Feign简单分析

太过爱你忘了你带给我的痛 2022-04-16 02:16 129阅读 0赞

\#Feign简单分析  
@(Feign)\[Spring\]\[spring cloud\]\[feign\]\[ribbon\]

第一步：把feign相关类分装成spring内部BeanDefinition

**pring-cloud-netflix-core.jar EnableFeignClients.java**

**spring-cloud-netflix-core.jar FeignClientsRegistrar.java**

**spring-cloud-netflix-core.jar FeignClientFactoryBean.java**

第二步：通过ioc容器初始化BeanDefinition得到feign的bean

> 如果项目引用了spring-cloud-netflix-core.jar DefaultFeignLoadBalancedConfiguration.java，则会加载LoadBalancerFeignClient，使用它进行请求发送；否则，以Client.java的实现类Default进行请求发送；LoadBalancerFeignClient中默认使用Ribbon请求

**spring-cloud-netflix-core.jar FeignClientFactoryBean.java**

@Override
    public Object getObject() throws Exception { 
          FeignContext context =  applicationContext.getBean(FeignContext.class);
          Feign.Builder builder = feign(context);
          if (!StringUtils.hasText(this.url)) { 
                 String url;
                 if (!this.name.startsWith("http")) { 
                        url = "http://" + this.name;
                 }
                 else { 
                        url = this.name;
                 }
                 url += cleanPath();
                 return loadBalance(builder, context, new  HardCodedTarget<>(this.type,
                              this.name, url));
          }
          if (StringUtils.hasText(this.url) && !this.url.startsWith("http"))  { 
                 this.url = "http://" + this.url;
          }
          String url = this.url + cleanPath();
          return targeter.target(this, builder, context, new  HardCodedTarget<>(
                        this.type, this.name, url));
    }
    
    
    protected <T> T loadBalance(Feign.Builder builder, FeignContext context,
                 HardCodedTarget<T> target) { 
          Client client = getOptional(context, Client.class);
          if (client != null) { 
                 builder.client(client);
                 return targeter.target(this, builder, context, target);
          }
          throw new IllegalStateException(
                        "No Feign Client for loadBalancing defined. Did you forget to include spring-cloud-starter-ribbon?");
    }

**spring-cloud-netflix-core.jar DefaultFeignLoadBalancedConfiguration.java**

@Configuration
    class DefaultFeignLoadBalancedConfiguration { 
           @Bean
           @ConditionalOnMissingBean
           public Client feignClient(CachingSpringLoadBalancerFactory  cachingFactory,
                                                     SpringClientFactory  clientFactory) { 
                 return new LoadBalancerFeignClient(new Client.Default(null, null),
                               cachingFactory, clientFactory);
           }
    }

**spring-cloud-netflix-core.jar LoadBalancerFeignClient.java**

@Override
    public Response execute(Request request, Request.Options options) throws  IOException { 
          try { 
                 URI asUri = URI.create(request.url());
                 String clientName = asUri.getHost();
                 URI uriWithoutHost = cleanUrl(request.url(), clientName);
                 FeignLoadBalancer.RibbonRequest ribbonRequest = new  FeignLoadBalancer.RibbonRequest(
                              this.delegate, request, uriWithoutHost);
                 IClientConfig requestConfig = getClientConfig(options,  clientName);
                 return  lbClient(clientName).executeWithLoadBalancer(ribbonRequest,
                              requestConfig).toResponse();
          }
          catch (ClientException e) { 
                 IOException io = findIOException(e);
                 if (io != null) { 
                        throw io;
                 }
                 throw new RuntimeException(e);
          }
    }

第三步：运行时通过ReflectiveFeign调用MethodHandler  
**feign-core.jar ReflectiveFeign.java**

**feign-core.jar MethodHandler.java**

**feign-core.jar Client.java**