服務調用Ribbon、Fegin
Ribbon實現負載均衡的原理
1：LoadBalancerAutoConfiguration這個類，這個類主要做的就是把LoadBalancer攔截器封裝到RestTemplte攔截器集合里面去。
2：然后在代碼里面調用restTemplate.getForObject或者其他方法的時候，就會調用到這個攔截器。
3：在LoadBalancer攔截器類中，就會調用intercept方法，這個方法就會通過execute方法獲取負載均衡器以及通過負載均衡算法和得到的servicename去獲取一臺具體的服務。然后通過http調用。
4：而且ribbon會定時的去更新Nocas中的服務注冊中心將其保存在本地，而且在負載均衡真正調用之前的時候也會去更新。
Fegin
1：從@EnableFeginClients注解看，這個注解里面有一個Import注解@Import（FeginClientRegistrat.class）;這個類的方法registerFeginClients方法就能掃描主啟動類包同機以及下級包中所有符合@FeginClient的類注入到容器當中。
2：然后loadBalance通過jdk動態(tài)代理最總生成LoadBalanceFeginClient，這個類中的execute方法中最終去調用我們的ribbon實現負載均衡。

@SpringBootApplication
@EnableFeignClients/此注解/
public class  OrderFeignMain80 {public static void main(String[] args) {SpringApplication.run(OrderFeignMain80.class,args);}
}

//
// Source code recreated from a .class file by IntelliJ IDEA
// (powered by FernFlower decompiler)
//package org.springframework.cloud.openfeign;import java.lang.annotation.Documented;
import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;
import org.springframework.context.annotation.Import;@Retention(RetentionPolicy.RUNTIME)
@Target({ElementType.TYPE})
@Documented
@Import({FeignClientsRegistrar.class})//此注解
public @interface EnableFeignClients {String[] value() default {};String[] basePackages() default {};Class<?>[] basePackageClasses() default {};Class<?>[] defaultConfiguration() default {};Class<?>[] clients() default {};
}

FeignClientsRegistrar類

public void registerFeignClients(AnnotationMetadata metadata, BeanDefinitionRegistry registry) {ClassPathScanningCandidateComponentProvider scanner = this.getScanner();scanner.setResourceLoader(this.resourceLoader);Map<String, Object> attrs = metadata.getAnnotationAttributes(EnableFeignClients.class.getName());AnnotationTypeFilter annotationTypeFilter = new AnnotationTypeFilter(FeignClient.class);//此方法Class<?>[] clients = attrs == null ? null : (Class[])((Class[])attrs.get("clients"));Object basePackages;if (clients != null && clients.length != 0) {final Set<String> clientClasses = new HashSet();basePackages = new HashSet();Class[] var9 = clients;int var10 = clients.length;for(int var11 = 0; var11 < var10; ++var11) {Class<?> clazz = var9[var11];((Set)basePackages).add(ClassUtils.getPackageName(clazz));clientClasses.add(clazz.getCanonicalName());}AbstractClassTestingTypeFilter filter = new AbstractClassTestingTypeFilter() {protected boolean match(ClassMetadata metadata) {String cleaned = metadata.getClassName().replaceAll("\\$", ".");return clientClasses.contains(cleaned);}};scanner.addIncludeFilter(new FeignClientsRegistrar.AllTypeFilter(Arrays.asList(filter, annotationTypeFilter)));} else {scanner.addIncludeFilter(annotationTypeFilter);basePackages = this.getBasePackages(metadata);}Iterator var17 = ((Set)basePackages).iterator();while(var17.hasNext()) {String basePackage = (String)var17.next();Set<BeanDefinition> candidateComponents = scanner.findCandidateComponents(basePackage);Iterator var21 = candidateComponents.iterator();while(var21.hasNext()) {BeanDefinition candidateComponent = (BeanDefinition)var21.next();if (candidateComponent instanceof AnnotatedBeanDefinition) {AnnotatedBeanDefinition beanDefinition = (AnnotatedBeanDefinition)candidateComponent;AnnotationMetadata annotationMetadata = beanDefinition.getMetadata();Assert.isTrue(annotationMetadata.isInterface(), "@FeignClient can only be specified on an interface");Map<String, Object> attributes = annotationMetadata.getAnnotationAttributes(FeignClient.class.getCanonicalName());String name = this.getClientName(attributes);this.registerClientConfiguration(registry, name, attributes.get("configuration"));this.registerFeignClient(registry, annotationMetadata, attributes);}}}}