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

Demo地址

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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