@EnableDiscoveryClient与Nacos的服务注册与拉取

​  前一阵看到有篇博客说cloud从Edgware版本开始,可以不加@EnableDiscoveryClient注解,只要配置好注册中心的相关配置即可自动开启服务注册功能,比较好奇其中的原理,研究了一番特意记录下来

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环境:
 SpringBoot: 2.3.5
 SpringCloud: Hoxton.SR8
 SpringCloudAlibaba: 2.2.3

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配置信息:

@SpringBootApplication
//autoRegiste属性值默认为true可以不配置此属性
@EnableDiscoveryClient(autoRegister = true)
public class NacosApplication {
    
    public static void main(String[] args) {
        SpringApplication.run(NacosApplication.class, args);
    }
    
}

spring:
  application:
    name: nacosTest
  cloud:
    nacos:
      discovery:
        enabled: true(默认为true,可以不配置此属性)
        server-addr: 192.168.1.10:8848
        username: nacos
        password: nacos

配置的作用:

nacos.discovery.enabled: 开启服务的注册与发现功能;
注册成功后可以在nacos的web端界面看到服务的相关信息

同时,具备拉取服务信息的功能, discoveryClient.getInstances()方法可以返回服务的详细配置信息

@Resource
private DiscoveryClient discoveryClient;

@GetMapping("/client")
public List<ServiceInstance> client() {
    return discoveryClient.getInstances("服务名称");
}

@EnableDiscoveryClient(autoRegister = true); 开启服务自动注册功能,项目启动后能在nacos的web端界面看到服务的相关信息,并且具备拉取服务信息的功能(前提是nacos.discovery.enabled不为false)
@EnableDiscoveryClient(autoRegister = false); 关闭服务自动注册功能, 项目启动后nacos的web端界面没有此项目的信息,但是依然具备拉取服务信息的功能(前提是nacos.discovery.enabled不为false)

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实现逻辑:

@EnableDiscoveryClient

打开@EnableDiscoveryClient注解(代码里只保留了重点)

@Import(EnableDiscoveryClientImportSelector.class)
public @interface EnableDiscoveryClient {
	boolean autoRegister() default true;
}

进入EnableDiscoveryClientImportSelector类

@Override
public String[] selectImports(AnnotationMetadata metadata) {
    String[] imports = super.selectImports(metadata);

    AnnotationAttributes attributes = AnnotationAttributes.fromMap(
        metadata.getAnnotationAttributes(getAnnotationClass().getName(), true));
	//获取@EnableDiscoveryClient的autoRegister属性
    boolean autoRegister = attributes.getBoolean("autoRegister");
	//开启自动注册的话,将AutoServiceRegistrationConfiguration类的全限定名返回,会被spring加载到bean容器
    if (autoRegister) {
        List<String> importsList = new ArrayList<>(Arrays.asList(imports));
        importsList.add(
            "org.springframework.cloud.client.serviceregistry.AutoServiceRegistrationConfiguration");
        imports = importsList.toArray(new String[0]);
    }
    //关闭自动注册的话,将***.auto-registration.enabled设置为false,放入环境属性中(其他地方会用到)
    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;
}

既然开启自动注册服务会返回一个叫AutoServiceRegistrationConfiguration的类,那就打开看一下:
此类是实现自动注册的入口,具体的逻辑在由注册中心实现(如Nacos\Eureka…)

//当**.registration.enabled属性为true时,此配置类会被加载
//spring-cloud-commons.jar包内的spring-configuration-metadata.json定义了此属性默认为true
//即: 不配置@EnableDiscoveryClient或者配置@EnableDiscoveryClient设置autoRegister为true时
//AutoServiceRegistrationConfiguration会被加载,当@EnableDiscoveryClient设置autoRegister
//属性为false时,此配置类不会被加载
@Configuration(proxyBeanMethods = false)
@EnableConfigurationProperties(AutoServiceRegistrationProperties.class)
@ConditionalOnProperty(value = "spring.cloud.service-registry.auto-registration.enabled",
		matchIfMissing = true)
public class AutoServiceRegistrationConfiguration {

}

到现在似乎还没发现太多有用的信息,那继续看Nacos的源码

Nacos:

