SpringCloud Alibaba 核心组件解析:服务调用和负载均衡

// 官方：OpenFeign + Resilience4J
@FeignClient(value = "service-name")
public interface Api { ... }
// + yaml 配置 + @CircuitBreaker 注解
// Alibaba：OpenFeign + Sentinel
@FeignClient(value = "nacos-payment-provider", fallback = Fallback.class)
public interface PayFeignSentinelApi { ... }
// + feign.sentinel.enabled: true
// → 更简洁，Sentinel 控制台可实时查看 Feign 调用数据

// @FeignClient 的 fallback 参数 = Sentinel 降级的兜底类
@FeignClient(value = "nacos-payment-provider",
             fallback = PayFeignSentinelApiFallBack.class)
public interface PayFeignSentinelApi {
    @GetMapping("/pay/nacos/get/{orderNo}")
    ResultData getPayByOrderNo(@PathVariable("orderNo") String orderNo);
}

@Component  // ← 必须加，否则 Spring 找不到
public class PayFeignSentinelApiFallBack implements PayFeignSentinelApi {
    @Override
    public ResultData getPayByOrderNo(String orderNo) {
        return ResultData.fail(
            ReturnCodeEnum.RC500.getCode(),
            "对方服务宕机或不可用，FallBack服务降级o(╥﹏╥)o"
        );
    }
}

# 激活 Sentinel 对 Feign 的支持（核心开关！）
feign:
  sentinel:
    enabled: true    # 不加这行，fallback 不生效！
service-url:
  nacos-user-service: http://nacos-payment-provider

@RestController
public class OrderNacosController {
    @Resource
    private PayFeignSentinelApi payFeignSentinelApi;
    @GetMapping(value = "/consumer/pay/nacos/get/{orderNo}")
    public ResultData getPayByOrderNo(@PathVariable("orderNo") String orderNo) {
        return payFeignSentinelApi.getPayByOrderNo(orderNo);
    }
}

@Configuration
public class RestTemplateConfig {
    @Bean
    @LoadBalanced
    public RestTemplate restTemplate() {
        return new RestTemplate();
    }
}
// 使用
@GetMapping("/consumer/pay/nacos/{id}")
public String paymentInfo(@PathVariable("id") Integer id) {
    return restTemplate.getForObject(
        "http://nacos-payment-provider/pay/nacos/" + id, String.class);
}

Consumer 调用 payFeignSentinelApi.getPayByOrderNo()
    │
    ├→ Feign 调用成功 → 返回正常结果 ✅
    │
    └→ Feign 调用失败（超时/异常/Provider 宕机）
         │
         └→ Sentinel 拦截 → 走 PayFeignSentinelApiFallBack.getPayByOrderNo()
              │
              └→ 返回 "对方服务宕机或不可用..."