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深入Spring Boot：快速集成Dubbo + Hystrix
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背景
Hystrix 旨在通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具備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應用里，怎么把Dubbo和Hystrix結合起來使用。
Spring Boot應用
生成dubbo集成spring boot的應用
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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：
| 1 2 3 4 5 | <dependency> ????<groupId>org.springframework.cloud</groupId> ????<artifactId>spring-cloud-starter-netflix-hystrix</artifactId> ????<version>1.4.4.RELEASE</version> </dependency> |
然后在Application類上增加@EnableHystrix來啟用hystrix starter：
| 1 2 3 | @SpringBootApplication @EnableHystrix public class ProviderApplication { |
配置Provider端
在Dubbo的Provider上增加@HystrixCommand配置，這樣子調用就會經過Hystrix代理。
| 1 2 3 4 5 6 7 8 9 10 11 12 | @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
對于Consumer端，則可以增加一層method調用，并在method上配置@HystrixCommand。當調用出錯時，會走到fallbackMethod = "reliable"的調用里。
| 1 2 3 4 5 6 7 8 9 10 | @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"; } |
通過上面的配置，很簡單地就完成了Spring Boot里Dubbo + Hystrix的集成。
傳統Spring Annotation應用
Demo地址
傳統spring annotation應用的配置其實也很簡單，和spring boot應用不同的是：
| 1 2 3 4 5 6 7 8 9 10 11 12 | @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(); ????} } |
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Hystrix集成Spring AOP原理
在上面的例子里可以看到，Hystrix對Spring的集成是通過Spring AOP來實現的。下面簡單分析下實現。
| 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 | @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; ????} |
spring-cloud-starter-netflix-hystrix的代碼分析
| 1 2 3 4 5 6 7 | @EnableCircuitBreaker public @interface EnableHystrix { } ? @Import(EnableCircuitBreakerImportSelector.class) public @interface EnableCircuitBreaker { } |
| 1 2 | org.springframework.cloud.client.circuitbreaker.EnableCircuitBreaker=\ org.springframework.cloud.netflix.hystrix.HystrixCircuitBreakerConfiguration |
| 1 2 3 4 5 6 7 | @Configuration public class HystrixCircuitBreakerConfiguration { ? ????@Bean ????public HystrixCommandAspect hystrixCommandAspect() { ????????return new HystrixCommandAspect(); ????} |
可見spring-cloud-starter-netflix-hystrix實際上也是創建了HystrixCommandAspect來集成Hystrix。
另外spring-cloud-starter-netflix-hystrix里還有metrics, health, dashboard等集成。
總結
- 對于dubbo provider的@Service是一個spring bean，直接在上面配置@HystrixCommand即可
- 對于dubbo consumer的@Reference，可以通過加一層簡單的spring method包裝，配置@HystrixCommand即可
- Hystrix本身提供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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