Spring-cloud Feign 的深入理解

 @Override public void registerBeanDefinitions(AnnotationMetadata metadata, BeanDefinitionRegistry registry) { //注册feign配置信息 registerDefaultConfiguration(metadata, registry); //注册feign client registerFeignClients(metadata, registry); } private void registerFeignClient(BeanDefinitionRegistry registry, AnnotationMetadata annotationMetadata, Map attributes) { String className = annotationMetadata.getClassName(); //准备注入FeignClientFactoryBean BeanDefinitionBuilder definition = BeanDefinitionBuilder .genericBeanDefinition(FeignClientFactoryBean.class); ... }

 @Override public Object getObject() throws Exception { FeignContext context = applicationContext.getBean(FeignContext.class); //构建Feign.Builder Feign.Builder builder = feign(context); //如果注解没有指定URL 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)); } //如果指定了URL if (StringUtils.hasText(this.url) && !this.url.startsWith("http")) { this.url = "http://" + this.url; } String url = this.url + cleanPath(); Client client = getOptional(context, Client.class); if (client != null) { if (client instanceof LoadBalancerFeignClient) { // 因为指定了URL且classpath下有Ribbon，获取client的delegate（unwrap） // not load balancing because we have a url, // but ribbon is on the classpath, so unwrap client = ((LoadBalancerFeignClient)client).getDelegate(); } builder.client(client); } Targeter targeter = get(context, Targeter.class); return targeter.target(this, builder, context, new HardCodedTarget<>( this.type, this.name, url)); } protected  T loadBalance(Feign.Builder builder, FeignContext context, HardCodedTarget target) { //获取Feign Client实例 Client client = getOptional(context, Client.class); if (client != null) { builder.client(client); //DefaultTargeter或者HystrixTargeter Targeter targeter = get(context, Targeter.class); //调用builder的target，其中就调用了Feign的newInstance return targeter.target(this, builder, context, target); } throw new IllegalStateException( "No Feign Client for loadBalancing defined. Did you forget to include spring-cloud-starter-netflix-ribbon?"); }

 @Bean @Scope("prototype") @ConditionalOnMissingBean public Feign.Builder feignBuilder(Retryer retryer) { return Feign.builder().retryer(retryer); } 

 public Feign build() { SynchronousMethodHandler.Factory synchronousMethodHandlerFactory = new SynchronousMethodHandler.Factory(client, retryer, requestInterceptors, logger, logLevel, decode404); ParseHandlersByName handlersByName = new ParseHandlersByName(contract, options, encoder, decoder, errorDecoder, synchronousMethodHandlerFactory); //ReflectiveFeign构造参数 //ParseHandlersByName作用是通过传入的target返回代理接口下的方法的各种信息（MethodHandler） //Contract：解析接口的方法注解规则，生成MethodMetadata //Options：Request超时配置 //Encoder：请求编码器 //Decoder：返回解码器 //ErrorDecoder：错误解码器 //SynchronousMethodHandler.Factory是构建SynchronousMethodHandler的工厂 //Client：代表真正执行HTTP的组件 //Retryer：该组决定了在http请求失败时是否需要重试 //RequestInterceptor：请求前的拦截器 //Logger：记录日志组件，包含各个阶段记录日志的方法和留给用户自己实现的log方法 //Logger.Level：日志级别 //decode404：处理404的策略，返回空还是报错 //synchronousMethodHandlerFactory通过所有的信息去包装一个synchronousMethodHandler，在调用invoke方法的时候执行HTTP return new ReflectiveFeign(handlersByName, invocationHandlerFactory); } 

 /** * creates an api binding to the {@code target}. As this invokes reflection, care should be taken * to cache the result. */ @SuppressWarnings("unchecked") @Override //接收Target参数（包含feign代理接口的类型class，名称，http URL） public  T newInstance(Target target) { //首先通过**ParseHandlersByName**解析出接口中包含的方法，包装RequestTemplate，组装成 Map nameToHandler = targetToHandlersByName.apply(target); Map methodToHandler = new LinkedHashMap(); //接口default方法List List defaultMethodHandlers = new LinkedList(); 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))); } } //InvocationHandlerFactory.Default()返回了一个ReflectiveFeign.FeignInvocationHandler对象，通过传入的methodHandler map 调用目标对象的对应方法 InvocationHandler handler = factory.create(target, methodToHandler); //生成JDK代理对象 T proxy = (T) Proxy.newProxyInstance(target.type().getClassLoader(), new Class[]{target.type()}, handler); //绑定接口的默认方法到代理对象 for(DefaultMethodHandler defaultMethodHandler : defaultMethodHandlers) { defaultMethodHandler.bindTo(proxy); } return proxy; } 

 @Override public Object invoke(Object[] argv) throws Throwable { //工厂创建请求模版 RequestTemplate template = buildTemplateFromArgs.create(argv); //每次克隆一个新的Retryer Retryer retryer = this.retryer.clone(); while (true) { try { //这里调用实际的Feign client execute return executeAndDecode(template); } catch (RetryableException e) { //失败重试 retryer.continueOrPropagate(e); if (logLevel != Logger.Level.NONE) { logger.logRetry(metadata.configKey(), logLevel); } continue; } } } 

 @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); //delegate这里是Client.Default实例，底层调用的是java.net原生网络访问 FeignLoadBalancer.RibbonRequest ribbonRequest = new FeignLoadBalancer.RibbonRequest( this.delegate, request, uriWithoutHost); IClientConfig requestConfig = getClientConfig(options, clientName); //executeWithLoadBalancer会根据ribbon的负载均衡算法构建url，这里不展开 return lbClient(clientName).executeWithLoadBalancer(ribbonRequest, requestConfig).toResponse(); } catch (ClientException e) { IOException io = findIOException(e); if (io != null) { throw io; } throw new RuntimeException(e); } }