原文出处:hengyunabc
背景
Dubbo是Alibaba开源的、目前国内最流行的 java RPC 框架。而 Hystrix 旨在通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。它具备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。
本文将介绍在 Spring Boot 中 结合 Dubbo和Hystrix。
- https://github.com/Netflix/Hystrix
- https://github.com/apache/incubator-dubbo
为了简化开发,可以在这里直接生成 Spring Boot + dubbo 的工程:http://start.dubbo.io/
配置spring-cloud-starter-netflix-hystrix
Spring Boot 官方提供了对 hystrix 的集成,可以直接在 pom.xml 里加入依赖:
<dependency>
<groupId>org.springframework.cloud</groupId>
<artifactId>spring-cloud-starter-netflix-hystrix</artifactId>
<version>1.4.4.RELEASE</version>
</dependency>
然后在 Spring Boot 启动类上增加 @EnableHystrix
来启用 hystrix starter:
@SpringBootApplication
@EnableHystrix
public class SimpleApplication {
配置Provider端
在Dubbo的Provider上增加 @HystrixCommand
配置,这样子调用就会经过Hystrix代理。
@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,则可以增加一层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。
@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";
}
通过上面的配置,很简单地就完成了Spring Boot里Dubbo + Hystrix的集成。
传统 Springannotation应用的配置
传统 Springannotation应用的配置其实也很简单,和Spring Boot应用不同的是:
- 显式配置Spring AOP支持:
@EnableAspectJAutoProxy
- 显式通过
@Configuration
配置 HystrixCommandAspect Bean。
@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对Spring的集成是通过Spring AOP来实现的。下面简单分析下实现。
@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 里定义了两个注解的AspectJ Pointcut:@HystrixCommand, @HystrixCollapser。所有带这两个注解的spring bean都会经过AOP处理
-
在
@Around AOP
处理函数里,可以看到Hystrix会创建出HystrixInvokable,再通过CommandExecutor来执行。
spring-cloud-starter-netflix-hystrix
的代码分析
@EnableHystrix
引入了 @EnableCircuitBreaker
,@EnableCircuitBreaker
引入了EnableCircuitBreakerImportSelector
@EnableCircuitBreaker
public @interface EnableHystrix {
}
@Import(EnableCircuitBreakerImportSelector.class)
public @interface EnableCircuitBreaker {
}
-
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里可以找到下面的配置,也就是引入了HystrixCircuitBreakerConfiguration。 org.springframework.cloud.client.circuitbreaker.EnableCircuitBreaker=
org.springframework.cloud.netflix.hystrix.HystrixCircuitBreakerConfiguration -
在HystrixCircuitBreakerConfiguration里可以发现创建了HystrixCommandAspect @Configuration
public class HystrixCircuitBreakerConfiguration {@Bean
public HystrixCommandAspect hystrixCommandAspect() {
return new HystrixCommandAspect();
}
可见 spring-cloud-starter-netflix-hystrix
实际上也是创建了 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即可
- 对于dubbo consumer的@Reference,可以通过加一层简单的spring method包装,配置
@HystrixCommand
即可 - Hystrix本身提供HystrixCommandAspect来集成Spring AOP,配置了
@HystrixCommand
和@HystrixCollapser
的 Spring method 都会被Hystrix处理
相关链接
- https://github.com/Netflix/Hystrix
- https://github.com/apache/incubator-dubbo
- http://start.dubbo.io/
- https://cloud.spring.io/spring-cloud-netflix/single/spring-cloud-netflix.html#_circuit_breaker_hystrix_clients