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服务调用Ribbon、Fegin
Ribbon实现负载均衡的原理
1：LoadBalancerAutoConfiguration这个类，这个类主要做的就是把LoadBalancer拦截器封装到RestTemplte拦截器集合里面去。
2：然后在代码里面调用restTemplate.getForObject或者其他方法的时候，就会调用到这个拦截器。
3：在LoadBalancer拦截器类中，就会调用intercept方法，这个方法就会通过execute方法获取负载均衡器以及通过负载均衡算法和得到的servicename去获取一台具体的服务。然后通过http调用。
4：而且ribbon会定时的去更新Nocas中的服务注册中心将其保存在本地，而且在负载均衡真正调用之前的时候也会去更新。
Fegin
1：从@EnableFeginClients注解看，这个注解里面有一个Import注解@Import（FeginClientRegistrat.class）;这个类的方法registerFeginClients方法就能扫描主启动类包同机以及下级包中所有符合@FeginClient的类注入到容器当中。
2：然后loadBalance通过jdk动态代理最总生成LoadBalanceFeginClient，这个类中的execute方法中最终去调用我们的ribbon实现负载均衡。

@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类

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);}}}}