startConfigCenter时，不会使用自己扩展的ZookeeperTransports

[CodingSinger]

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• I have checked the FAQ of this repository and believe that this is not a duplicate.

Environment

• Dubbo version: 2.7.2
• Operating System version: macOS 10.12.6
• Java version: 1.8

Steps to reproduce this issue

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Expected Result

What do you expected from the above steps？

    ZookeeperDynamicConfiguration(URL url, ZookeeperTransporter zookeeperTransporter) {
        this.url = url;
        rootPath = "/" + url.getParameter(CONFIG_NAMESPACE_KEY, DEFAULT_GROUP) + "/config";

        initializedLatch = new CountDownLatch(1);
        this.cacheListener = new CacheListener(rootPath, initializedLatch);
        this.executor = Executors.newFixedThreadPool(1, new NamedThreadFactory(this.getClass().getSimpleName(), true));

        zkClient = zookeeperTransporter.connect(url);
        zkClient.addDataListener(rootPath, cacheListener, executor);
        try {
            // Wait for connection
            this.initializedLatch.await();
        } catch (InterruptedException e) {
            logger.warn("Failed to build local cache for config center (zookeeper)." + url);
        }
    }

zkClient = zookeeperTransporter.connect(url);会通过URL中的client参数来正确选择自适应扩展来初始化zk客户端。但在初始化配置中心的时候，URL是由ConfigCenterConfig得到的，此时URL中无client的信息，所以这个地方创建zk还是用的默认的zkClient。希望和注册中心时候一样获取自己扩展的zkClient

Actual Result

What actually happens?

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[CodingSinger]

需要在

   registries.stream().filter(RegistryConfig::isZookeeperProtocol).findFirst().ifPresent(rc -> {
            // we use the loading status of DynamicConfiguration to decide whether ConfigCenter has been initiated.
            Environment.getInstance().getDynamicConfiguration().orElseGet(() -> {
                ConfigManager configManager = ConfigManager.getInstance();
                ConfigCenterConfig cc = configManager.getConfigCenter().orElse(new ConfigCenterConfig());
                cc.setProtocol(rc.getProtocol());
                cc.setAddress(rc.getAddress());
                cc.setHighestPriority(false);
                cc.setClient(rc.getClient)); // 改进
                setConfigCenter(cc);
                startConfigCenter();
                return null;
            });
        });

ConfigCenterConfig中应该增加client属性，以将zk的ZookeeperTransporter方式传递给ConfigCenterConfig，保证此处zk客户端初始化和ZookeeperRegistry初始化zk客户端的方式一样。

[lexburner]

看起来是 configcenter 加载 ZookeeperTransporter 的逻辑跟 registry 那块的逻辑不一致，没有根据 client 字段去加载 SPI 扩展。有兴趣的话可以提交一个 pr 帮忙修复一下

[CodingSinger]

好的，我试试提pr

[chickenlj]

Fixed by #4513