SpringCloud升级之路2020.0.x版-28.OpenFeign的生命周期-进行调用

public Object invoke(Object[] argv) throws Throwable {
    //使用前面一章分析创建的创建的请求模板工厂 `RequestTemplate.Factory`，创建请求模板 `RequestTemplate`。
    RequestTemplate template = buildTemplateFromArgs.create(argv);
    //读取 Options 配置
    Options options = findOptions(argv);
    //使用配置的 Retryer 创建新的 Retryer
    Retryer retryer = this.retryer.clone();
    while (true) {
      try {
        //执行请求并将响应反序列化
        return executeAndDecode(template, options);
      } catch (RetryableException e) {
        //如果抛出 RetryableException，则使用 retryer 判断是否重试，如果需要重试，则继续请求即重试，否则，抛出异常。
        try {
          retryer.continueOrPropagate(e);
        } catch (RetryableException th) {
          Throwable cause = th.getCause();
          if (propagationPolicy == UNWRAP && cause != null) {
            throw cause;
          } else {
            throw th;
          }
        }
        if (logLevel != Logger.Level.NONE) {
          logger.logRetry(metadata.configKey(), logLevel);
        }
        continue;
      }
    }
  }

Request targetRequest(RequestTemplate template) {
    //如果配置了 RequestInterceptor，则执行每一个 RequestInterceptor
    for (RequestInterceptor interceptor : requestInterceptors) {
      interceptor.apply(template);
    }
    //将请求模板 RequestTemplate 转化为实际请求 Request
    return target.apply(template);
}
Object executeAndDecode(RequestTemplate template, Options options) throws Throwable {
    Request request = targetRequest(template);
    if (logLevel != Logger.Level.NONE) {
      logger.logRequest(metadata.configKey(), logLevel, request);
    }
    Response response;
    long start = System.nanoTime();
    try {
      //通过 Client 执行 Request
      response = client.execute(request, options);
      // ensure the request is set. TODO: remove in Feign 12
      response = response.toBuilder()
          .request(request)
          .requestTemplate(template)
          .build();
    } catch (IOException e) {
      if (logLevel != Logger.Level.NONE) {
        logger.logIOException(metadata.configKey(), logLevel, e, elapsedTime(start));
      }
      throw errorExecuting(request, e);
    }
    long elapsedTime = TimeUnit.NANOSECONDS.toMillis(System.nanoTime() - start);
    boolean shouldClose = true;
    try {
      if (logLevel != Logger.Level.NONE) {
        response =
            logger.logAndRebufferResponse(metadata.configKey(), logLevel, response, elapsedTime);
      }
      //如果响应码是 2XX，使用 Decoder 解析 Response
      if (response.status() >= 200 && response.status() < 300) {
        if (void.class == metadata.returnType()) {
          return null;
        } else {
          Object result = decode(response);
          shouldClose = closeAfterDecode;
          return result;
        }
      } else if (decode404 && response.status() == 404 && void.class != metadata.returnType()) {
        //如果响应码是 404，并且在前面一章介绍的配置中配置了 decode404 为 true， 使用 Decoder 解析 Response
        Object result = decode(response);
        shouldClose = closeAfterDecode;
        return result;
      } else {
        //对于其他响应码，使用 errorDecoder 解析，可以自己实现 errorDecoder 抛出 RetryableException 来走入重试逻辑
        throw errorDecoder.decode(metadata.configKey(), response);
      }
    } catch (IOException e) {
      if (logLevel != Logger.Level.NONE) {
        logger.logIOException(metadata.configKey(), logLevel, e, elapsedTime);
      }
      //如果抛出 IOException，直接封装成 RetryableException 抛出
      throw errorReading(request, response, e);
    } finally {
      if (shouldClose) {
        ensureClosed(response.body());
      }
    }
}
static FeignException errorReading(Request request, Response response, IOException cause) {
    return new FeignException(
        response.status(),
        format("%s reading %s %s", cause.getMessage(), request.httpMethod(), request.url()),
        request,
        cause,
        request.body(),
        request.headers());
}