Eureka是我接触分布式软件和服务的第一个框架，所以其原理和实现我的好好研究一下，Eureka可以参看这篇博文：http://springcloud.cn/view/29

　　初学者会在教程中看到使用@EnableEurekaClient,下面看看这个注解干了啥事。

@Order(2147483547)
public class EnableDiscoveryClientImportSelector extends SpringFactoryImportSelector<EnableDiscoveryClient> {
    public EnableDiscoveryClientImportSelector() {
    }

    public String[] selectImports(AnnotationMetadata metadata) {
        String[] imports = super.selectImports(metadata);
        AnnotationAttributes attributes = AnnotationAttributes.fromMap(metadata.getAnnotationAttributes(this.getAnnotationClass().getName(), true));
        // 这个代码确实很难看，它是自动配置了哪些类呢？
　　　　　boolean autoRegister = attributes.getBoolean("autoRegister");
        if (autoRegister) {
            List<String> importsList = new ArrayList(Arrays.asList(imports));
            importsList.add("org.springframework.cloud.client.serviceregistry.AutoServiceRegistrationConfiguration");
            imports = (String[])importsList.toArray(new String[0]);
        } else {
            Environment env = this.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;
    }
    protected boolean isEnabled() {
        return (Boolean)this.getEnvironment().getProperty("spring.cloud.discovery.enabled", Boolean.class, Boolean.TRUE);
    }
    protected boolean hasDefaultFactory() {
        return true;
    }
}