一、报错情况：

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;

二、报错原因：

当前我的springboot版本 2.4.3 ，springcloud版本 2020.0.2
出现这个问题是没有loadbalancer，但是nacos中ribbon会造成loadbalancer包失效,所以在包中移除ribbion依赖，并加入loadbalancer依赖；

三、解决方案：
网上有方案建议降低springboot和springcloud版本，我个人不太喜欢这种方案，咱们总不能阻止版本进步吧。
按照上面说的在nacos"包中移除ribbion依赖，并加入loadbalancer依赖"

<!--服务注册-->
<dependency>
    <groupId>org.springframework.cloud</groupId>
    <artifactId>spring-cloud-starter-alibaba-nacos-discovery</artifactId>
    <!--不使用Ribbon 进行客户端负载均衡-->
    <exclusions>
        <exclusion>
            <groupId>org.springframework.cloud</groupId>
            <artifactId>spring-cloud-starter-netflix-ribbon</artifactId>
        </exclusion>
    </exclusions>
</dependency>
<!--使用Spring Cloud LoadBalancer 进行客户端负载均衡-->
<dependency>
    <groupId>org.springframework.cloud</groupId>
    <artifactId>spring-cloud-loadbalancer</artifactId>
</dependency>

四、修复后显示如下：

启动提供者服务时：

2021-05-21 16:34:23 |WARN  |main |LoadBalancerCacheAutoConfiguration.java:82 |org.springframework.cloud.loadbalancer.config.LoadBalancerCacheAutoConfiguration$LoadBalancerCaffeineWarnLogger |Spring Cloud LoadBalancer is currently working with the default cache. You can switch to using Caffeine cache, by adding it and org.springframework.cache.caffeine.CaffeineCacheManager to the classpath.

 启动消费者服务时：

2021-05-21 16:34:23 |WARN  |main |LoadBalancerCacheAutoConfiguration.java:82 |org.springframework.cloud.loadbalancer.config.LoadBalancerCacheAutoConfiguration$LoadBalancerCaffeineWarnLogger |Spring Cloud LoadBalancer is currently working with the default cache. You can switch to using Caffeine cache, by adding it and org.springframework.cache.caffeine.CaffeineCacheManager to the classpath.

--调用服务时：---

2021-05-21 16:36:40 |WARN  |http-nio-8001-exec-9 |ServiceInstanceListSupplierBuilder.java:229 |org.springframework.cloud.loadbalancer.core.ServiceInstanceListSupplierBuilder |LoadBalancerCacheManager not available, returning delegate without caching.