Java Feign client Fallback - 无法调用 fallback

Question

我正在尝试通过 Java 中 Feign 客户端 的工作来理解并调用 Fallback 以防万一错误，我遇到了一些困难。我写了最简单的例子来理解它是如何工作的，但我似乎很困惑。请帮助我了解我的错误所在。

我还在 github 上发布了这个例子以方便使用： https://github.com/ksereda/feign-fallback-example

client通过Feign调用service-one，接收字符串"Get String from SERVICE-ONE".

сlient也是通过Feign调用service-two得到字符串"Get String from SERVICE-TWO".

先决条件：在 service-two 不可用的情况下，client 必须调用 Fallback class，其中调用 service-three 被指示而不是 "Get String from SERVICE-TWO"，client 应该得到 "Get String from SERVICE-THREE" 来自 服务三.

service-two和service-three是一样的，只是return个字符串不同

服务一码：

@RestController
@RequestMapping("/")
public class OneController {

    Logger logger = Logger.getLogger(OneController.class.getName());

    @GetMapping("/getStringFromServiceOne")
    public String getString() {
        logger.info("Get String from SERVICE-ONE");
        return "Get String from SERVICE-ONE";
    }

}

服务二码:

@RestController
@RequestMapping("/")
public class TwoController {

    Logger logger = Logger.getLogger(TwoController.class.getName());

    @GetMapping("/getStringFromServiceTwo")
    public String getString() {
        logger.info("Get String from SERVICE-TWO");
        return "Get String from SERVICE-TWO";
    }

}

服务-三码:

@RestController
@RequestMapping("/")
public class ThreeController {

    Logger logger = Logger.getLogger(ThreeController.class.getName());

    @GetMapping("/getStringFromServiceThree")
    public String getString() {
        logger.info("Get String from SERVICE-THREE");
        return "Get String from SERVICE-THREE";
    }

}

客户代码：

控制器：

@RestController
@RequestMapping("/")
public class ClientController {

   Logger logger = Logger.getLogger(ClientController.class.getName());

    @Autowired
    private ServiceOneFeignClient serviceOneFeignClient;

    @Autowired
    private ServiceTwoFeignClient serviceTwoFeignClient;

    @RequestMapping(path = "/getDataFromServiceOneByFeign")
    public String getDataFromServiceOne() {
        String result = serviceOneFeignClient.getString();
        logger.info("Calling through Feign Client");
        return result;
    }

    @RequestMapping(path = "/getDataFromServiceTwoByFeign")
    public String getDataFromServiceTwo() {
        String result = serviceTwoFeignClient.getString();
        logger.info("Calling through Feign Client");
        return result;
    }

}

伪装 1：

@FeignClient(name = "service-one", url = "http://localhost:8081/")
public interface ServiceOneFeignClient {

    @GetMapping("/getStringFromServiceOne")
    String getString();

}

和伪装 2：

@FeignClient(name = "service-two", url = "http://localhost:8082/", fallback = Fallback.class)
public interface ServiceTwoFeignClient {

    @GetMapping("/getStringFromServiceTwo")
    String getString();

}

和伪装 3：

@FeignClient(name = "service-three", url = "http://localhost:8083/")
public interface ServiceThreeFeignClient {

    @GetMapping("/getStringFromServiceThree")
    String getString();

}

主要class:

@SpringBootApplication
@EnableFeignClients
@EnableCircuitBreaker
@EnableHystrix
public class ClientApplication {

    public static void main(String[] args) {
        SpringApplication.run(ClientApplication.class, args);
    }

}

和application.yml文件

server:
  port: 8070

feign:
  hystrix:
    enabled: true

我在这里创建了 Fallback class

@Component
public class Fallback implements ServiceThreeFeignClient {

    @Override
    public String getString() {
        System.out.println("Called MOVIE-SERVICE with Fallback class!");
        return new String("FALLBACK STRING");
    }

}

这里如果service-two不可用，我想调用service-three

但是当我启动我的应用程序时，我立即收到错误消息：

Caused by: java.lang.IllegalStateException: Incompatible fallback instance. Fallback/fallbackFactory of type class com.example.client.service.Fallback is not assignable to interface com.example.client.service.ServiceTwoFeignClient for feign client service-two
    at org.springframework.cloud.openfeign.HystrixTargeter.getFromContext(HystrixTargeter.java:86) ~[spring-cloud-openfeign-core-2.1.1.RELEASE.jar:2.1.1.RELEASE]
    at org.springframework.cloud.openfeign.HystrixTargeter.targetWithFallback(HystrixTargeter.java:70) ~[spring-cloud-openfeign-core-2.1.1.RELEASE.jar:2.1.1.RELEASE]
    at org.springframework.cloud.openfeign.HystrixTargeter.target(HystrixTargeter.java:46) ~[spring-cloud-openfeign-core-2.1.1.RELEASE.jar:2.1.1.RELEASE]
    at org.springframework.cloud.openfeign.FeignClientFactoryBean.getTarget(FeignClientFactoryBean.java:284) ~[spring-cloud-openfeign-core-2.1.1.RELEASE.jar:2.1.1.RELEASE]
    at org.springframework.cloud.openfeign.FeignClientFactoryBean.getObject(FeignClientFactoryBean.java:247) ~[spring-cloud-openfeign-core-2.1.1.RELEASE.jar:2.1.1.RELEASE]
    at org.springframework.beans.factory.support.FactoryBeanRegistrySupport.doGetObjectFromFactoryBean(FactoryBeanRegistrySupport.java:171) ~[spring-beans-5.1.7.RELEASE.jar:5.1.7.RELEASE]

他写的我看懂了：必须注明

implements ServiceTwoFeignClient

改为

implements ServiceThreeFeignClient

但如果服务二不可用，我想呼叫服务三。

我不明白该怎么做。我将不胜感激你的帮助。谢谢

Answer 1

我在后备方案中决定了 class:

@Component
public class Fallback implements ServiceTwoFeignClient {

    @Autowired
    private ServiceThreeFeignClient serviceThreeFeignClient;

    @Override
    public String getString() {
        return serviceThreeFeignClient.getString();
    }

}

Java Feign client Fallback - 无法调用 fallback

Java Feign client Fallback - can't call fallback

java

hystrix

spring-cloud-feign

feign

circuit-breaker