dubbo 学习

dubbo provider、consumer启动的时候，如果没有指定协议，则默认是dubbo协议，对应代码如下：

String name = protocolConfig.getName();
if (name == null || name.length() == 0) {
    name = "dubbo";
}

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dubbo注册到zookeeper中，节点是持久化的节点来的，节点如下：
[dubbo%3A%2F%2F10.100.97.26%3A20881%2Fcom.drafire.user.IUserService%3Fapplication%3Duser-provider%26dubbo%3D2.5.3%26interface%3Dcom.drafire.user.IUserService%26methods%3Dlogin%26owner%3Ddrafire%26pid%3D21568%26side%3Dprovider%26timestamp%3D1552035568717]

解码后如下：

[dubbo://10.100.97.26:20881/com.drafire.user.IUserService?application=user-provider&dubbo=2.5.3&interface=com.drafire.user.IUserService&methods=login&owner=drafire&pid=21568&side=provider&timestamp=1552035568717]

从这里可以看出，这个是一个无序的节点，因为有序的节点建立后，节点后面会有一串数字，数字从：10000000000 开始。如下所示：

[zk: localhost:2181(CONNECTED) 32] create -s /test/node1 abc
Created /test/node10000000000

查看该节点的性质： get /dubbo/com.drafire.user.IUserService/providers，结果如下：

null
cZxid = 0x400000004
ctime = Fri Mar 08 00:59:43 PST 2019
mZxid = 0x400000004
mtime = Fri Mar 08 00:59:43 PST 2019
pZxid = 0x400000005
cversion = 1
dataVersion = 0
aclVersion = 0
ephemeralOwner = 0x0
dataLength = 0
numChildren = 1

从这里可以看出，这个是持久化节点。如果是临时节点，这了会有个临时拥有者，是一串数字并且值大于0

从源码也可以看出是新建的持久化非有序节点，代码如下：

// comalibabadubbo2.5.3dubbo-2.5.3-sources.jar!comalibabadubbo
egistryzookeeperookeeperRegistry.java
 protected void doSubscribe(final URL url, final NotifyListener listener) {
        try {
            if (Constants.ANY_VALUE.equals(url.getServiceInterface())) {
                String root = toRootPath();
                ConcurrentMap<NotifyListener, ChildListener> listeners = zkListeners.get(url);
                if (listeners == null) {
                    zkListeners.putIfAbsent(url, new ConcurrentHashMap<NotifyListener, ChildListener>());
                    listeners = zkListeners.get(url);
                }
                ChildListener zkListener = listeners.get(listener);
                if (zkListener == null) {
                    listeners.putIfAbsent(listener, new ChildListener() {
                        public void childChanged(String parentPath, List<String> currentChilds) {
                            for (String child : currentChilds) {
                                if (! anyServices.contains(child)) {
                                    anyServices.add(child);
                                    subscribe(url.setPath(child).addParameters(Constants.INTERFACE_KEY, child, 
                                            Constants.CHECK_KEY, String.valueOf(false)), listener);
                                }
                            }
                        }
                    });
                    zkListener = listeners.get(listener);
                }
                zkClient.create(root, false);
                List<String> services = zkClient.addChildListener(root, zkListener);
                if (services != null && services.size() > 0) {
                    anyServices.addAll(services);
                    for (String service : services) {
                        subscribe(url.setPath(service).addParameters(Constants.INTERFACE_KEY, service, 
                                Constants.CHECK_KEY, String.valueOf(false)), listener);
                    }
                }
            } else {
                List<URL> urls = new ArrayList<URL>();
                for (String path : toCategoriesPath(url)) {
                    ConcurrentMap<NotifyListener, ChildListener> listeners = zkListeners.get(url);
                    if (listeners == null) {
                        zkListeners.putIfAbsent(url, new ConcurrentHashMap<NotifyListener, ChildListener>());
                        listeners = zkListeners.get(url);
                    }
                    ChildListener zkListener = listeners.get(listener);
                    if (zkListener == null) {
                        listeners.putIfAbsent(listener, new ChildListener() {
                            public void childChanged(String parentPath, List<String> currentChilds) {
                                ZookeeperRegistry.this.notify(url, listener, toUrlsWithEmpty(url, parentPath, currentChilds));
                            }
                        });
                        zkListener = listeners.get(listener);
                    }
                    zkClient.create(path, false);           //这里创建了持久化的非有序节点
                    List<String> children = zkClient.addChildListener(path, zkListener);
                    if (children != null) {
                        urls.addAll(toUrlsWithEmpty(url, path, children));
                    }
                }
                notify(url, listener, urls);
            }
        } catch (Throwable e) {
            throw new RpcException("Failed to subscribe " + url + " to zookeeper " + getUrl() + ", cause: " + e.getMessage(), e);
        }
    }