@EnableDiscoveryClient 是如何实现服务注册的？
我们首先需要了解 Spring-Cloud-Commons 这个模块，Spring-Cloud-Commons 是 Spring-Cloud 官方提供的一套抽象层，类似于 JDBC 一样，提供了一套规范，具体的实现有实现厂商去根据标准实现，在Finchley版中， Spring-Cloud-Commons 共提供了６个模块标准规范。
actuator
circuitbreaker
discovery
hypermedia
loadbalancer
serviceregistry
在今天的文章中，我们一起来探讨学习一下 discovery、serviceregistry这两个模块，我们使用 alibaba 的 nacos-discovery 实现来进行学习。
@EnableDiscoveryClient 注解做了什么事？
@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Inherited
@Import(EnableDiscoveryClientImportSelector.class)public @interface EnableDiscoveryClient { /**
* If true, the ServiceRegistry will automatically register the local server. */
boolean autoRegister() default true;
}从EnableDiscoveryClient源码可以看出该接口有一个autoRegister()方法默认返回值是true，它还做了一件非常重要的事，引用了EnableDiscoveryClientImportSelector类。为什么说这个类非常重要呢？我们来看看就知道了
EnableDiscoveryClientImportSelector 类做了什么事？
@Order(Ordered.LOWEST_PRECEDENCE - 100)public class EnableDiscoveryClientImportSelector extends SpringFactoryImportSelector {
@Override public String[] selectImports(AnnotationMetadata metadata) {
String[] imports = super.selectImports(metadata);
AnnotationAttributes attributes = AnnotationAttributes.fromMap(
metadata.getAnnotationAttributes(getAnnotationClass().getName(), true)); boolean autoRegister = attributes.getBoolean("autoRegister"); if (autoRegister) {
ListimportsList = new ArrayList<>(Arrays.asList(imports));
importsList.add("org.springframework.cloud.client.serviceregistry.AutoServiceRegistrationConfiguration");
imports = importsList.toArray(new String[0]);
} else {
Environment env = getEnvironment(); if(ConfigurableEnvironment.class.isInstance(env)) {
ConfigurableEnvironment configEnv = (ConfigurableEnvironment)env;
LinkedHashMapmap = new LinkedHashMap<>();
map.put("spring.cloud.service-registry.auto-registration.enabled", false);
MapPropertySource propertySource = new MapPropertySource( "springCloudDiscoveryClient", map);
configEnv.getPropertySources().addLast(propertySource);
}
} return imports;
}
@Override protected boolean isEnabled() { return getEnvironment().getProperty( "spring.cloud.discovery.enabled", Boolean.class, Boolean.TRUE);
}
@Override protected boolean hasDefaultFactory() { return true;
}
}将焦点聚集到selectImports()方法上，该类获取了autoRegister 的值。
当autoRegister=true 时，将AutoServiceRegistrationConfiguration类添加到自动装配中，系统就会去自动装配AutoServiceRegistrationConfiguration类，在具体的实现中自动装配类都是在这个AutoServiceRegistrationConfiguration类自动装配完成后才装配的，也就是说autoRegister=true就更够实现服务注册
当autoRegister=false时，将spring.cloud.service-registry.auto-registration.enabled 设置成了 false，这样跟注册相关的类将不会自动装配，因为自动注册相关的类都有一个条件装配@ConditionalOnProperty(value = "spring.cloud.service-registry.auto-registration.enabled", matchIfMissing = true),换句话说如果我们不想该服务注册到注册中心，只是想从注册中心拉取服务，我们只需要引导类上的注解改成@EnableDiscoveryClient(autoRegister = false)
nacos 是如何根据标准去实现服务注册的?
