五、eureka客戶端自動配置

所有文章

https://www.cnblogs.com/lay2017/p/11908715.html

 

正文

前面的幾篇文章中，我們從eureka Server端的角度看了看eureka的幾個核心要點。本文開始，將從eureka client端的角度了解它。同樣的，基於spring cloud的eureka client將先看看它的自動配置。

 

@EnableDiscoveryClient開關自動注冊服務

我們先從注解開始，注解意味着開啟了eureka client

@SpringBootApplication
@EnableDiscoveryClient public class ConsumerApplication {

    public static void main(String[] args) {
        SpringApplication.run(ConsumerApplication.class, args);
    }

}

打開注解看看，你會發現這里的autoRegister默認值是true。也就是說，如果你配置為false，那么就不會自動注冊

@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Inherited
@Import(EnableDiscoveryClientImportSelector.class)
public @interface EnableDiscoveryClient {

    /**
     * If true, the ServiceRegistry will automatically register the local server.
     * @return - {@code true} if you want to automatically register.
     */
    boolean autoRegister() default true;

}

稍微不同於Server端的是，client端不是直接引入一個Configuration而是通過一個ImportSelector來導入類。跟進EnableDiscoveryClientImportSelector類

@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 {
            // ...
        }

        return imports;
    }

}

selectImports方法主要就是導入了一個類AutoServiceRegistrationCofiguration，我們看看導入的這個類干了啥

@Configuration
@EnableConfigurationProperties(AutoServiceRegistrationProperties.class) @ConditionalOnProperty(value = "spring.cloud.service-registry.auto-registration.enabled", matchIfMissing = true) public class AutoServiceRegistrationConfiguration {

}

好吧，只是簡單的加載了一些屬性，如果沒有配置該屬性那么將會是默認值（eureka啟動的大部分默認值都是true，所以你會發現，即使沒有添加@EnableDiscoveryClient注解，使用默認值也是可以的）。

 

EurekaClientAutoConfiguration自動配置客戶端

EurekaClientAutoConfiguration這個自動配置類就比較可怕了，代碼顯得比服務端多了不少。

@Configuration
@EnableConfigurationProperties
@ConditionalOnClass(EurekaClientConfig.class)
@Import(DiscoveryClientOptionalArgsConfiguration.class)
@ConditionalOnProperty(value = "eureka.client.enabled", matchIfMissing = true)
@ConditionalOnDiscoveryEnabled
@AutoConfigureBefore({ NoopDiscoveryClientAutoConfiguration.class,
        CommonsClientAutoConfiguration.class, ServiceRegistryAutoConfiguration.class })
@AutoConfigureAfter(name = {
        "org.springframework.cloud.autoconfigure.RefreshAutoConfiguration",
        "org.springframework.cloud.netflix.eureka.EurekaDiscoveryClientConfiguration",
        "org.springframework.cloud.client.serviceregistry.AutoServiceRegistrationAutoConfiguration" })
public class EurekaClientAutoConfiguration {
    // ...
}

注解比較多，但是沒那么復雜。就是加載一些附加的配置，以及判斷一下是否開始自動配置。下面，我們再看看內部添加了哪些東西（只關注幾個核心的）

 

配置當前實例信息

配置實例信息包含很多，不過核心的無非就是名稱、唯一標識、IP地址、端口等等

@Bean
@ConditionalOnMissingBean(value = EurekaInstanceConfig.class,
        search = SearchStrategy.CURRENT)
public EurekaInstanceConfigBean eurekaInstanceConfigBean(InetUtils inetUtils,
        ManagementMetadataProvider managementMetadataProvider) {
    // ...
    EurekaInstanceConfigBean instance = new EurekaInstanceConfigBean(inetUtils);

    instance.setNonSecurePort(serverPort);
    instance.setInstanceId(getDefaultInstanceId(env));
    instance.setPreferIpAddress(preferIpAddress);
    instance.setSecurePortEnabled(isSecurePortEnabled);
    if (StringUtils.hasText(ipAddress)) {
        instance.setIpAddress(ipAddress);
    }

    // ...

    setupJmxPort(instance, jmxPort);
    return instance;
}

 

負責注冊的Bean

@Bean
public EurekaServiceRegistry eurekaServiceRegistry() {
    return new EurekaServiceRegistry();
}

 

自動注冊調用的Bean

@Bean
@ConditionalOnBean(AutoServiceRegistrationProperties.class)
@ConditionalOnProperty(
        value = "spring.cloud.service-registry.auto-registration.enabled",
        matchIfMissing = true)
public EurekaAutoServiceRegistration eurekaAutoServiceRegistration(
        ApplicationContext context, EurekaServiceRegistry registry,
        EurekaRegistration registration) {
    return new EurekaAutoServiceRegistration(context, registry, registration);
}

 

Eureka待注冊的對象

這個對象會包含上面的eurekaInstanceIConfigBean

@Bean
@ConditionalOnBean(AutoServiceRegistrationProperties.class)
@ConditionalOnProperty(
        value = "spring.cloud.service-registry.auto-registration.enabled",
        matchIfMissing = true)
public EurekaRegistration eurekaRegistration(EurekaClient eurekaClient,
        CloudEurekaInstanceConfig instanceConfig,
        ApplicationInfoManager applicationInfoManager, @Autowired(
                required = false) ObjectProvider<HealthCheckHandler> healthCheckHandler) {
    return EurekaRegistration.builder(instanceConfig).with(applicationInfoManager)
            .with(eurekaClient).with(healthCheckHandler).build();
}

 

總結

eureka客戶端的自動配置，其實就是做了一些注冊等操作之前的准備。准備實例信息，配置eureka框架的東西。代碼很多，但是邏輯並不復雜。下一篇文章，我們將看看如何自動注冊。