SpringCloud实战之路 | 源码篇（三）Hystrix核心源码剖析

SpringCloud实战之路 | 源码篇（三）Hystrix核心源码剖析

文章内容输出来源：拉勾教育Java高薪训练营；

分析入口@EnableCircuitBreaker 开启熔断器功能
@EnableCircuitBreaker注解开启熔断器

@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Inherited
//import了一个selector（spring的扩展点）
@Import(EnableCircuitBreakerImportSelector.class)
public @interface EnableCircuitBreaker {

}

查看EnableCircuitBreakerImportSelector类

@Order(Ordered.LOWEST_PRECEDENCE - 100)
//在父类SpringFactoryImportSelector中传入了一个@EnableCircuitBreaker注解类
public class EnableCircuitBreakerImportSelector extends
		SpringFactoryImportSelector<EnableCircuitBreaker> {
	
	//获取熔断器是否启用配置
	@Override
	protected boolean isEnabled() {
		return getEnvironment().getProperty(
				"spring.cloud.circuit.breaker.enabled", Boolean.class, Boolean.TRUE);
	}

}

查看SpringFactoryImportSelector类

	protected SpringFactoryImportSelector() {
		//获取到子类传递到父类的泛型，这里就是@EnableCircuitBreaker注解类
		this.annotationClass = (Class<T>) GenericTypeResolver
				.resolveTypeArgument(this.getClass(), SpringFactoryImportSelector.class);
	}
	
	/**
	 *在selectImports该方法中根据传递进来的泛型全限定类名（@EnableCircuitBreaker就是该注解的全限定类名），
	 *作为key去spring.factories中，查找对应配置类进行注入
	 */
	@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
		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.factories
找到对应的配置类HystrixCircuitBreakerConfiguration

org.springframework.boot.autoconfigure.EnableAutoConfiguration=\
org.springframework.cloud.netflix.hystrix.HystrixAutoConfiguration,\
org.springframework.cloud.netflix.hystrix.security.HystrixSecurityAutoConfiguration

#####就是这个，找到对应的配置类HystrixCircuitBreakerConfiguration
org.springframework.cloud.client.circuitbreaker.EnableCircuitBreaker=\
org.springframework.cloud.netflix.hystrix.HystrixCircuitBreakerConfiguration

查看HystrixCircuitBreakerConfiguration配置类

@Configuration
public class HystrixCircuitBreakerConfiguration {
	
	/**
	 * 这里注入了一个切面HystrixCommandAspect，Hystrix就是利用切面机制工作的 
	 */
	@Bean
	public HystrixCommandAspect hystrixCommandAspect() {
		return new HystrixCommandAspect();
	}

}

查看切面类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();
    }

	//定义切点  加了@HystrixCommand注解的方法
	@Pointcut("@annotation(com.netflix.hystrix.contrib.javanica.annotation.HystrixCommand)")
    public void hystrixCommandAnnotationPointcut() {
    }

    @Pointcut("@annotation(com.netflix.hystrix.contrib.javanica.annotation.HystrixCollapser)")
    public void hystrixCollapserAnnotationPointcut() {
    }
    
	//环绕通知方法
	@Around("hystrixCommandAnnotationPointcut() || hystrixCollapserAnnotationPointcut()")
    public Object methodsAnnotatedWithHystrixCommand(final ProceedingJoinPoint joinPoint) throws Throwable {
    	//获取原始目标方法
        Method method = getMethodFromTarget(joinPoint);
        Validate.notNull(method, "failed to get method from joinPoint: %s", joinPoint);
        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");
        }
        //根据方法类型获取到用于封装MetaHolder的工厂，这里从一个map中获取，这个map存着两种工厂
        //（@HystrixCommand和@HystrixCollapser）
        MetaHolderFactory metaHolderFactory = META_HOLDER_FACTORY_MAP.get(HystrixPointcutType.of(method));
        //获取封装方法的元数据（元数据指的是比如方法的签名，方法上加的注解信息，参数，注解上配置回退方法这些都属于元数据）封装成一个MetaHolder
        MetaHolder metaHolder = metaHolderFactory.create(joinPoint);
        //封装成一个可执行的组件
        //在这里会进行一些资源初始化 进入查看该方法
        HystrixInvokable invokable = HystrixCommandFactory.getInstance().create(metaHolder);
        ExecutionType executionType = metaHolder.isCollapserAnnotationPresent() ?
                metaHolder.getCollapserExecutionType() : metaHolder.getExecutionType();

        Object result;
        try {
            if (!metaHolder.isObservable()) {
                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;
    }