我们先看看在org.springframework.cloud.alibaba.nacos包下的NacosDiscoveryAutoConfiguration类
NacosDiscoveryAutoConfiguration类做了些什么？
@Configuration
@EnableConfigurationProperties
@ConditionalOnNacosDiscoveryEnabled
@ConditionalOnProperty(value = "spring.cloud.service-registry.auto-registration.enabled", matchIfMissing = true)
@AutoConfigureAfter({ AutoServiceRegistrationConfiguration.class,
AutoServiceRegistrationAutoConfiguration.class })public class NacosDiscoveryAutoConfiguration {
@Bean public NacosServiceRegistry nacosServiceRegistry(
NacosDiscoveryProperties nacosDiscoveryProperties) { return new NacosServiceRegistry(nacosDiscoveryProperties);
}
@Bean
@ConditionalOnBean(AutoServiceRegistrationProperties.class) public NacosRegistration nacosRegistration(
NacosDiscoveryProperties nacosDiscoveryProperties,
ApplicationContext context) { return new NacosRegistration(nacosDiscoveryProperties, context);
}
@Bean
@ConditionalOnBean(AutoServiceRegistrationProperties.class) public NacosAutoServiceRegistration nacosAutoServiceRegistration(
NacosServiceRegistry registry,
AutoServiceRegistrationProperties autoServiceRegistrationProperties,
NacosRegistration registration) { return new NacosAutoServiceRegistration(registry,
autoServiceRegistrationProperties, registration);
}
}该类的自动装配是在AutoServiceRegistrationConfiguration之后完成，当autoRegister设置为false时，NacosDiscoveryAutoConfiguration就不会装配，也就意味着服务不会像注册中心进行注册。好了我们还是来看看NacosDiscoveryAutoConfiguration干了些啥吧，主要是装配了NacosServiceRegistry、NacosRegistration、NacosAutoServiceRegistration三个bean，来看看三个bean干了那些骚操作。
NacosServiceRegistry类做了些什么？
public class NacosServiceRegistry implements ServiceRegistry { private static final Logger log = LoggerFactory.getLogger(NacosServiceRegistry.class); private final NacosDiscoveryProperties nacosDiscoveryProperties; private final NamingService namingService; public NacosServiceRegistry(NacosDiscoveryProperties nacosDiscoveryProperties) { this.nacosDiscoveryProperties = nacosDiscoveryProperties; this.namingService = nacosDiscoveryProperties.namingServiceInstance();
}
@Override public void register(Registration registration) { if (StringUtils.isEmpty(registration.getServiceId())) {
log.warn("No service to register for nacos client..."); return;
}
String serviceId = registration.getServiceId();
Instance instance = new Instance();
instance.setIp(registration.getHost());
instance.setPort(registration.getPort());
instance.setWeight(nacosDiscoveryProperties.getWeight());
instance.setClusterName(nacosDiscoveryProperties.getClusterName());
instance.setMetadata(registration.getMetadata()); try {
namingService.registerInstance(serviceId, instance);
log.info("nacos registry, {} {}:{} register finished", serviceId,
instance.getIp(), instance.getPort());
} catch (Exception e) {
log.error("nacos registry, {} register failed...{},", serviceId,
registration.toString(), e);
}
}
@Override public void deregister(Registration registration) {
log.info("De-registering from Nacos Server now..."); if (StringUtils.isEmpty(registration.getServiceId())) {
log.warn("No dom to de-register for nacos client..."); return;
}
NamingService namingService = nacosDiscoveryProperties.namingServiceInstance();
String serviceId = registration.getServiceId(); try {
namingService.deregisterInstance(serviceId, registration.getHost(),
registration.getPort(), nacosDiscoveryProperties.getClusterName());
} catch (Exception e) {
log.error("ERR_NACOS_DEREGISTER, de-register failed...{},",
registration.toString(), e);
}
log.info("De-registration finished.");
}
@Override public void close() {
}
@Override public void setStatus(Registration registration, String status) { // nacos doesn't support set status of a particular registration. }
@Override public T getStatus(Registration registration) { // nacos doesn't support query status of a particular registration.
return null;
}
}该类实现了 spring-cloud-commons 提供的 ServiceRegistry 接口，重写了register、deregister两个方法，在register
方法中主要是将配置文件装换成Instance实例，调用了namingService.registerInstance(serviceId, instance);方法，这个方法应该是服务端提供的服务注册方法。这一顿操作之后，服务就注册好了。
NacosRegistration类做了些什么?
