Ribbon 源码分析之 @LoadBalanced 与 LoadBalancerClient

public interface LoadBalancerClient {   /**    * Choose a ServiceInstance from the LoadBalancer for the specified service    * @param serviceId the service id to look up the LoadBalancer    * @return a ServiceInstance that matches the serviceId    */   ServiceInstance choose(String serviceId);
   /**    * execute request using a ServiceInstance from the LoadBalancer for the specified    * service    * @param serviceId the service id to look up the LoadBalancer    * @param request allows implementations to execute pre and post actions such as    * incrementing metrics    * @return the result of the LoadBalancerRequest callback on the selected    * ServiceInstance    */   <T> T execute(String serviceId, LoadBalancerRequest<T> request) throws IOException;
   /**    * Create a proper URI with a real host and port for systems to utilize.    * Some systems use a URI with the logical serivce name as the host,    * such as http://myservice/path/to/service.  This will replace the    * service name with the host:port from the ServiceInstance.    * @param instance    * @param original a URI with the host as a logical service name    * @return a reconstructed URI    */   URI reconstructURI(ServiceInstance instance, URI original);
}

import java.util.ArrayList;import java.util.Collections;import java.util.List;
import org.springframework.beans.factory.SmartInitializingSingleton;import org.springframework.beans.factory.annotation.Autowired;import org.springframework.boot.autoconfigure.condition.ConditionalOnBean;import org.springframework.boot.autoconfigure.condition.ConditionalOnClass;import org.springframework.boot.autoconfigure.condition.ConditionalOnMissingBean;import org.springframework.context.annotation.Bean;import org.springframework.context.annotation.Configuration;import org.springframework.http.client.ClientHttpRequestInterceptor;import org.springframework.web.client.RestTemplate;
/** * Auto configuration for Ribbon (client side load balancing). * * @author Spencer Gibb * @author Dave Syer */@Configuration@ConditionalOnClass(RestTemplate.class)@ConditionalOnBean(LoadBalancerClient.class)public class LoadBalancerAutoConfiguration {
  @LoadBalanced  @Autowired(required = false)  private List<RestTemplate> restTemplates = Collections.emptyList();
  @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);          }        }      }    };  }
  @Bean  @ConditionalOnMissingBean  public RestTemplateCustomizer restTemplateCustomizer(      final LoadBalancerInterceptor loadBalancerInterceptor) {    return new RestTemplateCustomizer() {      @Override      public void customize(RestTemplate restTemplate) {        List<ClientHttpRequestInterceptor> list = new ArrayList<>(            restTemplate.getInterceptors());        list.add(loadBalancerInterceptor);        restTemplate.setInterceptors(list);      }    };  }
  @Bean  public LoadBalancerInterceptor ribbonInterceptor(      LoadBalancerClient loadBalancerClient) {    return new LoadBalancerInterceptor(loadBalancerClient);  }
}