Spring Cloud 学习笔记(八) 之 源码分析 客户消费端 注册到Eureka注册中心的流程

启用客户端的入口
@EnableDiscoveryClient
@SpringBootApplication
public class StudyApplication {
    @Bean
    @LoadBalanced
    RestTemplate restTemplate(){
        return new RestTemplate();
    }
    public static void main(String[] args) {
        SpringApplication.run(StudyApplication.class, args);
    }

}

关键是@EnableDiscoveryClient，我们来看下@EnableDiscoveryClient

/**
 * 用于启用DiscoveryClient的注释.
 * @author Spencer Gibb
 */
@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Inherited
@Import(EnableDiscoveryClientImportSelector.class)
public @interface EnableDiscoveryClient {

	/**
	 * 如果为True，会自动的注册到本地服务上去.
	 */
	boolean autoRegister() default true;
}

我们点进去 EnableDiscoveryClientImportSelector 这个类，看一下源码

package org.springframework.cloud.client.discovery;

public class EnableDiscoveryClientImportSelector extends SpringFactoryImportSelector<EnableDiscoveryClient> 


@Override
	public String[] selectImports(AnnotationMetadata metadata) {
		String[] imports = super.selectImports(metadata);//可以看到，他在这里调用了一下父类的selectImports方法

		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;
	}

 那么我们进到父类

org.springframework.cloud.commons.util

public abstract class SpringFactoryImportSelector<T>
		implements DeferredImportSelector, BeanClassLoaderAware, EnvironmentAware

@Override
	public String[] selectImports(AnnotationMetadata metadata) {
		if (!isEnabled()) {
			return new String[0];
		}
		AnnotationAttributes attributes = AnnotationAttributes.fromMap(
				metadata.getAnnotationAttributes(this.annotationClass.getName(), true));

		Assert.notNull(attributes, "No " + getSimpleName() + " attributes found. Is "
				+ metadata.getClassName() + " annotated with @" + getSimpleName() + "?");

		// Find all possible auto configuration classes, filtering duplicates
        //这是关键代码，他调用了一下loadFactoryNames(),这个方法会自动加载配置。
		List<String> factories = new ArrayList<>(new LinkedHashSet<>(SpringFactoriesLoader
				.loadFactoryNames(this.annotationClass, this.beanClassLoader)));

		if (factories.isEmpty() && !hasDefaultFactory()) {
			throw new IllegalStateException("Annotation @" + getSimpleName()
					+ " found, but there are no implementations. Did you forget to include a starter?");
		}

		if (factories.size() > 1) {
			// there should only ever be one DiscoveryClient, but there might be more than
			// one factory
			log.warn("More than one implementation " + "of @" + getSimpleName()
					+ " (now relying on @Conditionals to pick one): " + factories);
		}

		return factories.toArray(new String[factories.size()]);
	}

 我们看一下loadFactoryNames怎么实现的

/**
	 * Load the fully qualified class names of factory implementations of the
	 * given type from {@value #FACTORIES_RESOURCE_LOCATION}, using the given
	 * class loader.
	 * @param factoryClass the interface or abstract class representing the factory
	 * @param classLoader the ClassLoader to use for loading resources; can be
	 * {@code null} to use the default
	 * @see #loadFactories
	 * @throws IllegalArgumentException if an error occurs while loading factory names
	 */
	public static List<String> loadFactoryNames(Class<?> factoryClass, @Nullable ClassLoader classLoader) {
		String factoryClassName = factoryClass.getName();
		return loadSpringFactories(classLoader).getOrDefault(factoryClassName, Collections.emptyList());
	}

他调用了一下loadSpringFactories(classLoader)

我们看一下这个方法怎么实现的

private static Map<String, List<String>> loadSpringFactories(@Nullable ClassLoader classLoader) {
        //首先从cache中找，看有没有这个配置，有的话直接返回
        MultiValueMap<String, String> result = cache.get(classLoader);
		if (result != null) {
			return result;
		}

		try {
			Enumeration<URL> urls = (classLoader != null ?
					classLoader.getResources(FACTORIES_RESOURCE_LOCATION) :
					ClassLoader.getSystemResources(FACTORIES_RESOURCE_LOCATION));
			result = new LinkedMultiValueMap<>();
			while (urls.hasMoreElements()) {
				URL url = urls.nextElement();
				UrlResource resource = new UrlResource(url);
				Properties properties = PropertiesLoaderUtils.loadProperties(resource);
				for (Map.Entry<?, ?> entry : properties.entrySet()) {
					List<String> factoryClassNames = Arrays.asList(
							StringUtils.commaDelimitedListToStringArray((String) entry.getValue()));
					result.addAll((String) entry.getKey(), factoryClassNames);
				}
			}
			cache.put(classLoader, result);
			return result;
		}
		catch (IOException ex) {
			throw new IllegalArgumentException("Unable to load factories from location [" +
					FACTORIES_RESOURCE_LOCATION + "]", ex);
		}
	}

注册入口 
org.springframework.cloud.netflix.eureka.EurekaClientAutoConfiguration.java
@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);
	}

实际执行注册的任务类及方法
com.netflix.discovery.InstanceInfoReplicator.java

public void run() {
        try {
            discoveryClient.refreshInstanceInfo();

            Long dirtyTimestamp = instanceInfo.isDirtyWithTime();
            if (dirtyTimestamp != null) {
                discoveryClient.register();
                instanceInfo.unsetIsDirty(dirtyTimestamp);
            }
        } catch (Throwable t) {
            logger.warn("There was a problem with the instance info replicator", t);
        } finally {
            Future next = scheduler.schedule(this, replicationIntervalSeconds, TimeUnit.SECONDS);
            scheduledPeriodicRef.set(next);
        }
}

最终执行的注册类及方法
com.netflix.discovery.DiscoveryClient.java

/**
     * 用适当的REST调用来注册Eureka服务
     */
    boolean register() throws Throwable {
        logger.info(PREFIX + "{}: registering service...", appPathIdentifier);
        EurekaHttpResponse<Void> httpResponse;
        try {
            httpResponse = eurekaTransport.registrationClient.register(instanceInfo);
        } catch (Exception e) {
            logger.warn(PREFIX + "{} - registration failed {}", appPathIdentifier, e.getMessage(), e);
            throw e;
        }
        if (logger.isInfoEnabled()) {
            logger.info(PREFIX + "{} - registration status: {}", appPathIdentifier, httpResponse.getStatusCode());
        }
        return httpResponse.getStatusCode() == 204;
}

未完待续。。。