public class NacosRegistration implements Registration, ServiceInstance { public static final String MANAGEMENT_PORT = "management.port"; public static final String MANAGEMENT_CONTEXT_PATH = "management.context-path"; public static final String MANAGEMENT_ADDRESS = "management.address"; public static final String MANAGEMENT_ENDPOINT_BASE_PATH = "management.endpoints.web.base-path"; private NacosDiscoveryProperties nacosDiscoveryProperties; private ApplicationContext context; public NacosRegistration(NacosDiscoveryProperties nacosDiscoveryProperties,
ApplicationContext context) { this.nacosDiscoveryProperties = nacosDiscoveryProperties; this.context = context;
}
@PostConstruct public void init() {
Mapmetadata = nacosDiscoveryProperties.getMetadata();
Environment env = context.getEnvironment();
String endpointBasePath = env.getProperty(MANAGEMENT_ENDPOINT_BASE_PATH); if (!StringUtils.isEmpty(endpointBasePath)) {
metadata.put(MANAGEMENT_ENDPOINT_BASE_PATH, endpointBasePath);
}
Integer managementPort = ManagementServerPortUtils.getPort(context); if (null != managementPort) {
metadata.put(MANAGEMENT_PORT, managementPort.toString());
String contextPath = env
.getProperty("management.server.servlet.context-path");
String address = env.getProperty("management.server.address"); if (!StringUtils.isEmpty(contextPath)) {
metadata.put(MANAGEMENT_CONTEXT_PATH, contextPath);
} if (!StringUtils.isEmpty(address)) {
metadata.put(MANAGEMENT_ADDRESS, address);
}
}
}
@Override public String getServiceId() { return nacosDiscoveryProperties.getService();
}
@Override public String getHost() { return nacosDiscoveryProperties.getIp();
}
@Override public int getPort() { return nacosDiscoveryProperties.getPort();
} public void setPort(int port) { this.nacosDiscoveryProperties.setPort(port);
}
@Override public boolean isSecure() { return nacosDiscoveryProperties.isSecure();
}
@Override public URI getUri() { return DefaultServiceInstance.getUri(this);
}
@Override public Map getMetadata() { return nacosDiscoveryProperties.getMetadata();
} public boolean isRegisterEnabled() { return nacosDiscoveryProperties.isRegisterEnabled();
} public String getCluster() { return nacosDiscoveryProperties.getClusterName();
} public float getRegisterWeight() { return nacosDiscoveryProperties.getWeight();
} public NacosDiscoveryProperties getNacosDiscoveryProperties() { return nacosDiscoveryProperties;
} public NamingService getNacosNamingService() { return nacosDiscoveryProperties.namingServiceInstance();
}
@Override public String toString() { return "NacosRegistration{" + "nacosDiscoveryProperties="
+ nacosDiscoveryProperties + '}';
}
}该类主要是装配了一些management管理类的配置信息
NacosAutoServiceRegistration类做了些什么事情?
public class NacosAutoServiceRegistration extends AbstractAutoServiceRegistration { private static final Logger log = LoggerFactory
.getLogger(NacosAutoServiceRegistration.class); private NacosRegistration registration; public NacosAutoServiceRegistration(ServiceRegistry serviceRegistry,
AutoServiceRegistrationProperties autoServiceRegistrationProperties,
NacosRegistration registration) { super(serviceRegistry, autoServiceRegistrationProperties); this.registration = registration;
}
@Deprecated public void setPort(int port) {
getPort().set(port);
}
@Override protected NacosRegistration getRegistration() { if (this.registration.getPort() < 0 && this.getPort().get() > 0) { this.registration.setPort(this.getPort().get());
}
Assert.isTrue(this.registration.getPort() > 0, "service.port has not been set"); return this.registration;
}
@Override protected NacosRegistration getManagementRegistration() { return null;
}
@Override protected void register() { if (!this.registration.getNacosDiscoveryProperties().isRegisterEnabled()) {
log.debug("Registration disabled."); return;
} if (this.registration.getPort() < 0) { this.registration.setPort(getPort().get());
} super.register();
}
@Override protected void registerManagement() { if (!this.registration.getNacosDiscoveryProperties().isRegisterEnabled()) { return;
} super.registerManagement();
}
@Override protected Object getConfiguration() { return this.registration.getNacosDiscoveryProperties();
}
