if (i > 0) {
 4             create(path.substring(0, i), false);
 5         }
 6         if (ephemeral) {
 7             createEphemeral(path);
 8         } else {
 9             createPersistent(path);
10         }
11     }

这里实际上是通过递归分别创建持久化的/dubbo，/dubbo/com.alibaba.dubbo.demo.DemoService以及/dubbo/com.alibaba.dubbo.demo.DemoService/providers节点；最后创建临时节点/dubbo/com.alibaba.dubbo.demo.DemoService/providers/dubbo%3A%2F%2F10.10.10.10%3A20880%2Fcom.alibaba.dubbo.demo.DemoService%3Fanyhost%3Dtrue%26application%3Ddemo-provider%26dubbo%3D2.0.0%26generic%3Dfalse%26interface%3Dcom.alibaba.dubbo.demo.DemoService%26methods%3DsayHello%26pid%3D5148%26side%3Dprovider%26timestamp%3D1507291294629，而实际上，如果使用了curator的话，可以直接使用递归创建节点即可（结合zk的特性，只有最后一个字节点可以是临时节点，父节点一定是持久化节点），这里这样的写法应该是兼容不能递归创建节点的Zkclient客户端。值得注意的是，url.getParameter(Constants.DYNAMIC_KEY, true)为true则最终创建的节点是临时节点，否则是持久化节点。

创建节点的操作是在CuratorZookeeperClient中进行的。

 1     public void createPersistent(String path) {
 2         try {
 3             client.create().forPath(path);
 4         } catch (NodeExistsException e) {
 5         } catch (Exception e) {
 6             throw new IllegalStateException(e.getMessage(), e);
 7         }
 8     }
 9 
10     public void createEphemeral(String path) {
11         try {
12             client.create().withMode(CreateMode.EPHEMERAL).forPath(path);
13         } catch (NodeExistsException e) {
14         } catch (Exception e) {
15             throw new IllegalStateException(e.getMessage(), e);
16         }
17     }

到此为止，我们去zk上看一下节点的创建情况。

或者从zkui上看一下：

隐藏掉的是ip：10.10.10.10。

到目前为止，我们再来看看ZookeeperRegistry的属性变化。相较于注册前：

Set<URL> registered：[ dubbo://10.10.10.10:20880/com.alibaba.dubbo.demo.DemoService?anyhost=true&application=demo-provider&dubbo=2.0.0&generic=false&interface=com.alibaba.dubbo.demo.DemoService&methods=sayHello&pid=5214&side=provider&timestamp=1507293238549 ]

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原文地址：https://www.cnblogs.com/java-zhao/p/7629027.html

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