找到nacos的spring.factories文件,这是配置自动配置类的地方,文件路径:
spring-cloud-starter-alibaba-nacos-discovery.jar/META-INF/spring.factories
文件信息:

org.springframework.boot.autoconfigure.EnableAutoConfiguration=\
  com.alibaba.cloud.nacos.discovery.NacosDiscoveryAutoConfiguration,\
  com.alibaba.cloud.nacos.ribbon.RibbonNacosAutoConfiguration,\
  com.alibaba.cloud.nacos.endpoint.NacosDiscoveryEndpointAutoConfiguration,\
  com.alibaba.cloud.nacos.registry.NacosServiceRegistryAutoConfiguration,\
  com.alibaba.cloud.nacos.discovery.NacosDiscoveryClientConfiguration,\
  com.alibaba.cloud.nacos.discovery.reactive.NacosReactiveDiscoveryClientConfiguration,\
  com.alibaba.cloud.nacos.discovery.configclient.NacosConfigServerAutoConfiguration,\
  com.alibaba.cloud.nacos.NacosServiceAutoConfiguration
org.springframework.cloud.bootstrap.BootstrapConfiguration=\
  com.alibaba.cloud.nacos.discovery.configclient.NacosDiscoveryClientConfigServiceBootstrapConfiguration

既然有BootstrapConfiguration,那就先看最后一行的NacosDiscoveryClientConfigServiceBootstrapConfiguration

//删减了部分代码,便于阅读
@ImportAutoConfiguration({NacosDiscoveryClientConfiguration.class})
public class NacosDiscoveryClientConfigServiceBootstrapConfiguration {

}

继续进入NacosDiscoveryClientConfiguration

//删减了部分代码,便于阅读
//spring.cloud.nacos.discovery.enabled=true时,此配置类才会加载
@ConditionalOnNacosDiscoveryEnabled
@AutoConfigureAfter(NacosDiscoveryAutoConfiguration.class)
public class NacosDiscoveryClientConfiguration {
	@Bean
	public DiscoveryClient nacosDiscoveryClient(NacosServiceDiscovery nacosServiceDiscovery) {
		return new NacosDiscoveryClient(nacosServiceDiscovery);
	}
}

此配置类注入了一个bean: NacosDiscoveryClient, 这个类实现了DiscoveryClient接口, 我们上边的测试用例
discoveryClient.getInstances(“服务名称”), 调用的getInstances方法,实际上就是调用了Nacos官方提供的NacosDiscoveryClient重写的getInstances方法,
至此,Nacos的的服务拉取搞明白了: 无论是否配置@EnableDiscoveryClient,只要spring.cloud.nacos.discovery.enabled不设置为false,服务就具有拉取注册中心信息的功能
​

那服务注册功能呢? 返回spring.factories打开第五行的类: NacosServiceRegistryAutoConfiguration
服务自动注册逻辑:

@Configuration(proxyBeanMethods = false)
@EnableConfigurationProperties
//确保spring.cloud.nacos.discovery.enabled为true(开启nacos的服务注册与发现功能)
@ConditionalOnNacosDiscoveryEnabled
//默认为true,使用@EnableDiscoveryClient注解配置autoRegister为false时,次属性值为false
//即: 此类不被加载,即: 服务不具备自动注册功能
@ConditionalOnProperty(value = "spring.cloud.service-registry.auto-registration.enabled",
		matchIfMissing = true)
@AutoConfigureAfter({ AutoServiceRegistrationConfiguration.class,
		AutoServiceRegistrationAutoConfiguration.class,
		NacosDiscoveryAutoConfiguration.class })
public class NacosServiceRegistryAutoConfiguration {

	@Bean
	public NacosServiceRegistry nacosServiceRegistry(
			NacosDiscoveryProperties nacosDiscoveryProperties) {
		return new NacosServiceRegistry(nacosDiscoveryProperties);
	}

	@Bean
	@ConditionalOnBean(AutoServiceRegistrationProperties.class)
	public NacosRegistration nacosRegistration(
			ObjectProvider<List<NacosRegistrationCustomizer>> registrationCustomizers,
			NacosDiscoveryProperties nacosDiscoveryProperties,
			ApplicationContext context) {
		return new NacosRegistration(registrationCustomizers.getIfAvailable(),
				nacosDiscoveryProperties, context);
	}

	@Bean
	@ConditionalOnBean(AutoServiceRegistrationProperties.class)
	public NacosAutoServiceRegistration nacosAutoServiceRegistration(
			NacosServiceRegistry registry,
			AutoServiceRegistrationProperties autoServiceRegistrationProperties,
			NacosRegistration registration) {
		return new NacosAutoServiceRegistration(registry,
				autoServiceRegistrationProperties, registration);
	}

}

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实验结论:

配置	效果
不配置@EnableDiscoveryClient,不配置nacos.discovery.enable	具有服务自动注册功能,具有拉取服务信息功能
不配置@EnableDiscoveryClient,配置nacos.discovery.enable=false	服务注册与拉取服务信息功能都不具备
配置@EnableDiscoveryClient(autoRegister=false),配置nacos.discovery.enable=true	不具有服务注册功能,具有拉取服务信息功能
配置@EnableDiscoveryClient(autoRegister=false),配置nacos.discovery.enable=false	服务注册与拉取服务信息功能都不具备

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最后:

才疏学浅,难免有疏漏或者错误的地方,希望各位不吝指教