@Override protected boolean isEnabled() { return this.registration.getNacosDiscoveryProperties().isRegisterEnabled();
}
@Override
@SuppressWarnings("deprecation") protected String getAppName() {
String appName = registration.getNacosDiscoveryProperties().getService(); return StringUtils.isEmpty(appName) ? super.getAppName() : appName;
}
}这个类主要是调用NacosServiceRegistry的register()方法，我们来关注一下他的父类AbstractAutoServiceRegistration的start()，这个才是启动方法。
public void start() { if (!isEnabled()) { if (logger.isDebugEnabled()) {
logger.debug("Discovery Lifecycle disabled. Not starting");
} return;
} // only initialize if nonSecurePort is greater than 0 and it isn't already running // because of containerPortInitializer below
if (!this.running.get()) {
register(); if (shouldRegisterManagement()) {
registerManagement();
} this.context.publishEvent( new InstanceRegisteredEvent<>(this, getConfiguration())); this.running.compareAndSet(false, true);
}
}
......省略 protected void register() { this.serviceRegistry.register(getRegistration());
}在start()方法里调用了NacosAutoServiceRegistration.register方法，NacosAutoServiceRegistration.register的方法里又调用了父类AbstractAutoServiceRegistration.register方法，在父类AbstractAutoServiceRegistration.register方法里调用了NacosServiceRegistry.register方法，实现了服务注册。
服务注册大概经历了这么多，有兴趣的可以自己出看看源码，相信你肯定比我理解的更好。下面是个人学习 Nacos 服务注册的源码阅读流程图,其他的实现也差不多，主要是要理解 Spring-Cloud-Commons 的规范。
通过上面我们知道了 Spring-Cloud-Commons 模块实现了一套规范，我们直接去看在服务发现的规范是什么？我们能够找到DiscoveryClient接口。
public interface DiscoveryClient { /**
* A human readable description of the implementation, used in HealthIndicator
* @return the description */
String description(); /**
* Get all ServiceInstances associated with a particular serviceId
* @param serviceId the serviceId to query
* @return a List of ServiceInstance */
List getInstances(String serviceId); /**
* @return all known service ids */
List getServices();
}里面就提供了三个接口，我们接下来看看nacos是如何实现的?
public class NacosDiscoveryClient implements DiscoveryClient { private static final Logger log = LoggerFactory.getLogger(NacosDiscoveryClient.class); public static final String DESCRIPTION = "Spring Cloud Nacos Discovery Client"; private NacosDiscoveryProperties discoveryProperties; public NacosDiscoveryClient(NacosDiscoveryProperties discoveryProperties) { this.discoveryProperties = discoveryProperties;
}
@Override public String description() { return DESCRIPTION;
}
@Override public List getInstances(String serviceId) { try {
Listinstances = discoveryProperties.namingServiceInstance()
.selectInstances(serviceId, true); return hostToServiceInstanceList(instances, serviceId);
} catch (Exception e) { throw new RuntimeException( "Can not get hosts from nacos server. serviceId: " + serviceId, e);
}
} private static ServiceInstance hostToServiceInstance(Instance instance,
String serviceId) {
NacosServiceInstance nacosServiceInstance = new NacosServiceInstance();
nacosServiceInstance.setHost(instance.getIp());
nacosServiceInstance.setPort(instance.getPort());
nacosServiceInstance.setServiceId(serviceId);
Mapmetadata = new HashMap<>();
metadata.put("nacos.instanceId", instance.getInstanceId());
metadata.put("nacos.weight", instance.getWeight() + "");
metadata.put("nacos.healthy", instance.isHealthy() + "");
metadata.put("nacos.cluster", instance.getClusterName() + "");
metadata.putAll(instance.getMetadata());
nacosServiceInstance.setMetadata(metadata); if (metadata.containsKey("secure")) { boolean secure = Boolean.parseBoolean(metadata.get("secure"));
nacosServiceInstance.setSecure(secure);
} return nacosServiceInstance;
} private static List hostToServiceInstanceList(
List instances, String serviceId) {
Listresult = new ArrayList<>(instances.size()); for (Instance instance : instances) {
result.add(hostToServiceInstance(instance, serviceId));
} return result;
}
@Override public List getServices() { try {
ListViewservices = discoveryProperties.namingServiceInstance()
.getServicesOfServer(1, Integer.MAX_VALUE); return services.getData();
} catch (Exception e) {
log.error("get service name from nacos server fail,", e); return Collections.emptyList();
}
}
}这里面的逻辑非常简单，就不过多赘述了，有兴趣的小伙伴，可以自行去研究喔。
整个服务注册与发现差不多就是这样子，因为涉及的内容非常多，在很多地方小弟我确实看不懂，在上述中肯定有非常多的错误还请大神们多多指教。