}

HystrixCommandFactory 的create()方法

public class HystrixCommandFactory {

    private static final HystrixCommandFactory INSTANCE = new HystrixCommandFactory();

    private HystrixCommandFactory() {

    }

    public static HystrixCommandFactory getInstance() {
        return INSTANCE;
    }

    public HystrixInvokable create(MetaHolder metaHolder) {
        HystrixInvokable executable;
        //这里会根据元数据类型进行一些判断
        if (metaHolder.isCollapserAnnotationPresent()) {//@HystrixCollapser的
            executable = new CommandCollapser(metaHolder);
        } else if (metaHolder.isObservable()) {//是否异步处理
            executable = new GenericObservableCommand(HystrixCommandBuilderFactory.getInstance().create(metaHolder));
        } else {//一般会进入这个GenericCommand
        
            executable = new GenericCommand(HystrixCommandBuilderFactory.getInstance().create(metaHolder));
        }
        return executable;
    }
}

查看GenericCommand类
该类中有两个重要的方法run() 和getFallback()

public class GenericCommand extends AbstractHystrixCommand<Object> {
	//根据元数据信息找到目标原始方法 调用原始方法执行
	@Override
    protected Object run() throws Exception {
        LOGGER.debug("execute command: {}", getCommandKey().name());
        return process(new Action() {
            @Override
            Object execute() {
                return getCommandAction().execute(getExecutionType());
            }
        });
    }

	//根据元数据信息找到回退的方法 调用回退的方法
    @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();
        }
    }
}

同时在GenericCommand其父类的构造器中会进行一些资源的初始化工作
GenericCommand ->AbstractHystrixCommand—>HystrixCommand—>AbstractCommand

//做一些资源初始化
protected AbstractCommand(HystrixCommandGroupKey group, HystrixCommandKey key, HystrixThreadPoolKey threadPoolKey, HystrixCircuitBreaker circuitBreaker, HystrixThreadPool threadPool,
            HystrixCommandProperties.Setter commandPropertiesDefaults, HystrixThreadPoolProperties.Setter threadPoolPropertiesDefaults,
            HystrixCommandMetrics metrics, TryableSemaphore fallbackSemaphore, TryableSemaphore executionSemaphore,
            HystrixPropertiesStrategy propertiesStrategy, HystrixCommandExecutionHook executionHook) {

        this.commandGroup = initGroupKey(group);
        this.commandKey = initCommandKey(key, getClass());
        this.properties = initCommandProperties(this.commandKey, propertiesStrategy, commandPropertiesDefaults);
        //这里初始化了线程池（之前元数据中存了具体配置信息，这里会传递过来进行初始化，他会把线程池进行缓存放进一个concurrentHashMap中，先获取 获取不到就创建）
        this.threadPoolKey = initThreadPoolKey(threadPoolKey, this.commandGroup, this.properties.executionIsolationThreadPoolKeyOverride().get());
        //一些指标的初始化，根据这些指标来决定是否断路之类的一些操作
        this.metrics = initMetrics(metrics, this.commandGroup, this.threadPoolKey, this.commandKey, this.properties);
        //断路器初始化
        this.circuitBreaker = initCircuitBreaker(this.properties.circuitBreakerEnabled().get(), circuitBreaker, this.commandGroup, this.commandKey, this.properties, this.metrics);
        this.threadPool = initThreadPool(threadPool, this.threadPoolKey, threadPoolPropertiesDefaults);

        //Strategies from plugins
        this.eventNotifier = HystrixPlugins.getInstance().getEventNotifier();
        this.concurrencyStrategy = HystrixPlugins.getInstance().getConcurrencyStrategy();
        HystrixMetricsPublisherFactory.createOrRetrievePublisherForCommand(this.commandKey, this.commandGroup, this.metrics, this.circuitBreaker, this.properties);
        this.executionHook = initExecutionHook(executionHook);

        this.requestCache = HystrixRequestCache.getInstance(this.commandKey, this.concurrencyStrategy);
        this.currentRequestLog = initRequestLog(this.properties.requestLogEnabled().get(), this.concurrencyStrategy);

        /* fallback semaphore override if applicable */
        this.fallbackSemaphoreOverride = fallbackSemaphore;

        /* execution semaphore override if applicable */
        this.executionSemaphoreOverride = executionSemaphore;
    }

接下来回到之前的切面类HystrixCommandAspect
查看切面类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();
    }

	//定义切点  加了@HystrixCommand注解的方法
	@Pointcut("@annotation(com.netflix.hystrix.contrib.javanica.annotation.HystrixCommand)")
    public void hystrixCommandAnnotationPointcut() {
    }

