@Retention(RetentionPolicy.RUNTIME)
@Target({ElementType.TYPE})
@Documented
@Import({FeignClientsRegistrar.class})
public @interface EnableFeignClients {...}

class FeignClientsRegistrar implements ImportBeanDefinitionRegistrar, ResourceLoaderAware, EnvironmentAware {
  ...
  
  //实现ImportBeanDefinitionRegistrar的接口
  public void registerBeanDefinitions(AnnotationMetadata metadata, BeanDefinitionRegistry registry) {
        this.registerDefaultConfiguration(metadata, registry);
        this.registerFeignClients(metadata, registry);
    }
  
  ...
}

class FeignClientFactoryBean implements FactoryBean<Object>, InitializingBean, ApplicationContextAware {
...
  
    protected Builder feign(FeignContext context) {
        FeignLoggerFactory loggerFactory = (FeignLoggerFactory)this.get(context, FeignLoggerFactory.class);
        Logger logger = loggerFactory.create(this.type);
  
  			//feign构造器获取
        Builder builder = ((Builder)this.get(context, Builder.class)).logger(logger).encoder((Encoder)this.get(context, Encoder.class)).decoder((Decoder)this.get(context, Decoder.class)).contract((Contract)this.get(context, Contract.class));
  
  			//feignclient配置加载
        this.configureFeign(context, builder);
        return builder;
    }
  
  //实现FactoryBean结构，为feign增加装饰器模式
    public Object getObject() throws Exception {
        return this.getTarget();
    }

    <T> T getTarget() {
        FeignContext context = (FeignContext)this.applicationContext.getBean(FeignContext.class);
      
      //获取feign的构造器
        Builder builder = this.feign(context);
        if (!StringUtils.hasText(this.url)) {
            if (!this.name.startsWith("http")) {
                this.url = "http://" + this.name;
            } else {
                this.url = this.name;
            }
          
          //如果没有ur则走负载均衡
            this.url = this.url + this.cleanPath();
          //生成代理对象
          //1.生成请求客户端，内部用到了ribbon的负载均衡
            return this.loadBalance(builder, context, new HardCodedTarget(this.type, this.name, this.url));
        } else {
            if (StringUtils.hasText(this.url) && !this.url.startsWith("http")) {
                this.url = "http://" + this.url;
            }

            String url = this.url + this.cleanPath();
          //生成请求客户端，内部用到了ribbon的负载均衡
            Client client = (Client)this.getOptional(context, Client.class);
            if (client != null) {
                if (client instanceof LoadBalancerFeignClient) {
                    client = ((LoadBalancerFeignClient)client).getDelegate();
                }

                builder.client(client);
            }
          
          //如果有url则走直接链接
            Targeter targeter = (Targeter)this.get(context, Targeter.class);
          //生成代理对象
            return targeter.target(this, builder, context, new HardCodedTarget(this.type, this.name, url));
        }
    }
  
...
}

public static class Builder {
  ...
  
public Feign build() {
    Factory synchronousMethodHandlerFactory = new Factory(this.client, this.retryer, this.requestInterceptors, this.logger, this.logLevel, this.decode404, this.closeAfterDecode, this.propagationPolicy);
    ParseHandlersByName handlersByName = new ParseHandlersByName(this.contract, this.options, this.encoder, this.decoder, this.queryMapEncoder, this.errorDecoder, synchronousMethodHandlerFactory);
  //代理生成
    return new ReflectiveFeign(handlersByName, this.invocationHandlerFactory, this.queryMapEncoder);
}
  
  ...
}

public class ReflectiveFeign extends Feign {
  ...
public <T> T newInstance(Target<T> target) {
    // 1. Contract 将 target.type 接口类上的方法和注解解析成 MethodMetadata，
    //    并转换成内部的MethodHandler处理方式
    Map<String, MethodHandler> nameToHandler = targetToHandlersByName.apply(target);
    Map<Method, MethodHandler> methodToHandler = new LinkedHashMap<Method, MethodHandler>();
    List<DefaultMethodHandler> defaultMethodHandlers = new LinkedList<DefaultMethodHandler>();

    for (Method method : target.type().getMethods()) {
        if (method.getDeclaringClass() == Object.class) {
            continue;
        } else if (Util.isDefault(method)) {
            DefaultMethodHandler handler = new DefaultMethodHandler(method);
            defaultMethodHandlers.add(handler);
            methodToHandler.put(method, handler);
        } else {
            methodToHandler.put(method, nameToHandler.get(Feign.configKey(target.type(), method)));
        }
    }

    // 2. 生成 target.type 的 jdk 动态代理对象
    InvocationHandler handler = factory.create(target, methodToHandler);
    T proxy = (T) Proxy.newProxyInstance(target.type().getClassLoader(),
                                         new Class<?>[]{target.type()}, handler);

    for (DefaultMethodHandler defaultMethodHandler : defaultMethodHandlers) {
        defaultMethodHandler.bindTo(proxy);
    }
    return proxy;
}

  ...
}

public class LoadBalancerFeignClient implements Client {
  ...
  
  public Response execute(Request request, Options options) throws IOException {
        try {
            URI asUri = URI.create(request.url());
            String clientName = asUri.getHost();
            URI uriWithoutHost = cleanUrl(request.url(), clientName);
          //获取ribbon请求
            RibbonRequest ribbonRequest = new RibbonRequest(this.delegate, request, uriWithoutHost);
            IClientConfig requestConfig = this.getClientConfig(options, clientName);
          //执行客户端负载均衡
            return ((RibbonResponse)this.lbClient(clientName).executeWithLoadBalancer(ribbonRequest, requestConfig)).toResponse();
        } catch (ClientException var8) {
            IOException io = this.findIOException(var8);
            if (io != null) {
                throw io;
            } else {
                throw new RuntimeException(var8);
            }
        }
    }
    
  ...
}