在集成nacos时，使用FeignClient请求接口时，报AbstractMethodError，首先反应这肯定是版本兼容的问题，但解决版本兼容也花了很久，试各种版本
错误如下：
Caused by: java.lang.AbstractMethodError: org.springframework.cloud.netflix.ribbon.RibbonLoadBalancerClient.choose(Ljava/lang/String;Lorg/springframework/cloud/client/loadbalancer/Request;)Lorg/springframework/cloud/client/ServiceInstance;
at org.springframework.cloud.openfeign.loadbalancer.FeignBlockingLoadBalancerClient.execute(FeignBlockingLoadBalancerClient.java:88) ~[spring-cloud-openfeign-core-3.0.3.jar:3.0.3]
at feign.SynchronousMethodHandler.executeAndDecode(SynchronousMethodHandler.java:119) ~[feign-core-10.12.jar:?]
at feign.SynchronousMethodHandler.invoke(SynchronousMethodHandler.java:89) ~[feign-core-10.12.jar:?]
at feign.ReflectiveFeign$FeignInvocationHandler.invoke(ReflectiveFeign.java:100) ~[feign-core-10.12.jar:?]
at com.sun.proxy.$Proxy138.create2(Unknown Source) ~[?:?]
at com.mucang.demo.TestsController.create(TestsController.java:20) ~[classes/:?]
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[?:1.8.0_301]
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) ~[?:1.8.0_301]
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[?:1.8.0_301]
at java.lang.reflect.Method.invoke(Method.java:498) ~[?:1.8.0_301]
at org.springframework.web.method.support.InvocableHandlerMethod.doInvoke(InvocableHandlerMethod.java:197) ~[spring-web-5.3.9.jar:5.3.9]
at org.springframework.web.method.support.InvocableHandlerMethod.invokeForRequest(InvocableHandlerMethod.java:141) ~[spring-web-5.3.9.jar:5.3.9]
at org.springframework.web.servlet.mvc.method.annotation.ServletInvocableHandlerMethod.invokeAndHandle(ServletInvocableHandlerMethod.java:106) ~[spring-webmvc-5.3.9.jar:5.3.9]
at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.invokeHandlerMethod(RequestMappingHandlerAdapter.java:895) ~[spring-webmvc-5.3.9.jar:5.3.9]
at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.handleInternal(RequestMappingHandlerAdapter.java:808) ~[spring-webmvc-5.3.9.jar:5.3.9]
at org.springframework.web.servlet.mvc.method.AbstractHandlerMethodAdapter.handle(AbstractHandlerMethodAdapter.java:87) ~[spring-webmvc-5.3.9.jar:5.3.9]
at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:1064) [spring-webmvc-5.3.9.jar:5.3.9]
... 47 more
原因: 在引入nacos-discovery时自动会引入ribbion，（项目 fhadmin.cn）但引入的版本与springcloud引入的openfeign版本不匹配导致异常
<dependency>
? ? ? <groupId>com.alibaba.cloud</groupId>
? ? ? <artifactId>spring-cloud-starter-alibaba-nacos-discovery</artifactId>
</dependency>
解决：
更换版本至匹配 , 以下是我用的版本
spring-cloud-alibaba-dependencies 2021.1
spring-boot-starter-parent? 2.4.9
spring-cloud-dependencies 2020.0.3