    @Pointcut("@annotation(com.netflix.hystrix.contrib.javanica.annotation.HystrixCollapser)")
    public void hystrixCollapserAnnotationPointcut() {
    }
    
	//环绕通知方法
	@Around("hystrixCommandAnnotationPointcut() || hystrixCollapserAnnotationPointcut()")
    public Object methodsAnnotatedWithHystrixCommand(final ProceedingJoinPoint joinPoint) throws Throwable {
    	//获取原始目标方法
        Method method = getMethodFromTarget(joinPoint);
        Validate.notNull(method, "failed to get method from joinPoint: %s", joinPoint);
        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");
        }
        //根据方法类型获取到用于封装MetaHolder的工厂，这里从一个map中获取，这个map存着两种工厂
        //（@HystrixCommand和@HystrixCollapser）
        MetaHolderFactory metaHolderFactory = META_HOLDER_FACTORY_MAP.get(HystrixPointcutType.of(method));
        //获取封装方法的元数据（元数据指的是比如方法的签名，方法上加的注解信息，参数，注解上配置回退方法这些都属于元数据）封装成一个MetaHolder
        MetaHolder metaHolder = metaHolderFactory.create(joinPoint);
        //封装成一个可执行的组件
        //在这里会进行一些资源初始化 进入查看该方法（这里的逻辑在上面已经分析过了）
        HystrixInvokable invokable = HystrixCommandFactory.getInstance().create(metaHolder);
        ExecutionType executionType = metaHolder.isCollapserAnnotationPresent() ?
                metaHolder.getCollapserExecutionType() : metaHolder.getExecutionType();
		
		//返回结果
        Object result;
        try {
            if (!metaHolder.isObservable()) {//是否是响应式的（由于我们这些都是同步的会走这个逻辑）
                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;
    }

}

查看CommandExecutor类

public class CommandExecutor {

    /**
     * Calls a method of {@link HystrixExecutable} in accordance with specified execution type.
     *
     * @param invokable  {@link HystrixInvokable}
     * @param metaHolder {@link MetaHolder}
     * @return the result of invocation of specific method.
     * @throws RuntimeException
     */
    public static Object execute(HystrixInvokable invokable, ExecutionType executionType, MetaHolder metaHolder) throws RuntimeException {
        Validate.notNull(invokable);
        Validate.notNull(metaHolder);

        switch (executionType) {
            case SYNCHRONOUS: { //同步进入该方法
            	//会进行一个类型转换  然后执行execute()方法
                return castToExecutable(invokable, executionType).execute();
            }
            case ASYNCHRONOUS: {
                HystrixExecutable executable = castToExecutable(invokable, executionType);
                if (metaHolder.hasFallbackMethodCommand()
                        && ExecutionType.ASYNCHRONOUS == metaHolder.getFallbackExecutionType()) {
                    return new FutureDecorator(executable.queue());
                }
                return executable.queue();
            }
            case OBSERVABLE: {
                HystrixObservable observable = castToObservable(invokable);
                return ObservableExecutionMode.EAGER == metaHolder.getObservableExecutionMode() ? observable.observe() : observable.toObservable();
            }
            default:
                throw new RuntimeException("unsupported execution type: " + executionType);
        }
    }
    
	private static HystrixExecutable castToExecutable(HystrixInvokable invokable, ExecutionType executionType) {
        if (invokable instanceof HystrixExecutable) {
            return (HystrixExecutable) invokable;
        }
        throw new RuntimeException("Command should implement " + HystrixExecutable.class.getCanonicalName() + " interface to execute in: " + executionType + " mode");
    }
}

查看HystrixCommand类

	public R execute() {
        try {
        	//queue()方法会返回Feture对象（封装异步处理的结果）
            return queue().get();
        } catch (Exception e) {
            throw Exceptions.sneakyThrow(decomposeException(e));
        }
    }
	public Future<R> queue() {
        /*
         * The Future returned by Observable.toBlocking().toFuture() does not implement the
         * interruption of the execution thread when the "mayInterrupt" flag of Future.cancel(boolean) is set to true;
         * thus, to comply with the contract of Future, we must wrap around it.
         */
         //future的获取，业务逻辑的执行，异常后对回退方法的调用一系列的处理都是用RxJava响应式编程的内容，了解到这里就ok
        final Future<R> delegate = toObservable().toBlocking().toFuture();
    	
   		..................................
   }

GenericCommand方法中根据元数据信息等重写了run()方法（对目标方法的调用），
getFallback()方法（对回退方法的调用），在RxJava处理过程中会完成对这两个方法的调用。