跟我學Spring Cloud（Finchley版）-14-Feign使用Hystrix

Feign默認已經整合了Hystrix，本節詳細探討Feign使用Hystrix的具體細節。

服務降級

• 加配置，默認Feign是不啓用Hystrix的，須要添加以下配置啓用Hystrix，這樣全部的Feign Client都會受到Hystrix保護！

  feign:
    hystrix:
      enabled: true

• 提供Fallback：

  @FeignClient(name = "microservice-provider-user", fallback = UserFeignClientFallback.class)
  public interface UserFeignClient {
    @GetMapping("/users/{id}")
    User findById(@PathVariable("id") Long id);
  }
  
  @Component
  class UserFeignClientFallback implements UserFeignClient {
    @Override
    public User findById(Long id) {
      return new User(id, "默認用戶", "默認用戶", 0, new BigDecimal(1));
    }
  }

得到形成fallback的緣由

@FeignClient(name = "microservice-provider-user", fallbackFactory = UserFeignClientFallbackFactory.class)
public interface UserFeignClient {
  @GetMapping("/users/{id}")
  User findById(@PathVariable("id") Long id);
}

@Component
@Slf4j
class UserFeignClientFallbackFactory implements FallbackFactory<UserFeignClient> {
  @Override
  public UserFeignClient create(Throwable throwable) {
    return new UserFeignClient() {
      @Override
      public User findById(Long id) {
        log.error("進入回退邏輯", throwable);
        return new User(id, "默認用戶", "默認用戶", 0, new BigDecimal(1));
      }
    };
  }
}

Feign啓用/禁用Hystrix

全局啓用

feign.hystrix.enabled: true

全局禁用

feign.hystrix.enabled: false

或直接省略不寫。

局部啓用

利用Feign配置的自定義，爲指定Feign Client指定以下配置類便可，Feign配置自定義詳見：跟我學Spring Cloud（Finchley版）-10-Feign深刻

public class FeignDisableHystrixConfiguration {
    @Bean
	@Scope("prototype")
	public HystrixFeign.Builder feignBuilder() {
		return HystrixFeign.builder();
	}
}

局部禁用

public class FeignDisableHystrixConfiguration {
    @Bean
	@Scope("prototype")
	public Feign.Builder feignBuilder() {
		return Feign.builder();
	}
}

配套代碼

服務降級：

• GitHub：https://github.com/eacdy/spring-cloud-study/tree/master/2018-Finchley/microservice-consumer-movie-feign-hystrix
• Gitee：https://gitee.com/itmuch/spring-cloud-study/tree/master/2018-Finchley/microservice-consumer-movie-feign-hystrix

得到形成fallback的緣由：

• GitHub：https://github.com/eacdy/spring-cloud-study/tree/master/2018-Finchley/microservice-consumer-movie-feign-hystrix-fallback-factory
• Gitee：https://gitee.com/itmuch/spring-cloud-study/tree/master/2018-Finchley/microservice-consumer-movie-feign-hystrix-fallback-factory

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