深入Spring Boot：快速集成Dubbo + Hystrix-白红宇

背景

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。Hystrix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。

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：

<dependency>

<groupId>org.springframework.cloud</groupId>

<artifactId>spring-cloud-starter-netflix-hystrix</artifactId>

<version>

1.4

.

4

.RELEASE</version>

</dependency>

然后在Application类上增加@EnableHystrix来启用hystrix starter：

@SpringBootApplication

@EnableHystrix

public

class

ProviderApplication {

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Spring Annotation应用

传统spring annotation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。

1 2	`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

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