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Spring-cloud Feign 的深入理解

更新時間：2019年02月11日 15:51:44 作者：Degaulle

這篇文章主要介紹了Spring-cloud Feign 的深入理解，小編覺得挺不錯的，現(xiàn)在分享給大家，也給大家做個參考。一起跟隨小編過來看看吧

feign的調(diào)用流程

讀取注解信息：EnableFeignClients-->FeignClientsRegistrar-->FeignClientFactoryBean
feigh流程：ReflectiveFeign-->Contract-->SynchronousMethodHandler
相關(guān)configuration：FeignClientsConfiguration，F(xiàn)eignAutoConfiguration，DefaultFeignLoadBalancedConfiguration，F(xiàn)eignRibbonClientAutoConfiguration（Ribbon）

在FeignClientsRegistrar中：

  @Override
  public void registerBeanDefinitions(AnnotationMetadata metadata,
      BeanDefinitionRegistry registry) {
    //注冊feign配置信息
    registerDefaultConfiguration(metadata, registry);
    //注冊feign client
    registerFeignClients(metadata, registry);
  }

  private void registerFeignClient(BeanDefinitionRegistry registry,
      AnnotationMetadata annotationMetadata, Map<String, Object> attributes) {
    String className = annotationMetadata.getClassName();
    //準備注入FeignClientFactoryBean
    BeanDefinitionBuilder definition = BeanDefinitionBuilder
        .genericBeanDefinition(FeignClientFactoryBean.class);
    ...
  }

查看FeignClientFactoryBean：

  @Override
  public Object getObject() throws Exception {
    FeignContext context = applicationContext.getBean(FeignContext.class);
    //構(gòu)建Feign.Builder
    Feign.Builder builder = feign(context);
    //如果注解沒有指定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) {
        // 因為指定了URL且classpath下有Ribbon，獲取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> T loadBalance(Feign.Builder builder, FeignContext context,
      HardCodedTarget<T> target) {
    //獲取Feign Client實例
    Client client = getOptional(context, Client.class);
    if (client != null) {
      builder.client(client);
      //DefaultTargeter或者HystrixTargeter
      Targeter targeter = get(context, Targeter.class);
      //調(diào)用builder的target，其中就調(diào)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?");
  }

在FeignClientsConfiguration配置了Feign.Builder，prototype類型:

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

Feign的Builder.build返回了一個ReflectiveFeign:

  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構(gòu)造參數(shù)
   //ParseHandlersByName作用是通過傳入的target返回代理接口下的方法的各種信息（MethodHandler）
   //Contract：解析接口的方法注解規(guī)則，生成MethodMetadata
   //Options：Request超時配置
   //Encoder：請求編碼器
   //Decoder：返回解碼器
   //ErrorDecoder：錯誤解碼器
   //SynchronousMethodHandler.Factory是構(gòu)建SynchronousMethodHandler的工廠
   //Client：代表真正執(zhí)行HTTP的組件
   //Retryer：該組決定了在http請求失敗時是否需要重試
   //RequestInterceptor：請求前的攔截器
   //Logger：記錄日志組件，包含各個階段記錄日志的方法和留給用戶自己實現(xiàn)的log方法
   //Logger.Level：日志級別
   //decode404：處理404的策略，返回空還是報錯
   //synchronousMethodHandlerFactory通過所有的信息去包裝一個synchronousMethodHandler，在調(diào)用invoke方法的時候執(zhí)行HTTP
   return new ReflectiveFeign(handlersByName, invocationHandlerFactory);
  }

在調(diào)用Feign.Builder的target的時候，調(diào)用了ReflectiveFeign.newInstance:

 /**
  * 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參數(shù)（包含feign代理接口的類型class，名稱，http URL）
 public <T> T newInstance(Target<T> target) {
  //首先通過**ParseHandlersByName**解析出接口中包含的方法，包裝RequestTemplate，組裝成<name, MethodHandler>
  Map<String, MethodHandler> nameToHandler = targetToHandlersByName.apply(target);
  Map<Method, MethodHandler> methodToHandler = new LinkedHashMap<Method, MethodHandler>();
  //接口default方法List
  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)));
   }
  }
  //InvocationHandlerFactory.Default()返回了一個ReflectiveFeign.FeignInvocationHandler對象，通過傳入的methodHandler map 調(diào)用目標對象的對應(yīng)方法
  InvocationHandler handler = factory.create(target, methodToHandler);
  //生成JDK代理對象
  T proxy = (T) Proxy.newProxyInstance(target.type().getClassLoader(), new Class<?>[]{target.type()}, handler);
  //綁定接口的默認方法到代理對象
  for(DefaultMethodHandler defaultMethodHandler : defaultMethodHandlers) {
   defaultMethodHandler.bindTo(proxy);
  }
  return proxy;
 }

生成Feign代理對象的基本流程圖：

當調(diào)用接口方法時，實際上就是調(diào)用代理對象invoke方法：

 @Override
 public Object invoke(Object[] argv) throws Throwable {
  //工廠創(chuàng)建請求模版
  RequestTemplate template = buildTemplateFromArgs.create(argv);
  //每次克隆一個新的Retryer
  Retryer retryer = this.retryer.clone();
  while (true) {
   try {
    //這里調(diào)用實際的Feign client execute
    return executeAndDecode(template);
   } catch (RetryableException e) {
    //失敗重試
    retryer.continueOrPropagate(e);
    if (logLevel != Logger.Level.NONE) {
     logger.logRetry(metadata.configKey(), logLevel);
    }
    continue;
   }
  }
 }

在DefaultFeignLoadBalancedConfiguration里實例化了LoadBalancerFeignClient

  @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這里是Client.Default實例，底層調(diào)用的是java.net原生網(wǎng)絡(luò)訪問
      FeignLoadBalancer.RibbonRequest ribbonRequest = new FeignLoadBalancer.RibbonRequest(
          this.delegate, request, uriWithoutHost);

      IClientConfig requestConfig = getClientConfig(options, clientName);
      //executeWithLoadBalancer會根據(jù)ribbon的負載均衡算法構(gòu)建url，這里不展開
      return lbClient(clientName).executeWithLoadBalancer(ribbonRequest,
          requestConfig).toResponse();
    }
    catch (ClientException e) {
      IOException io = findIOException(e);
      if (io != null) {
        throw io;
      }
      throw new RuntimeException(e);
    }
  }

以上就是本文的全部內(nèi)容，希望對大家的學(xué)習有所幫助，也希望大家多多支持腳本之家。

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