try{
     feign.api();
  }catch(){
  return fallback();
 }

HystrixInvocationHandler (feign.hystrix)

@Override
  public Object invoke(final Object proxy, final Method method, final Object[] args)
      throws Throwable {
    .............
  // setterMethodMap 封裝 hystrixCommand 配置信息（超時(shí)時(shí)間、是否重試.....）
    HystrixCommand<Object> hystrixCommand = new HystrixCommand<Object>(setterMethodMap.get(method)) {
      @Override
      protected Object run() throws Exception {
        ....
        HystrixInvocationHandler.this.dispatch.get(method).invoke(args);
       ....
      }
      @Override
      protected Object getFallback() {
        .........
      }
    };
   ......
    return hystrixCommand.execute();
  }

Feign build(final FallbackFactory<?> nullableFallbackFactory) {
      super.invocationHandlerFactory(new InvocationHandlerFactory() {
        // 重新定義一個(gè) InvocationHandler 實(shí)現(xiàn) 類似 aop效果
        @Override public InvocationHandler create(Target target,
            Map<Method, MethodHandler> dispatch) {
          return new HystrixInvocationHandler(target, dispatch, setterFactory, nullableFallbackFactory);
        }
      });
      super.contract(new HystrixDelegatingContract(contract));
      return super.build();
    }

java.lang.reflect.InvocationHandler#invoke

feign.hystrix.HystrixInvocationHandler#invoke

this.dispatch.get(method).invoke(args);

import feign.Feign;
import org.springframework.cloud.openfeign.FeignClient;
import org.springframework.stereotype.Component;
/**
 * 自定義feign 構(gòu)建
 * @author hgf
 */
public class CusFeignBuilder extends Feign.Builder{
    public CusFeignBuilder() {
        this.invocationHandlerFactory((target, dispatch) -> {
            Class<?> type = target.type();
            FeignClient annotation = type.getAnnotation(FeignClient.class);
            // 構(gòu)造 fallback 實(shí)例
            Object fallBackObj = null;
            if (annotation != null && !annotation.fallback().equals(void.class)) {
                try {
                    fallBackObj = annotation.fallback().newInstance();
                } catch (InstantiationException | IllegalAccessException e) {
                    e.printStackTrace();
                }
            }
            return new CusFeignInvocationHandler(target, dispatch, fallBackObj);
        });
    }
}

import feign.Feign;
import feign.InvocationHandlerFactory;
import feign.Target;
import lombok.extern.slf4j.Slf4j;
import org.springframework.cloud.openfeign.FeignClient;
import java.lang.reflect.InvocationHandler;
import java.lang.reflect.Method;
import java.lang.reflect.Proxy;
import java.util.Map;
import java.util.concurrent.ConcurrentHashMap;
import static com.eco.common.utils.Md5Util.logger;
import static feign.Util.checkNotNull;
/**
 * 自定義的feign調(diào)用
 */
@Slf4j
public class CusFeignInvocationHandler implements InvocationHandler {
    private final Target target;
    private final Map<Method, InvocationHandlerFactory.MethodHandler> dispatch;
    private final Object fallbackObj;
    private final Map<String, Method> fallbackMethodMap = new ConcurrentHashMap<>();
    CusFeignInvocationHandler(Target target, Map<Method, InvocationHandlerFactory.MethodHandler> dispatch, Object  fallbackObj) {
        this.target = checkNotNull(target, "target");
        this.dispatch = checkNotNull(dispatch, "dispatch for %s", target);
        this.fallbackObj = fallbackObj;
    }
    public Object feignInvoke(Object proxy, Method method, Object[] args) throws Throwable {
        if ("equals".equals(method.getName())) {
            try {
                Object
                        otherHandler =
                        args.length > 0 && args[0] != null ? Proxy.getInvocationHandler(args[0]) : null;
                return equals(otherHandler);
            } catch (IllegalArgumentException e) {
                return false;
            }
        } else if ("hashCode".equals(method.getName())) {
            return hashCode();
        } else if ("toString".equals(method.getName())) {
            return toString();
        }
        return dispatch.get(method).invoke(args);
    }
    @Override
    public boolean equals(Object obj) {
        if (obj instanceof CusFeignInvocationHandler) {
            CusFeignInvocationHandler other = (CusFeignInvocationHandler) obj;
            return target.equals(other.target);
        }
        return false;
    }
    @Override
    public int hashCode() {
        return target.hashCode();
    }
    @Override
    public String toString() {
        return target.toString();
    }
    @Override
    public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
        try {
            return feignInvoke(proxy, method, args);
        } catch (Throwable throwable) {
            String configKey = Feign.configKey(target.type(), method);
            logger.error("{} 請求 出現(xiàn)異常 ==> {}", configKey, throwable.getMessage());
            try {
                return getFallbackReturn(method, args, throwable);
            } catch (Throwable e) {
                throw throwable;
            }
        }
    }
    /**
     * 反射調(diào)用 {@link FeignClient#fallback()}生成失敗返回值
     * @param method            當(dāng)前feign方法
     * @param args              參數(shù)
     * @param throwable         異常
     */
    public Object getFallbackReturn(Method method, Object[] args, Throwable throwable) throws Throwable {
        if (fallbackObj == null) {
            throw new RuntimeException("fallbackObj is null");
        }
        String configKey = Feign.configKey(target.type(), method);
        Method fallbackMethod = fallbackMethodMap.get(configKey);
        if (fallbackMethod == null) {
            Class<?> declaringClass = method.getDeclaringClass();
            FeignClient annotation = declaringClass.getAnnotation(FeignClient.class);
            if (annotation == null) {
                throw new RuntimeException("FeignClient annotation not found");
            }
            // 失敗返回
            Class<?> fallback = annotation.fallback();
            fallbackMethod = fallback.getMethod(method.getName(), method.getParameterTypes());
            fallbackMethodMap.put(configKey, fallbackMethod);
        }
        if (fallbackMethod == null) {
            throw new RuntimeException("fallbackMethodMap not found");
        }
        return fallbackMethod.invoke(fallbackObj, args);
    }
}

@Bean
    CusFeignBuilder cusFeignBuilder(){
        return new CusFeignBuilder();
    }

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

feign.sentinel.enabled=true

@Component
public class DeviceApiFallBack implements DeviceApi{
  @Override
        public ServerResponse<String> login(String appId) {
            return ServerResponse.createByErrorMessage("請求失敗");
        }
}