SpringCloud-Hystrix-初始化

@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Inherited
@SpringBootApplication
@EnableDiscoveryClient
// 此註解是CircuitBreaker初始化的入口
@EnableCircuitBreaker
public @interface SpringCloudApplication {

}

@EnableCircuitBreaker初始化機制

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

}

@Order(Ordered.LOWEST_PRECEDENCE - 100)
public class EnableCircuitBreakerImportSelector
		extends SpringFactoryImportSelector<EnableCircuitBreaker> {

	@Override
	protected boolean isEnabled() {
		return getEnvironment().getProperty("spring.cloud.circuit.breaker.enabled",
				Boolean.class, Boolean.TRUE);
	}

}

spring-cloud-netflix-hystrix-2.2.1.RELEASE.jar!/META-INF/spring.factories

org.springframework.cloud.client.circuitbreaker.EnableCircuitBreaker=\
org.springframework.cloud.netflix.hystrix.HystrixCircuitBreakerConfiguration

	@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
		//基於SpringFactoriesLoader解析上述配置
		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
			this.log.warn("More than one implementation " + "of @" + getSimpleName()
					+ " (now relying on @Conditionals to pick one): " + factories);
		}

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

HystrixCircuitBreakerConfiguration

@Configuration(proxyBeanMethods = false)
public class HystrixCircuitBreakerConfiguration {

	@Bean
	public HystrixCommandAspect hystrixCommandAspect() {
		return new HystrixCommandAspect();
	}

	@Bean
	public HystrixShutdownHook hystrixShutdownHook() {
		return new HystrixShutdownHook();
	}

	@Bean
	public HasFeatures hystrixFeature() {
		return HasFeatures
				.namedFeatures(new NamedFeature("Hystrix", HystrixCommandAspect.class));
	}

	/**
	 * {@link DisposableBean} that makes sure that Hystrix internal state is cleared when
	 * {@link ApplicationContext} shuts down.
	 */
	private class HystrixShutdownHook implements DisposableBean {

		@Override
		public void destroy() throws Exception {
			// Just call Hystrix to reset thread pool etc.
			Hystrix.reset();
		}

	}

}