背景：内部要进行应用jdk&springboot升级，因此也需要将Spring Cloud Hystrix 替换成alibaba sentinel。

依赖

<dependency><groupId>com.alibaba.cloud</groupId><artifactId>spring-cloud-starter-alibaba-sentinel</artifactId><version>2022.0.0.0-RC2</version>
</dependency><dependency><groupId>com.alibaba.csp</groupId><artifactId>sentinel-datasource-nacos</artifactId><version>1.8.6</version>
</dependency>

开启Feign对Sentinel的支持

sentinel官方文档

出现错误日志时的代码

import org.springframework.cloud.openfeign.FeignClient;
import org.springframework.web.bind.annotation.PostMapping;
import org.springframework.web.bind.annotation.RequestParam;/*** @Author: WeiXiang* @Desc:* @Date: Create in 5:09 PM on 2020/6/23.*/
@FeignClient(value = "messageCenter", path = "/messageCenter/cloudService")
public interface JobApplyRest {/*** 获取用户最近的报名兼职list** @desc:* @author: WeiXiang* @date: 9:04 PM 2020/6/23*/@PostMapping("/userLastMonthApplyPartJob")String userLastMonthApplyPartJob(@RequestParam("userId") Long userId, @RequestParam("size") Integer size);
}

当达到熔断条件时，则抛出以下错误信息

错误被解决后的代码

解决方案：在FeignClient上，配置自定义fallback熔断降级处理方法

import org.springframework.cloud.openfeign.FeignClient;
import org.springframework.web.bind.annotation.PostMapping;
import org.springframework.web.bind.annotation.RequestParam;/*** @Author: WeiXiang* @Desc:* @Date: Create in 5:09 PM on 2020/6/23.*/
@FeignClient(value = "messageCenter", path = "/messageCenter/cloudService", fallback = JobApplyRestFallback.class)
public interface JobApplyRest {/*** 获取用户最近的报名兼职list** @desc:* @author: WeiXiang* @date: 9:04 PM 2020/6/23*/@PostMapping("/userLastMonthApplyPartJob")String userLastMonthApplyPartJob(@RequestParam("userId") Long userId, @RequestParam("size") Integer size);
}

JobApplyRestFallback类

import lombok.extern.slf4j.Slf4j;
import org.springframework.stereotype.Service;/*** @description: 报名单服务容错类* @author: jiusi* @create: 2023-09-01 10:23:47*/
@Service
@Slf4j
public class JobApplyRestFallback implements JobApplyRest{@Overridepublic String userLastMonthApplyPartJob(Long userId, Integer size) {log.warn("熔断降级开启JobApplyRest#userLastMonthApplyPartJob：userId:{}", userId);return null;}
}

 至此，java.lang.reflect.UndeclaredThrowableException 错误被解决。

问题原因：

sentinel通过代理实现熔断降级，当达到设置的阈值条件时，内部就抛出的自定义受检异常。但该受检异常并未在被代理对象接口定义中进行声明（即：Rest feignClient为被代理对象），那么这个异常就会被JVM包装成UndeclaredThrowableException进行抛出。