LoadBalancerClient接口 同包有个叫LoadBalancerAutoConfiguration,看名字就是负载均衡自动化配置的

@Configuration
//必须有RestTemplate类
@ConditionalOnClass(RestTemplate.class)
//必须有LoadBalancerClient的实现bean(`RibbonLoadBalancerClient` )
@ConditionalOnBean(LoadBalancerClient.class)
public class LoadBalancerAutoConfiguration {

//所有被@LoadBalanced注解的restTemplate
    @LoadBalanced
    @Autowired(required = false)
    private List<RestTemplate> restTemplates = Collections.emptyList();

//对上面 所有restTemplate对象列表初始化,   包括都用下面的Customizer来定制
    @Bean
    public SmartInitializingSingleton loadBalancedRestTemplateInitializer(
            final List<RestTemplateCustomizer> customizers) {
            
        return new SmartInitializingSingleton() {
        
            @Override
            public void afterSingletonsInstantiated() {
                for (RestTemplate restTemplate : LoadBalancerAutoConfiguration.this.restTemplates) {
                    for (RestTemplateCustomizer customizer : customizers) {
                        customizer.customize(restTemplate);
                    }
                }
            }
            
        };
    }

//创建一个 用于改造RestTemplate     的bean   
// 用于RestTemplate加上 下面那个拦截器
    @Bean
    @ConditionalOnMissingBean
    public RestTemplateCustomizer restTemplateCustomizer(
            final LoadBalancerInterceptor loadBalancerInterceptor) {
            
        return new RestTemplateCustomizer() {
            @Override
            public void customize(RestTemplate restTemplate) {
            //原来的拦截器
                List<ClientHttpRequestInterceptor> list = new ArrayList<>(
                        restTemplate.getInterceptors());
                
                //新加一个负载均衡的拦截器LoadBalancerInterceptor 就是下面这个
                list.add(loadBalancerInterceptor);
                restTemplate.setInterceptors(list);
            }
        };
    }

//创建一个拦截器bean       用于对发起请求的拦截
//这个就是负载均衡  拦截器!!!
    @Bean
    public LoadBalancerInterceptor ribbonInterceptor(
            LoadBalancerClient loadBalancerClient) {
            
        //LoadBalancerClient唯一的实现类就是`RibbonLoadBalancerClient`  之前看的
        return new LoadBalancerInterceptor(loadBalancerClient);
    }

}

看来 LoadBalancerAutoConfiguration,负载均衡自动化配置 就是把@LoadBalanced注解的restTemplate 都加上一个负载均衡拦截器LoadBalancerInterceptor,传入LoadBalancerInterceptor的是LoadBalancerClient 唯一的实现类RibbonLoadBalancerClient