关于spring-cloud-commons

spring-cloud-commons依赖中 提供了 springCloud技术栈的一些编程模型，例如 服务注册与发现，用于服务保护的熔断器模式等等 spring-cloud-commons 在下文中简称 scc.

spring-cloud-commons 服务注册

scc中首先提供了服务实例的标准接口ServiceInstance，包含了单个实例的基本信息代码如下

public interface ServiceInstance {
    default String getInstanceId() {
        return null;
    }

    String getServiceId();

    String getHost();

    int getPort();

    boolean isSecure();

    URI getUri();

    Map<String, String> getMetadata();

    default String getScheme() {
        return null;
    }
}

其次 org.springframework.cloud.client.serviceregistry.ServiceRegistry接口提供服务注册规范

public interface ServiceRegistry<R extends Registration> {

	/**
	 * Registers the registration. A registration typically has information about an
	 * instance, such as its hostname and port.
	 * @param registration registration meta data
	 */
	void register(R registration);

	/**
	 * Deregisters the registration.
	 * @param registration registration meta data
	 */
	void deregister(R registration);

	/**
	 * Closes the ServiceRegistry. This is a lifecycle method.
	 */
	void close();

	/**
	 * Sets the status of the registration. The status values are determined by the
	 * individual implementations.
	 * @param registration The registration to update.
	 * @param status The status to set.
	 * @see org.springframework.cloud.client.serviceregistry.endpoint.ServiceRegistryEndpoint
	 */
	void setStatus(R registration, String status);

	/**
	 * Gets the status of a particular registration.
	 * @param registration The registration to query.
	 * @param <T> The type of the status.
	 * @return The status of the registration.
	 * @see org.springframework.cloud.client.serviceregistry.endpoint.ServiceRegistryEndpoint
	 */
	<T> T getStatus(R registration);

}

其中 Registration继承了ServiceInstance，例如nacos注册中心，NacosRegistration实现了Registration与ServiceInstance，用于服务注册时获取服务实例信息

# spring-cloud-commons 服务发现

org.springframework.cloud.client.discovery.DiscoveryClient接口提供了服务发现的规范，代码如下

public interface DiscoveryClient extends Ordered {

	/**
	 * Default order of the discovery client.
	 */
	int DEFAULT_ORDER = 0;

	/**
	 * A human-readable description of the implementation, used in HealthIndicator.
	 * @return The description.
	 */
	String description();

	/**
	 * Gets all ServiceInstances associated with a particular serviceId.
	 * @param serviceId The serviceId to query.
	 * @return A List of ServiceInstance.
	 */
	List<ServiceInstance> getInstances(String serviceId);

	/**
	 * @return All known service IDs.
	 */
	List<String> getServices();

	/**
	 * Can be used to verify the client is valid and able to make calls.
	 * <p>
	 * A successful invocation with no exception thrown implies the client is able to make
	 * calls.
	 * <p>
	 * The default implementation simply calls {@link #getServices()} - client
	 * implementations can override with a lighter weight operation if they choose to.
	 */
	default void probe() {
		getServices();
	}

	/**
	 * Default implementation for getting order of discovery clients.
	 * @return order
	 */
	@Override
	default int getOrder() {
		return DEFAULT_ORDER;
	}

例如spring-cloud--alibaba-nacos注册中心通过实现 DiscoveryClient接口进行服务发现，代码如下

public class NacosDiscoveryClient implements DiscoveryClient {

	private static final Logger log = LoggerFactory.getLogger(NacosDiscoveryClient.class);

	/**
	 * Nacos Discovery Client Description.
	 */
	public static final String DESCRIPTION = "Spring Cloud Nacos Discovery Client";

	private NacosServiceDiscovery serviceDiscovery;

	public NacosDiscoveryClient(NacosServiceDiscovery nacosServiceDiscovery) {
		this.serviceDiscovery = nacosServiceDiscovery;
	}

	@Override
	public String description() {
		return DESCRIPTION;
	}

	@Override
	public List<ServiceInstance> getInstances(String serviceId) {
		try {
			return serviceDiscovery.getInstances(serviceId);
		}
		catch (Exception e) {
			throw new RuntimeException(
					"Can not get hosts from nacos server. serviceId: " + serviceId, e);
		}
	}

	@Override
	public List<String> getServices() {
		try {
			return serviceDiscovery.getServices();
		}
		catch (Exception e) {
			log.error("get service name from nacos server fail,", e);
			return Collections.emptyList();
		}
	}

}