org.apache.dubbo.registry.client.ServiceDiscovery SPI，提供自定义的注册中心实现。在 服务发现 一章中，我们了解了 Dubbo 内置的几个核心注册中心实现 Nacos、Zookeeper 的使用方式与工作原理。本文讲解如何通过扩展 org.apache.dubbo.registry.client.ServiceDiscovery 和 org.apache.dubbo.registry.nacos.NacosServiceDiscoveryFactory SPI，提供自定义的注册中心实现。
本示例的完整源码请参见 dubbo-registry-etcd。除了本示例之外，Dubbo 核心仓库 apache/dubbo 以及扩展库 apache/dubbo-spi-extensions 中的众多注册中心扩展实现，都可以作为扩展参考实现：
# Dubbo对外支持的常用注册中心实现
nacos=org.apache.dubbo.registry.nacos.NacosServiceDiscoveryFactory
zookeeper=org.apache.dubbo.registry.zookeeper.ZookeeperServiceDiscoveryFactory
通过扩展 SPI 实现基于的 etcd 注册中心。
首先，通过继承 AbstractServiceDiscoveryFactory 实现 ServiceDiscoveryFactory 接口
public class EtcdServiceDiscoveryFactory extends AbstractServiceDiscoveryFactory {
@Override
protected ServiceDiscovery createDiscovery(URL registryURL) {
return new EtcdServiceDiscovery(applicationModel, registryURL);
}
}
EtcdServiceDiscovery 的一些关键方法与实现如下：
public class EtcdServiceDiscovery extends AbstractServiceDiscovery {
private final Set<String> services = new ConcurrentHashSet<>();
private final Map<String, InstanceChildListener> childListenerMap = new ConcurrentHashMap<>();
EtcdClient etcdClient;
public EtcdServiceDiscovery(ApplicationModel applicationModel, URL registryURL) {
super(applicationModel, registryURL);
EtcdTransporter etcdTransporter = applicationModel.getExtensionLoader(EtcdTransporter.class).getAdaptiveExtension();
etcdClient = etcdTransporter.connect(registryURL);
etcdClient.addStateListener(state -> {
if (state == StateListener.CONNECTED) {
try {
recover();
} catch (Exception e) {
logger.error(e.getMessage(), e);
}
}
});
this.registryURL = registryURL;
}
@Override
public void doRegister(ServiceInstance serviceInstance) {
try {
String path = toPath(serviceInstance);
etcdClient.putEphemeral(path, new Gson().toJson(serviceInstance));
services.add(serviceInstance.getServiceName());
} catch (Throwable e) {
throw new RpcException("Failed to register " + serviceInstance + " to etcd " + etcdClient.getUrl()
+ ", cause: " + (OptionUtil.isProtocolError(e)
? "etcd3 registry may not be supported yet or etcd3 registry is not available."
: e.getMessage()), e);
}
}
@Override
protected void doUnregister(ServiceInstance serviceInstance) {
try {
String path = toPath(serviceInstance);
etcdClient.delete(path);
services.remove(serviceInstance.getServiceName());
} catch (Throwable e) {
throw new RpcException("Failed to unregister " + serviceInstance + " to etcd " + etcdClient.getUrl() + ", cause: " + e.getMessage(), e);
}
}
@Override
public void addServiceInstancesChangedListener(ServiceInstancesChangedListener listener) throws NullPointerException, IllegalArgumentException {
for (String serviceName : listener.getServiceNames()) {
registerServiceWatcher(serviceName, listener);
}
}
@Override
public List<ServiceInstance> getInstances(String serviceName) {
List<String> children = etcdClient.getChildren(toParentPath(serviceName));
if (CollectionUtils.isEmpty(children)) {
return Collections.emptyList();
}
List<ServiceInstance> list = new ArrayList<>(children.size());
for (String child : children) {
ServiceInstance serviceInstance = new Gson().fromJson(etcdClient.getKVValue(child), DefaultServiceInstance.class);
list.add(serviceInstance);
}
return list;
}
}
在 resources/META-INF/dubbo/org.apache.dubbo.registry.client.ServiceDiscoveryFactory 文件中添加如下配置：
etcd=org.apache.dubbo.registry.etcd.EtcdServiceDiscoveryFactory
要开启 etcd 作为注册中心，修改应用中的 resources/application.properties 文件中的 registry 配置如下：
dubbo.registry.address=etcd://host:port