spring cloud 源碼 Hystrix

Hystrix源碼

入口@EnableCircuitBreaker注解

@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Inherited
//導入斷路器導入選擇器
@Import(EnableCircuitBreakerImportSelector.class)
public @interface EnableCircuitBreaker {

}
           

進入org.springframework.cloud.client.circuitbreaker.EnableCircuitBreakerImportSelector

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

	@Override
	protected boolean isEnabled() {
		//從環境變量中取值，預設true（擷取開關）
		return getEnvironment().getProperty(
				"spring.cloud.circuit.breaker.enabled", Boolean.class, Boolean.TRUE);
	}

}
           

進入父類org.springframework.cloud.commons.util.SpringFactoryImportSelector

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

	private ClassLoader beanClassLoader;
	
	private Class<T> annotationClass;

	private Environment environment;

	private final Log log = LogFactory.getLog(SpringFactoryImportSelector.class);

	//擷取子類傳入的泛型（上面的EnableCircuitBreaker）
	@SuppressWarnings("unchecked")
	protected SpringFactoryImportSelector() {
		this.annotationClass = (Class<T>) GenericTypeResolver
				.resolveTypeArgument(this.getClass(), SpringFactoryImportSelector.class);
	}
	
	//spring會把傳回的String[]數組的類（數組裝的類的全限定名）注入到spring容器中去
	@Override
	public String[] selectImports(AnnotationMetadata metadata) {
		if (!isEnabled()) {
			return new String[0];
		}
		//獲得傳入的泛型的全限定名
		AnnotationAttributes attributes = AnnotationAttributes.fromMap(
				metadata.getAnnotationAttributes(this.annotationClass.getName(), true));

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

		//根據全限定名去spring.factories中找它對應的value，如下圖
		// Find all possible auto configuration classes, filtering duplicates
		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()]);
	}
	
}
           

spring cloud是基于springboot的架構，它會加載每個包裡面的spring.factories中的類

是以說這裡會掃描并注入HystrixCircuitBreakerConfiguration

進入org.springframework.cloud.netflix.hystrix.HystrixCircuitBreakerConfiguration

@Configuration
public class HystrixCircuitBreakerConfiguration {

	//注入了HystrixCommandAspect，Hystrix靠這個切面機制做事
	@Bean
	public HystrixCommandAspect hystrixCommandAspect() {
		return new HystrixCommandAspect();
	}
	//...
}
           

進入com.netflix.hystrix.contrib.javanica.aop.aspectj.HystrixCommandAspect

@Aspect
public class HystrixCommandAspect {

    private static final Map<HystrixPointcutType, MetaHolderFactory> META_HOLDER_FACTORY_MAP;

    static {
        META_HOLDER_FACTORY_MAP = ImmutableMap.<HystrixPointcutType, MetaHolderFactory>builder()
                .put(HystrixPointcutType.COMMAND, new CommandMetaHolderFactory())
                .put(HystrixPointcutType.COLLAPSER, new CollapserMetaHolderFactory())
                .build();
    }
	//切入點，加了HystrixCommand注解的方法
    @Pointcut("@annotation(com.netflix.hystrix.contrib.javanica.annotation.HystrixCommand)")
    public void hystrixCommandAnnotationPointcut() {
    }
	//批量處理的注解
    @Pointcut("@annotation(com.netflix.hystrix.contrib.javanica.annotation.HystrixCollapser)")
    public void hystrixCollapserAnnotationPointcut() {
    }
	//環繞通知，Hystrix主要處理邏輯
    @Around("hystrixCommandAnnotationPointcut() || hystrixCollapserAnnotationPointcut()")
    public Object methodsAnnotatedWithHystrixCommand(final ProceedingJoinPoint joinPoint) throws Throwable {
    	//擷取原始目标方法
        Method method = getMethodFromTarget(joinPoint);
        Validate.notNull(method, "failed to get method from joinPoint: %s", joinPoint);
        //不能同時有HystrixCommand和HystrixCollapser這兩個注解
        if (method.isAnnotationPresent(HystrixCommand.class) && method.isAnnotationPresent(HystrixCollapser.class)) {
            throw new IllegalStateException("method cannot be annotated with HystrixCommand and HystrixCollapser " +
                    "annotations at the same time");
        }
        MetaHolderFactory metaHolderFactory = META_HOLDER_FACTORY_MAP.get(HystrixPointcutType.of(method));
        //封裝中繼資料
        MetaHolder metaHolder = metaHolderFactory.create(joinPoint);
        //建立可執行器對象（GenericCommand）
        HystrixInvokable invokable = HystrixCommandFactory.getInstance().create(metaHolder);
        ExecutionType executionType = metaHolder.isCollapserAnnotationPresent() ?
                metaHolder.getCollapserExecutionType() : metaHolder.getExecutionType();

        Object result;
        try {
            if (!metaHolder.isObservable()) {
            	//根據executionType同步，異步，還是觀察者執行不同的方法
            	//通常執行同步方法最後在com.netflix.hystrix.HystrixCommand#queue方法傳回future對象
                result = CommandExecutor.execute(invokable, executionType, metaHolder);
            } else {
                result = executeObservable(invokable, executionType, metaHolder);
            }
        } catch (HystrixBadRequestException e) {
            throw e.getCause();
        } catch (HystrixRuntimeException e) {
            throw hystrixRuntimeExceptionToThrowable(metaHolder, e);
        }
        return result;
    }
    //...
}
           

進入com.netflix.hystrix.contrib.javanica.command.GenericCommand

public class GenericCommand extends AbstractHystrixCommand<Object> {

    private static final Logger LOGGER = LoggerFactory.getLogger(GenericCommand.class);

    public GenericCommand(HystrixCommandBuilder builder) {
        super(builder);
    }
    //封裝了對原始目标方法的調用
    @Override
    protected Object run() throws Exception {
        LOGGER.debug("execute command: {}", getCommandKey().name());
        return process(new Action() {
            @Override
            Object execute() {
                return getCommandAction().execute(getExecutionType());
            }
        });
    }
    //封裝了對回退方法的調用
    //在GenericCommand的上層類構造函數中會完成資源的初始化，比如線程池
    @Override
    protected Object getFallback() {
        final CommandAction commandAction = getFallbackAction();
        if (commandAction != null) {
            try {
                return process(new Action() {
                    @Override
                    Object execute() {
                        MetaHolder metaHolder = commandAction.getMetaHolder();
                        Object[] args = createArgsForFallback(metaHolder, getExecutionException());
                        return commandAction.executeWithArgs(metaHolder.getFallbackExecutionType(), args);
                    }
                });
            } catch (Throwable e) {
                LOGGER.error(FallbackErrorMessageBuilder.create()
                        .append(commandAction, e).build());
                throw new FallbackInvocationException(unwrapCause(e));
            }
        } else {
            return super.getFallback();
        }
    }

}