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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
?
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：
- 顯式配置Spring AOP支持：
@EnableAspectJAutoProxy - 顯式通過
@Configuration配置HystrixCommandAspect?Bean。
| 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();
????}
}
|
?
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;
????}
|
HystrixCommandAspect里定義了兩個注解的AspectJ Pointcut：@HystrixCommand,?@HystrixCollapser。所有帶這兩個注解的spring bean都會經過AOP處理- 在
@Around?AOP處理函數里，可以看到Hystrix會創建出HystrixInvokable，再通過CommandExecutor來執行
spring-cloud-starter-netflix-hystrix的代碼分析
@EnableHystrix?引入了@EnableCircuitBreaker，@EnableCircuitBreaker引入了EnableCircuitBreakerImportSelector | 1 2 3 4 5 6 7 | @EnableCircuitBreaker
public @interface EnableHystrix {
}
? @Import(EnableCircuitBreakerImportSelector.class)
public @interface EnableCircuitBreaker {
}
|
EnableCircuitBreakerImportSelector繼承了SpringFactoryImportSelector<EnableCircuitBreaker>，使spring加載META-INF/spring.factories里的EnableCircuitBreaker聲明的配置在META-INF/spring.factories里可以找到下面的配置，也就是引入了HystrixCircuitBreakerConfiguration。 | 1 2 | org.springframework.cloud.client.circuitbreaker.EnableCircuitBreaker=\
org.springframework.cloud.netflix.hystrix.HystrixCircuitBreakerConfiguration
|
- 在
HystrixCircuitBreakerConfiguration里可以發現創建了HystrixCommandAspect | 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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