@EnableDiscoveryClient 注解如何实现服务注册与发现
@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<EnableDiscoveryClient> {
@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) {
List<String> importsList = 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;
LinkedHashMap<String, Object> map = 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<Registration> {
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> 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() {
Map<String, String> metadata = 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<String, String> 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<Registration> {
private static final Logger log = LoggerFactory
.getLogger(NacosAutoServiceRegistration.class);
private NacosRegistration registration;
public NacosAutoServiceRegistration(ServiceRegistry<Registration> 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。
@EnableDiscoveryClient 是如何实现服务发现?
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<ServiceInstance> getInstances(String serviceId);
/**
* @return all known service ids
*/
List<String> 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<ServiceInstance> getInstances(String serviceId) {
try {
List<Instance> instances = 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);
Map<String, String> metadata = 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<ServiceInstance> hostToServiceInstanceList(
List<Instance> instances, String serviceId) {
List<ServiceInstance> result = new ArrayList<>(instances.size());
for (Instance instance : instances) {
result.add(hostToServiceInstance(instance, serviceId));
}
return result;
}
@Override
public List<String> getServices() {
try {
ListView<String> services = 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。
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