深刻Spring Boot：快速集成Dubbo + Hystrix

背景

Hystrix 旨在經過控制那些訪問遠程系統、服務和第三方庫的節點，從而對延遲和故障提供更強大的容錯能力。Hystrix具有擁有回退機制和斷路器功能的線程和信號隔離，請求緩存和請求打包，以及監控和配置等功能。

Dubbo是Alibaba開源的，目前國內最流行的java rpc框架。

本文介紹在spring應用裏，怎麼把Dubbo和Hystrix結合起來使用。

Spring Boot應用

生成dubbo集成spring boot的應用

配置spring-cloud-starter-netflix-hystrix

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

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

而後在Application類上增長@EnableHystrix來啓用hystrix starter：

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@SpringBootApplication @EnableHystrix public class ProviderApplication {

配置Provider端

在Dubbo的Provider上增長@HystrixCommand配置，這樣子調用就會通過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

對於Consumer端，則能夠增長一層method調用，並在method上配置@HystrixCommand。當調用出錯時，會走到fallbackMethod = "reliable"的調用裏。

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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" ; }

經過上面的配置，很簡單地就完成了Spring Boot裏Dubbo + Hystrix的集成。

傳統Spring Annotation應用

傳統spring annotation應用的配置其實也很簡單，和spring boot應用不一樣的是：

1. 顯式配置Spring AOP支持：@EnableAspectJAutoProxy
2. 顯式經過@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

在上面的例子裏能夠看到，Hystrix對Spring的集成是經過Spring AOP來實現的。下面簡單分析下實現。

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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裏定義了兩個註解的AspectJ Pointcut：@HystrixCommand, @HystrixCollapser。全部帶這兩個註解的spring bean都會通過AOP處理
2. 在@Around AOP處理函數裏，能夠看到Hystrix會建立出HystrixInvokable，再經過CommandExecutor來執行

spring-cloud-starter-netflix-hystrix的代碼分析

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繼承了SpringFactoryImportSelector<EnableCircuitBreaker>，使spring加載META-INF/spring.factories裏的EnableCircuitBreaker聲明的配置在META-INF/spring.factories裏能夠找到下面的配置，也就是引入了HystrixCircuitBreakerConfiguration。

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

3. 在HystrixCircuitBreakerConfiguration裏能夠發現建立了HystrixCommandAspect

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

可見spring-cloud-starter-netflix-hystrix實際上也是建立了HystrixCommandAspect來集成Hystrix。

另外spring-cloud-starter-netflix-hystrix裏還有metrics, health, dashboard等集成。

總結

• 對於dubbo provider的@Service是一個spring bean，直接在上面配置@HystrixCommand便可
• 對於dubbo consumer的@Reference，能夠經過加一層簡單的spring method包裝，配置@HystrixCommand便可
• Hystrix自己提供HystrixCommandAspect來集成Spring AOP，配置了@HystrixCommand和@HystrixCollapser的spring method都會被Hystrix處理

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