深刻Spring Boot：快速集成Dubbo + Hystrix

背景

Hystrix 旨在经过控制那些访问远程系统、服务和第三方库的节点，从而对延迟和故障提供更强大的容错能力。Hystrix具有拥有回退机制和断路器功能的线程和信号隔离，请求缓存和请求打包，以及监控和配置等功能。

Dubbo是Alibaba开源的，目前国内最流行的java rpc框架。

本文介绍在spring应用里，怎么把Dubbo和Hystrix结合起来使用。

Spring Boot应用

生成dubbo集成spring boot的应用

配置spring-cloud-starter-netflix-hystrix

spring boot官方提供了对hystrix的集成，直接在pom.xml里加入依赖：

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<dependency> <groupId>org.springframework.cloud</groupId> <artifactId>spring-cloud-starter-netflix-hystrix</artifactId> <version> 1.4 . 4 .RELEASE</version> </dependency>

而后在Application类上增长@EnableHystrix来启用hystrix starter：

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@SpringBootApplication @EnableHystrix public class ProviderApplication {

配置Provider端

在Dubbo的Provider上增长@HystrixCommand配置，这样子调用就会通过Hystrix代理。

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@Service (version = "1.0.0" ) public class HelloServiceImpl implements HelloService { @HystrixCommand (commandProperties = { @HystrixProperty (name = "circuitBreaker.requestVolumeThreshold" , value = "10" ), @HystrixProperty (name = "execution.isolation.thread.timeoutInMilliseconds" , value = "2000" ) }) @Override public String sayHello(String name) { // System.out.println("async provider received: " + name); // return "annotation: hello, " + name; throw new RuntimeException( "Exception to show hystrix enabled." ); } }

配置Consumer端

对于Consumer端，则能够增长一层method调用，并在method上配置@HystrixCommand。当调用出错时，会走到fallbackMethod = "reliable"的调用里。

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@Reference (version = "1.0.0" ) private HelloService demoService; @HystrixCommand (fallbackMethod = "reliable" ) public String doSayHello(String name) { return demoService.sayHello(name); } public String reliable(String name) { return "hystrix fallback value" ; }

经过上面的配置，很简单地就完成了Spring Boot里Dubbo + Hystrix的集成。

传统Spring Annotation应用

传统spring annotation应用的配置其实也很简单，和spring boot应用不一样的是：

1. 显式配置Spring AOP支持：@EnableAspectJAutoProxy
2. 显式经过@Configuration配置HystrixCommandAspect Bean。

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@Configuration @EnableDubbo (scanBasePackages = "com.alibaba.dubbo.samples.annotation.action" ) @PropertySource ( "classpath:/spring/dubbo-consumer.properties" ) @ComponentScan (value = { "com.alibaba.dubbo.samples.annotation.action" }) @EnableAspectJAutoProxy static public class ConsumerConfiguration { @Bean public HystrixCommandAspect hystrixCommandAspect() { return new HystrixCommandAspect(); } }

Hystrix集成Spring AOP原理

在上面的例子里能够看到，Hystrix对Spring的集成是经过Spring AOP来实现的。下面简单分析下实现。

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@Aspect public class HystrixCommandAspect { @Pointcut ( "@annotation(com.netflix.hystrix.contrib.javanica.annotation.HystrixCommand)" ) public void hystrixCommandAnnotationPointcut() { } @Pointcut ( "@annotation(com.netflix.hystrix.contrib.javanica.annotation.HystrixCollapser)" ) public void hystrixCollapserAnnotationPointcut() { } @Around ( "hystrixCommandAnnotationPointcut() || hystrixCollapserAnnotationPointcut()" ) public Object methodsAnnotatedWithHystrixCommand( final ProceedingJoinPoint joinPoint) throws Throwable { 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" ); } MetaHolderFactory metaHolderFactory = META_HOLDER_FACTORY_MAP.get(HystrixPointcutType.of(method)); MetaHolder metaHolder = metaHolderFactory.create(joinPoint); 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() != null ? e.getCause() : e; } catch (HystrixRuntimeException e) { throw hystrixRuntimeExceptionToThrowable(metaHolder, e); } return result; }

1. HystrixCommandAspect里定义了两个注解的AspectJ Pointcut：@HystrixCommand, @HystrixCollapser。全部带这两个注解的spring bean都会通过AOP处理
2. 在@Around AOP处理函数里，能够看到Hystrix会建立出HystrixInvokable，再经过CommandExecutor来执行

spring-cloud-starter-netflix-hystrix的代码分析

1. @EnableHystrix 引入了@EnableCircuitBreaker，@EnableCircuitBreaker引入了EnableCircuitBreakerImportSelector

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   @EnableCircuitBreaker public @interface EnableHystrix { } @Import (EnableCircuitBreakerImportSelector. class ) public @interface EnableCircuitBreaker { }

2. EnableCircuitBreakerImportSelector继承了SpringFactoryImportSelector<EnableCircuitBreaker>，使spring加载META-INF/spring.factories里的EnableCircuitBreaker声明的配置在META-INF/spring.factories里能够找到下面的配置，也就是引入了HystrixCircuitBreakerConfiguration。

   1 2	org.springframework.cloud.client.circuitbreaker.EnableCircuitBreaker=\ org.springframework.cloud.netflix.hystrix.HystrixCircuitBreakerConfiguration

3. 在HystrixCircuitBreakerConfiguration里能够发现建立了HystrixCommandAspect

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

可见spring-cloud-starter-netflix-hystrix实际上也是建立了HystrixCommandAspect来集成Hystrix。

另外spring-cloud-starter-netflix-hystrix里还有metrics, health, dashboard等集成。

总结

• 对于dubbo provider的@Service是一个spring bean，直接在上面配置@HystrixCommand便可
• 对于dubbo consumer的@Reference，能够经过加一层简单的spring method包装，配置@HystrixCommand便可
• Hystrix自己提供HystrixCommandAspect来集成Spring AOP，配置了@HystrixCommand和@HystrixCollapser的spring method都会被Hystrix处理

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