0.9.0.RELEASE版本的spring cloud alibaba sentinel+feign降级处理实例

　　既然用到了feign，那么主要是针对服务消费方的降级处理。我们基于0.9.0.RELEASE版本的spring cloud alibaba nacos+feign实例添油加醋，把sentinel功能加上去：

　　1、pom引入sentinel依赖：

        <dependency>
            <groupId>org.springframework.cloud</groupId>
            <artifactId>spring-cloud-starter-alibaba-sentinel</artifactId>
        </dependency>

　　2、application配置哨兵控制台地址、开启feign+sentinel：

#哨兵
spring.cloud.sentinel.transport.dashboard=localhost:8080
#打开sentinel
feign.sentinel.enabled=true

　　3、启动类在@FeignClient注解中指定降级处理类和配置类：

import lombok.extern.slf4j.Slf4j;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.cloud.client.discovery.EnableDiscoveryClient;
import org.springframework.cloud.openfeign.EnableFeignClients;
import org.springframework.cloud.openfeign.FeignClient;
import org.springframework.context.annotation.Bean;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RestController;

@EnableFeignClients
@EnableDiscoveryClient
@SpringBootApplication
public class TransConsumerApplication {

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

    @Slf4j
    @RestController
    static class TestController {

        @Autowired
        private ApplicationApi applicationApi;

        @GetMapping("/sayhello")
        public String sayhello() {
            return "say: " + applicationApi.hello();
        }

        @GetMapping("/sayhey")
        public String sayhey() {
            return "say: " + applicationApi.hey();
        }

    }

    @FeignClient(name = "lxytrans-provider", fallback = TestFallback.class, configuration = FeignConfiguration.class)
    interface ApplicationApi {

        @GetMapping("/hello")
        String hello();

        @GetMapping("/hey")
        String hey();

    }

    class TestFallback implements ApplicationApi {

        @Override
        public String hello() {
            return "hello feign fallback.";
        }

        @Override
        public String hey() {
            return "hey feign fallback.";
        }
    }

    class FeignConfiguration {
        @Bean
        public TestFallback testFallback() {
            return new TestFallback();
        }
    }

}

　　跑起来后，调用一把这两个接口，可以发现哨兵控制台多了消费方：

　　此处无需配置流控、降级，我们的服务方维持原来的流控、降级处理（参见0.9.0.RELEASE版本的spring cloud alibaba sentinel限流、降级处理实例）。调用sayhey，服务方时延2秒，超时直接熔断：

　　再让消费方通过jmeter调用sayhello，前面3个正常返回，后面两个因为服务方限流而熔断：